/src/xz/src/liblzma/common/stream_decoder_mt.c

Source
// SPDX-License-Identifier: 0BSD

///////////////////////////////////////////////////////////////////////////////
//
/// \file       stream_decoder_mt.c
/// \brief      Multithreaded .xz Stream decoder
//
//  Authors:    Sebastian Andrzej Siewior
//              Lasse Collin
//
///////////////////////////////////////////////////////////////////////////////

#include "common.h"
#include "block_decoder.h"
#include "stream_decoder.h"
#include "index.h"
#include "outqueue.h"


typedef enum {
  /// Waiting for work.
  /// Main thread may change this to THR_RUN or THR_EXIT.
  THR_IDLE,

  /// Decoding is in progress.
  /// Main thread may change this to THR_IDLE or THR_EXIT.
  /// The worker thread may change this to THR_IDLE.
  THR_RUN,

  /// The main thread wants the thread to exit.
  THR_EXIT,

} worker_state;


struct worker_thread {
  /// Worker state is protected with our mutex.
  worker_state state;

  /// Input buffer that will contain the whole Block except Block Header.
  uint8_t *in;

  /// Amount of memory allocated for "in"
  size_t in_size;

  /// Number of bytes written to "in" by the main thread
  size_t in_filled;

  /// Number of bytes consumed from "in" by the worker thread.
  size_t in_pos;

  /// Amount of uncompressed data that has been decoded. This local
  /// copy is needed because updating outbuf->pos requires locking
  /// the main mutex (coder->mutex).
  size_t out_pos;

  /// Pointer to the main structure is needed to (1) lock the main
  /// mutex (coder->mutex) when updating outbuf->pos and (2) when
  /// putting this thread back to the stack of free threads.
  struct lzma_stream_coder *coder;

  /// The allocator is set by the main thread. Since a copy of the
  /// pointer is kept here, the application must not change the
  /// allocator before calling lzma_end().
  const lzma_allocator *allocator;

  /// Output queue buffer to which the uncompressed data is written.
  lzma_outbuf *outbuf;

  /// Amount of compressed data that has already been decompressed.
  /// This is updated from in_pos when our mutex is locked.
  /// This is size_t, not uint64_t, because per-thread progress
  /// is limited to sizes of allocated buffers.
  size_t progress_in;

  /// Like progress_in but for uncompressed data.
  size_t progress_out;

  /// Updating outbuf->pos requires locking the main mutex
  /// (coder->mutex). Since the main thread will only read output
  /// from the oldest outbuf in the queue, only the worker thread
  /// that is associated with the oldest outbuf needs to update its
  /// outbuf->pos. This avoids useless mutex contention that would
  /// happen if all worker threads were frequently locking the main
  /// mutex to update their outbuf->pos.
  ///
  /// When partial_update_enabled is true, this worker thread will
  /// update outbuf->pos and outbuf->decoder_in_pos after each call
  /// to the Block decoder. This is initially false. Main thread may
  /// set this to true.
  bool partial_update_enabled;

  /// Once the main thread has set partial_updated_enabled = true,
  /// we will do the first partial update as soon as we can and
  /// set partial_update_started = true. After the first update,
  /// we only update if we have made progress. This avoids useless
  /// locking of thr->coder->mutex.
  bool partial_update_started;

  /// Block decoder
  lzma_next_coder block_decoder;

  /// Thread-specific Block options are needed because the Block
  /// decoder modifies the struct given to it at initialization.
  lzma_block block_options;

  /// Filter chain memory usage
  uint64_t mem_filters;

  /// Next structure in the stack of free worker threads.
  struct worker_thread *next;

  mythread_mutex mutex;
  mythread_cond cond;

  /// The ID of this thread is used to join the thread
  /// when it's not needed anymore.
  mythread thread_id;
};


struct lzma_stream_coder {
  enum {
    SEQ_STREAM_HEADER,
    SEQ_BLOCK_HEADER,
    SEQ_BLOCK_INIT,
    SEQ_BLOCK_THR_INIT,
    SEQ_BLOCK_THR_RUN,
    SEQ_BLOCK_DIRECT_INIT,
    SEQ_BLOCK_DIRECT_RUN,
    SEQ_INDEX_WAIT_OUTPUT,
    SEQ_INDEX_DECODE,
    SEQ_STREAM_FOOTER,
    SEQ_STREAM_PADDING,
    SEQ_ERROR,
  } sequence;

  /// Block decoder
  lzma_next_coder block_decoder;

  /// Every Block Header will be decoded into this structure.
  /// This is also used to initialize a Block decoder when in
  /// direct mode. In threaded mode, a thread-specific copy will
  /// be made for decoder initialization because the Block decoder
  /// will modify the structure given to it.
  lzma_block block_options;

  /// Buffer to hold a filter chain for Block Header decoding and
  /// initialization. These are freed after successful Block decoder
  /// initialization or at stream_decoder_mt_end(). The thread-specific
  /// copy of block_options won't hold a pointer to filters[] after
  /// initialization.
  lzma_filter filters[LZMA_FILTERS_MAX + 1];

  /// Stream Flags from Stream Header
  lzma_stream_flags stream_flags;

  /// Index is hashed so that it can be compared to the sizes of Blocks
  /// with O(1) memory usage.
  lzma_index_hash *index_hash;


  /// Maximum wait time if cannot use all the input and cannot
  /// fill the output buffer. This is in milliseconds.
  uint32_t timeout;


  /// Error code from a worker thread.
  ///
  /// \note       Use mutex.
  lzma_ret thread_error;

  /// Error code to return after pending output has been copied out. If
  /// set in read_output_and_wait(), this is a mirror of thread_error.
  /// If set in stream_decode_mt() then it's, for example, error that
  /// occurred when decoding Block Header.
  lzma_ret pending_error;

  /// Number of threads that will be created at maximum.
  uint32_t threads_max;

  /// Number of thread structures that have been initialized from
  /// "threads", and thus the number of worker threads actually
  /// created so far.
  uint32_t threads_initialized;

  /// Array of allocated thread-specific structures. When no threads
  /// are in use (direct mode) this is NULL. In threaded mode this
  /// points to an array of threads_max number of worker_thread structs.
  struct worker_thread *threads;

  /// Stack of free threads. When a thread finishes, it puts itself
  /// back into this stack. This starts as empty because threads
  /// are created only when actually needed.
  ///
  /// \note       Use mutex.
  struct worker_thread *threads_free;

  /// The most recent worker thread to which the main thread writes
  /// the new input from the application.
  struct worker_thread *thr;

  /// Output buffer queue for decompressed data from the worker threads
  ///
  /// \note       Use mutex with operations that need it.
  lzma_outq outq;

  mythread_mutex mutex;
  mythread_cond cond;


  /// Memory usage that will not be exceeded in multi-threaded mode.
  /// Single-threaded mode can exceed this even by a large amount.
  uint64_t memlimit_threading;

  /// Memory usage limit that should never be exceeded.
  /// LZMA_MEMLIMIT_ERROR will be returned if decoding isn't possible
  /// even in single-threaded mode without exceeding this limit.
  uint64_t memlimit_stop;

  /// Amount of memory in use by the direct mode decoder
  /// (coder->block_decoder). In threaded mode this is 0.
  uint64_t mem_direct_mode;

  /// Amount of memory needed by the running worker threads.
  /// This doesn't include the memory needed by the output buffer.
  ///
  /// \note       Use mutex.
  uint64_t mem_in_use;

  /// Amount of memory used by the idle (cached) threads.
  ///
  /// \note       Use mutex.
  uint64_t mem_cached;


  /// Amount of memory needed for the filter chain of the next Block.
  uint64_t mem_next_filters;

  /// Amount of memory needed for the thread-specific input buffer
  /// for the next Block.
  uint64_t mem_next_in;

  /// Amount of memory actually needed to decode the next Block
  /// in threaded mode. This is
  /// mem_next_filters + mem_next_in + memory needed for lzma_outbuf.
  uint64_t mem_next_block;


  /// Amount of compressed data in Stream Header + Blocks that have
  /// already been finished.
  ///
  /// \note       Use mutex when worker threads might be active.
  uint64_t progress_in;

  /// Amount of uncompressed data in Blocks that have already
  /// been finished.
  ///
  /// \note       Use mutex when worker threads might be active.
  uint64_t progress_out;


  /// If true, LZMA_NO_CHECK is returned if the Stream has
  /// no integrity check.
  bool tell_no_check;

