/src/vvenc/source/Lib/Utilities/NoMallocThreadPool.h

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/** \file     NoMallocThreadPool.h
    \brief    thread pool
*/

#pragma once

#include <thread>
#include <mutex>
#include <condition_variable>
#include <atomic>
#include <chrono>
#include <array>

#ifdef HAVE_PTHREADS
#include <pthread.h>
#endif

#include "CommonLib/CommonDef.h"
#if ENABLE_TIME_PROFILING_MT_MODE
#include "CommonLib/TimeProfiler.h"
#endif

//! \ingroup Utilities
//! \{

namespace vvenc {

#ifdef TRACE_ENABLE_ITT
static __itt_domain* itt_domain_thrd = __itt_domain_create( "Threading" );

static __itt_string_handle* itt_handle_TPspinWait = __itt_string_handle_create( "Spin_Wait" );
static __itt_string_handle* itt_handle_TPblocked  = __itt_string_handle_create( "Blocked" );
static __itt_string_handle* itt_handle_TPaddTask  = __itt_string_handle_create( "Add_Task" );

//static long itt_TP_blocked = 1;

#endif //TRACE_ENABLE_ITT

#if ENABLE_VALGRIND_CODE
typedef std::unique_lock< std::mutex > MutexLock;
#endif

// block threads after busy-waiting this long
const static auto BUSY_WAIT_TIME = [] {
  const char *env = getenv( "BUSY_WAIT_TIME" );
  if( env )
    return std::chrono::milliseconds( atoi( env ) );
  return std::chrono::milliseconds( 1 );
}();


// enable this if tasks need to be added from mutliple threads
#define ADD_TASK_THREAD_SAFE 1


// ---------------------------------------------------------------------------
// Synchronization tools
// ---------------------------------------------------------------------------

struct Barrier
{
  void unlock()
  {
    m_lockState.store( false );
  }

  void lock()
  {
    m_lockState.store( true );
  }

  bool isBlocked() const
  {
    return m_lockState;
  }

  Barrier()  = default;
  ~Barrier() = default;
  explicit Barrier( bool locked ) : m_lockState( locked ) {}

  Barrier( const Barrier & ) = delete;
  Barrier( Barrier && )      = delete;

  Barrier& operator=( const Barrier & ) = delete;
  Barrier& operator=( Barrier && )      = delete;

private:
  std::atomic_bool m_lockState{ true };
};

struct BlockingBarrier
{
  void unlock()
  {
    std::unique_lock<std::mutex> l( m_lock );
    m_intBarrier.unlock();
    if( !m_intBarrier.isBlocked() )
    {
      m_cond.notify_all();
    }
  }

  void lock()
  {
    std::unique_lock<std::mutex> l( m_lock );
    m_intBarrier.lock();
  }

  bool isBlocked() const
  {
    return m_intBarrier.isBlocked();
  }

  void wait() const
  {
    BlockingBarrier* nonconst = const_cast<BlockingBarrier*>(this);

    std::unique_lock<std::mutex> l( nonconst->m_lock );
    nonconst->m_cond.wait( l, [this] { return !m_intBarrier.isBlocked(); } );
  }

  BlockingBarrier()  = default;
  ~BlockingBarrier() { std::unique_lock<std::mutex> l( m_lock ); } // ensure all threads have unlocked the mutex, when we start destruction

  BlockingBarrier( const BlockingBarrier& ) = delete;
  BlockingBarrier( BlockingBarrier&& )      = delete;

  BlockingBarrier& operator=( const BlockingBarrier& ) = delete;
  BlockingBarrier& operator=( BlockingBarrier&& ) = delete;

  // cast to const ref Barrier, so we can use it for thread pool tasks:
  operator const Barrier&() const { return m_intBarrier; }

private:
  Barrier                 m_intBarrier;
  std::condition_variable m_cond;
  std::mutex              m_lock;
};

struct WaitCounter
{
  int operator++()
  {
    std::unique_lock<std::mutex> l( m_lock );
    done.lock();
    return ++m_count;
  }

  int operator--()
  {
    std::unique_lock<std::mutex> l( m_lock );
    const unsigned int new_count = --m_count;
    if( new_count == 0 )
    {
      m_cond.notify_all();
      done.unlock();
    }
    l.unlock(); // unlock mutex after done-barrier to prevent race between barrier and counter
    return new_count;
  }

  bool isBlocked() const
  {
    return 0 != m_count;
  }

  void wait() const
  {
    WaitCounter* nonconst = const_cast<WaitCounter*>(this);

    std::unique_lock<std::mutex> l( nonconst->m_lock );
    nonconst->m_cond.wait( l, [this] { return m_count == 0; } );
  }

