ext/mysqlnd: Use relaxed atomics for statistics in ZTS builds

In ZTS builds every statistics update locked a mutex, and the global
statistics are one object shared by all threads of the process. The
values are now atomic_uint_least64_t updated with relaxed atomic
additions, and LOCK_access is removed. NTS builds are unchanged.

FrankenPHP 1.13.1 in worker mode with 16 threads, one prepared SELECT
of 20 rows per request, AMD Ryzen 9 5950X, GCC 15.2. CPU time per
request with statistics on (the default), by the cores FrankenPHP
runs on:
- 4 cores of one CCD:       0.3029 -> 0.2722 ms (-10%)
- 4 cores, two on each CCD: 0.3553 -> 0.2934 ms (-17%)
- 8 cores of one CCD:       0.3810 -> 0.2739 ms (-28%)
- 8 cores, four on each CCD: 0.5274 -> 0.2781 ms (-47%)
Statistics on now cost 0.6-1.4% over statistics off, against 12%,
23%, 41% and 91% before.

Author: ArtUkrainskiy

UPGRADING.INTERNALS

@@ -74,6 +74,13 @@ PHP 8.7 INTERNALS UPGRADE NOTES
     mysqlnd_reverse_api_register_api() and mysqlnd_reverse_api_get_api_list()
     no longer exist.
 
+- Mysqlnd:
+  . In ZTS builds the values of MYSQLND_STATS are atomic_uint_least64_t and
+    the LOCK_access member was removed. The MYSQLND_INC_STATISTIC*() and
+    MYSQLND_DEC_STATISTIC() macros update them with relaxed atomic additions.
+  . The MYSQLND_STATS_LOCK() and MYSQLND_STATS_UNLOCK() macros were removed.
+    MYSQLND_STATS_UPDATE_VALUE() is now an expression instead of a block.
+
 - Standard:
   . php_explode() now takes a HashTable* instead of a zval* to store the
     resulting parts. It already expected the zval* to be IS_ARRAY.

ext/mysqlnd/mysqlnd_block_alloc.c

@@ -53,7 +53,6 @@ PHPAPI void
 mysqlnd_mempool_destroy(MYSQLND_MEMORY_POOL * pool)
 {
 	DBG_ENTER("mysqlnd_mempool_destroy");
-	/* mnd_free will reference LOCK_access and might crash, depending on the caller...*/
 	zend_arena_destroy(pool->arena);
 	DBG_VOID_RETURN;
 }

ext/mysqlnd/mysqlnd_driver.c

@@ -69,7 +69,6 @@ PHPAPI void mysqlnd_library_init(void)
 		mysqlnd_conn_set_methods(&MYSQLND_CLASS_METHOD_TABLE_NAME(mysqlnd_conn));
 		mysqlnd_conn_data_set_methods(&MYSQLND_CLASS_METHOD_TABLE_NAME(mysqlnd_conn_data));
 		_mysqlnd_init_ps_subsystem();
-		/* Should be calloc, as mnd_calloc will reference LOCK_access*/
 		mysqlnd_stats_init(&mysqlnd_global_stats, STAT_LAST, 1);
 		mysqlnd_plugin_subsystem_init();
 		{

ext/mysqlnd/mysqlnd_statistics.c

@@ -201,7 +201,12 @@ mysqlnd_fill_stats_hash(const MYSQLND_STATS * const stats, const MYSQLND_STRING
 	for (i = 0; i < stats->count; i++) {
 		char tmp[25];
 
-		snprintf(tmp, sizeof(tmp), "%" PRIu64, stats->values[i]);
+#ifdef ZTS
+		uint64_t value = atomic_load_explicit(&stats->values[i], memory_order_relaxed);
+#else
+		uint64_t value = stats->values[i];
+#endif
+		snprintf(tmp, sizeof(tmp), "%" PRIu64, value);
 		add_assoc_string_ex(return_value, names[i].s, names[i].l, tmp);
 	}
 }
@@ -216,7 +221,9 @@ mysqlnd_stats_init(MYSQLND_STATS ** stats, const size_t statistic_count, const b
 	*stats = pecalloc(1, size, persistent);
 	(*stats)->count = statistic_count;
 #ifdef ZTS
-	(*stats)->LOCK_access = tsrm_mutex_alloc();
+	for (size_t i = 0; i < statistic_count; i++) {
+		atomic_init(&(*stats)->values[i], 0);
+	}
 #endif
 }
 /* }}} */
@@ -226,10 +233,7 @@ mysqlnd_stats_init(MYSQLND_STATS ** stats, const size_t statistic_count, const b
 PHPAPI void
 mysqlnd_stats_end(MYSQLND_STATS * stats, const bool persistent)
 {
-#ifdef ZTS
-	tsrm_mutex_free(stats->LOCK_access);
-#endif
-	/* mnd_free will reference LOCK_access and crash...*/
+	/* mnd_free would update the statistics being freed */
 	pefree(stats, persistent);
 }
 /* }}} */

ext/mysqlnd/mysqlnd_statistics.h

@@ -17,19 +17,12 @@
 #define MYSQLND_STATISTICS_H
 
 #ifdef ZTS
-#define MYSQLND_STATS_LOCK(stats) tsrm_mutex_lock((stats)->LOCK_access)
-#define MYSQLND_STATS_UNLOCK(stats) tsrm_mutex_unlock((stats)->LOCK_access)
+#define MYSQLND_STATS_UPDATE_VALUE(stats, statistic, value) \
+	atomic_fetch_add_explicit(&(stats)->values[(statistic)], (value), memory_order_relaxed)
 #else
-#define MYSQLND_STATS_LOCK(stats)
-#define MYSQLND_STATS_UNLOCK(stats)
-#endif
-
 #define MYSQLND_STATS_UPDATE_VALUE(stats, statistic, value) \
-	{ \
-			MYSQLND_STATS_LOCK(stats); \
-			(stats)->values[(statistic)] += (value); \
-			MYSQLND_STATS_UNLOCK(_p_s); \
-	}
+	((stats)->values[(statistic)] += (value))
+#endif
 
 #define MYSQLND_DEC_STATISTIC(enabler, stats, statistic) \
  { \

ext/mysqlnd/mysqlnd_structs.h

@@ -292,13 +292,24 @@ typedef enum_func_status  (*mysqlnd_fetch_row_func)(MYSQLND_RES *result,
 
 typedef struct st_mysqlnd_stats MYSQLND_STATS;
 
+#if defined(ZTS) && defined(__cplusplus)
+/* The C11 atomics used by struct st_mysqlnd_stats and the MYSQLND_*_STATISTIC*() macros */
+extern "C++" {
+using std::atomic_uint_least64_t;
+using std::atomic_fetch_add_explicit;
+using std::atomic_load_explicit;
+using std::memory_order_relaxed;
+}
+#endif
+
 struct st_mysqlnd_stats
 {
 	size_t					count;
 #ifdef ZTS
-	MUTEX_T	LOCK_access;
-#endif
+	atomic_uint_least64_t values[] ZEND_ELEMENT_COUNT(count);
+#else
 	uint64_t values[] ZEND_ELEMENT_COUNT(count);
+#endif
 };