/src/git/name-hash.c

Source
/*
 * name-hash.c
 *
 * Hashing names in the index state
 *
 * Copyright (C) 2008 Linus Torvalds
 */

#define USE_THE_REPOSITORY_VARIABLE
#define DISABLE_SIGN_COMPARE_WARNINGS

#include "git-compat-util.h"
#include "environment.h"
#include "gettext.h"
#include "name-hash.h"
#include "object.h"
#include "read-cache-ll.h"
#include "thread-utils.h"
#include "trace.h"
#include "trace2.h"
#include "sparse-index.h"

struct dir_entry {
  struct hashmap_entry ent;
  struct dir_entry *parent;
  int nr;
  unsigned int namelen;
  char name[FLEX_ARRAY];
};

static int dir_entry_cmp(const void *cmp_data UNUSED,
       const struct hashmap_entry *eptr,
       const struct hashmap_entry *entry_or_key,
       const void *keydata)
{
  const struct dir_entry *e1, *e2;
  const char *name = keydata;

  e1 = container_of(eptr, const struct dir_entry, ent);
  e2 = container_of(entry_or_key, const struct dir_entry, ent);

  return e1->namelen != e2->namelen || strncasecmp(e1->name,
      name ? name : e2->name, e1->namelen);
}

static struct dir_entry *find_dir_entry__hash(struct index_state *istate,
    const char *name, unsigned int namelen, unsigned int hash)
{
  struct dir_entry key;
  hashmap_entry_init(&key.ent, hash);
  key.namelen = namelen;
  return hashmap_get_entry(&istate->dir_hash, &key, ent, name);
}

static struct dir_entry *find_dir_entry(struct index_state *istate,
    const char *name, unsigned int namelen)
{
  return find_dir_entry__hash(istate, name, namelen, memihash(name, namelen));
}

static struct dir_entry *hash_dir_entry(struct index_state *istate,
    struct cache_entry *ce, int namelen)
{
  /*
   * Throw each directory component in the hash for quick lookup
   * during a git status. Directory components are stored without their
   * closing slash.  Despite submodules being a directory, they never
   * reach this point, because they are stored
   * in index_state.name_hash (as ordinary cache_entries).
   */
  struct dir_entry *dir;

  /* get length of parent directory */
  while (namelen > 0 && !is_dir_sep(ce->name[namelen - 1]))
    namelen--;
  if (namelen <= 0)
    return NULL;
  namelen--;

  /* lookup existing entry for that directory */
  dir = find_dir_entry(istate, ce->name, namelen);
  if (!dir) {
    /* not found, create it and add to hash table */
    FLEX_ALLOC_MEM(dir, name, ce->name, namelen);
    hashmap_entry_init(&dir->ent, memihash(ce->name, namelen));
    dir->namelen = namelen;
    hashmap_add(&istate->dir_hash, &dir->ent);

    /* recursively add missing parent directories */
    dir->parent = hash_dir_entry(istate, ce, namelen);
  }
  return dir;
}

static void add_dir_entry(struct index_state *istate, struct cache_entry *ce)
{
  /* Add reference to the directory entry (and parents if 0). */
  struct dir_entry *dir = hash_dir_entry(istate, ce, ce_namelen(ce));
  while (dir && !(dir->nr++))
    dir = dir->parent;
}

static void remove_dir_entry(struct index_state *istate, struct cache_entry *ce)
{
  /*
   * Release reference to the directory entry. If 0, remove and continue
   * with parent directory.
   */
  struct dir_entry *dir = hash_dir_entry(istate, ce, ce_namelen(ce));
  while (dir && !(--dir->nr)) {
    struct dir_entry *parent = dir->parent;
    hashmap_remove(&istate->dir_hash, &dir->ent, NULL);
    free(dir);
    dir = parent;
  }
}

static void hash_index_entry(struct index_state *istate, struct cache_entry *ce)
{
  if (ce->ce_flags & CE_HASHED)
    return;
  ce->ce_flags |= CE_HASHED;

