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authorBrandon Williams <bmwill@google.com>2017-01-28 02:02:01 (GMT)
committerJunio C Hamano <gitster@pobox.com>2017-02-01 21:46:53 (GMT)
commit1a600b7555205f80b276659db4fd521658642505 (patch)
tree7cce47514bdbb976ab4844c2a8efd9296c3ac37c /attr.c
parent428103c7f1a0cb8bb1432214efa60abc5bd5f198 (diff)
downloadgit-1a600b7555205f80b276659db4fd521658642505.zip
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attr: use hashmap for attribute dictionary
The current implementation of the attribute dictionary uses a custom hashtable. This modernizes the dictionary by converting it to the builtin 'hashmap' structure. Also, in order to enable a threaded API in the future add an accompanying mutex which must be acquired prior to accessing the dictionary of interned attributes. Signed-off-by: Brandon Williams <bmwill@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'attr.c')
-rw-r--r--attr.c173
1 files changed, 128 insertions, 45 deletions
diff --git a/attr.c b/attr.c
index 9fe848f..e008f30 100644
--- a/attr.c
+++ b/attr.c
@@ -14,6 +14,7 @@
#include "dir.h"
#include "utf8.h"
#include "quote.h"
+#include "thread-utils.h"
const char git_attr__true[] = "(builtin)true";
const char git_attr__false[] = "\0(builtin)false";
@@ -23,28 +24,17 @@ static const char git_attr__unknown[] = "(builtin)unknown";
#define ATTR__UNSET NULL
#define ATTR__UNKNOWN git_attr__unknown
-/* This is a randomly chosen prime. */
-#define HASHSIZE 257
-
#ifndef DEBUG_ATTR
#define DEBUG_ATTR 0
#endif
-/*
- * NEEDSWORK: the global dictionary of the interned attributes
- * must stay a singleton even after we become thread-ready.
- * Access to these must be surrounded with mutex when it happens.
- */
struct git_attr {
- struct git_attr *next;
- unsigned h;
- int attr_nr;
+ int attr_nr; /* unique attribute number */
int maybe_macro;
int maybe_real;
- char name[FLEX_ARRAY];
+ char name[FLEX_ARRAY]; /* attribute name */
};
static int attr_nr;
-static struct git_attr *(git_attr_hash[HASHSIZE]);
/*
* NEEDSWORK: maybe-real, maybe-macro are not property of
@@ -63,15 +53,94 @@ const char *git_attr_name(const struct git_attr *attr)
return attr->name;
}
-static unsigned hash_name(const char *name, int namelen)
+struct attr_hashmap {
+ struct hashmap map;
+#ifndef NO_PTHREADS
+ pthread_mutex_t mutex;
+#endif
+};
+
+static inline void hashmap_lock(struct attr_hashmap *map)
+{
+#ifndef NO_PTHREADS
+ pthread_mutex_lock(&map->mutex);
+#endif
+}
+
+static inline void hashmap_unlock(struct attr_hashmap *map)
{
- unsigned val = 0, c;
+#ifndef NO_PTHREADS
+ pthread_mutex_unlock(&map->mutex);
+#endif
+}
- while (namelen--) {
- c = *name++;
- val = ((val << 7) | (val >> 22)) ^ c;
- }
- return val;
+/*
+ * The global dictionary of all interned attributes. This
+ * is a singleton object which is shared between threads.
+ * Access to this dictionary must be surrounded with a mutex.
+ */
+static struct attr_hashmap g_attr_hashmap;
+
+/* The container for objects stored in "struct attr_hashmap" */
+struct attr_hash_entry {
+ struct hashmap_entry ent; /* must be the first member! */
+ const char *key; /* the key; memory should be owned by value */
+ size_t keylen; /* length of the key */
+ void *value; /* the stored value */
+};
+
+/* attr_hashmap comparison function */
+static int attr_hash_entry_cmp(const struct attr_hash_entry *a,
+ const struct attr_hash_entry *b,
+ void *unused)
+{
+ return (a->keylen != b->keylen) || strncmp(a->key, b->key, a->keylen);
+}
+
+/* Initialize an 'attr_hashmap' object */
+static void attr_hashmap_init(struct attr_hashmap *map)
+{
+ hashmap_init(&map->map, (hashmap_cmp_fn) attr_hash_entry_cmp, 0);
+}
+
+/*
+ * Retrieve the 'value' stored in a hashmap given the provided 'key'.
