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

Cheaper than fcntl(F_SETLK).  The same is done already on Windows, so
if that works, why not use it everywhere?  (Of course, only if the
compiler supports this C11 feature.)

As a bonus, the code in this commit also works on C++ via C++11
std::atomic, just in case somebody adds some C++ code to the opcache
extension one day.

Author: MaxKellermann

ext/opcache/ZendAccelerator.c

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

ext/opcache/ZendAccelerator.h

@@ -55,6 +55,14 @@
 #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)
@@ -261,7 +269,13 @@ typedef struct _zend_accel_shared_globals {
 	bool       restart_pending;
 	zend_accel_restart_reason restart_reason;
 	bool       cache_status_before_restart;
-#ifdef ZEND_WIN32
+#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)
 	LONGLONG   mem_usage;
 	LONGLONG   restart_in;
 #endif

ext/opcache/config.m4

@@ -23,6 +23,8 @@ 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