From 25e735239c971a71c2feab65f19793c4edb60db9 Mon Sep 17 00:00:00 2001
From: Tomas Gunnarsson <tommi@webrtc.org>
Date: Mon, 19 Apr 2021 10:14:10 +0200
Subject: [PATCH] Add support for setting the initial state to the pending task
 flag.

This is useful in cases where a class needs to use a flag for controlling
operations on a task queue but initialization needs to complete before
tasks are allowed to run.

Example CL that needs this (for MediaChannel):
https://webrtc-review.googlesource.com/c/src/+/215405

Bug: webrtc:11993
Change-Id: Icd7dd16ee7447647266d6de000a4db3fd0447618
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/215583
Commit-Queue: Tommi <tommi@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33773}
---
 .../task_utils/pending_task_safety_flag.cc    | 13 ++++++++++--
 .../task_utils/pending_task_safety_flag.h     |  7 ++++++-
 .../pending_task_safety_flag_unittest.cc      | 21 ++++++++++++++++++-
 3 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/rtc_base/task_utils/pending_task_safety_flag.cc b/rtc_base/task_utils/pending_task_safety_flag.cc
index 595457dc0e..b83d714916 100644
--- a/rtc_base/task_utils/pending_task_safety_flag.cc
+++ b/rtc_base/task_utils/pending_task_safety_flag.cc
@@ -16,12 +16,21 @@ namespace webrtc {
 
 // static
 rtc::scoped_refptr<PendingTaskSafetyFlag> PendingTaskSafetyFlag::Create() {
-  return new rtc::RefCountedObject<PendingTaskSafetyFlag>();
+  return new rtc::RefCountedObject<PendingTaskSafetyFlag>(true);
 }
 
 rtc::scoped_refptr<PendingTaskSafetyFlag>
 PendingTaskSafetyFlag::CreateDetached() {
-  auto safety_flag = Create();
+  rtc::scoped_refptr<PendingTaskSafetyFlag> safety_flag(
+      new rtc::RefCountedObject<PendingTaskSafetyFlag>(true));
+  safety_flag->main_sequence_.Detach();
+  return safety_flag;
+}
+
+rtc::scoped_refptr<PendingTaskSafetyFlag>
+PendingTaskSafetyFlag::CreateDetachedInactive() {
+  rtc::scoped_refptr<PendingTaskSafetyFlag> safety_flag(
+      new rtc::RefCountedObject<PendingTaskSafetyFlag>(false));
   safety_flag->main_sequence_.Detach();
   return safety_flag;
 }
diff --git a/rtc_base/task_utils/pending_task_safety_flag.h b/rtc_base/task_utils/pending_task_safety_flag.h
index abfce26ad8..4864b5de3b 100644
--- a/rtc_base/task_utils/pending_task_safety_flag.h
+++ b/rtc_base/task_utils/pending_task_safety_flag.h
@@ -58,10 +58,15 @@ namespace webrtc {
 class PendingTaskSafetyFlag : public rtc::RefCountInterface {
  public:
   static rtc::scoped_refptr<PendingTaskSafetyFlag> Create();
+
   // Creates a flag, but with its SequenceChecker initially detached. Hence, it
   // may be created on a different thread than the flag will be used on.
   static rtc::scoped_refptr<PendingTaskSafetyFlag> CreateDetached();
 
+  // Same as `CreateDetached()` except the initial state of the returned flag
+  // will be `!alive()`.
+  static rtc::scoped_refptr<PendingTaskSafetyFlag> CreateDetachedInactive();
+
   ~PendingTaskSafetyFlag() = default;
 
   void SetNotAlive();
@@ -84,7 +89,7 @@ class PendingTaskSafetyFlag : public rtc::RefCountInterface {
   bool alive() const;
 
  protected:
-  PendingTaskSafetyFlag() = default;
+  explicit PendingTaskSafetyFlag(bool alive) : alive_(alive) {}
 
  private:
   bool alive_ = true;
diff --git a/rtc_base/task_utils/pending_task_safety_flag_unittest.cc b/rtc_base/task_utils/pending_task_safety_flag_unittest.cc
index 6df2fe2ffb..07bbea296e 100644
--- a/rtc_base/task_utils/pending_task_safety_flag_unittest.cc
+++ b/rtc_base/task_utils/pending_task_safety_flag_unittest.cc
@@ -156,8 +156,27 @@ TEST(PendingTaskSafetyFlagTest, PendingTaskDropped) {
   blocker.Set();
 
   // Run an empty task on tq1 to flush all the queued tasks.
-  tq1.SendTask([]() {}, RTC_FROM_HERE);
+  tq1.WaitForPreviouslyPostedTasks();
   ASSERT_FALSE(owner);
   EXPECT_FALSE(stuff_done);
 }
+
+TEST(PendingTaskSafetyFlagTest, PendingTaskNotAliveInitialized) {
+  TaskQueueForTest tq("PendingTaskNotAliveInitialized");
+
+  // Create a new flag that initially not `alive`.
+  auto flag = PendingTaskSafetyFlag::CreateDetachedInactive();
+  tq.SendTask([&flag]() { EXPECT_FALSE(flag->alive()); }, RTC_FROM_HERE);
+
+  bool task_1_ran = false;
+  bool task_2_ran = false;
+  tq.PostTask(ToQueuedTask(flag, [&task_1_ran]() { task_1_ran = true; }));
+  tq.PostTask([&flag]() { flag->SetAlive(); });
+  tq.PostTask(ToQueuedTask(flag, [&task_2_ran]() { task_2_ran = true; }));
+
+  tq.WaitForPreviouslyPostedTasks();
+  EXPECT_FALSE(task_1_ran);
+  EXPECT_TRUE(task_2_ran);
+}
+
 }  // namespace webrtc