  /// If true, LZMA_UNSUPPORTED_CHECK is returned if the Stream has
  /// an integrity check that isn't supported by this liblzma build.
  bool tell_unsupported_check;

  /// If true, LZMA_GET_CHECK is returned after decoding Stream Header.
  bool tell_any_check;

  /// If true, we will tell the Block decoder to skip calculating
  /// and verifying the integrity check.
  bool ignore_check;

  /// If true, we will decode concatenated Streams that possibly have
  /// Stream Padding between or after them. LZMA_STREAM_END is returned
  /// once the application isn't giving us any new input (LZMA_FINISH),
  /// and we aren't in the middle of a Stream, and possible
  /// Stream Padding is a multiple of four bytes.
  bool concatenated;

  /// If true, we will return any errors immediately instead of first
  /// producing all output before the location of the error.
  bool fail_fast;


  /// When decoding concatenated Streams, this is true as long as we
  /// are decoding the first Stream. This is needed to avoid misleading
  /// LZMA_FORMAT_ERROR in case the later Streams don't have valid magic
  /// bytes.
  bool first_stream;

  /// This is used to track if the previous call to stream_decode_mt()
  /// had output space (*out_pos < out_size) and managed to fill the
  /// output buffer (*out_pos == out_size). This may be set to true
  /// in read_output_and_wait(). This is read and then reset to false
  /// at the beginning of stream_decode_mt().
  ///
  /// This is needed to support applications that call lzma_code() in
  /// such a way that more input is provided only when lzma_code()
  /// didn't fill the output buffer completely. Basically, this makes
  /// it easier to convert such applications from single-threaded
  /// decoder to multi-threaded decoder.
  bool out_was_filled;

  /// Write position in buffer[] and position in Stream Padding
  size_t pos;

  /// Buffer to hold Stream Header, Block Header, and Stream Footer.
  /// Block Header has biggest maximum size.
  uint8_t buffer[LZMA_BLOCK_HEADER_SIZE_MAX];
};


/// Enables updating of outbuf->pos. This is a callback function that is
/// used with lzma_outq_enable_partial_output().
static void
worker_enable_partial_update(void *thr_ptr)
{
  struct worker_thread *thr = thr_ptr;

  mythread_sync(thr->mutex) {
    thr->partial_update_enabled = true;
    mythread_cond_signal(&thr->cond);
  }
}


static MYTHREAD_RET_TYPE
worker_decoder(void *thr_ptr)
{
  struct worker_thread *thr = thr_ptr;
  size_t in_filled;
  bool partial_update_enabled;
  lzma_ret ret;

next_loop_lock:

  mythread_mutex_lock(&thr->mutex);
next_loop_unlocked:

  if (thr->state == THR_IDLE) {
    mythread_cond_wait(&thr->cond, &thr->mutex);
    goto next_loop_unlocked;
  }

  if (thr->state == THR_EXIT) {
    mythread_mutex_unlock(&thr->mutex);

    lzma_free(thr->in, thr->allocator);
    lzma_next_end(&thr->block_decoder, thr->allocator);

    mythread_mutex_destroy(&thr->mutex);
    mythread_cond_destroy(&thr->cond);

    return MYTHREAD_RET_VALUE;
  }

  assert(thr->state == THR_RUN);

  // Update progress info for get_progress().
  thr->progress_in = thr->in_pos;
  thr->progress_out = thr->out_pos;

  // If we don't have any new input, wait for a signal from the main
  // thread except if partial output has just been enabled
  // (partial_update_enabled is true but _started is false). In that
  // case we will do one normal run so that the partial output info
  // gets passed to the main thread. The call to block_decoder.code()
  // is useless but harmless as it can occur only once per Block.
  in_filled = thr->in_filled;
  partial_update_enabled = thr->partial_update_enabled;

  if (in_filled == thr->in_pos && !(partial_update_enabled
      && !thr->partial_update_started)) {
    mythread_cond_wait(&thr->cond, &thr->mutex);
    goto next_loop_unlocked;
  }

  mythread_mutex_unlock(&thr->mutex);

  // Pass the input in small chunks to the Block decoder.
  // This way we react reasonably fast if we are told to stop/exit,
  // and (when partial update is enabled) we tell about our progress
  // to the main thread frequently enough.
  const size_t chunk_size = 16384;
  if ((in_filled - thr->in_pos) > chunk_size)
    in_filled = thr->in_pos + chunk_size;

  ret = thr->block_decoder.code(
      thr->block_decoder.coder, thr->allocator,
      thr->in, &thr->in_pos, in_filled,
      thr->outbuf->buf, &thr->out_pos,
      thr->outbuf->allocated, LZMA_RUN);

  if (ret == LZMA_OK) {
    if (partial_update_enabled) {
      // Remember that we have done at least one partial
      // update. After the first update we won't do updates
      // unless we have made progress.
      thr->partial_update_started = true;

      // The main thread is reading decompressed data
      // from thr->outbuf. Tell the main thread about
      // our progress.
      //
      // NOTE: It's possible that we consumed input without
      // producing any new output so it's possible that only
      // in_pos has changed. If thr->partial_update_started
      // was false, it is possible that neither in_pos nor
      // out_pos has changed.
      mythread_sync(thr->coder->mutex) {
        thr->outbuf->pos = thr->out_pos;
        thr->outbuf->decoder_in_pos = thr->in_pos;
        mythread_cond_signal(&thr->coder->cond);
      }
    }

    goto next_loop_lock;
  }

  // Either we finished successfully (LZMA_STREAM_END) or an error
  // occurred.
  //
  // The sizes are in the Block Header and the Block decoder
  // checks that they match, thus we know these:
  assert(ret != LZMA_STREAM_END || thr->in_pos == thr->in_size);
  assert(ret != LZMA_STREAM_END
    || thr->out_pos == thr->block_options.uncompressed_size);

  mythread_sync(thr->mutex) {
    // Block decoder ensures this, but do a sanity check anyway
    // because thr->in_filled < thr->in_size means that the main
    // thread is still writing to thr->in.
    if (ret == LZMA_STREAM_END && thr->in_filled != thr->in_size) {
      assert(0);
      ret = LZMA_PROG_ERROR;
    }

    if (thr->state != THR_EXIT)
      thr->state = THR_IDLE;
  }

  // Free the input buffer. Don't update in_size as we need
  // it later to update thr->coder->mem_in_use.
  //
  // This step is skipped if an error occurred because the main thread
  // might still be writing to thr->in. The memory will be freed after
  // threads_end() sets thr->state = THR_EXIT.
  if (ret == LZMA_STREAM_END) {
    lzma_free(thr->in, thr->allocator);
    thr->in = NULL;
  }

  mythread_sync(thr->coder->mutex) {
    // Move our progress info to the main thread.
    thr->coder->progress_in += thr->in_pos;
    thr->coder->progress_out += thr->out_pos;
    thr->progress_in = 0;
    thr->progress_out = 0;

    // Mark the outbuf as finished.
    thr->outbuf->pos = thr->out_pos;
    thr->outbuf->decoder_in_pos = thr->in_pos;
    thr->outbuf->finished = true;
    thr->outbuf->finish_ret = ret;
    thr->outbuf = NULL;

    // If an error occurred, tell it to the main thread.
    if (ret != LZMA_STREAM_END
        && thr->coder->thread_error == LZMA_OK)
      thr->coder->thread_error = ret;

    // Return the worker thread to the stack of available
    // threads only if no errors occurred.
    if (ret == LZMA_STREAM_END) {
      // Update memory usage counters.
      thr->coder->mem_in_use -= thr->in_size;
      thr->coder->mem_in_use -= thr->mem_filters;
      thr->coder->mem_cached += thr->mem_filters;

      // Put this thread to the stack of free threads.
      thr->next = thr->coder->threads_free;
      thr->coder->threads_free = thr;
    }

    mythread_cond_signal(&thr->coder->cond);
  }

  goto next_loop_lock;
}


/// Tells the worker threads to exit and waits for them to terminate.
static void
threads_end(struct lzma_stream_coder *coder, const lzma_allocator *allocator)
{
  for (uint32_t i = 0; i < coder->threads_initialized; ++i) {
    mythread_sync(coder->threads[i].mutex) {
      coder->threads[i].state = THR_EXIT;
      mythread_cond_signal(&coder->threads[i].cond);
    }
  }

  for (uint32_t i = 0; i < coder->threads_initialized; ++i)
    mythread_join(coder->threads[i].thread_id);

  lzma_free(coder->threads, allocator);
  coder->threads_initialized = 0;
  coder->threads = NULL;
  coder->threads_free = NULL;

