Revert "ext/opcache: use C11 atomics for "restart_in" (php#10276)"

This reverts commit 061fcdb.

While the commit does indeed improve performance, @dstogov complained
that it disables the code path calling kill_all_lockers(), and thus
hanging workers are never killed and restarted.
php#10276 (comment)

The fact that this feature was not implemented in the existing atomic
code path (i.e. Windows) did not mean that the feature was considered
not strictly necessary, but that the Windows implementation just did
not need the feature because SAPIs that work on Windows do not manage
child processes
php#10276 (comment)
php#10276 (comment)

Author: MaxKellermann

ext/opcache/ZendAccelerator.c

@@ -135,11 +135,7 @@ static void preload_shutdown(void);
 static void preload_activate(void);
 static void preload_restart(void);
 
-#ifdef HAVE_STDATOMIC_H
-# define INCREMENT(v) (++ZCSG(v))
-# define DECREMENT(v) (--ZCSG(v))
-# define LOCKVAL(v)   atomic_load(&ZCSG(v))
-#elif defined(ZEND_WIN32)
+#ifdef ZEND_WIN32
 # define INCREMENT(v) InterlockedIncrement64(&ZCSG(v))
 # define DECREMENT(v) InterlockedDecrement64(&ZCSG(v))
 # define LOCKVAL(v)   (ZCSG(v))
@@ -277,7 +273,7 @@ static ZEND_INI_MH(accel_include_path_on_modify)
 
 static inline void accel_restart_enter(void)
 {
-#ifdef INCREMENT
+#ifdef ZEND_WIN32
 	INCREMENT(restart_in);
 #else
 	struct flock restart_in_progress;
@@ -296,7 +292,7 @@ static inline void accel_restart_enter(void)
 
 static inline void accel_restart_leave(void)
 {
-#ifdef DECREMENT
+#ifdef ZEND_WIN32
 	ZCSG(restart_in_progress) = false;
 	DECREMENT(restart_in);
 #else
@@ -317,9 +313,7 @@ static inline void accel_restart_leave(void)
 static inline int accel_restart_is_active(void)
 {
 	if (ZCSG(restart_in_progress)) {
-#ifdef LOCKVAL
-		return LOCKVAL(restart_in) != 0;
-#else
+#ifndef ZEND_WIN32
 		struct flock restart_check;
 
 		restart_check.l_type = F_WRLCK;
@@ -337,6 +331,8 @@ static inline int accel_restart_is_active(void)
 		} else {
 			return 1;
 		}
+#else
+		return LOCKVAL(restart_in) != 0;
 #endif
 	}
 	return 0;
@@ -345,7 +341,7 @@ static inline int accel_restart_is_active(void)
 /* Creates a read lock for SHM access */
 static inline zend_result accel_activate_add(void)
 {
-#ifdef INCREMENT
+#ifdef ZEND_WIN32
 	SHM_UNPROTECT();
 	INCREMENT(mem_usage);
 	SHM_PROTECT();
@@ -368,7 +364,7 @@ static inline zend_result accel_activate_add(void)
 /* Releases a lock for SHM access */
 static inline void accel_deactivate_sub(void)
 {
-#ifdef DECREMENT
+#ifdef ZEND_WIN32
 	if (ZCG(counted)) {
 		SHM_UNPROTECT();
 		DECREMENT(mem_usage);
@@ -391,7 +387,7 @@ static inline void accel_deactivate_sub(void)
 
 static inline void accel_unlock_all(void)
 {
-#ifdef DECREMENT
+#ifdef ZEND_WIN32
 	accel_deactivate_sub();
 #else
 	struct flock mem_usage_unlock_all;
@@ -832,7 +828,7 @@ static void accel_use_shm_interned_strings(void)
 	HANDLE_UNBLOCK_INTERRUPTIONS();
 }
 
-#ifndef LOCKVAL
+#ifndef ZEND_WIN32
 static inline void kill_all_lockers(struct flock *mem_usage_check)
 {
 	int tries;
@@ -899,7 +895,7 @@ static inline void kill_all_lockers(struct flock *mem_usage_check)
 
 static inline int accel_is_inactive(void)
 {
-#ifdef LOCKVAL
+#ifdef ZEND_WIN32
 	if (LOCKVAL(mem_usage) == 0) {
 		return SUCCESS;
 	}

ext/opcache/ZendAccelerator.h

@@ -55,14 +55,6 @@
 #include "zend_accelerator_hash.h"
 #include "zend_accelerator_debug.h"
 
-#ifdef HAVE_STDATOMIC_H
-# ifdef __cplusplus
-#  include <atomic>
-# else
-#  include <stdatomic.h>
-# endif
-#endif // HAVE_STDATOMIC_H
-
 #ifndef PHPAPI
 # ifdef ZEND_WIN32
 #  define PHPAPI __declspec(dllimport)
@@ -269,13 +261,7 @@ typedef struct _zend_accel_shared_globals {
 	bool       restart_pending;
 	zend_accel_restart_reason restart_reason;
 	bool       cache_status_before_restart;
-#ifdef HAVE_STDATOMIC_H
-# ifdef __cplusplus
-	std::atomic_llong mem_usage, restart_in;
-# else
-	atomic_llong mem_usage, restart_in;
-# endif
-#elif defined(ZEND_WIN32)
+#ifdef ZEND_WIN32
 	LONGLONG   mem_usage;
 	LONGLONG   restart_in;
 #endif

ext/opcache/config.m4

@@ -23,8 +23,6 @@ if test "$PHP_OPCACHE" != "no"; then
   dnl Always build as shared extension
   ext_shared=yes
 
-  AC_CHECK_HEADERS([stdatomic.h])
-
   if test "$PHP_HUGE_CODE_PAGES" = "yes"; then
     AC_DEFINE(HAVE_HUGE_CODE_PAGES, 1, [Define to enable copying PHP CODE pages into HUGE PAGES (experimental)])
   fi