  if (!S_ISSPARSEDIR(ce->ce_mode)) {
    hashmap_entry_init(&ce->ent, memihash(ce->name, ce_namelen(ce)));
    hashmap_add(&istate->name_hash, &ce->ent);
  }

  if (ignore_case)
    add_dir_entry(istate, ce);
}

static int cache_entry_cmp(const void *cmp_data UNUSED,
         const struct hashmap_entry *eptr,
         const struct hashmap_entry *entry_or_key,
         const void *remove)
{
  const struct cache_entry *ce1, *ce2;

  ce1 = container_of(eptr, const struct cache_entry, ent);
  ce2 = container_of(entry_or_key, const struct cache_entry, ent);

  /*
   * For remove_name_hash, find the exact entry (pointer equality); for
   * index_file_exists, find all entries with matching hash code and
   * decide whether the entry matches in same_name.
   */
  return remove ? !(ce1 == ce2) : 0;
}

static int lazy_try_threaded = 1;
static int lazy_nr_dir_threads;

/*
 * Set a minimum number of cache_entries that we will handle per
 * thread and use that to decide how many threads to run (up to
 * the number on the system).
 *
 * For guidance setting the lower per-thread bound, see:
 *     t/helper/test-lazy-init-name-hash --analyze
 */
#define LAZY_THREAD_COST (2000)

/*
 * We use n mutexes to guard n partitions of the "istate->dir_hash"
 * hashtable.  Since "find" and "insert" operations will hash to a
 * particular bucket and modify/search a single chain, we can say
 * that "all chains mod n" are guarded by the same mutex -- rather
 * than having a single mutex to guard the entire table.  (This does
 * require that we disable "rehashing" on the hashtable.)
 *
 * So, a larger value here decreases the probability of a collision
 * and the time that each thread must wait for the mutex.
 */
#define LAZY_MAX_MUTEX   (32)

static pthread_mutex_t *lazy_dir_mutex_array;

/*
 * An array of lazy_entry items is used by the n threads in
 * the directory parse (first) phase to (lock-free) store the
 * intermediate results.  These values are then referenced by
 * the 2 threads in the second phase.
 */
struct lazy_entry {
  struct dir_entry *dir;
  unsigned int hash_dir;
  unsigned int hash_name;
};

/*
 * Decide if we want to use threads (if available) to load
 * the hash tables.  We set "lazy_nr_dir_threads" to zero when
 * it is not worth it.
 */
static int lookup_lazy_params(struct index_state *istate)
{
  int nr_cpus;

  lazy_nr_dir_threads = 0;

  if (!lazy_try_threaded)
    return 0;

  /*
   * If we are respecting case, just use the original
   * code to build the "istate->name_hash".  We don't
   * need the complexity here.
   */
  if (!ignore_case)
    return 0;

  nr_cpus = online_cpus();
  if (nr_cpus < 2)
    return 0;

  if (istate->cache_nr < 2 * LAZY_THREAD_COST)
    return 0;

  if (istate->cache_nr < nr_cpus * LAZY_THREAD_COST)
    nr_cpus = istate->cache_nr / LAZY_THREAD_COST;
  lazy_nr_dir_threads = nr_cpus;
  return lazy_nr_dir_threads;
}

/*
 * Initialize n mutexes for use when searching and inserting
 * into "istate->dir_hash".  All "dir" threads are trying
 * to insert partial pathnames into the hash as they iterate
 * over their portions of the index, so lock contention is
 * high.
 *
 * However, the hashmap is going to put items into bucket
 * chains based on their hash values.  Use that to create n
 * mutexes and lock on mutex[bucket(hash) % n].  This will
 * decrease the collision rate by (hopefully) a factor of n.
 */
static void init_dir_mutex(void)
{
  int j;

