Thread-safe RTCInitFieldTrialDictionary (#116)

Author: hiroshihorie

sdk/objc/api/peerconnection/RTCFieldTrials.mm

@@ -10,47 +10,58 @@
 
 #import "RTCFieldTrials.h"
 
+#import <os/lock.h>
 #include <memory>
-
 #import "base/RTCLogging.h"
 
 #include "system_wrappers/include/field_trial.h"
 
 NSString *const kRTCFieldTrialAudioForceABWENoTWCCKey = @"WebRTC-Audio-ABWENoTWCC";
-NSString * const kRTCFieldTrialFlexFec03AdvertisedKey = @"WebRTC-FlexFEC-03-Advertised";
-NSString * const kRTCFieldTrialFlexFec03Key = @"WebRTC-FlexFEC-03";
-NSString * const kRTCFieldTrialH264HighProfileKey = @"WebRTC-H264HighProfile";
-NSString * const kRTCFieldTrialMinimizeResamplingOnMobileKey =
+NSString *const kRTCFieldTrialFlexFec03AdvertisedKey = @"WebRTC-FlexFEC-03-Advertised";
+NSString *const kRTCFieldTrialFlexFec03Key = @"WebRTC-FlexFEC-03";
+NSString *const kRTCFieldTrialH264HighProfileKey = @"WebRTC-H264HighProfile";
+NSString *const kRTCFieldTrialMinimizeResamplingOnMobileKey =
  @"WebRTC-Audio-MinimizeResamplingOnMobile";
 NSString *const kRTCFieldTrialUseNWPathMonitor = @"WebRTC-Network-UseNWPathMonitor";
-NSString * const kRTCFieldTrialEnabledValue = @"Enabled";
+NSString *const kRTCFieldTrialEnabledValue = @"Enabled";
 
 // InitFieldTrialsFromString stores the char*, so the char array must outlive
 // the application.
 static char *gFieldTrialInitString = nullptr;
+static os_unfair_lock fieldTrialLock = OS_UNFAIR_LOCK_INIT;
 
 void RTCInitFieldTrialDictionary(NSDictionary<NSString *, NSString *> *fieldTrials) {
  if (!fieldTrials) {
  RTCLogWarning(@"No fieldTrials provided.");
  return;
  }
+
  // Assemble the keys and values into the field trial string.
- // We don't perform any extra format checking. That should be done by the underlying WebRTC calls.
  NSMutableString *fieldTrialInitString = [NSMutableString string];
  for (NSString *key in fieldTrials) {
  NSString *fieldTrialEntry = [NSString stringWithFormat:@"%@/%@/", key, fieldTrials[key]];
  [fieldTrialInitString appendString:fieldTrialEntry];
  }
+
  size_t len = fieldTrialInitString.length + 1;
+
+ // Locking before modifying global variable
+ os_unfair_lock_lock(&fieldTrialLock);
  if (gFieldTrialInitString != nullptr) {
  delete[] gFieldTrialInitString;
+ gFieldTrialInitString = nullptr;
  }
+
  gFieldTrialInitString = new char[len];
- if (![fieldTrialInitString getCString:gFieldTrialInitString
- maxLength:len
- encoding:NSUTF8StringEncoding]) {
+ bool success = [fieldTrialInitString getCString:gFieldTrialInitString
+ maxLength:len
+ encoding:NSUTF8StringEncoding];
+ if (!success) {
  RTCLogError(@"Failed to convert field trial string.");
+ os_unfair_lock_unlock(&fieldTrialLock);
  return;
  }
+
  webrtc::field_trial::InitFieldTrialsFromString(gFieldTrialInitString);
+ os_unfair_lock_unlock(&fieldTrialLock);
 }