  // The threads don't update these when they exit. Do it here.
  coder->mem_in_use = 0;
  coder->mem_cached = 0;

  return;
}


/// Tell worker threads to stop without doing any cleaning up.
/// The clean up will be done when threads_exit() is called;
/// it's not possible to reuse the threads after threads_stop().
///
/// This is called before returning an unrecoverable error code
/// to the application. It would be waste of processor time
/// to keep the threads running in such a situation.
static void
threads_stop(struct lzma_stream_coder *coder)
{
  for (uint32_t i = 0; i < coder->threads_initialized; ++i) {
    // The threads that are in the THR_RUN state will stop
    // when they check the state the next time. There's no
    // need to signal coder->threads[i].cond.
    mythread_sync(coder->threads[i].mutex) {
      coder->threads[i].state = THR_IDLE;
    }
  }

  return;
}


/// Initialize a new worker_thread structure and create a new thread.
static lzma_ret
initialize_new_thread(struct lzma_stream_coder *coder,
    const lzma_allocator *allocator)
{
  // Allocate the coder->threads array if needed. It's done here instead
  // of when initializing the decoder because we don't need this if we
  // use the direct mode (we may even free coder->threads in the middle
  // of the file if we switch from threaded to direct mode).
  if (coder->threads == NULL) {
    coder->threads = lzma_alloc(
      coder->threads_max * sizeof(struct worker_thread),
      allocator);

    if (coder->threads == NULL)
      return LZMA_MEM_ERROR;
  }

  // Pick a free structure.
  assert(coder->threads_initialized < coder->threads_max);
  struct worker_thread *thr
      = &coder->threads[coder->threads_initialized];

  if (mythread_mutex_init(&thr->mutex))
    goto error_mutex;

  if (mythread_cond_init(&thr->cond))
    goto error_cond;

  thr->state = THR_IDLE;
  thr->in = NULL;
  thr->in_size = 0;
  thr->allocator = allocator;
  thr->coder = coder;
  thr->outbuf = NULL;
  thr->block_decoder = LZMA_NEXT_CODER_INIT;
  thr->mem_filters = 0;

  if (mythread_create(&thr->thread_id, worker_decoder, thr))
    goto error_thread;

  ++coder->threads_initialized;
  coder->thr = thr;

  return LZMA_OK;

error_thread:
  mythread_cond_destroy(&thr->cond);

error_cond:
  mythread_mutex_destroy(&thr->mutex);

error_mutex:
  return LZMA_MEM_ERROR;
}


static lzma_ret
get_thread(struct lzma_stream_coder *coder, const lzma_allocator *allocator)
{
  // If there is a free structure on the stack, use it.
  mythread_sync(coder->mutex) {
    if (coder->threads_free != NULL) {
      coder->thr = coder->threads_free;
      coder->threads_free = coder->threads_free->next;

      // The thread is no longer in the cache so subtract
      // it from the cached memory usage. Don't add it
      // to mem_in_use though; the caller will handle it
      // since it knows how much memory it will actually
      // use (the filter chain might change).
      coder->mem_cached -= coder->thr->mem_filters;
    }
  }

  if (coder->thr == NULL) {
    assert(coder->threads_initialized < coder->threads_max);

    // Initialize a new thread.
    return_if_error(initialize_new_thread(coder, allocator));
  }

  coder->thr->in_filled = 0;
  coder->thr->in_pos = 0;
  coder->thr->out_pos = 0;

  coder->thr->progress_in = 0;
  coder->thr->progress_out = 0;

  coder->thr->partial_update_enabled = false;
  coder->thr->partial_update_started = false;

  return LZMA_OK;
}


static lzma_ret
read_output_and_wait(struct lzma_stream_coder *coder,
    const lzma_allocator *allocator,
    uint8_t *restrict out, size_t *restrict out_pos,
    size_t out_size,
    bool *input_is_possible,
    bool waiting_allowed,
    mythread_condtime *wait_abs, bool *has_blocked)
{
  lzma_ret ret = LZMA_OK;

  mythread_sync(coder->mutex) {
    do {
      // Get as much output from the queue as is possible
      // without blocking.
      const size_t out_start = *out_pos;
      do {
        ret = lzma_outq_read(&coder->outq, allocator,
            out, out_pos, out_size,
            NULL, NULL);

        // If a Block was finished, tell the worker
        // thread of the next Block (if it is still
        // running) to start telling the main thread
        // when new output is available.
        if (ret == LZMA_STREAM_END)
          lzma_outq_enable_partial_output(
            &coder->outq,
            &worker_enable_partial_update);

        // Loop until a Block wasn't finished.
        // It's important to loop around even if
        // *out_pos == out_size because there could
        // be an empty Block that will return
        // LZMA_STREAM_END without needing any
        // output space.
      } while (ret == LZMA_STREAM_END);

      // Check if lzma_outq_read reported an error from
      // the Block decoder.
      if (ret != LZMA_OK)
        break;

      // If the output buffer is now full but it wasn't full
      // when this function was called, set out_was_filled.
      // This way the next call to stream_decode_mt() knows
      // that some output was produced and no output space
      // remained in the previous call to stream_decode_mt().
      if (*out_pos == out_size && *out_pos != out_start)
        coder->out_was_filled = true;

      // Check if any thread has indicated an error.
      if (coder->thread_error != LZMA_OK) {
        // If LZMA_FAIL_FAST was used, report errors
        // from worker threads immediately.
        if (coder->fail_fast) {
          ret = coder->thread_error;
          break;
        }

        // Otherwise set pending_error. The value we
        // set here will not actually get used other
        // than working as a flag that an error has
        // occurred. This is because in SEQ_ERROR
        // all output before the error will be read
        // first by calling this function, and once we
        // reach the location of the (first) error the
        // error code from the above lzma_outq_read()
        // will be returned to the application.
        //
        // Use LZMA_PROG_ERROR since the value should
        // never leak to the application. It's
        // possible that pending_error has already
        // been set but that doesn't matter: if we get
        // here, pending_error only works as a flag.
        coder->pending_error = LZMA_PROG_ERROR;
      }

      // Check if decoding of the next Block can be started.
      // The memusage of the active threads must be low
      // enough, there must be a free buffer slot in the
      // output queue, and there must be a free thread
      // (that can be either created or an existing one
      // reused).
      //
      // NOTE: This is checked after reading the output
      // above because reading the output can free a slot in
      // the output queue and also reduce active memusage.
      //
      // NOTE: If output queue is empty, then input will
      // always be possible.
      if (input_is_possible != NULL
          && coder->memlimit_threading
            - coder->mem_in_use
            - coder->outq.mem_in_use
            >= coder->mem_next_block
          && lzma_outq_has_buf(&coder->outq)
          && (coder->threads_initialized
              < coder->threads_max
            || coder->threads_free
              != NULL)) {
        *input_is_possible = true;
        break;
      }

      // If the caller doesn't want us to block, return now.
      if (!waiting_allowed)
        break;

      // This check is needed only when input_is_possible
      // is NULL. We must return if we aren't waiting for
      // input to become possible and there is no more
      // output coming from the queue.
      if (lzma_outq_is_empty(&coder->outq)) {
        assert(input_is_possible == NULL);
        break;
      }

      // If there is more data available from the queue,
      // our out buffer must be full and we need to return
      // so that the application can provide more output
      // space.
      //
      // NOTE: In general lzma_outq_is_readable() can return
      // true also when there are no more bytes available.
      // This can happen when a Block has finished without
      // providing any new output. We know that this is not
      // the case because in the beginning of this loop we
      // tried to read as much as possible even when we had
      // no output space left and the mutex has been locked
      // all the time (so worker threads cannot have changed
      // anything). Thus there must be actual pending output
      // in the queue.
      if (lzma_outq_is_readable(&coder->outq)) {
        assert(*out_pos == out_size);
        break;
      }

