Fix crashes by concurrency

Classes/Telemetry/BITChannel.m

@@ -214,37 +214,43 @@ - (NSUInteger)maxBatchSize {
 }
 
 - (void)invalidateTimer {
-  if ([self timerIsRunning]) {
-    dispatch_source_cancel((dispatch_source_t)self.timerSource);
-    self.timerSource = nil;
+  @synchronized(self) {
+    if (self.timerSource != nil) {
+      dispatch_source_cancel((dispatch_source_t)self.timerSource);
+      self.timerSource = nil;
+    }
   }
 }
 
 -(BOOL)timerIsRunning {
-  return self.timerSource != nil;
+  @synchronized(self) {
+    return self.timerSource != nil;
+  }
 }
 
 - (void)startTimer {
-  // Reset timer, if it is already running
-  if ([self timerIsRunning]) {
+  @synchronized(self) {
+
+    // Reset timer, if it is already running.
     [self invalidateTimer];
-  }
-
-  self.timerSource = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, self.dataItemsOperations);
-  dispatch_source_set_timer((dispatch_source_t)self.timerSource, dispatch_walltime(NULL, NSEC_PER_SEC * self.batchInterval), 1ull * NSEC_PER_SEC, 1ull * NSEC_PER_SEC);
-  __weak typeof(self) weakSelf = self;
-  dispatch_source_set_event_handler((dispatch_source_t)self.timerSource, ^{
-    typeof(self) strongSelf = weakSelf;
-    if (strongSelf) {
-      if (strongSelf.dataItemCount > 0) {
-        [strongSelf persistDataItemQueue];
-      } else {
-        strongSelf.channelBlocked = NO;
+
+    dispatch_source_t timerSource = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, self.dataItemsOperations);
+    dispatch_source_set_timer(timerSource, dispatch_walltime(NULL, NSEC_PER_SEC * self.batchInterval), 1ull * NSEC_PER_SEC, 1ull * NSEC_PER_SEC);
+    __weak typeof(self) weakSelf = self;
+    dispatch_source_set_event_handler(timerSource, ^{
+      typeof(self) strongSelf = weakSelf;
+      if (strongSelf) {
+        if (strongSelf.dataItemCount > 0) {
+          [strongSelf persistDataItemQueue];
+        } else {
+          strongSelf.channelBlocked = NO;
+        }
+        [strongSelf invalidateTimer];
       }
-      [strongSelf invalidateTimer];
-    }
-  });
-  dispatch_resume((dispatch_source_t)self.timerSource);
+    });
+    dispatch_resume(timerSource);
+    self.timerSource = timerSource;
+  }
 }
 
 /**

Classes/Telemetry/BITMetricsManager.m

@@ -233,31 +233,39 @@ - (void)trackDataItem:(BITTelemetryData *)dataItem {
 #pragma mark - Custom getter
 
 - (BITChannel *)channel {
-  if (!_channel) {
-    _channel = [[BITChannel alloc] initWithTelemetryContext:self.telemetryContext persistence:self.persistence];
+  @synchronized(self) {
+    if (!_channel) {
+      _channel = [[BITChannel alloc] initWithTelemetryContext:self.telemetryContext persistence:self.persistence];
+    }
+    return _channel;
   }
-  return _channel;
 }
 
 - (BITTelemetryContext *)telemetryContext {
-  if (!_telemetryContext) {
-    _telemetryContext = [[BITTelemetryContext alloc] initWithAppIdentifier:self.appIdentifier persistence:self.persistence];
+  @synchronized(self) {
+    if (!_telemetryContext) {
+      _telemetryContext = [[BITTelemetryContext alloc] initWithAppIdentifier:self.appIdentifier persistence:self.persistence];
+    }
+    return _telemetryContext;
   }
-  return _telemetryContext;
 }
 
 - (BITPersistence *)persistence {
-  if (!_persistence) {
-    _persistence = [BITPersistence new];
+  @synchronized(self) {
+    if (!_persistence) {
+      _persistence = [BITPersistence new];
+    }
+    return _persistence;
   }
-  return _persistence;
 }
 
 - (NSUserDefaults *)userDefaults {
-  if (!_userDefaults) {
-    _userDefaults = [NSUserDefaults standardUserDefaults];
+  @synchronized(self) {
+    if (!_userDefaults) {
+      _userDefaults = [NSUserDefaults standardUserDefaults];
+    }
+    return _userDefaults;
   }
-  return _userDefaults;
 }
 
 @end

Classes/Telemetry/BITTelemetryContext.m

@@ -352,12 +352,13 @@ - (void)setDeviceType:(NSString *)deviceType {
 #pragma mark - Helper
 
 - (NSDictionary *)contextDictionary {
-  NSMutableDictionary *contextDictionary = [NSMutableDictionary new];
-  [contextDictionary addEntriesFromDictionary:self.tags];
-  [contextDictionary addEntriesFromDictionary:[self.session serializeToDictionary]];
-  [contextDictionary addEntriesFromDictionary:[self.user serializeToDictionary]];
-
-  return contextDictionary;
+  __block NSMutableDictionary *tmp = [NSMutableDictionary new];
+  dispatch_sync(self.operationsQueue, ^{
+    [tmp addEntriesFromDictionary:self.tags];
+    [tmp addEntriesFromDictionary:[self.session serializeToDictionary]];
+    [tmp addEntriesFromDictionary:[self.user serializeToDictionary]];
+  });
+  return tmp;
 }
 
 - (NSDictionary *)tags {