  CALLOC_ARRAY(lazy_dir_mutex_array, LAZY_MAX_MUTEX);

  for (j = 0; j < LAZY_MAX_MUTEX; j++)
    init_recursive_mutex(&lazy_dir_mutex_array[j]);
}

static void cleanup_dir_mutex(void)
{
  int j;

  for (j = 0; j < LAZY_MAX_MUTEX; j++)
    pthread_mutex_destroy(&lazy_dir_mutex_array[j]);

  free(lazy_dir_mutex_array);
}

static void lock_dir_mutex(int j)
{
  pthread_mutex_lock(&lazy_dir_mutex_array[j]);
}

static void unlock_dir_mutex(int j)
{
  pthread_mutex_unlock(&lazy_dir_mutex_array[j]);
}

static inline int compute_dir_lock_nr(
  const struct hashmap *map,
  unsigned int hash)
{
  return hashmap_bucket(map, hash) % LAZY_MAX_MUTEX;
}

static struct dir_entry *hash_dir_entry_with_parent_and_prefix(
  struct index_state *istate,
  struct dir_entry *parent,
  struct strbuf *prefix)
{
  struct dir_entry *dir;
  unsigned int hash;
  int lock_nr;

  /*
   * Either we have a parent directory and path with slash(es)
   * or the directory is an immediate child of the root directory.
   */
  assert((parent != NULL) ^ (strchr(prefix->buf, '/') == NULL));

  if (parent)
    hash = memihash_cont(parent->ent.hash,
      prefix->buf + parent->namelen,
      prefix->len - parent->namelen);
  else
    hash = memihash(prefix->buf, prefix->len);

  lock_nr = compute_dir_lock_nr(&istate->dir_hash, hash);
  lock_dir_mutex(lock_nr);

  dir = find_dir_entry__hash(istate, prefix->buf, prefix->len, hash);
  if (!dir) {
    FLEX_ALLOC_MEM(dir, name, prefix->buf, prefix->len);
    hashmap_entry_init(&dir->ent, hash);
    dir->namelen = prefix->len;
    dir->parent = parent;
    hashmap_add(&istate->dir_hash, &dir->ent);

    if (parent) {
      unlock_dir_mutex(lock_nr);

      /* All I really need here is an InterlockedIncrement(&(parent->nr)) */
      lock_nr = compute_dir_lock_nr(&istate->dir_hash, parent->ent.hash);
      lock_dir_mutex(lock_nr);
      parent->nr++;
    }
  }

  unlock_dir_mutex(lock_nr);

  return dir;
}

/*
 * handle_range_1() and handle_range_dir() are derived from
 * clear_ce_flags_1() and clear_ce_flags_dir() in unpack-trees.c
 * and handle the iteration over the entire array of index entries.
 * They use recursion for adjacent entries in the same parent
 * directory.
 */
static int handle_range_1(
  struct index_state *istate,
  int k_start,
  int k_end,
  struct dir_entry *parent,
  struct strbuf *prefix,
  struct lazy_entry *lazy_entries);

static int handle_range_dir(
  struct index_state *istate,
  int k_start,
  int k_end,
  struct dir_entry *parent,
  struct strbuf *prefix,
  struct lazy_entry *lazy_entries,
  struct dir_entry **dir_new_out)
{
  int rc, k;
  int input_prefix_len = prefix->len;
  struct dir_entry *dir_new;

  dir_new = hash_dir_entry_with_parent_and_prefix(istate, parent, prefix);

  strbuf_addch(prefix, '/');

  /*
   * Scan forward in the index array for index entries having the same
   * path prefix (that are also in this directory).
   */
  if (k_start + 1 >= k_end)
    k = k_end;
  else if (strncmp(istate->cache[k_start + 1]->name, prefix->buf, prefix->len) > 0)
    k = k_start + 1;
  else if (strncmp(istate->cache[k_end - 1]->name, prefix->buf, prefix->len) == 0)
    k = k_end;
  else {
    int begin = k_start;
    int end = k_end;
    assert(begin >= 0);
    while (begin < end) {
      int mid = begin + ((end - begin) >> 1);
      int cmp = strncmp(istate->cache[mid]->name, prefix->buf, prefix->len);
      if (cmp == 0) /* mid has same prefix; look in second part */
        begin = mid + 1;
      else if (cmp > 0) /* mid is past group; look in first part */
        end = mid;
      else
        die("cache entry out of order");
    }
    k = begin;
  }

