odb: only freshen pack files every 2 seconds

Since writing multiple objects may all already exist in a single
packfile, avoid freshening that packfile repeatedly in a tight loop.
Instead, only freshen pack files every 2 seconds.

src/fileops.c

@@ -837,16 +837,13 @@ int git_futils_cp(const char *from, const char *to, mode_t filemode)
 	return cp_by_fd(ifd, ofd, true);
 }
 
-int git_futils_touch(const char *path)
+int git_futils_touch(const char *path, time_t *when)
 {
 	struct p_timeval times[2];
-	time_t now = time(NULL);
 	int ret;
 
-	times[0].tv_sec = now;
-	times[0].tv_usec = 0;
-	times[1].tv_sec = now;
-	times[1].tv_usec = 0;
+	times[0].tv_sec =  times[1].tv_sec  = when ? *when : time(NULL);
+	times[0].tv_usec = times[1].tv_usec = 0;
 
 	ret = p_utimes(path, times);
 

src/fileops.h

@@ -185,9 +185,10 @@ extern int git_futils_cp(
 	mode_t filemode);
 
 /**
- * Set the files atime and mtime to the current time.
+ * Set the files atime and mtime to the given time, or the current time
+ * if `ts` is NULL.
  */
-extern int git_futils_touch(const char *path);
+extern int git_futils_touch(const char *path, time_t *when);
 
 /**
  * Flags that can be passed to `git_futils_cp_r`.

src/odb_loose.c

@@ -929,7 +929,7 @@ static int loose_backend__freshen(
 	if (object_file_name(&path, backend, oid) < 0)
 		return -1;
 
-	error = git_futils_touch(path.ptr);
+	error = git_futils_touch(path.ptr, NULL);
 	git_buf_free(&path);
 
 	return error;

src/odb_pack.c

@@ -20,6 +20,9 @@
 
 #include "git2/odb_backend.h"
 
+/* re-freshen pack files no more than every 2 seconds */
+#define FRESHEN_FREQUENCY 2
+
 struct pack_backend {
 	git_odb_backend parent;
 	git_vector packs;
@@ -367,12 +370,22 @@ static int pack_backend__freshen(
 	git_odb_backend *backend, const git_oid *oid)
 {
 	struct git_pack_entry e;
+	time_t now;
 	int error;
 
 	if ((error = pack_entry_find(&e, (struct pack_backend *)backend, oid)) < 0)
 		return error;
 
-	return git_futils_touch(e.p->pack_name);
+	now = time(NULL);
+
+	if (e.p->last_freshen > now - FRESHEN_FREQUENCY)
+		return 0;
+
+	if ((error = git_futils_touch(e.p->pack_name, &now)) < 0)
+		return error;
+
+	e.p->last_freshen = now;
+	return 0;
 }
 
 static int pack_backend__read(

src/pack.h

@@ -102,6 +102,8 @@ struct git_pack_file {
 
 	git_pack_cache bases; /* delta base cache */
 
+	time_t last_freshen; /* last time the packfile was freshened */
+
 	/* something like ".git/objects/pack/xxxxx.pack" */
 	char pack_name[GIT_FLEX_ARRAY]; /* more */
 };

tests/odb/freshen.c

@@ -68,6 +68,7 @@ void test_odb_freshen__packed_object(void)
 	cl_must_pass(p_utimes("testrepo.git/objects/pack/" PACKED_FN, old_times));
 	cl_must_pass(p_lstat("testrepo.git/objects/pack/" PACKED_FN, &before));
 
+	/* ensure that packfile is freshened */
 	cl_git_pass(git_odb_write(&id, odb, PACKED_STR,
 		CONST_STRLEN(PACKED_STR), GIT_OBJ_BLOB));
 	cl_assert_equal_oid(&expected_id, &id);
@@ -75,5 +76,18 @@ void test_odb_freshen__packed_object(void)
 
 	cl_assert(before.st_atime < after.st_atime);
 	cl_assert(before.st_mtime < after.st_mtime);
+
+	memcpy(&before, &after, sizeof(struct stat));
+
+	/* ensure that the pack file is not freshened again immediately */
+	cl_git_pass(git_odb_write(&id, odb, PACKED_STR,
+		CONST_STRLEN(PACKED_STR), GIT_OBJ_BLOB));
+	cl_assert_equal_oid(&expected_id, &id);
+	cl_must_pass(p_lstat("testrepo.git/objects/pack/" PACKED_FN, &after));
+
+	cl_assert(before.st_atime == after.st_atime);
+	cl_assert(before.st_atime_nsec == after.st_atime_nsec);
+	cl_assert(before.st_mtime == after.st_mtime);
+	cl_assert(before.st_mtime_nsec == after.st_mtime_nsec);
 }