+ * If there is no matching entry, return NULL.
+ */
+static void *attr_hashmap_get(struct attr_hashmap *map,
+ const char *key, size_t keylen)
+{
+ struct attr_hash_entry k;
+ struct attr_hash_entry *e;
+
+ if (!map->map.tablesize)
+ attr_hashmap_init(map);
+
+ hashmap_entry_init(&k, memhash(key, keylen));
+ k.key = key;
+ k.keylen = keylen;
+ e = hashmap_get(&map->map, &k, NULL);
+
+ return e ? e->value : NULL;
+}
+
+/* Add 'value' to a hashmap based on the provided 'key'. */
+static void attr_hashmap_add(struct attr_hashmap *map,
+ const char *key, size_t keylen,
+ void *value)
+{
+ struct attr_hash_entry *e;
+
+ if (!map->map.tablesize)
+ attr_hashmap_init(map);
+
+ e = xmalloc(sizeof(struct attr_hash_entry));
+ hashmap_entry_init(e, memhash(key, keylen));
+ e->key = key;
+ e->keylen = keylen;
+ e->value = value;
+
+ hashmap_add(&map->map, e);
}
static int attr_name_valid(const char *name, size_t namelen)
@@ -103,37 +172,44 @@ static void report_invalid_attr(const char *name, size_t len,
strbuf_release(&err);
}
-static struct git_attr *git_attr_internal(const char *name, int len)
+/*
+ * Given a 'name', lookup and return the corresponding attribute in the global
+ * dictionary. If no entry is found, create a new attribute and store it in
+ * the dictionary.
+ */
+static struct git_attr *git_attr_internal(const char *name, int namelen)
{
- unsigned hval = hash_name(name, len);
- unsigned pos = hval % HASHSIZE;
struct git_attr *a;
- for (a = git_attr_hash[pos]; a; a = a->next) {
- if (a->h == hval &&
- !memcmp(a->name, name, len) && !a->name[len])
- return a;
- }
-
- if (!attr_name_valid(name, len))
+ if (!attr_name_valid(name, namelen))
return NULL;
- FLEX_ALLOC_MEM(a, name, name, len);
- a->h = hval;
- a->next = git_attr_hash[pos];
- a->attr_nr = attr_nr++;
- a->maybe_macro = 0;
- a->maybe_real = 0;
- git_attr_hash[pos] = a;
+ hashmap_lock(&g_attr_hashmap);
+
+ a = attr_hashmap_get(&g_attr_hashmap, name, namelen);
+
+ if (!a) {
+ FLEX_ALLOC_MEM(a, name, name, namelen);
+ a->attr_nr = g_attr_hashmap.map.size;
+ a->maybe_real = 0;
+ a->maybe_macro = 0;
+
+ attr_hashmap_add(&g_attr_hashmap, a->name, namelen, a);
+ assert(a->attr_nr == (g_attr_hashmap.map.size - 1));
+
+ /*
+ * NEEDSWORK: per git_attr_check check_all_attr
+ * will be initialized a lot more lazily, not
+ * like this, and not here.
+ */
+ REALLOC_ARRAY(check_all_attr, ++attr_nr);
+ check_all_attr[a->attr_nr].attr = a;
+ check_all_attr[a->attr_nr].value = ATTR__UNKNOWN;
+ assert(a->attr_nr == (attr_nr - 1));
+ }
+
+ hashmap_unlock(&g_attr_hashmap);
- /*
- * NEEDSWORK: per git_attr_check check_all_attr
- * will be initialized a lot more lazily, not
- * like this, and not here.
- */
- REALLOC_ARRAY(check_all_attr, attr_nr);
- check_all_attr[a->attr_nr].attr = a;
- check_all_attr[a->attr_nr].value = ATTR__UNKNOWN;
return a;
}
@@ -941,3 +1017,10 @@ void git_attr_set_direction(enum git_attr_direction new, struct index_state *ist
drop_attr_stack();
use_index = istate;
}
+
+void attr_start(void)
+{
+#ifndef NO_PTHREADS
+ pthread_mutex_init(&g_attr_hashmap.mutex, NULL);
+#endif
+}