      // If the application stops providing more input
      // in the middle of a Block, there will eventually
      // be one worker thread left that is stuck waiting for
      // more input (that might never arrive) and a matching
      // outbuf which the worker thread cannot finish due
      // to lack of input. We must detect this situation,
      // otherwise we would end up waiting indefinitely
      // (if no timeout is in use) or keep returning
      // LZMA_TIMED_OUT while making no progress. Thus, the
      // application would never get LZMA_BUF_ERROR from
      // lzma_code() which would tell the application that
      // no more progress is possible. No LZMA_BUF_ERROR
      // means that, for example, truncated .xz files could
      // cause an infinite loop.
      //
      // A worker thread doing partial updates will
      // store not only the output position in outbuf->pos
      // but also the matching input position in
      // outbuf->decoder_in_pos. Here we check if that
      // input position matches the amount of input that
      // the worker thread has been given (in_filled).
      // If so, we must return and not wait as no more
      // output will be coming without first getting more
      // input to the worker thread. If the application
      // keeps calling lzma_code() without providing more
      // input, it will eventually get LZMA_BUF_ERROR.
      //
      // NOTE: We can read partial_update_enabled and
      // in_filled without thr->mutex as only the main thread
      // modifies these variables. decoder_in_pos requires
      // coder->mutex which we are already holding.
      if (coder->thr != NULL &&
          coder->thr->partial_update_enabled) {
        // There is exactly one outbuf in the queue.
        assert(coder->thr->outbuf == coder->outq.head);
        assert(coder->thr->outbuf == coder->outq.tail);

        if (coder->thr->outbuf->decoder_in_pos
            == coder->thr->in_filled)
          break;
      }

      // Wait for input or output to become possible.
      if (coder->timeout != 0) {
        // See the comment in stream_encoder_mt.c
        // about why mythread_condtime_set() is used
        // like this.
        //
        // FIXME?
        // In contrast to the encoder, this calls
        // _condtime_set while the mutex is locked.
        if (!*has_blocked) {
          *has_blocked = true;
          mythread_condtime_set(wait_abs,
              &coder->cond,
              coder->timeout);
        }

        if (mythread_cond_timedwait(&coder->cond,
            &coder->mutex,
            wait_abs) != 0) {
          ret = LZMA_TIMED_OUT;
          break;
        }
      } else {
        mythread_cond_wait(&coder->cond,
            &coder->mutex);
      }
    } while (ret == LZMA_OK);
  }

  // If we are returning an error, then the application cannot get
  // more output from us and thus keeping the threads running is
  // useless and waste of CPU time.
  if (ret != LZMA_OK && ret != LZMA_TIMED_OUT)
    threads_stop(coder);

  return ret;
}


static lzma_ret
decode_block_header(struct lzma_stream_coder *coder,
    const lzma_allocator *allocator, const uint8_t *restrict in,
    size_t *restrict in_pos, size_t in_size)
{
  if (*in_pos >= in_size)
    return LZMA_OK;

  if (coder->pos == 0) {
    // Detect if it's Index.
    if (in[*in_pos] == INDEX_INDICATOR)
      return LZMA_INDEX_DETECTED;

    // Calculate the size of the Block Header. Note that
    // Block Header decoder wants to see this byte too
    // so don't advance *in_pos.
    coder->block_options.header_size
        = lzma_block_header_size_decode(
          in[*in_pos]);
  }

  // Copy the Block Header to the internal buffer.
  lzma_bufcpy(in, in_pos, in_size, coder->buffer, &coder->pos,
      coder->block_options.header_size);

  // Return if we didn't get the whole Block Header yet.
  if (coder->pos < coder->block_options.header_size)
    return LZMA_OK;

  coder->pos = 0;

  // Version 1 is needed to support the .ignore_check option.
  coder->block_options.version = 1;

  // Block Header decoder will initialize all members of this array
  // so we don't need to do it here.
  coder->block_options.filters = coder->filters;

  // Decode the Block Header.
  return_if_error(lzma_block_header_decode(&coder->block_options,
      allocator, coder->buffer));

  // If LZMA_IGNORE_CHECK was used, this flag needs to be set.
  // It has to be set after lzma_block_header_decode() because
  // it always resets this to false.
  coder->block_options.ignore_check = coder->ignore_check;

  // coder->block_options is ready now.
  return LZMA_STREAM_END;
}


/// Get the size of the Compressed Data + Block Padding + Check.
static size_t
comp_blk_size(const struct lzma_stream_coder *coder)
{
  return vli_ceil4(coder->block_options.compressed_size)
      + lzma_check_size(coder->stream_flags.check);
}


/// Returns true if the size (compressed or uncompressed) is such that
/// threaded decompression cannot be used. Sizes that are too big compared
/// to SIZE_MAX must be rejected to avoid integer overflows and truncations
/// when lzma_vli is assigned to a size_t.
static bool
is_direct_mode_needed(lzma_vli size)
{
  return size == LZMA_VLI_UNKNOWN || size > SIZE_MAX / 3;
}


static lzma_ret
stream_decoder_reset(struct lzma_stream_coder *coder,
    const lzma_allocator *allocator)
{
  // Initialize the Index hash used to verify the Index.
  coder->index_hash = lzma_index_hash_init(coder->index_hash, allocator);
  if (coder->index_hash == NULL)
    return LZMA_MEM_ERROR;

  // Reset the rest of the variables.
  coder->sequence = SEQ_STREAM_HEADER;
  coder->pos = 0;

  return LZMA_OK;
}


static lzma_ret
stream_decode_mt(void *coder_ptr, const lzma_allocator *allocator,
     const uint8_t *restrict in, size_t *restrict in_pos,
     size_t in_size,
     uint8_t *restrict out, size_t *restrict out_pos,
     size_t out_size, lzma_action action)
{
  struct lzma_stream_coder *coder = coder_ptr;

  mythread_condtime wait_abs;
  bool has_blocked = false;

  // Determine if in SEQ_BLOCK_HEADER and SEQ_BLOCK_THR_RUN we should
  // tell read_output_and_wait() to wait until it can fill the output
  // buffer (or a timeout occurs). Two conditions must be met:
  //
  // (1) If the caller provided no new input. The reason for this
  //     can be, for example, the end of the file or that there is
  //     a pause in the input stream and more input is available
  //     a little later. In this situation we should wait for output
  //     because otherwise we would end up in a busy-waiting loop where
  //     we make no progress and the application just calls us again
  //     without providing any new input. This would then result in
  //     LZMA_BUF_ERROR even though more output would be available
  //     once the worker threads decode more data.
  //
  // (2) Even if (1) is true, we will not wait if the previous call to
  //     this function managed to produce some output and the output
  //     buffer became full. This is for compatibility with applications
  //     that call lzma_code() in such a way that new input is provided
  //     only when the output buffer didn't become full. Without this
  //     trick such applications would have bad performance (bad
  //     parallelization due to decoder not getting input fast enough).
  //
  //     NOTE: Such loops might require that timeout is disabled (0)
  //     if they assume that output-not-full implies that all input has
  //     been consumed. If and only if timeout is enabled, we may return
  //     when output isn't full *and* not all input has been consumed.
  //
  // However, if LZMA_FINISH is used, the above is ignored and we always
  // wait (timeout can still cause us to return) because we know that
  // we won't get any more input. This matters if the input file is
  // truncated and we are doing single-shot decoding, that is,
  // timeout = 0 and LZMA_FINISH is used on the first call to
  // lzma_code() and the output buffer is known to be big enough
  // to hold all uncompressed data:
  //
  //   - If LZMA_FINISH wasn't handled specially, we could return
  //     LZMA_OK before providing all output that is possible with the
  //     truncated input. The rest would be available if lzma_code() was
  //     called again but then it's not single-shot decoding anymore.
  //
  //   - By handling LZMA_FINISH specially here, the first call will
  //     produce all the output, matching the behavior of the
  //     single-threaded decoder.
  //
  // So it's a very specific corner case but also easy to avoid. Note
  // that this special handling of LZMA_FINISH has no effect for
  // single-shot decoding when the input file is valid (not truncated);
  // premature LZMA_OK wouldn't be possible as long as timeout = 0.
  const bool waiting_allowed = action == LZMA_FINISH
      || (*in_pos == in_size && !coder->out_was_filled);
  coder->out_was_filled = false;

  while (true)
  switch (coder->sequence) {
  case SEQ_STREAM_HEADER: {
    // Copy the Stream Header to the internal buffer.
    const size_t in_old = *in_pos;
    lzma_bufcpy(in, in_pos, in_size, coder->buffer, &coder->pos,
        LZMA_STREAM_HEADER_SIZE);
    coder->progress_in += *in_pos - in_old;

    // Return if we didn't get the whole Stream Header yet.
    if (coder->pos < LZMA_STREAM_HEADER_SIZE)
      return LZMA_OK;

    coder->pos = 0;

