index-pack: drop type_cas mutex

The type_cas lock lost all of its callers in f08cbf6 (index-pack:
make quantum of work smaller, 2020-09-08), so we can safely delete it.
The compiler didn't alert us that the variable became unused, because we
still call pthread_mutex_init() and pthread_mutex_destroy() on it.

It's worth considering also whether that commit was in error to remove
the use of the lock. Why don't we need it now, if we did before, as
described in ab791dd (index-pack: fix race condition with duplicate
bases, 2014-08-29)? I think the answer is that we now look at and assign
the child_obj->real_type field in the main thread while holding the
work_lock(). So we don't have to worry about racing with the worker
threads.

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

builtin/index-pack.c

@@ -159,10 +159,6 @@ static pthread_mutex_t deepest_delta_mutex;
 #define deepest_delta_lock()	lock_mutex(&deepest_delta_mutex)
 #define deepest_delta_unlock()	unlock_mutex(&deepest_delta_mutex)
 
-static pthread_mutex_t type_cas_mutex;
-#define type_cas_lock()		lock_mutex(&type_cas_mutex)
-#define type_cas_unlock()	unlock_mutex(&type_cas_mutex)
-
 static pthread_key_t key;
 
 static inline void lock_mutex(pthread_mutex_t *mutex)
@@ -186,7 +182,6 @@ static void init_thread(void)
 	init_recursive_mutex(&read_mutex);
 	pthread_mutex_init(&counter_mutex, NULL);
 	pthread_mutex_init(&work_mutex, NULL);
-	pthread_mutex_init(&type_cas_mutex, NULL);
 	if (show_stat)
 		pthread_mutex_init(&deepest_delta_mutex, NULL);
 	pthread_key_create(&key, NULL);
@@ -209,7 +204,6 @@ static void cleanup_thread(void)
 	pthread_mutex_destroy(&read_mutex);
 	pthread_mutex_destroy(&counter_mutex);
 	pthread_mutex_destroy(&work_mutex);
-	pthread_mutex_destroy(&type_cas_mutex);
 	if (show_stat)
 		pthread_mutex_destroy(&deepest_delta_mutex);
 	for (i = 0; i < nr_threads; i++)