  WaitCounter() = default;
  ~WaitCounter() { std::unique_lock<std::mutex> l( m_lock ); }   // ensure all threads have unlocked the mutex, when we start destruction

  WaitCounter( const WaitCounter & ) = delete;
  WaitCounter( WaitCounter && )      = delete;

  WaitCounter &operator=( const WaitCounter & ) = delete;
  WaitCounter &operator=( WaitCounter && )      = delete;

  Barrier done{ false };

private:
  std::condition_variable m_cond;
  std::mutex              m_lock;
  unsigned int            m_count = 0;
};



// ---------------------------------------------------------------------------
// Thread Pool
// ---------------------------------------------------------------------------

using CBarrierVec = std::vector<const Barrier*>;

class NoMallocThreadPool
{
  typedef enum
  {
    FREE = 0,
    PREPARING,
    WAITING,
    RUNNING
  } TaskState;

  using TaskFunc = bool ( * )( int, void * );

  struct Slot
  {
    TaskFunc               func      { nullptr };
    TaskFunc               readyCheck{ nullptr };
    void*                  param     { nullptr };
    WaitCounter*           counter   { nullptr };
    Barrier*               done      { nullptr };
    CBarrierVec            barriers;
    std::atomic<TaskState> state     { FREE };
  };


  class ChunkedTaskQueue
  {
    constexpr static int ChunkSize = 128;

    class Chunk
    {
      std::array<Slot, ChunkSize> m_slots;
      std::atomic<Chunk*>         m_next{ nullptr };
      Chunk&                      m_firstChunk;

      Chunk( Chunk* firstPtr ) : m_firstChunk{ *firstPtr } {}

      friend class ChunkedTaskQueue;
    };

  public:
    class Iterator
    {
      Slot*  m_slot  = nullptr;
      Chunk* m_chunk = nullptr;

    public:
      Iterator() = default;
      Iterator( Slot* slot, Chunk* chunk ) : m_slot( slot ), m_chunk( chunk ) {}

      Iterator& operator++()
      {
        CHECKD( m_slot == nullptr, "incrementing invalid iterator" );
        CHECKD( m_chunk == nullptr, "incrementing invalid iterator" );

        if( m_slot != &m_chunk->m_slots.back() )
        {
          ++m_slot;
        }
        else
        {
          m_chunk = m_chunk->m_next;
          if( m_chunk )
          {
            m_slot  = &m_chunk->m_slots.front();
          }
          else
          {
            m_slot  = nullptr;
          }
        }
        return *this;
      }

      // increment iterator and wrap around, if end is reached
      Iterator& incWrap()
      {
        CHECKD( m_slot == nullptr, "incrementing invalid iterator" );
        CHECKD( m_chunk == nullptr, "incrementing invalid iterator" );

        if( m_slot != &m_chunk->m_slots.back() )
        {
          ++m_slot;
        }
        else
        {
          if( (Chunk*)m_chunk->m_next )
          {
            m_chunk = m_chunk->m_next;
          }
          else
          {
            m_chunk = &m_chunk->m_firstChunk;
          }
          m_slot = &m_chunk->m_slots.front();
        }
        return *this;
      }

      bool operator==( const Iterator& rhs ) const { return m_slot == rhs.m_slot; } // don't need to compare m_chunk, because m_slot is a pointer
      bool operator!=( const Iterator& rhs ) const { return m_slot != rhs.m_slot; } // don't need to compare m_chunk, because m_slot is a pointer

      Slot& operator*() { return *m_slot; }

      bool isValid() const { return m_slot != nullptr && m_chunk != nullptr; }

      using iterator_category = std::forward_iterator_tag;
      using value_type        = Slot;
      using pointer           = Slot*;
      using reference         = Slot&;
      using difference_type   = ptrdiff_t;
    };

    ChunkedTaskQueue() = default;
    ~ChunkedTaskQueue()
    {
      Chunk* next = m_firstChunk.m_next;
      while( next )
      {
        Chunk* curr = next;
        next = curr->m_next;
        delete curr;
      }
    }

    ChunkedTaskQueue( const ChunkedTaskQueue& ) = delete;
    ChunkedTaskQueue( ChunkedTaskQueue&& )      = delete;

