git/name-hash.c

/*
 * name-hash.c
 *
 * Hashing names in the index state
 *
 * Copyright (C) 2008 Linus Torvalds
 */
#include "cache.h"
#include "thread-utils.h"
#include "trace2.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 *unused_cmp_data,
			 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;
	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 *unused_cmp_data,
			   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;

	lazy_dir_mutex_array = xcalloc(LAZY_MAX_MUTEX, sizeof(pthread_mutex_t));

	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;
		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);

	lazy_entries = xcalloc(istate->cache_nr, sizeof(struct lazy_entry));
	td_dir = xcalloc(lazy_nr_dir_threads, sizeof(struct lazy_dir_thread_data));
	td_name = xcalloc(1, sizeof(struct lazy_name_thread_data));

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

	lazy_init_name_hash(istate);
	dir = find_dir_entry(istate, name, 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);
	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);

	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);
}