Nguyễn Thái Ngọc DuyThese extra comments should be make it easier to understand how to use locks in pack-objects delta search code. For reference, see
8ecce684a3 (basic threaded delta search - 2007-09-06) 384b32c09b (pack-objects: fix threaded load balancing - 2007-12-08) 50f22ada52 (threaded pack-objects: Use condition... - 2007-12-16)
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> --- builtin/pack-objects.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)
Show changes to builtin/pack-objects.c +19 −0
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c index ebc8cefb53..6270f74c0b 100644 --- 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 {
-- 2.18.0.656.gda699b98b3