    // Decode the Stream Header.
    const lzma_ret ret = lzma_stream_header_decode(
        &coder->stream_flags, coder->buffer);
    if (ret != LZMA_OK)
      return ret == LZMA_FORMAT_ERROR && !coder->first_stream
          ? LZMA_DATA_ERROR : ret;

    // If we are decoding concatenated Streams, and the later
    // Streams have invalid Header Magic Bytes, we give
    // LZMA_DATA_ERROR instead of LZMA_FORMAT_ERROR.
    coder->first_stream = false;

    // Copy the type of the Check so that Block Header and Block
    // decoders see it.
    coder->block_options.check = coder->stream_flags.check;

    // Even if we return LZMA_*_CHECK below, we want
    // to continue from Block Header decoding.
    coder->sequence = SEQ_BLOCK_HEADER;

    // Detect if there's no integrity check or if it is
    // unsupported if those were requested by the application.
    if (coder->tell_no_check && coder->stream_flags.check
        == LZMA_CHECK_NONE)
      return LZMA_NO_CHECK;

    if (coder->tell_unsupported_check
        && !lzma_check_is_supported(
          coder->stream_flags.check))
      return LZMA_UNSUPPORTED_CHECK;

    if (coder->tell_any_check)
      return LZMA_GET_CHECK;

    FALLTHROUGH;
  }

  case SEQ_BLOCK_HEADER: {
    const size_t in_old = *in_pos;
    const lzma_ret ret = decode_block_header(coder, allocator,
        in, in_pos, in_size);

    // Worker threads may finish earlier Blocks and need to update
    // coder->progress_in at the same time with us.
    mythread_sync(coder->mutex) {
      coder->progress_in += *in_pos - in_old;
    }

    if (ret == LZMA_OK) {
      // We didn't decode the whole Block Header yet.
      //
      // Read output from the queue before returning. This
      // is important because it is possible that the
      // application doesn't have any new input available
      // immediately. If we didn't try to copy output from
      // the output queue here, lzma_code() could end up
      // returning LZMA_BUF_ERROR even though queued output
      // is available.
      //
      // If the lzma_code() call provided at least one input
      // byte, only copy as much data from the output queue
      // as is available immediately. This way the
      // application will be able to provide more input
      // without a delay.
      //
      // On the other hand, if lzma_code() was called with
      // an empty input buffer(*), treat it specially: try
      // to fill the output buffer even if it requires
      // waiting for the worker threads to provide output
      // (timeout, if specified, can still cause us to
      // return).
      //
      //   - This way the application will be able to get all
      //     data that can be decoded from the input provided
      //     so far.
      //
      //   - We avoid both premature LZMA_BUF_ERROR and
      //     busy-waiting where the application repeatedly
      //     calls lzma_code() which immediately returns
      //     LZMA_OK without providing new data.
      //
      //   - If the queue becomes empty, we won't wait
      //     anything and will return LZMA_OK immediately
      //     (coder->timeout is completely ignored).
      //
      // (*) See the comment at the beginning of this
      //     function how waiting_allowed is determined
      //     and why there is an exception to the rule
      //     of "called with an empty input buffer".
      assert(*in_pos == in_size);

      // If LZMA_FINISH was used we know that we won't get
      // more input, so the file must be truncated if we
      // get here. If worker threads don't detect any
      // errors, eventually there will be no more output
      // while we keep returning LZMA_OK which gets
      // converted to LZMA_BUF_ERROR in lzma_code().
      //
      // If fail-fast is enabled then we will return
      // immediately using LZMA_DATA_ERROR instead of
      // LZMA_OK or LZMA_BUF_ERROR. Rationale for the
      // error code:
      //
      //   - Worker threads may have a large amount of
      //     not-yet-decoded input data and we don't
      //     know for sure if all data is valid. Bad
      //     data there would result in LZMA_DATA_ERROR
      //     when fail-fast isn't used.
      //
      //   - Immediate LZMA_BUF_ERROR would be a bit weird
      //     considering the older liblzma code. lzma_code()
      //     even has an assertion to prevent coders from
      //     returning LZMA_BUF_ERROR directly.
      //
      // The downside of this is that with fail-fast apps
      // cannot always distinguish between corrupt and
      // truncated files.
      if (action == LZMA_FINISH && coder->fail_fast) {
        // We won't produce any more output. Stop
        // the unfinished worker threads so they
        // won't waste CPU time.
        threads_stop(coder);
        return LZMA_DATA_ERROR;
      }

      // read_output_and_wait() will call threads_stop()
      // if needed so with that we can use return_if_error.
      return_if_error(read_output_and_wait(coder, allocator,
        out, out_pos, out_size,
        NULL, waiting_allowed,
        &wait_abs, &has_blocked));

      if (coder->pending_error != LZMA_OK) {
        coder->sequence = SEQ_ERROR;
        break;
      }

      return LZMA_OK;
    }

    if (ret == LZMA_INDEX_DETECTED) {
      coder->sequence = SEQ_INDEX_WAIT_OUTPUT;
      break;
    }

    // See if an error occurred.
    if (ret != LZMA_STREAM_END) {
      // NOTE: Here and in all other places where
      // pending_error is set, it may overwrite the value
      // (LZMA_PROG_ERROR) set by read_output_and_wait().
      // That function might overwrite value set here too.
      // These are fine because when read_output_and_wait()
      // sets pending_error, it actually works as a flag
      // variable only ("some error has occurred") and the
      // actual value of pending_error is not used in
      // SEQ_ERROR. In such cases SEQ_ERROR will eventually
      // get the correct error code from the return value of
      // a later read_output_and_wait() call.
      coder->pending_error = ret;
      coder->sequence = SEQ_ERROR;
      break;
    }

    // Calculate the memory usage of the filters / Block decoder.
    coder->mem_next_filters = lzma_raw_decoder_memusage(
        coder->filters);

    if (coder->mem_next_filters == UINT64_MAX) {
      // One or more unknown Filter IDs.
      coder->pending_error = LZMA_OPTIONS_ERROR;
      coder->sequence = SEQ_ERROR;
      break;
    }

    coder->sequence = SEQ_BLOCK_INIT;
    FALLTHROUGH;
  }

  case SEQ_BLOCK_INIT: {
    // Check if decoding is possible at all with the current
    // memlimit_stop which we must never exceed.
    //
    // This needs to be the first thing in SEQ_BLOCK_INIT
    // to make it possible to restart decoding after increasing
    // memlimit_stop with lzma_memlimit_set().
    if (coder->mem_next_filters > coder->memlimit_stop) {
      // Flush pending output before returning
      // LZMA_MEMLIMIT_ERROR. If the application doesn't
      // want to increase the limit, at least it will get
      // all the output possible so far.
      return_if_error(read_output_and_wait(coder, allocator,
          out, out_pos, out_size,
          NULL, true, &wait_abs, &has_blocked));

      if (!lzma_outq_is_empty(&coder->outq))
        return LZMA_OK;

      return LZMA_MEMLIMIT_ERROR;
    }

    // Check if the size information is available in Block Header.
    // If it is, check if the sizes are small enough that we don't
    // need to worry *too* much about integer overflows later in
    // the code. If these conditions are not met, we must use the
    // single-threaded direct mode.
    if (is_direct_mode_needed(coder->block_options.compressed_size)
        || is_direct_mode_needed(
        coder->block_options.uncompressed_size)) {
      coder->sequence = SEQ_BLOCK_DIRECT_INIT;
      break;
    }

    // Calculate the amount of memory needed for the input and
    // output buffers in threaded mode.
    //
    // These cannot overflow because we already checked that
    // the sizes are small enough using is_direct_mode_needed().
    coder->mem_next_in = comp_blk_size(coder);
    const uint64_t mem_buffers = coder->mem_next_in
        + lzma_outq_outbuf_memusage(
        coder->block_options.uncompressed_size);

    // Add the amount needed by the filters.
    // Avoid integer overflows.
    if (UINT64_MAX - mem_buffers < coder->mem_next_filters) {
      // Use direct mode if the memusage would overflow.
      // This is a theoretical case that shouldn't happen
      // in practice unless the input file is weird (broken
      // or malicious).
      coder->sequence = SEQ_BLOCK_DIRECT_INIT;
      break;
    }

    // Amount of memory needed to decode this Block in
    // threaded mode:
    coder->mem_next_block = coder->mem_next_filters + mem_buffers;

