Introduce global task queue factory.

Bug: webrtc:10191
Change-Id: I7bdc97fd626da955b9194a9a0d8ed4f5aebddf66
Reviewed-on: https://webrtc-review.googlesource.com/c/118120
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26315}

api/task_queue/BUILD.gn

@@ -34,3 +34,32 @@ rtc_source_set("task_queue_factory") {
     "//third_party/abseil-cpp/absl/strings",
   ]
 }
+
+rtc_source_set("default_task_queue_factory") {
+  # TODO(bugs.webrtc.org/10191): Make public when implemented for all
+  # supported platforms.
+  visibility = [ ":global_task_queue_factory" ]
+  sources = [
+    "default_task_queue_factory.cc",
+    "default_task_queue_factory.h",
+  ]
+  deps = [
+    ":task_queue_factory",
+    "../../rtc_base:checks",
+  ]
+}
+
+rtc_source_set("global_task_queue_factory") {
+  # TODO(danilchap): Remove this target when task queue factory propagated to
+  # all components that create TaskQueues.
+  visibility = [ "*" ]
+  sources = [
+    "global_task_queue_factory.cc",
+    "global_task_queue_factory.h",
+  ]
+  deps = [
+    ":default_task_queue_factory",
+    ":task_queue_factory",
+    "../../rtc_base:checks",
+  ]
+}

api/task_queue/default_task_queue_factory.cc

@@ -0,0 +1,22 @@
+/*
+ *  Copyright 2019 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 "api/task_queue/default_task_queue_factory.h"
+
+#include "rtc_base/checks.h"
+
+namespace webrtc {
+
+std::unique_ptr<TaskQueueFactory> CreateDefaultTaskQueueFactory() {
+  RTC_CHECK(false)
+      << "Default task queue is not implemented for current platform, "
+         "overwrite the task queue implementation by setting global factory.";
+}
+
+}  // namespace webrtc

api/task_queue/default_task_queue_factory.h

@@ -0,0 +1,23 @@
+/*
+ *  Copyright 2019 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 API_TASK_QUEUE_DEFAULT_TASK_QUEUE_FACTORY_H_
+#define API_TASK_QUEUE_DEFAULT_TASK_QUEUE_FACTORY_H_
+
+#include <memory>
+
+#include "api/task_queue/task_queue_factory.h"
+
+namespace webrtc {
+
+std::unique_ptr<TaskQueueFactory> CreateDefaultTaskQueueFactory();
+
+}  // namespace webrtc
+
+#endif  // API_TASK_QUEUE_DEFAULT_TASK_QUEUE_FACTORY_H_

api/task_queue/global_task_queue_factory.cc

@@ -0,0 +1,40 @@
+/*
+ *  Copyright 2019 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 "api/task_queue/global_task_queue_factory.h"
+
+#include "api/task_queue/default_task_queue_factory.h"
+#include "rtc_base/checks.h"
+
+namespace webrtc {
+namespace {
+
+TaskQueueFactory* GlobalOrDefault(TaskQueueFactory* global) {
+  static TaskQueueFactory* const factory =
+      global ? global : CreateDefaultTaskQueueFactory().release();
+  return factory;
+}
+
+}  // namespace
+
+void SetGlobalTaskQueueFactory(std::unique_ptr<TaskQueueFactory> factory) {
+  RTC_CHECK(factory) << "Can't set nullptr TaskQueueFactory";
+  // Own, but never delete the global factory.
+  TaskQueueFactory* global = factory.release();
+  RTC_CHECK(GlobalOrDefault(global) == global)
+      << "Task queue factory set after another SetFactory or after a task "
+         "queue was created";
+}
+
+TaskQueueFactory& GlobalTaskQueueFactory() {
+  return *GlobalOrDefault(nullptr);
+}
+
+}  // namespace webrtc

api/task_queue/global_task_queue_factory.h

@@ -0,0 +1,27 @@
+/*
+ *  Copyright 2019 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 API_TASK_QUEUE_GLOBAL_TASK_QUEUE_FACTORY_H_
+#define API_TASK_QUEUE_GLOBAL_TASK_QUEUE_FACTORY_H_
+
+#include <memory>
+
+#include "api/task_queue/task_queue_factory.h"
+
+namespace webrtc {
+
+// May be called at most once, and before any TaskQueue is created.
+void SetGlobalTaskQueueFactory(std::unique_ptr<TaskQueueFactory> factory);
+
+// Returns TaskQueue factory. Always returns the same factory.
+TaskQueueFactory& GlobalTaskQueueFactory();
+
+}  // namespace webrtc
+
+#endif  // API_TASK_QUEUE_GLOBAL_TASK_QUEUE_FACTORY_H_