  /*
   * Recurse and process what we can of this subset [k_start, k).
   */
  rc = handle_range_1(istate, k_start, k, dir_new, prefix, lazy_entries);

  strbuf_setlen(prefix, input_prefix_len);

  *dir_new_out = dir_new;
  return rc;
}

static int handle_range_1(
  struct index_state *istate,
  int k_start,
  int k_end,
  struct dir_entry *parent,
  struct strbuf *prefix,
  struct lazy_entry *lazy_entries)
{
  int input_prefix_len = prefix->len;
  int k = k_start;

  while (k < k_end) {
    struct cache_entry *ce_k = istate->cache[k];
    const char *name, *slash;

    if (prefix->len && strncmp(ce_k->name, prefix->buf, prefix->len))
      break;

    name = ce_k->name + prefix->len;
    slash = strchr(name, '/');

    if (slash) {
      int len = slash - name;
      int processed;
      struct dir_entry *dir_new;

      strbuf_add(prefix, name, len);
      processed = handle_range_dir(istate, k, k_end, parent, prefix, lazy_entries, &dir_new);
      if (processed) {
        k += processed;
        strbuf_setlen(prefix, input_prefix_len);
        continue;
      }

      strbuf_addch(prefix, '/');
      processed = handle_range_1(istate, k, k_end, dir_new, prefix, lazy_entries);
      k += processed;
      strbuf_setlen(prefix, input_prefix_len);
      continue;
    }

    /*
     * It is too expensive to take a lock to insert "ce_k"
     * into "istate->name_hash" and increment the ref-count
     * on the "parent" dir.  So we defer actually updating
     * permanent data structures until phase 2 (where we
     * can change the locking requirements) and simply
     * accumulate our current results into the lazy_entries
     * data array).
     *
     * We do not need to lock the lazy_entries array because
     * we have exclusive access to the cells in the range
     * [k_start,k_end) that this thread was given.
     */
    lazy_entries[k].dir = parent;
    if (parent) {
      lazy_entries[k].hash_name = memihash_cont(
        parent->ent.hash,
        ce_k->name + parent->namelen,
        ce_namelen(ce_k) - parent->namelen);
      lazy_entries[k].hash_dir = parent->ent.hash;
    } else {
      lazy_entries[k].hash_name = memihash(ce_k->name, ce_namelen(ce_k));
    }

    k++;
  }

  return k - k_start;
}

struct lazy_dir_thread_data {
  pthread_t pthread;
  struct index_state *istate;
  struct lazy_entry *lazy_entries;
  int k_start;
  int k_end;
};

static void *lazy_dir_thread_proc(void *_data)
{
  struct lazy_dir_thread_data *d = _data;
  struct strbuf prefix = STRBUF_INIT;
  handle_range_1(d->istate, d->k_start, d->k_end, NULL, &prefix, d->lazy_entries);
  strbuf_release(&prefix);
  return NULL;
}

struct lazy_name_thread_data {
  pthread_t pthread;
  struct index_state *istate;
  struct lazy_entry *lazy_entries;
};

static void *lazy_name_thread_proc(void *_data)
{
  struct lazy_name_thread_data *d = _data;
  int k;

  for (k = 0; k < d->istate->cache_nr; k++) {
    struct cache_entry *ce_k = d->istate->cache[k];
    ce_k->ce_flags |= CE_HASHED;
    if (!S_ISSPARSEDIR(ce_k->ce_mode)) {
      hashmap_entry_init(&ce_k->ent, d->lazy_entries[k].hash_name);
      hashmap_add(&d->istate->name_hash, &ce_k->ent);
    }
  }

  return NULL;
}

static inline void lazy_update_dir_ref_counts(
  struct index_state *istate,
  struct lazy_entry *lazy_entries)
{
  int k;

