RCTProfile: Use C atomics instead of OSAtomic

Summary:
This will save us precious microseconds and it's prettier to look at.
Closes https://github.com/facebook/react-native/pull/15276

Differential Revision: D5531823

Pulled By: javache

fbshipit-source-id: f8a97ec2a03e3cfdf1801457a481ec62a9371eeb

React/Profiler/RCTProfile.m

@@ -10,7 +10,7 @@
 #import "RCTProfile.h"
 
 #import <dlfcn.h>
-#import <libkern/OSAtomic.h>
+#import <stdatomic.h>
 #import <mach/mach.h>
 #import <objc/message.h>
 #import <objc/runtime.h>
@@ -42,8 +42,7 @@ static NSString *const kProfilePrefix = @"rct_profile_";
 
 #pragma mark - Variables
 
-// This is actually a BOOL - but has to be compatible with OSAtomic
+static atomic_bool RCTProfileProfiling = ATOMIC_VAR_INIT(NO);
-static volatile uint32_t RCTProfileProfiling;
 
 static NSDictionary *RCTProfileInfo;
 static NSMutableDictionary *RCTProfileOngoingEvents;
@@ -439,18 +438,17 @@ dispatch_queue_t RCTProfileGetQueue(void)
 
 BOOL RCTProfileIsProfiling(void)
 {
-  return (BOOL)RCTProfileProfiling;
+  return atomic_load(&RCTProfileProfiling);
 }
 
 void RCTProfileInit(RCTBridge *bridge)
 {
   // TODO: enable assert JS thread from any file (and assert here)
-  if (RCTProfileIsProfiling()) {
+  BOOL wasProfiling = atomic_fetch_or(&RCTProfileProfiling, 1);
+  if (wasProfiling) {
     return;
   }
 
-  OSAtomicOr32Barrier(1, &RCTProfileProfiling);
-
   if (callbacks != NULL) {
     systrace_buffer = callbacks->start();
   } else {
@@ -493,13 +491,11 @@ void RCTProfileInit(RCTBridge *bridge)
 void RCTProfileEnd(RCTBridge *bridge, void (^callback)(NSString *))
 {
   // assert JavaScript thread here again
-
+  BOOL wasProfiling = atomic_fetch_and(&RCTProfileProfiling, 0);
-  if (!RCTProfileIsProfiling()) {
+  if (!wasProfiling) {
     return;
   }
 
-  OSAtomicAnd32Barrier(0, &RCTProfileProfiling);
-
   [[NSNotificationCenter defaultCenter] postNotificationName:RCTProfileDidEndProfiling
                                                       object:bridge];