Get rid of witness in malloc_mutex_t when !(configured w/ debug).

We don't touch witness at all when config_debug == false.  Let's only pay the
memory cost in malloc_mutex_s when needed. Note that when !config_debug, we keep
the field in a union so that we don't have to do #ifdefs in multiple places.

include/jemalloc/internal/mutex_structs.h

@@ -2,6 +2,8 @@
 #define JEMALLOC_INTERNAL_MUTEX_STRUCTS_H
 
 struct malloc_mutex_s {
+	union {
+		struct {
 #ifdef _WIN32
 #  if _WIN32_WINNT >= 0x0600
 			SRWLOCK         	lock;
@@ -18,7 +20,21 @@ struct malloc_mutex_s {
 #else
 			pthread_mutex_t		lock;
 #endif
+		};
+		/*
+		 * We only touch witness when configured w/ debug. However we
+		 * keep the field in a union when !debug so that we don't have
+		 * to pollute the code base with #ifdefs, while avoid paying the
+		 * memory cost.
+		 */
+#if !defined(JEMALLOC_DEBUG)
 		witness_t		witness;
+#endif
+	};
+
+#if defined(JEMALLOC_DEBUG)
+	witness_t		witness;
+#endif
 };
 
 #endif /* JEMALLOC_INTERNAL_MUTEX_STRUCTS_H */

include/jemalloc/internal/mutex_types.h

@@ -7,25 +7,25 @@ typedef struct malloc_mutex_s malloc_mutex_t;
 #  define MALLOC_MUTEX_INITIALIZER
 #elif (defined(JEMALLOC_OS_UNFAIR_LOCK))
 #  define MALLOC_MUTEX_INITIALIZER					\
-     {OS_UNFAIR_LOCK_INIT, WITNESS_INITIALIZER("mutex", WITNESS_RANK_OMIT)}
+     {{{OS_UNFAIR_LOCK_INIT}}, WITNESS_INITIALIZER("mutex", WITNESS_RANK_OMIT)}
 #elif (defined(JEMALLOC_OSSPIN))
 #  define MALLOC_MUTEX_INITIALIZER					\
-     {0, WITNESS_INITIALIZER("mutex", WITNESS_RANK_OMIT)}
+     {{{0}}, WITNESS_INITIALIZER("mutex", WITNESS_RANK_OMIT)}
 #elif (defined(JEMALLOC_MUTEX_INIT_CB))
 #  define MALLOC_MUTEX_INITIALIZER					\
-    {PTHREAD_MUTEX_INITIALIZER, NULL,					\
+     {{{PTHREAD_MUTEX_INITIALIZER, NULL}},				\
       WITNESS_INITIALIZER("mutex", WITNESS_RANK_OMIT)}
 #else
 #  if (defined(JEMALLOC_HAVE_PTHREAD_MUTEX_ADAPTIVE_NP) &&		\
        defined(PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP))
 #    define MALLOC_MUTEX_TYPE PTHREAD_MUTEX_ADAPTIVE_NP
 #    define MALLOC_MUTEX_INITIALIZER					\
-       {PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP,				\
+       {{{PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP}},			\
         WITNESS_INITIALIZER("mutex", WITNESS_RANK_OMIT)}
 #  else
 #    define MALLOC_MUTEX_TYPE PTHREAD_MUTEX_DEFAULT
 #    define MALLOC_MUTEX_INITIALIZER					\
-       {PTHREAD_MUTEX_INITIALIZER,					\
+       {{{PTHREAD_MUTEX_INITIALIZER}},					\
         WITNESS_INITIALIZER("mutex", WITNESS_RANK_OMIT)}
 #  endif
 #endif

include/jemalloc/internal/witness_types.h

@@ -55,6 +55,10 @@ typedef int witness_comp_t (const witness_t *, void *, const witness_t *,
 #define WITNESS_RANK_PROF_NEXT_THR_UID	WITNESS_RANK_LEAF
 #define WITNESS_RANK_PROF_THREAD_ACTIVE_INIT	WITNESS_RANK_LEAF
 
-#define WITNESS_INITIALIZER(name, rank) {name, rank, NULL, NULL, {NULL, NULL}}
+#if defined(JEMALLOC_DEBUG)
+#  define WITNESS_INITIALIZER(name, rank) {name, rank, NULL, NULL, {NULL, NULL}}
+#else
+#  define WITNESS_INITIALIZER(name, rank)
+#endif
 
 #endif /* JEMALLOC_INTERNAL_WITNESS_TYPES_H */