  for (k = 0; k < istate->cache_nr; k++) {
    if (lazy_entries[k].dir)
      lazy_entries[k].dir->nr++;
  }
}

static void threaded_lazy_init_name_hash(
  struct index_state *istate)
{
  int err;
  int nr_each;
  int k_start;
  int t;
  struct lazy_entry *lazy_entries;
  struct lazy_dir_thread_data *td_dir;
  struct lazy_name_thread_data *td_name;

  if (!HAVE_THREADS)
    return;

  k_start = 0;
  nr_each = DIV_ROUND_UP(istate->cache_nr, lazy_nr_dir_threads);

  CALLOC_ARRAY(lazy_entries, istate->cache_nr);
  CALLOC_ARRAY(td_dir, lazy_nr_dir_threads);
  CALLOC_ARRAY(td_name, 1);

  init_dir_mutex();

  /*
   * Phase 1:
   * Build "istate->dir_hash" using n "dir" threads (and a read-only index).
   */
  for (t = 0; t < lazy_nr_dir_threads; t++) {
    struct lazy_dir_thread_data *td_dir_t = td_dir + t;
    td_dir_t->istate = istate;
    td_dir_t->lazy_entries = lazy_entries;
    td_dir_t->k_start = k_start;
    k_start += nr_each;
    if (k_start > istate->cache_nr)
      k_start = istate->cache_nr;
    td_dir_t->k_end = k_start;
    err = pthread_create(&td_dir_t->pthread, NULL, lazy_dir_thread_proc, td_dir_t);
    if (err)
      die(_("unable to create lazy_dir thread: %s"), strerror(err));
  }
  for (t = 0; t < lazy_nr_dir_threads; t++) {
    struct lazy_dir_thread_data *td_dir_t = td_dir + t;
    if (pthread_join(td_dir_t->pthread, NULL))
      die("unable to join lazy_dir_thread");
  }

  /*
   * Phase 2:
   * Iterate over all index entries and add them to the "istate->name_hash"
   * using a single "name" background thread.
   * (Testing showed it wasn't worth running more than 1 thread for this.)
   *
   * Meanwhile, finish updating the parent directory ref-counts for each
   * index entry using the current thread.  (This step is very fast and
   * doesn't need threading.)
   */
  td_name->istate = istate;
  td_name->lazy_entries = lazy_entries;
  err = pthread_create(&td_name->pthread, NULL, lazy_name_thread_proc, td_name);
  if (err)
    die(_("unable to create lazy_name thread: %s"), strerror(err));

  lazy_update_dir_ref_counts(istate, lazy_entries);

  err = pthread_join(td_name->pthread, NULL);
  if (err)
    die(_("unable to join lazy_name thread: %s"), strerror(err));

  cleanup_dir_mutex();

  free(td_name);
  free(td_dir);
  free(lazy_entries);
}

static void lazy_init_name_hash(struct index_state *istate)
{

  if (istate->name_hash_initialized)
    return;
  trace_performance_enter();
  trace2_region_enter("index", "name-hash-init", istate->repo);
  hashmap_init(&istate->name_hash, cache_entry_cmp, NULL, istate->cache_nr);
  hashmap_init(&istate->dir_hash, dir_entry_cmp, NULL, istate->cache_nr);

  if (lookup_lazy_params(istate)) {
    /*
     * Disable item counting and automatic rehashing because
     * we do per-chain (mod n) locking rather than whole hashmap
     * locking and we need to prevent the table-size from changing
     * and bucket items from being redistributed.
     */
    hashmap_disable_item_counting(&istate->dir_hash);
    threaded_lazy_init_name_hash(istate);
    hashmap_enable_item_counting(&istate->dir_hash);
  } else {
    int nr;
    for (nr = 0; nr < istate->cache_nr; nr++)
      hash_index_entry(istate, istate->cache[nr]);
  }

  istate->name_hash_initialized = 1;
  trace2_region_leave("index", "name-hash-init", istate->repo);
  trace_performance_leave("initialize name hash");
}

