Support configuring dispatch queue in GRPCCall and below

4 files changed, 33 insertions, 4 deletions

diff --git a/src/objective-c/GRPCClient/GRPCCall.h b/src/objective-c/GRPCClient/GRPCCall.h
index 7645bb1d34..85c5b47c8e 100644
--- a/src/objective-c/GRPCClient/GRPCCall.h
+++ b/src/objective-c/GRPCClient/GRPCCall.h
@@ -253,6 +253,13 @@ extern id const kGRPCTrailersKey;
  */
 + (void)setCallSafety:(GRPCCallSafety)callSafety host:(NSString *)host path:(NSString *)path;
 
+/**
+ * Set the dispatch queue to be used for queue responses.
+ *
+ * This configuration is only effective before the call starts.
+ */
+- (void)setResponseDispatchQueue:(dispatch_queue_t)queue;
+
 // TODO(jcanizales): Let specify a deadline. As a category of GRXWriter?
 @end
 
diff --git a/src/objective-c/GRPCClient/GRPCCall.m b/src/objective-c/GRPCClient/GRPCCall.m
index 051138ea4d..f9d13fea57 100644
--- a/src/objective-c/GRPCClient/GRPCCall.m
+++ b/src/objective-c/GRPCClient/GRPCCall.m
@@ -113,6 +113,10 @@ static NSMutableDictionary *callFlags;
   // the SendClose op is added.
   BOOL _unaryCall;
   NSMutableArray *_unaryOpBatch;
+
+  // The dispatch queue to be used for enqueuing responses to user. Defaulted to the main dispatch
+  // queue
+  dispatch_queue_t _responseQueue;
 }
 
 @synthesize state = _state;
@@ -175,10 +179,19 @@ static NSMutableDictionary *callFlags;
       _unaryCall = YES;
       _unaryOpBatch = [NSMutableArray arrayWithCapacity:kMaxClientBatch];
     }
+
+    _responseQueue = dispatch_get_main_queue();
   }
   return self;
 }
 
+- (void)setResponseDispatchQueue:(dispatch_queue_t)queue {
+  if (_state != GRXWriterStateNotStarted) {
+    return;
+  }
+  _responseQueue = queue;
+}
+
 #pragma mark Finish
 
 - (void)finishWithError:(NSError *)errorOrNil {
@@ -424,7 +437,8 @@ static NSMutableDictionary *callFlags;
   // that the life of the instance is determined by this retain cycle.
   _retainSelf = self;
 
-  _responseWriteable = [[GRXConcurrentWriteable alloc] initWithWriteable:writeable];
+  _responseWriteable = [[GRXConcurrentWriteable alloc] initWithWriteable:writeable
+                                                           dispatchQueue:_responseQueue];
 
   _wrappedCall = [[GRPCWrappedCall alloc] initWithHost:_host path:_path];
   NSAssert(_wrappedCall, @"Error allocating RPC objects. Low memory?");
diff --git a/src/objective-c/RxLibrary/GRXConcurrentWriteable.h b/src/objective-c/RxLibrary/GRXConcurrentWriteable.h
index b2775f98b5..07004f6d4d 100644
--- a/src/objective-c/RxLibrary/GRXConcurrentWriteable.h
+++ b/src/objective-c/RxLibrary/GRXConcurrentWriteable.h
@@ -53,7 +53,9 @@
  * The GRXWriteable instance is retained until writesFinishedWithError: is sent to it, and released
  * after that.
  */
-- (instancetype)initWithWriteable:(id<GRXWriteable>)writeable NS_DESIGNATED_INITIALIZER;
+- (instancetype)initWithWriteable:(id<GRXWriteable>)writeable
+                    dispatchQueue:(dispatch_queue_t)queue NS_DESIGNATED_INITIALIZER;
+- (instancetype)initWithWriteable:(id<GRXWriteable>)writeable;
 
 /**
  * Enqueues writeValue: to be sent to the writeable in the main thread.
diff --git a/src/objective-c/RxLibrary/GRXConcurrentWriteable.m b/src/objective-c/RxLibrary/GRXConcurrentWriteable.m
index 08bd079aea..88aa7a7282 100644
--- a/src/objective-c/RxLibrary/GRXConcurrentWriteable.m
+++ b/src/objective-c/RxLibrary/GRXConcurrentWriteable.m
@@ -51,14 +51,20 @@
 }
 
 // Designated initializer
-- (instancetype)initWithWriteable:(id<GRXWriteable>)writeable {
+- (instancetype)initWithWriteable:(id<GRXWriteable>)writeable
+                    dispatchQueue:(dispatch_queue_t)queue {
   if (self = [super init]) {
-    _writeableQueue = dispatch_get_main_queue();
+    _writeableQueue = queue;
     _writeable = writeable;
   }
   return self;
 }
 
+- (instancetype)initWithWriteable:(id<GRXWriteable>)writeable {
+  return [self initWithWriteable:writeable
+                   dispatchQueue:dispatch_get_main_queue()];
+}
+
 - (void)enqueueValue:(id)value completionHandler:(void (^)())handler {
   dispatch_async(_writeableQueue, ^{
     // We're racing a possible cancellation performed by another thread. To turn all already-