pack-objects: document about thread synchronization

diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index e78f3f52203f369d63c6af6eefb7e21f48c83318..567f5b41b8900e99c7887aea8a30fdc407605237 100644 (file)
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -1852,18 +1852,30 @@ static int delta_cacheable(unsigned long src_size, unsigned long trg_size,
 
 #ifndef NO_PTHREADS
 
+/* Protect access to object database */
 static pthread_mutex_t read_mutex;
 #define read_lock()            pthread_mutex_lock(&read_mutex)
 #define read_unlock()          pthread_mutex_unlock(&read_mutex)
 
+/* Protect delta_cache_size */
 static pthread_mutex_t cache_mutex;
 #define cache_lock()           pthread_mutex_lock(&cache_mutex)
 #define cache_unlock()         pthread_mutex_unlock(&cache_mutex)
 
+/*
+ * Protect object list partitioning (e.g. struct thread_param) and
+ * progress_state
+ */
 static pthread_mutex_t progress_mutex;
 #define progress_lock()                pthread_mutex_lock(&progress_mutex)
 #define progress_unlock()      pthread_mutex_unlock(&progress_mutex)
 
+/*
+ * Access to struct object_entry is unprotected since each thread owns
+ * a portion of the main object list. Just don't access object entries
+ * ahead in the list because they can be stolen and would need
+ * progress_mutex for protection.
+ */
 #else
 
 #define read_lock()            (void)0
@@ -2245,12 +2257,19 @@ static void try_to_free_from_threads(size_t size)
 static try_to_free_t old_try_to_free_routine;
 
 /*
+ * The main object list is split into smaller lists, each is handed to
+ * one worker.
+ *
  * The main thread waits on the condition that (at least) one of the workers
  * has stopped working (which is indicated in the .working member of
  * struct thread_params).
+ *
  * When a work thread has completed its work, it sets .working to 0 and
  * signals the main thread and waits on the condition that .data_ready
  * becomes 1.
+ *
+ * The main thread steals half of the work from the worker that has
+ * most work left to hand it to the idle worker.
  */
 
 struct thread_params {
@@ -3134,18 +3153,18 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
                         N_("do not create an empty pack output")),
                OPT_BOOL(0, "revs", &use_internal_rev_list,
                         N_("read revision arguments from standard input")),
-               { OPTION_SET_INT, 0, "unpacked", &rev_list_unpacked, NULL,
-                 N_("limit the objects to those that are not yet packed"),
-                 PARSE_OPT_NOARG | PARSE_OPT_NONEG, NULL, 1 },
-               { OPTION_SET_INT, 0, "all", &rev_list_all, NULL,
-                 N_("include objects reachable from any reference"),
-                 PARSE_OPT_NOARG | PARSE_OPT_NONEG, NULL, 1 },
-               { OPTION_SET_INT, 0, "reflog", &rev_list_reflog, NULL,
-                 N_("include objects referred by reflog entries"),
-                 PARSE_OPT_NOARG | PARSE_OPT_NONEG, NULL, 1 },
-               { OPTION_SET_INT, 0, "indexed-objects", &rev_list_index, NULL,
-                 N_("include objects referred to by the index"),
-                 PARSE_OPT_NOARG | PARSE_OPT_NONEG, NULL, 1 },
+               OPT_SET_INT_F(0, "unpacked", &rev_list_unpacked,
+                             N_("limit the objects to those that are not yet packed"),
+                             1, PARSE_OPT_NONEG),
+               OPT_SET_INT_F(0, "all", &rev_list_all,
+                             N_("include objects reachable from any reference"),
+                             1, PARSE_OPT_NONEG),
+               OPT_SET_INT_F(0, "reflog", &rev_list_reflog,
+                             N_("include objects referred by reflog entries"),
+                             1, PARSE_OPT_NONEG),
+               OPT_SET_INT_F(0, "indexed-objects", &rev_list_index,
+                             N_("include objects referred to by the index"),
+                             1, PARSE_OPT_NONEG),
                OPT_BOOL(0, "stdout", &pack_to_stdout,
                         N_("output pack to stdout")),
                OPT_BOOL(0, "include-tag", &include_tag,