Leverage dispatch_queue_create_with_target when possible.

Replacing dispatch_queue_create followed by
dispatch_set_target_queue with dispatch_queue_create_with_target
is claimed to be source of GCD performance improvement:
https://developer.apple.com/videos/play/wwdc2017/706/
Video since 40 min. Slides since 199.

Bug: webrtc:9055
Change-Id: I0136f7faaef0951a7ad243bc8772f3ee952d5470
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/168491
Reviewed-by: Tommi <tommi@webrtc.org>
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Commit-Queue: Yura Yaroshevich <yura.yaroshevich@gmail.com>
Cr-Commit-Position: refs/heads/master@{#30781}

rtc_base/BUILD.gn

@@ -487,6 +487,7 @@ if (is_mac || is_ios) {
       ":checks",
       ":logging",
       "../api/task_queue",
+      "system:gcd_helpers",
       "//third_party/abseil-cpp/absl/strings",
     ]
   }

rtc_base/system/BUILD.gn

@@ -60,6 +60,13 @@ if (is_mac || is_ios) {
     deps = [ "..:checks" ]
     libs = [ "Foundation.framework" ]
   }
+
+  rtc_library("gcd_helpers") {
+    sources = [
+      "gcd_helpers.h",
+      "gcd_helpers.m",
+    ]
+  }
 }
 
 rtc_source_set("thread_registry") {

rtc_base/system/gcd_helpers.h

@@ -0,0 +1,29 @@
+/*
+ *  Copyright 2020 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef RTC_BASE_SYSTEM_GCD_HELPERS_H_
+#define RTC_BASE_SYSTEM_GCD_HELPERS_H_
+
+#include <dispatch/dispatch.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+DISPATCH_RETURNS_RETAINED DISPATCH_WARN_RESULT DISPATCH_NOTHROW dispatch_queue_t
+RTCDispatchQueueCreateWithTarget(const char* label,
+                                 dispatch_queue_attr_t attr,
+                                 dispatch_queue_t target);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif  // RTC_BASE_SYSTEM_GCD_HELPERS_H_

rtc_base/system/gcd_helpers.m

@@ -0,0 +1,22 @@
+/*
+ *  Copyright 2020 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "rtc_base/system/gcd_helpers.h"
+
+dispatch_queue_t RTCDispatchQueueCreateWithTarget(const char *label,
+                                                  dispatch_queue_attr_t attr,
+                                                  dispatch_queue_t target) {
+  if (@available(iOS 10, macOS 10.12, tvOS 10, watchOS 3, *)) {
+    return dispatch_queue_create_with_target(label, attr, target);
+  }
+  dispatch_queue_t queue = dispatch_queue_create(label, attr);
+  dispatch_set_target_queue(queue, target);
+  return queue;
+}

rtc_base/task_queue_gcd.cc

@@ -24,6 +24,7 @@
 #include "api/task_queue/task_queue_base.h"
 #include "rtc_base/checks.h"
 #include "rtc_base/logging.h"
+#include "rtc_base/system/gcd_helpers.h"
 
 namespace webrtc {
 namespace {
@@ -67,16 +68,16 @@ class TaskQueueGcd : public TaskQueueBase {
 };
 
 TaskQueueGcd::TaskQueueGcd(absl::string_view queue_name, int gcd_priority)
-    : queue_(dispatch_queue_create(std::string(queue_name).c_str(),
-                                   DISPATCH_QUEUE_SERIAL)),
+    : queue_(RTCDispatchQueueCreateWithTarget(
+          std::string(queue_name).c_str(),
+          DISPATCH_QUEUE_SERIAL,
+          dispatch_get_global_queue(gcd_priority, 0))),
       is_active_(true) {
   RTC_CHECK(queue_);
   dispatch_set_context(queue_, this);
   // Assign a finalizer that will delete the queue when the last reference
   // is released. This may run after the TaskQueue::Delete.
   dispatch_set_finalizer_f(queue_, &DeleteQueue);
-
-  dispatch_set_target_queue(queue_, dispatch_get_global_queue(gcd_priority, 0));
 }
 
 TaskQueueGcd::~TaskQueueGcd() = default;

sdk/BUILD.gn

@@ -573,6 +573,7 @@ if (is_ios || is_mac) {
         ":helpers_objc",
         ":video_objc",
         ":videoframebuffer_objc",
+        "../rtc_base/system:gcd_helpers",
       ]
     }
 

sdk/objc/components/capturer/RTCCameraVideoCapturer.m

@@ -21,6 +21,7 @@
 
 #import "helpers/AVCaptureSession+DevicePosition.h"
 #import "helpers/RTCDispatcher+Private.h"
+#include "rtc_base/system/gcd_helpers.h"
 
 const int64_t kNanosecondsPerSecond = 1000000000;
 
@@ -415,10 +416,10 @@ const int64_t kNanosecondsPerSecond = 1000000000;
 
 - (dispatch_queue_t)frameQueue {
   if (!_frameQueue) {
-    _frameQueue =
-        dispatch_queue_create("org.webrtc.cameravideocapturer.video", DISPATCH_QUEUE_SERIAL);
-    dispatch_set_target_queue(_frameQueue,
-                              dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0));
+    _frameQueue = RTCDispatchQueueCreateWithTarget(
+        "org.webrtc.cameravideocapturer.video",
+        DISPATCH_QUEUE_SERIAL,
+        dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0));
   }
   return _frameQueue;
 }

sdk/objc/components/capturer/RTCFileVideoCapturer.m

@@ -13,6 +13,7 @@
 #import "base/RTCLogging.h"
 #import "base/RTCVideoFrameBuffer.h"
 #import "components/video_frame_buffer/RTCCVPixelBuffer.h"
+#include "rtc_base/system/gcd_helpers.h"
 
 NSString *const kRTCFileVideoCapturerErrorDomain = @"org.webrtc.RTCFileVideoCapturer";
 
@@ -118,9 +119,10 @@ typedef NS_ENUM(NSInteger, RTCFileVideoCapturerStatus) {
 
 - (dispatch_queue_t)frameQueue {
   if (!_frameQueue) {
-    _frameQueue = dispatch_queue_create("org.webrtc.filecapturer.video", DISPATCH_QUEUE_SERIAL);
-    dispatch_set_target_queue(_frameQueue,
-                              dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0));
+    _frameQueue = RTCDispatchQueueCreateWithTarget(
+        "org.webrtc.filecapturer.video",
+        DISPATCH_QUEUE_SERIAL,
+        dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0));
   }
   return _frameQueue;
 }