[PATCH 5/8] read-cache: try index data from shared memory

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/config.txt |  4 ++++
 cache.h                  |  1 +
 config.c                 | 12 ++++++++++++
 environment.c            |  1 +
 read-cache.c             | 43 +++++++++++++++++++++++++++++++++++++++++++
 submodule.c              |  1 +
 6 files changed, 62 insertions(+)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index d8b6cc9..ccbe00b 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -617,6 +617,10 @@ relatively high IO latencies.  With this set to 'true', Git will do the
 index comparison to the filesystem data in parallel, allowing
 overlapping IO's.
 
+core.useReadCacheDaemon::
+	Use `git read-cache--daemon` to speed up index reading. See
+	linkgit:git-read-cache--daemon for more information.
+
 core.createObject::
 	You can set this to 'link', in which case a hardlink followed by
 	a delete of the source are used to make sure that object creation
diff --git a/cache.h b/cache.h
index d0ff11c..fb29c7e 100644
--- a/cache.h
+++ b/cache.h
@@ -603,6 +603,7 @@ extern size_t packed_git_limit;
 extern size_t delta_base_cache_limit;
 extern unsigned long big_file_threshold;
 extern unsigned long pack_size_limit_cfg;
+extern int use_read_cache_daemon;
 
 /*
  * Do replace refs need to be checked this run?  This variable is
diff --git a/config.c b/config.c
index a30cb5c..5c832ad 100644
--- a/config.c
+++ b/config.c
@@ -874,6 +874,18 @@ static int git_default_core_config(const char *var, const char *value)
 		return 0;
 	}
 
+#ifdef HAVE_SHM
+	/*
+	 * Currently git-read-cache--daemon is only built when
+	 * HAVE_SHM is set. Ignore user settings if HAVE_SHM is not
+	 * defined.
+	 */
+	if (!strcmp(var, "core.usereadcachedaemon")) {
+		use_read_cache_daemon = git_config_bool(var, value);
+		return 0;
+	}
+#endif
+
 	/* Add other config variables here and to Documentation/config.txt. */
 	return 0;
 }
diff --git a/environment.c b/environment.c
index 5c4815d..b76a414 100644
--- a/environment.c
+++ b/environment.c
@@ -63,6 +63,7 @@ int merge_log_config = -1;
 int precomposed_unicode = -1; /* see probe_utf8_pathname_composition() */
 struct startup_info *startup_info;
 unsigned long pack_size_limit_cfg;
+int use_read_cache_daemon;
 
 /*
  * The character that begins a commented line in user-editable file
diff --git a/read-cache.c b/read-cache.c
index a5031f3..0e46523 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1462,6 +1462,48 @@ static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk,
 	return ce;
 }
 
+static void *try_shm(void *mmap, size_t *mmap_size)
+{
+	struct strbuf sb = STRBUF_INIT;
+	size_t old_size = *mmap_size;
+	void *new_mmap;
+	struct stat st;
+	int fd;
+
+	if (old_size <= 20 || !use_read_cache_daemon)
+		return mmap;
+
+	strbuf_addf(&sb, "/git-index-%s.lock",
+		    sha1_to_hex((unsigned char *)mmap + old_size - 20));
+	fd = shm_open(sb.buf, O_RDONLY, 0777);
+	if (fd >= 0) {
+		close(fd);
+		return mmap;
+	}
+	strbuf_setlen(&sb, sb.len - 5); /* no ".lock" */
+	fd = shm_open(sb.buf, O_RDONLY, 0777);
+	strbuf_release(&sb);
+	if (fd < 0)
+		/*
+		 * git-read-cache--daemon is probably not started yet. For
+		 * simplicity, only start it at the next index update, which
+		 * should happen often.
+		 */
+		return mmap;
+	if (fstat(fd, &st)) {
+		close(fd);
+		return mmap;
+	}
+	new_mmap = xmmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+	close(fd);
+	if (new_mmap == MAP_FAILED)
+		return mmap;
+	munmap(mmap, old_size);
+	*mmap_size = st.st_size;
+	return new_mmap;
+}
+
+
 /* remember to discard_cache() before reading a different cache! */
 int do_read_index(struct index_state *istate, const char *path, int must_exist)
 {
@@ -1501,6 +1543,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 	}
 	close(fd);
 
+	mmap = try_shm(mmap, &mmap_size);
 	hdr = mmap;
 	if (verify_hdr(hdr, mmap_size) < 0)
 		goto unmap;
diff --git a/submodule.c b/submodule.c
index b80ecac..9872928 100644
--- a/submodule.c
+++ b/submodule.c
@@ -195,6 +195,7 @@ void gitmodules_config(void)
 		int pos;
 		strbuf_addstr(&gitmodules_path, work_tree);
 		strbuf_addstr(&gitmodules_path, "/.gitmodules");
+		git_config(git_default_config, NULL);
 		if (read_cache() < 0)
 			die("index file corrupt");
 		pos = cache_name_pos(".gitmodules", 11);
-- 
1.9.1.346.ga2b5940