introduce notes-cache interface
Notes provide a fast lookup mechanism for data keyed by sha1. This is ideal for caching certain operations, like textconv filters. This patch builds some infrastructure to make it simpler to use notes trees as caches. In particular, caches: 1. don't have arbitrary commit messages. They store a cache validity string in the commit, and clear the tree when the cache validity string changes. 2. don't keep any commit history. The accumulated history of a a cache is just useless cruft. 3. use a looser form of locking for ref updates. If two processes try to write to the cache simultaneously, it is OK if one overwrites the other, losing some changes. It's just a cache, so we will just end up with an extra miss. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Jeff King committed
Apr 1, 2010 at 20:07 UTC
a941d5e3958ece565570a2dc3a5476ff5242f340
3 files changed
+116
Makefile
+2
@@ -486,6 +486,7 @@ LIB_H += log-tree.h
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LIB_H += mailmap.h
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LIB_H += merge-recursive.h
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LIB_H += notes.h
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+LIB_H += notes-cache.h
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LIB_H += object.h
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LIB_H += pack.h
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LIB_H += pack-refs.h
@@ -575,6 +576,7 @@ LIB_OBJS += merge-file.o
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LIB_OBJS += merge-recursive.o
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LIB_OBJS += name-hash.o
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LIB_OBJS += notes.o
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+LIB_OBJS += notes-cache.o
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LIB_OBJS += object.o
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LIB_OBJS += pack-check.o
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LIB_OBJS += pack-refs.o
notes-cache.c
new
+94
@@ -0,0 +1,94 @@
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+#include "cache.h"
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+#include "notes-cache.h"
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+#include "commit.h"
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+#include "refs.h"
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+
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+static int notes_cache_match_validity(const char *ref, const char *validity)
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+{
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+ unsigned char sha1[20];
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+ struct commit *commit;
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+ struct pretty_print_context pretty_ctx;
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+ struct strbuf msg = STRBUF_INIT;
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+ int ret;
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+
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+ if (read_ref(ref, sha1) < 0)
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+ return 0;
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+
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+ commit = lookup_commit_reference_gently(sha1, 1);
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+ if (!commit)
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+ return 0;
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+
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+ memset(&pretty_ctx, 0, sizeof(pretty_ctx));
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+ format_commit_message(commit, "%s", &msg, &pretty_ctx);
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+ strbuf_trim(&msg);
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+
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+ ret = !strcmp(msg.buf, validity);
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+ strbuf_release(&msg);
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+
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+ return ret;
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+}
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+
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+void notes_cache_init(struct notes_cache *c, const char *name,
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+ const char *validity)
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+{
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+ struct strbuf ref = STRBUF_INIT;
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+ int flags = 0;
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+
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+ memset(c, 0, sizeof(*c));
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+ c->validity = xstrdup(validity);
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+
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+ strbuf_addf(&ref, "refs/notes/%s", name);
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+ if (!notes_cache_match_validity(ref.buf, validity))
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+ flags = NOTES_INIT_EMPTY;
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+ init_notes(&c->tree, ref.buf, combine_notes_overwrite, flags);
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+ strbuf_release(&ref);
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+}
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+
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+int notes_cache_write(struct notes_cache *c)
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+{
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+ unsigned char tree_sha1[20];
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+ unsigned char commit_sha1[20];
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+
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+ if (!c || !c->tree.initialized || !c->tree.ref || !*c->tree.ref)
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+ return -1;
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+ if (!c->tree.dirty)
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+ return 0;
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+
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+ if (write_notes_tree(&c->tree, tree_sha1))
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+ return -1;
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+ if (commit_tree(c->validity, tree_sha1, NULL, commit_sha1, NULL) < 0)
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+ return -1;
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+ if (update_ref("update notes cache", c->tree.ref, commit_sha1, NULL,
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+ 0, QUIET_ON_ERR) < 0)
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+ return -1;
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+
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+ return 0;
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+}
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+
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+char *notes_cache_get(struct notes_cache *c, unsigned char key_sha1[20],
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+ size_t *outsize)
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+{
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+ const unsigned char *value_sha1;
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+ enum object_type type;
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+ char *value;
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+ unsigned long size;
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+
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+ value_sha1 = get_note(&c->tree, key_sha1);
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+ if (!value_sha1)
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+ return NULL;
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+ value = read_sha1_file(value_sha1, &type, &size);
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+
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+ *outsize = size;
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+ return value;
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+}
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+
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+int notes_cache_put(struct notes_cache *c, unsigned char key_sha1[20],
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+ const char *data, size_t size)
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+{
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+ unsigned char value_sha1[20];
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+
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+ if (write_sha1_file(data, size, "blob", value_sha1) < 0)
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+ return -1;
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+ add_note(&c->tree, key_sha1, value_sha1, NULL);
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+ return 0;
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+}
notes-cache.h
new
+20
@@ -0,0 +1,20 @@
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+#ifndef NOTES_CACHE_H
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+#define NOTES_CACHE_H
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+
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+#include "notes.h"
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+
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+struct notes_cache {
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+ struct notes_tree tree;
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+ char *validity;
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+};
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+
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+void notes_cache_init(struct notes_cache *c, const char *name,
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+ const char *validity);
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+int notes_cache_write(struct notes_cache *c);
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+
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+char *notes_cache_get(struct notes_cache *c, unsigned char sha1[20], size_t
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+ *outsize);
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+int notes_cache_put(struct notes_cache *c, unsigned char sha1[20],
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+ const char *data, size_t size);
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+
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+#endif /* NOTES_CACHE_H */