[Crashlytics] Fix deadlock in user logging on reentrant queue access. (#16163)

Crashlytics/Crashlytics/Components/FIRCLSContext.m

@@ -245,6 +245,10 @@ void FIRCLSContextBaseInit(void) {
   NSString* exceptionQueueName = [sdkBundleID stringByAppendingString:@".exception"];
 
   _firclsLoggingQueue = dispatch_queue_create([loggingQueueName UTF8String], DISPATCH_QUEUE_SERIAL);
+  if (_firclsLoggingQueue) {
+    dispatch_queue_set_specific(_firclsLoggingQueue, &_firclsLoggingQueue, &_firclsLoggingQueue,
+                                NULL);
+  }
   _firclsBinaryImageQueue =
       dispatch_queue_create([binaryImagesQueueName UTF8String], DISPATCH_QUEUE_SERIAL);
   _firclsExceptionQueue =
@@ -437,3 +441,19 @@ bool FIRCLSContextRecordMetadata(NSString* rootPath, const FIRCLSContextInitData
 
   return true;
 }
+
+void FIRCLSExecuteOnLoggingQueue(void (^block)(void)) {
+  if (!block) {
+    return;
+  }
+
+  if (!_firclsLoggingQueue) {
+    FIRCLSSDKLogWarn(
+        "FIRCLSExecuteOnLoggingQueue invoked with NULL logging queue; running block inline.\n");
+    block();
+  } else if (dispatch_get_specific(&_firclsLoggingQueue) != NULL) {
+    block();
+  } else {
+    dispatch_sync(_firclsLoggingQueue, block);
+  }
+}

Crashlytics/Crashlytics/Components/FIRCLSGlobals.h

@@ -25,4 +25,6 @@ extern dispatch_queue_t _firclsExceptionQueue;
 #define FIRCLSGetBinaryImageQueue() (_firclsBinaryImageQueue)
 #define FIRCLSGetExceptionQueue() (_firclsExceptionQueue)
 
+void FIRCLSExecuteOnLoggingQueue(void (^block)(void));
+
 __END_DECLS

Crashlytics/Crashlytics/Components/FIRCLSUserLogging.m

@@ -283,7 +283,7 @@ void FIRCLSUserLoggingRecordKeysAndValues(NSDictionary *keysAndValues,
     }
   }
 
-  dispatch_sync(FIRCLSGetLoggingQueue(), ^{
+  FIRCLSExecuteOnLoggingQueue(^{
     FIRCLSUserLoggingWriteKeysAndValues(sanitizedKeysAndValues, storage, counter,
                                         containsNullValue);
   });
@@ -541,7 +541,7 @@ void FIRCLSUserLoggingWriteAndCheckABFiles(FIRCLSUserLoggingABStorage *storage,
     }
   }
 
-  dispatch_sync(FIRCLSGetLoggingQueue(), ^{
+  FIRCLSExecuteOnLoggingQueue(^{
     FIRCLSFile file;
 
     if (!FIRCLSFileInitWithPath(&file, *activePath, true)) {