doc: rewrite description for rev-parse --short

[git/git-svn.git] / name-hash.c

/*
 * name-hash.c
 *
 * Hashing names in the index state
 *
 * Copyright (C) 2008 Linus Torvalds
 */
#define NO_THE_INDEX_COMPATIBILITY_MACROS
#include "cache.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 struct dir_entry *e1,
                const struct dir_entry *e2, const char *name)
{
        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, hash);
        key.namelen = namelen;
        return hashmap_get(&istate->dir_hash, &key, 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, memihash(ce->name, namelen));
                dir->namelen = namelen;
                hashmap_add(&istate->dir_hash, dir);

                /* 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, 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, memihash(ce->name, ce_namelen(ce)));
        hashmap_add(&istate->name_hash, ce);

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

static int cache_entry_cmp(const struct cache_entry *ce1,
                const struct cache_entry *ce2, const void *remove)
{
        /*
         * 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;

#ifdef NO_PTHREADS

static inline int lookup_lazy_params(struct index_state *istate)
{
        return 0;
}

static inline void threaded_lazy_init_name_hash(
        struct index_state *istate)
{
}

#else

#include "thread-utils.h"

/*
 * Set a minimum number of cache_entries that we will handle per
 * thread and use that to decide how many threads to run (upto
 * 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) by 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, hash);
                dir->namelen = prefix->len;
                dir->parent = parent;
                hashmap_add(&istate->dir_hash, dir);

                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;
                while (begin < end) {
                        int mid = (begin + end) >> 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, d->lazy_entries[k].hash_name);
                hashmap_add(&d->istate->name_hash, ce_k);
        }

        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 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;

        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;
                if (pthread_create(&td_dir_t->pthread, NULL, lazy_dir_thread_proc, td_dir_t))
                        die("unable to create lazy_dir_thread");
        }
        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;
        if (pthread_create(&td_name->pthread, NULL, lazy_name_thread_proc, td_name))
                die("unable to create lazy_name_thread");

        lazy_update_dir_ref_counts(istate, lazy_entries);

        if (pthread_join(td_name->pthread, NULL))
                die("unable to join lazy_name_thread");

        cleanup_dir_mutex();

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

#endif

static void lazy_init_name_hash(struct index_state *istate)
{
        if (istate->name_hash_initialized)
                return;
        hashmap_init(&istate->name_hash, (hashmap_cmp_fn) cache_entry_cmp,
                        istate->cache_nr);
        hashmap_init(&istate->dir_hash, (hashmap_cmp_fn) dir_entry_cmp,
                        istate->cache_nr);

        if (lookup_lazy_params(istate)) {
                hashmap_disallow_rehash(&istate->dir_hash, 1);
                threaded_lazy_init_name_hash(istate);
                hashmap_disallow_rehash(&istate->dir_hash, 0);
        } else {
                int nr;
                for (nr = 0; nr < istate->cache_nr; nr++)
                        hash_index_entry(istate, istate->cache[nr]);
        }

        istate->name_hash_initialized = 1;
}

/*
 * 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, 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;

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

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

        lazy_init_name_hash(istate);

        ce = hashmap_get_from_hash(&istate->name_hash,
                                   memihash(name, namelen), NULL);
        while (ce) {
                if (same_name(ce, name, namelen, icase))
                        return ce;
                ce = hashmap_get_next(&istate->name_hash, ce);
        }
        return NULL;
}

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

        hashmap_free(&istate->name_hash, 0);
        hashmap_free(&istate->dir_hash, 1);
}