    // If this alone would exceed memlimit_threading, then we must
    // use the single-threaded direct mode.
    if (coder->mem_next_block > coder->memlimit_threading) {
      coder->sequence = SEQ_BLOCK_DIRECT_INIT;
      break;
    }

    // Use the threaded mode. Free the direct mode decoder in
    // case it has been initialized.
    lzma_next_end(&coder->block_decoder, allocator);
    coder->mem_direct_mode = 0;

    // Since we already know what the sizes are supposed to be,
    // we can already add them to the Index hash. The Block
    // decoder will verify the values while decoding.
    const lzma_ret ret = lzma_index_hash_append(coder->index_hash,
        lzma_block_unpadded_size(
          &coder->block_options),
        coder->block_options.uncompressed_size);
    if (ret != LZMA_OK) {
      coder->pending_error = ret;
      coder->sequence = SEQ_ERROR;
      break;
    }

    coder->sequence = SEQ_BLOCK_THR_INIT;
    FALLTHROUGH;
  }

  case SEQ_BLOCK_THR_INIT: {
    // We need to wait for a multiple conditions to become true
    // until we can initialize the Block decoder and let a worker
    // thread decode it:
    //
    //   - Wait for the memory usage of the active threads to drop
    //     so that starting the decoding of this Block won't make
    //     us go over memlimit_threading.
    //
    //   - Wait for at least one free output queue slot.
    //
    //   - Wait for a free worker thread.
    //
    // While we wait, we must copy decompressed data to the out
    // buffer and catch possible decoder errors.
    //
    // read_output_and_wait() does all the above.
    bool block_can_start = false;

    return_if_error(read_output_and_wait(coder, allocator,
        out, out_pos, out_size,
        &block_can_start, true,
        &wait_abs, &has_blocked));

    if (coder->pending_error != LZMA_OK) {
      coder->sequence = SEQ_ERROR;
      break;
    }

    if (!block_can_start) {
      // It's not a timeout because return_if_error handles
      // it already. Output queue cannot be empty either
      // because in that case block_can_start would have
      // been true. Thus the output buffer must be full and
      // the queue isn't empty.
      assert(*out_pos == out_size);
      assert(!lzma_outq_is_empty(&coder->outq));
      return LZMA_OK;
    }

    // We know that we can start decoding this Block without
    // exceeding memlimit_threading. However, to stay below
    // memlimit_threading may require freeing some of the
    // cached memory.
    //
    // Get a local copy of variables that require locking the
    // mutex. It is fine if the worker threads modify the real
    // values after we read these as those changes can only be
    // towards more favorable conditions (less memory in use,
    // more in cache).
    //
    // These are initialized to silence warnings.
    uint64_t mem_in_use = 0;
    uint64_t mem_cached = 0;
    struct worker_thread *thr = NULL;

    mythread_sync(coder->mutex) {
      mem_in_use = coder->mem_in_use;
      mem_cached = coder->mem_cached;
      thr = coder->threads_free;
    }

    // The maximum amount of memory that can be held by other
    // threads and cached buffers while allowing us to start
    // decoding the next Block.
    const uint64_t mem_max = coder->memlimit_threading
        - coder->mem_next_block;

    // If the existing allocations are so large that starting
    // to decode this Block might exceed memlimit_threads,
    // try to free memory from the output queue cache first.
    //
    // NOTE: This math assumes the worst case. It's possible
    // that the limit wouldn't be exceeded if the existing cached
    // allocations are reused.
    if (mem_in_use + mem_cached + coder->outq.mem_allocated
        > mem_max) {
      // Clear the outq cache except leave one buffer in
      // the cache if its size is correct. That way we
      // don't free and almost immediately reallocate
      // an identical buffer.
      lzma_outq_clear_cache2(&coder->outq, allocator,
        coder->block_options.uncompressed_size);
    }

    // If there is at least one worker_thread in the cache and
    // the existing allocations are so large that starting to
    // decode this Block might exceed memlimit_threads, free
    // memory by freeing cached Block decoders.
    //
    // NOTE: The comparison is different here than above.
    // Here we don't care about cached buffers in outq anymore
    // and only look at memory actually in use. This is because
    // if there is something in outq cache, it's a single buffer
    // that can be used as is. We ensured this in the above
    // if-block.
    uint64_t mem_freed = 0;
    if (thr != NULL && mem_in_use + mem_cached
        + coder->outq.mem_in_use > mem_max) {
      // Don't free the first Block decoder if its memory
      // usage isn't greater than what this Block will need.
      // Typically the same filter chain is used for all
      // Blocks so this way the allocations can be reused
      // when get_thread() picks the first worker_thread
      // from the cache.
      if (thr->mem_filters <= coder->mem_next_filters)
        thr = thr->next;

      while (thr != NULL) {
        lzma_next_end(&thr->block_decoder, allocator);
        mem_freed += thr->mem_filters;
        thr->mem_filters = 0;
        thr = thr->next;
      }
    }

    // Update the memory usage counters. Note that coder->mem_*
    // may have changed since we read them so we must subtract
    // or add the changes.
    mythread_sync(coder->mutex) {
      coder->mem_cached -= mem_freed;

      // Memory needed for the filters and the input buffer.
      // The output queue takes care of its own counter so
      // we don't touch it here.
      //
      // NOTE: After this, coder->mem_in_use +
      // coder->mem_cached might count the same thing twice.
      // If so, this will get corrected in get_thread() when
      // a worker_thread is picked from coder->free_threads
      // and its memory usage is subtracted from mem_cached.
      coder->mem_in_use += coder->mem_next_in
          + coder->mem_next_filters;
    }

    // Allocate memory for the output buffer in the output queue.
    lzma_ret ret = lzma_outq_prealloc_buf(
        &coder->outq, allocator,
        coder->block_options.uncompressed_size);
    if (ret != LZMA_OK) {
      threads_stop(coder);
      return ret;
    }

    // Set up coder->thr.
    ret = get_thread(coder, allocator);
    if (ret != LZMA_OK) {
      threads_stop(coder);
      return ret;
    }

    // The new Block decoder memory usage is already counted in
    // coder->mem_in_use. Store it in the thread too.
    coder->thr->mem_filters = coder->mem_next_filters;

    // Initialize the Block decoder.
    coder->thr->block_options = coder->block_options;
    ret = lzma_block_decoder_init(
          &coder->thr->block_decoder, allocator,
          &coder->thr->block_options);

    // Free the allocated filter options since they are needed
    // only to initialize the Block decoder.
    lzma_filters_free(coder->filters, allocator);
    coder->thr->block_options.filters = NULL;

    // Check if memory usage calculation and Block encoder
    // initialization succeeded.
    if (ret != LZMA_OK) {
      coder->pending_error = ret;
      coder->sequence = SEQ_ERROR;
      break;
    }

    // Allocate the input buffer.
    coder->thr->in_size = coder->mem_next_in;
    coder->thr->in = lzma_alloc(coder->thr->in_size, allocator);
    if (coder->thr->in == NULL) {
      threads_stop(coder);
      return LZMA_MEM_ERROR;
    }

    // Get the preallocated output buffer.
    coder->thr->outbuf = lzma_outq_get_buf(
        &coder->outq, coder->thr);

    // Start the decoder.
    mythread_sync(coder->thr->mutex) {
      assert(coder->thr->state == THR_IDLE);
      coder->thr->state = THR_RUN;
      mythread_cond_signal(&coder->thr->cond);
    }

    // Enable output from the thread that holds the oldest output
    // buffer in the output queue (if such a thread exists).
    mythread_sync(coder->mutex) {
      lzma_outq_enable_partial_output(&coder->outq,
          &worker_enable_partial_update);
    }

    coder->sequence = SEQ_BLOCK_THR_RUN;
    FALLTHROUGH;
  }

  case SEQ_BLOCK_THR_RUN: {
    if (action == LZMA_FINISH && coder->fail_fast) {
      // We know that we won't get more input and that
      // the caller wants fail-fast behavior. If we see
      // that we don't have enough input to finish this
      // Block, return LZMA_DATA_ERROR immediately.
      // See SEQ_BLOCK_HEADER for the error code rationale.
      const size_t in_avail = in_size - *in_pos;
      const size_t in_needed = coder->thr->in_size
          - coder->thr->in_filled;
      if (in_avail < in_needed) {
        threads_stop(coder);
        return LZMA_DATA_ERROR;
      }
    }

    // Copy input to the worker thread.
    size_t cur_in_filled = coder->thr->in_filled;
    lzma_bufcpy(in, in_pos, in_size, coder->thr->in,
        &cur_in_filled, coder->thr->in_size);