    // grow the queue by adding a chunk and return an iterator to the first new task-slot
    Iterator grow()
    {
      std::unique_lock<std::mutex> l( m_resizeMutex );  // prevent concurrent growth of the queue. Read access while growing is no problem

      m_lastChunk->m_next = new Chunk( &m_firstChunk );
      m_lastChunk         = m_lastChunk->m_next;

      return Iterator{ &m_lastChunk->m_slots.front(), m_lastChunk };
    }

    Iterator begin() { return Iterator{ &m_firstChunk.m_slots.front(), &m_firstChunk }; }
    Iterator end()   { return Iterator{ nullptr, nullptr }; }

  private:
    Chunk  m_firstChunk{ &m_firstChunk };
    Chunk* m_lastChunk = &m_firstChunk;

    std::mutex m_resizeMutex;
  };


public:
  NoMallocThreadPool( int numThreads = 1, const char *threadPoolName = nullptr, const VVEncCfg* encCfg = nullptr );
  ~NoMallocThreadPool();

  bool addBarrierTask( bool             ( *func )( int, void* ),
                       void*               param,
                       WaitCounter*        counter                    = nullptr,
                       Barrier*            done                       = nullptr,
                       const CBarrierVec&& barriers                   = {},
                       bool             ( *readyCheck )( int, void* ) = nullptr )
  {
    if( m_threads.empty() )
    {
      // if singlethreaded, execute all pending tasks
      if( m_nextFillSlot != m_tasks.begin() )
      {
        processTasksOnMainThread();
      }

      // when no barriers block this task, execute it directly
      if( std::none_of( barriers.begin(), barriers.end(), []( const Barrier* b ) { return b && b->isBlocked(); } )
          && ( !readyCheck || readyCheck( 0, param ) ) )
      {
        if( func( 0, param ) )
        {
          if( done != nullptr )
          {
            done->unlock();
          }
          return true;
        }
      }
    }

    while( true )
    {
#if ADD_TASK_THREAD_SAFE
      std::unique_lock<std::mutex> l(m_nextFillSlotMutex);
#endif
      CHECKD( !m_nextFillSlot.isValid(), "Next fill slot iterator should always be valid" );
      const auto startIt = m_nextFillSlot;

#if ADD_TASK_THREAD_SAFE
      l.unlock();
#endif

      bool first = true;
      for( auto it = startIt; it != startIt || first; it.incWrap() )
      {
#if ENABLE_VALGRIND_CODE
        MutexLock lock( m_extraMutex );
#endif

        first = false;

        auto& t = *it;
        auto expected = FREE;
        if( t.state.load( std::memory_order_relaxed ) == FREE && t.state.compare_exchange_strong( expected, PREPARING ) )
        {
          if( counter )
          {
            counter->operator++();
          }

          t.func       = func;
          t.readyCheck = readyCheck;
          t.param      = param;
          t.done       = done;
          t.counter    = counter;
          t.barriers   = std::move( barriers );
          t.state      = WAITING;

#if ADD_TASK_THREAD_SAFE
          l.lock();
#endif
          m_nextFillSlot.incWrap();
          return true;
        }
      }

#if ADD_TASK_THREAD_SAFE
      l.lock();
#endif
      m_nextFillSlot = m_tasks.grow();
    }
    return false;
  }

  bool processTasksOnMainThread();

  void shutdown( bool block );
  void waitForThreads();

  int numThreads() const { return (int)m_threads.size(); }
#if ENABLE_TIME_PROFILING_MT_MODE
  const std::vector< TProfiler* >& getProfilers() { return profilers; }
#endif

private:
#ifdef HAVE_PTHREADS
  struct PThread
  {
    PThread()                            = default;
    ~PThread()                           = default;

    PThread( const PThread& )            = delete;
    PThread& operator=( const PThread& ) = delete;

    PThread( PThread&& other ) { *this = std::move( other ); };
    PThread& operator=( PThread&& other );

    template<class TFunc, class... TArgs>
    PThread( TFunc&& func, TArgs&&... args );

    bool joinable() { return m_joinable; }
    void join();

  private:
    pthread_t m_id       = 0;
    bool      m_joinable = false;
  };
#endif   // HAVE_PTHREADS

#if HAVE_PTHREADS
  using ThreadImpl = PThread;
#else
  using ThreadImpl = std::thread;
#endif

  using TaskIterator = ChunkedTaskQueue::Iterator;

  // members
  std::string              m_poolName;
  std::atomic_bool         m_exitThreads{ false };
  std::vector<ThreadImpl>  m_threads;
  ChunkedTaskQueue         m_tasks;
  TaskIterator             m_nextFillSlot = m_tasks.begin();
#if ADD_TASK_THREAD_SAFE
  std::mutex               m_nextFillSlotMutex;
#endif
  std::mutex               m_idleMutex;
  std::atomic_uint         m_waitingThreads{ 0 };
#if ENABLE_VALGRIND_CODE
  std::mutex               m_extraMutex;
#endif
#if ENABLE_TIME_PROFILING_MT_MODE
  std::vector< TProfiler* > profilers;
#endif

  // internal functions
  void         threadProc  ( int threadId, const VVEncCfg& encCfg );
  TaskIterator findNextTask( int threadId, TaskIterator startSearch );
  bool         processTask ( int threadId, Slot& task );
};

} // namespace vvenc

//! \}


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Created: 2026-06-16 07:20