/*
 * A test routine for t/helper/ sources.
 *
 * Returns the number of threads used or 0 when
 * the non-threaded code path was used.
 *
 * Requesting threading WILL NOT override guards
 * in lookup_lazy_params().
 */
int test_lazy_init_name_hash(struct index_state *istate, int try_threaded)
{
  lazy_nr_dir_threads = 0;
  lazy_try_threaded = try_threaded;

  lazy_init_name_hash(istate);

  return lazy_nr_dir_threads;
}

void add_name_hash(struct index_state *istate, struct cache_entry *ce)
{
  if (istate->name_hash_initialized)
    hash_index_entry(istate, ce);
}

void remove_name_hash(struct index_state *istate, struct cache_entry *ce)
{
  if (!istate->name_hash_initialized || !(ce->ce_flags & CE_HASHED))
    return;
  ce->ce_flags &= ~CE_HASHED;
  hashmap_remove(&istate->name_hash, &ce->ent, ce);

  if (ignore_case)
    remove_dir_entry(istate, ce);
}

static int slow_same_name(const char *name1, int len1, const char *name2, int len2)
{
  if (len1 != len2)
    return 0;

  while (len1) {
    unsigned char c1 = *name1++;
    unsigned char c2 = *name2++;
    len1--;
    if (c1 != c2) {
      c1 = toupper(c1);
      c2 = toupper(c2);
      if (c1 != c2)
        return 0;
    }
  }
  return 1;
}

static int same_name(const struct cache_entry *ce, const char *name, int namelen, int icase)
{
  int len = ce_namelen(ce);

  /*
   * Always do exact compare, even if we want a case-ignoring comparison;
   * we do the quick exact one first, because it will be the common case.
   */
  if (len == namelen && !memcmp(name, ce->name, len))
    return 1;

  if (!icase)
    return 0;

  return slow_same_name(name, namelen, ce->name, len);
}

int index_dir_find(struct index_state *istate, const char *name, int namelen,
       struct strbuf *canonical_path)
{
  struct dir_entry *dir;

  lazy_init_name_hash(istate);
  expand_to_path(istate, name, namelen, 0);
  dir = find_dir_entry(istate, name, namelen);

  if (canonical_path && dir && dir->nr) {
    strbuf_reset(canonical_path);
    strbuf_add(canonical_path, dir->name, dir->namelen);
  }

  return dir && dir->nr;
}

void adjust_dirname_case(struct index_state *istate, char *name)
{
  const char *startPtr = name;
  const char *ptr = startPtr;

  lazy_init_name_hash(istate);
  expand_to_path(istate, name, strlen(name), 0);
  while (*ptr) {
    while (*ptr && *ptr != '/')
      ptr++;

    if (*ptr == '/') {
      struct dir_entry *dir;

      dir = find_dir_entry(istate, name, ptr - name);
      if (dir) {
        memcpy((void *)startPtr, dir->name + (startPtr - name), ptr - startPtr);
        startPtr = ptr + 1;
      }
      ptr++;
    }
  }
}

struct cache_entry *index_file_exists(struct index_state *istate, const char *name, int namelen, int icase)
{
  struct cache_entry *ce;
  unsigned int hash = memihash(name, namelen);

  lazy_init_name_hash(istate);
  expand_to_path(istate, name, namelen, icase);

  ce = hashmap_get_entry_from_hash(&istate->name_hash, hash, NULL,
           struct cache_entry, ent);
  hashmap_for_each_entry_from(&istate->name_hash, ce, ent) {
    if (same_name(ce, name, namelen, icase))
      return ce;
  }
  return NULL;
}

void free_name_hash(struct index_state *istate)
{
  if (!istate->name_hash_initialized)
    return;
  istate->name_hash_initialized = 0;

  hashmap_clear(&istate->name_hash);
  hashmap_clear_and_free(&istate->dir_hash, struct dir_entry, ent);
}

Coverage Report

Created: 2025-12-31 07:01