    // Tell the thread how much we copied.
    mythread_sync(coder->thr->mutex) {
      coder->thr->in_filled = cur_in_filled;

      // NOTE: Most of the time we are copying input faster
      // than the thread can decode so most of the time
      // calling mythread_cond_signal() is useless but
      // we cannot make it conditional because thr->in_pos
      // is updated without a mutex. And the overhead should
      // be very much negligible anyway.
      mythread_cond_signal(&coder->thr->cond);
    }

    // Read output from the output queue. Just like in
    // SEQ_BLOCK_HEADER, we wait to fill the output buffer
    // only if waiting_allowed was set to true in the beginning
    // of this function (see the comment there) and there is
    // no input available. In SEQ_BLOCK_HEADER, there is never
    // input available when read_output_and_wait() is called,
    // but here there can be when LZMA_FINISH is used, thus we
    // need to check if *in_pos == in_size. Otherwise we would
    // wait here instead of using the available input to start
    // a new thread.
    return_if_error(read_output_and_wait(coder, allocator,
        out, out_pos, out_size,
        NULL,
        waiting_allowed && *in_pos == in_size,
        &wait_abs, &has_blocked));

    if (coder->pending_error != LZMA_OK) {
      coder->sequence = SEQ_ERROR;
      break;
    }

    // Return if the input didn't contain the whole Block.
    //
    // NOTE: When we updated coder->thr->in_filled a few lines
    // above, the worker thread might by now have finished its
    // work and returned itself back to the stack of free threads.
    if (coder->thr->in_filled < coder->thr->in_size) {
      assert(*in_pos == in_size);
      return LZMA_OK;
    }

    // The whole Block has been copied to the thread-specific
    // buffer. Continue from the next Block Header or Index.
    coder->thr = NULL;
    coder->sequence = SEQ_BLOCK_HEADER;
    break;
  }

  case SEQ_BLOCK_DIRECT_INIT: {
    // Wait for the threads to finish and that all decoded data
    // has been copied to the output. That is, wait until the
    // output queue becomes empty.
    //
    // NOTE: No need to check for coder->pending_error as
    // we aren't consuming any input until the queue is empty
    // and if there is a pending error, read_output_and_wait()
    // will eventually return it before the queue is empty.
    return_if_error(read_output_and_wait(coder, allocator,
        out, out_pos, out_size,
        NULL, true, &wait_abs, &has_blocked));
    if (!lzma_outq_is_empty(&coder->outq))
      return LZMA_OK;

    // Free the cached output buffers.
    lzma_outq_clear_cache(&coder->outq, allocator);

    // Get rid of the worker threads, including the coder->threads
    // array.
    threads_end(coder, allocator);

    // Initialize the Block decoder.
    const lzma_ret ret = lzma_block_decoder_init(
        &coder->block_decoder, allocator,
        &coder->block_options);

    // Free the allocated filter options since they are needed
    // only to initialize the Block decoder.
    lzma_filters_free(coder->filters, allocator);
    coder->block_options.filters = NULL;

    // Check if Block decoder initialization succeeded.
    if (ret != LZMA_OK)
      return ret;

    // Make the memory usage visible to _memconfig().
    coder->mem_direct_mode = coder->mem_next_filters;

    coder->sequence = SEQ_BLOCK_DIRECT_RUN;
    FALLTHROUGH;
  }

  case SEQ_BLOCK_DIRECT_RUN: {
    const size_t in_old = *in_pos;
    const size_t out_old = *out_pos;
    const lzma_ret ret = coder->block_decoder.code(
        coder->block_decoder.coder, allocator,
        in, in_pos, in_size, out, out_pos, out_size,
        action);
    coder->progress_in += *in_pos - in_old;
    coder->progress_out += *out_pos - out_old;

    if (ret != LZMA_STREAM_END)
      return ret;

    // Block decoded successfully. Add the new size pair to
    // the Index hash.
    return_if_error(lzma_index_hash_append(coder->index_hash,
        lzma_block_unpadded_size(
          &coder->block_options),
        coder->block_options.uncompressed_size));

    coder->sequence = SEQ_BLOCK_HEADER;
    break;
  }

  case SEQ_INDEX_WAIT_OUTPUT:
    // Flush the output from all worker threads so that we can
    // decode the Index without thinking about threading.
    return_if_error(read_output_and_wait(coder, allocator,
        out, out_pos, out_size,
        NULL, true, &wait_abs, &has_blocked));

    if (!lzma_outq_is_empty(&coder->outq))
      return LZMA_OK;

    coder->sequence = SEQ_INDEX_DECODE;
    FALLTHROUGH;

  case SEQ_INDEX_DECODE: {
    // If we don't have any input, don't call
    // lzma_index_hash_decode() since it would return
    // LZMA_BUF_ERROR, which we must not do here.
    if (*in_pos >= in_size)
      return LZMA_OK;

    // Decode the Index and compare it to the hash calculated
    // from the sizes of the Blocks (if any).
    const size_t in_old = *in_pos;
    const lzma_ret ret = lzma_index_hash_decode(coder->index_hash,
        in, in_pos, in_size);
    coder->progress_in += *in_pos - in_old;
    if (ret != LZMA_STREAM_END)
      return ret;

    coder->sequence = SEQ_STREAM_FOOTER;
    FALLTHROUGH;
  }

  case SEQ_STREAM_FOOTER: {
    // Copy the Stream Footer to the internal buffer.
    const size_t in_old = *in_pos;
    lzma_bufcpy(in, in_pos, in_size, coder->buffer, &coder->pos,
        LZMA_STREAM_HEADER_SIZE);
    coder->progress_in += *in_pos - in_old;

    // Return if we didn't get the whole Stream Footer yet.
    if (coder->pos < LZMA_STREAM_HEADER_SIZE)
      return LZMA_OK;

    coder->pos = 0;

    // Decode the Stream Footer. The decoder gives
    // LZMA_FORMAT_ERROR if the magic bytes don't match,
    // so convert that return code to LZMA_DATA_ERROR.
    lzma_stream_flags footer_flags;
    const lzma_ret ret = lzma_stream_footer_decode(
        &footer_flags, coder->buffer);
    if (ret != LZMA_OK)
      return ret == LZMA_FORMAT_ERROR
          ? LZMA_DATA_ERROR : ret;

    // Check that Index Size stored in the Stream Footer matches
    // the real size of the Index field.
    if (lzma_index_hash_size(coder->index_hash)
        != footer_flags.backward_size)
      return LZMA_DATA_ERROR;

    // Compare that the Stream Flags fields are identical in
    // both Stream Header and Stream Footer.
    return_if_error(lzma_stream_flags_compare(
        &coder->stream_flags, &footer_flags));

    if (!coder->concatenated)
      return LZMA_STREAM_END;

    coder->sequence = SEQ_STREAM_PADDING;
    FALLTHROUGH;
  }

  case SEQ_STREAM_PADDING:
    assert(coder->concatenated);

    // Skip over possible Stream Padding.
    while (true) {
      if (*in_pos >= in_size) {
        // Unless LZMA_FINISH was used, we cannot
        // know if there's more input coming later.
        if (action != LZMA_FINISH)
          return LZMA_OK;

        // Stream Padding must be a multiple of
        // four bytes.
        return coder->pos == 0
            ? LZMA_STREAM_END
            : LZMA_DATA_ERROR;
      }

      // If the byte is not zero, it probably indicates
      // beginning of a new Stream (or the file is corrupt).
      if (in[*in_pos] != 0x00)
        break;

      ++*in_pos;
      ++coder->progress_in;
      coder->pos = (coder->pos + 1) & 3;
    }

    // Stream Padding must be a multiple of four bytes (empty
    // Stream Padding is OK).
    if (coder->pos != 0) {
      ++*in_pos;
      ++coder->progress_in;
      return LZMA_DATA_ERROR;
    }

    // Prepare to decode the next Stream.
    return_if_error(stream_decoder_reset(coder, allocator));
    break;

  case SEQ_ERROR:
    if (!coder->fail_fast) {
      // Let the application get all data before the point
      // where the error was detected. This matches the
      // behavior of single-threaded use.
      //
      // FIXME? Some errors (LZMA_MEM_ERROR) don't get here,
      // they are returned immediately. Thus in rare cases
      // the output will be less than in the single-threaded
      // mode. Maybe this doesn't matter much in practice.
      return_if_error(read_output_and_wait(coder, allocator,
          out, out_pos, out_size,
          NULL, true, &wait_abs, &has_blocked));

      // We get here only if the error happened in the main
      // thread, for example, unsupported Block Header.
      if (!lzma_outq_is_empty(&coder->outq))
        return LZMA_OK;
    }

    // We only get here if no errors were detected by the worker
    // threads. Errors from worker threads would have already been
    // returned by the call to read_output_and_wait() above.
    return coder->pending_error;

  default:
    assert(0);
    return LZMA_PROG_ERROR;
  }

  // Never reached
}


static void
stream_decoder_mt_end(void *coder_ptr, const lzma_allocator *allocator)
{
  struct lzma_stream_coder *coder = coder_ptr;

  threads_end(coder, allocator);
  lzma_outq_end(&coder->outq, allocator);

  lzma_next_end(&coder->block_decoder, allocator);
  lzma_filters_free(coder->filters, allocator);
  lzma_index_hash_end(coder->index_hash, allocator);

  lzma_free(coder, allocator);
  return;
}


static lzma_check
stream_decoder_mt_get_check(const void *coder_ptr)
{
  const struct lzma_stream_coder *coder = coder_ptr;
  return coder->stream_flags.check;
}


static lzma_ret
stream_decoder_mt_memconfig(void *coder_ptr, uint64_t *memusage,
    uint64_t *old_memlimit, uint64_t new_memlimit)
{
  // NOTE: This function gets/sets memlimit_stop. For now,
  // memlimit_threading cannot be modified after initialization.
  //
  // *memusage will include cached memory too. Excluding cached memory
  // would be misleading and it wouldn't help the applications to
  // know how much memory is actually needed to decompress the file
  // because the higher the number of threads and the memlimits are
  // the more memory the decoder may use.
  //
  // Setting a new limit includes the cached memory too and too low
  // limits will be rejected. Alternative could be to free the cached
  // memory immediately if that helps to bring the limit down but
  // the current way is the simplest. It's unlikely that limit needs
  // to be lowered in the middle of a file anyway; the typical reason
  // to want a new limit is to increase after LZMA_MEMLIMIT_ERROR
  // and even such use isn't common.
  struct lzma_stream_coder *coder = coder_ptr;

  mythread_sync(coder->mutex) {
    *memusage = coder->mem_direct_mode
        + coder->mem_in_use
        + coder->mem_cached
        + coder->outq.mem_allocated;
  }

  // If no filter chains are allocated, *memusage may be zero.
  // Always return at least LZMA_MEMUSAGE_BASE.
  if (*memusage < LZMA_MEMUSAGE_BASE)
    *memusage = LZMA_MEMUSAGE_BASE;

  *old_memlimit = coder->memlimit_stop;

  if (new_memlimit != 0) {
    if (new_memlimit < *memusage)
      return LZMA_MEMLIMIT_ERROR;

    coder->memlimit_stop = new_memlimit;
  }

  return LZMA_OK;
}


static void
stream_decoder_mt_get_progress(void *coder_ptr,
    uint64_t *progress_in, uint64_t *progress_out)
{
  struct lzma_stream_coder *coder = coder_ptr;

  // Lock coder->mutex to prevent finishing threads from moving their
  // progress info from the worker_thread structure to lzma_stream_coder.
  mythread_sync(coder->mutex) {
    *progress_in = coder->progress_in;
    *progress_out = coder->progress_out;

    for (size_t i = 0; i < coder->threads_initialized; ++i) {
      mythread_sync(coder->threads[i].mutex) {
        *progress_in += coder->threads[i].progress_in;
        *progress_out += coder->threads[i]
            .progress_out;
      }
    }
  }

  return;
}


static lzma_ret
stream_decoder_mt_init(lzma_next_coder *next, const lzma_allocator *allocator,
           const lzma_mt *options)
{
  struct lzma_stream_coder *coder;

  if (options->threads == 0 || options->threads > LZMA_THREADS_MAX)
    return LZMA_OPTIONS_ERROR;

  if (options->flags & ~LZMA_SUPPORTED_FLAGS)
    return LZMA_OPTIONS_ERROR;

  lzma_next_coder_init(&stream_decoder_mt_init, next, allocator);

  coder = next->coder;
  if (!coder) {
    coder = lzma_alloc(sizeof(struct lzma_stream_coder), allocator);
    if (coder == NULL)
      return LZMA_MEM_ERROR;

    next->coder = coder;

    if (mythread_mutex_init(&coder->mutex)) {
      lzma_free(coder, allocator);
      return LZMA_MEM_ERROR;
    }

    if (mythread_cond_init(&coder->cond)) {
      mythread_mutex_destroy(&coder->mutex);
      lzma_free(coder, allocator);
      return LZMA_MEM_ERROR;
    }

    next->code = &stream_decode_mt;
    next->end = &stream_decoder_mt_end;
    next->get_check = &stream_decoder_mt_get_check;
    next->memconfig = &stream_decoder_mt_memconfig;
    next->get_progress = &stream_decoder_mt_get_progress;

    coder->filters[0].id = LZMA_VLI_UNKNOWN;
    memzero(&coder->outq, sizeof(coder->outq));

    coder->block_decoder = LZMA_NEXT_CODER_INIT;
    coder->mem_direct_mode = 0;

    coder->index_hash = NULL;
    coder->threads = NULL;
    coder->threads_free = NULL;
    coder->threads_initialized = 0;
  }

  // Cleanup old filter chain if one remains after unfinished decoding
  // of a previous Stream.
  lzma_filters_free(coder->filters, allocator);

  // By allocating threads from scratch we can start memory-usage
  // accounting from scratch, too. Changes in filter and block sizes may
  // affect number of threads.
  //
  // Reusing threads doesn't seem worth it. Unlike the single-threaded
  // decoder, with some types of input file combinations reusing
  // could leave quite a lot of memory allocated but unused (first
  // file could allocate a lot, the next files could use fewer
  // threads and some of the allocations from the first file would not
  // get freed unless memlimit_threading forces us to clear caches).
  //
  // NOTE: The direct mode decoder isn't freed here if one exists.
  // It will be reused or freed as needed in the main loop.
  threads_end(coder, allocator);

  // All memusage counters start at 0 (including mem_direct_mode).
  // The little extra that is needed for the structs in this file
  // get accounted well enough by the filter chain memory usage
  // which adds LZMA_MEMUSAGE_BASE for each chain. However,
  // stream_decoder_mt_memconfig() has to handle this specially so that
  // it will never return less than LZMA_MEMUSAGE_BASE as memory usage.
  coder->mem_in_use = 0;
  coder->mem_cached = 0;
  coder->mem_next_block = 0;

  coder->progress_in = 0;
  coder->progress_out = 0;

  coder->sequence = SEQ_STREAM_HEADER;
  coder->thread_error = LZMA_OK;
  coder->pending_error = LZMA_OK;
  coder->thr = NULL;

  coder->timeout = options->timeout;

  coder->memlimit_threading = my_max(1, options->memlimit_threading);
  coder->memlimit_stop = my_max(1, options->memlimit_stop);
  if (coder->memlimit_threading > coder->memlimit_stop)
    coder->memlimit_threading = coder->memlimit_stop;

  coder->tell_no_check = (options->flags & LZMA_TELL_NO_CHECK) != 0;
  coder->tell_unsupported_check
      = (options->flags & LZMA_TELL_UNSUPPORTED_CHECK) != 0;
  coder->tell_any_check = (options->flags & LZMA_TELL_ANY_CHECK) != 0;
  coder->ignore_check = (options->flags & LZMA_IGNORE_CHECK) != 0;
  coder->concatenated = (options->flags & LZMA_CONCATENATED) != 0;
  coder->fail_fast = (options->flags & LZMA_FAIL_FAST) != 0;

  coder->first_stream = true;
  coder->out_was_filled = false;
  coder->pos = 0;

  coder->threads_max = options->threads;

  return_if_error(lzma_outq_init(&coder->outq, allocator,
               coder->threads_max));

  return stream_decoder_reset(coder, allocator);
}


extern LZMA_API(lzma_ret)
lzma_stream_decoder_mt(lzma_stream *strm, const lzma_mt *options)
{
  lzma_next_strm_init(stream_decoder_mt_init, strm, options);

  strm->internal->supported_actions[LZMA_RUN] = true;
  strm->internal->supported_actions[LZMA_FINISH] = true;

  return LZMA_OK;
}

Coverage Report

Created: 2026-11-12 06:33