Delete FakeIceTransport usage of AsyncInvoker

Bug: webrtc:12339
Change-Id: I1656bef5178dd150f5069d743ea7236dc0cb0300
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/212500
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Tommi <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33509}

p2p/BUILD.gn

@@ -144,6 +144,8 @@ if (rtc_include_tests) {
       "../api:libjingle_peerconnection_api",
       "../rtc_base",
       "../rtc_base:rtc_base_approved",
+      "../rtc_base/task_utils:pending_task_safety_flag",
+      "../rtc_base/task_utils:to_queued_task",
     ]
     absl_deps = [
       "//third_party/abseil-cpp/absl/algorithm:container",

p2p/base/fake_ice_transport.h

@@ -20,8 +20,9 @@
 #include "absl/types/optional.h"
 #include "api/ice_transport_interface.h"
 #include "p2p/base/ice_transport_internal.h"
-#include "rtc_base/async_invoker.h"
 #include "rtc_base/copy_on_write_buffer.h"
+#include "rtc_base/task_utils/pending_task_safety_flag.h"
+#include "rtc_base/task_utils/to_queued_task.h"
 
 namespace cricket {
 
@@ -305,12 +306,12 @@ class FakeIceTransport : public IceTransportInternal {
     if (!combine_outgoing_packets_ || send_packet_.size() > len) {
       rtc::CopyOnWriteBuffer packet(std::move(send_packet_));
       if (async_) {
-        invoker_.AsyncInvokeDelayed<void>(
-            RTC_FROM_HERE, network_thread_,
-            [this, packet] {
-              RTC_DCHECK_RUN_ON(network_thread_);
-              FakeIceTransport::SendPacketInternal(packet);
-            },
+        network_thread_->PostDelayedTask(
+            ToQueuedTask(task_safety_.flag(),
+                         [this, packet] {
+                           RTC_DCHECK_RUN_ON(network_thread_);
+                           FakeIceTransport::SendPacketInternal(packet);
+                         }),
             async_delay_ms_);
       } else {
         SendPacketInternal(packet);
@@ -389,7 +390,6 @@ class FakeIceTransport : public IceTransportInternal {
     }
   }
 
-  rtc::AsyncInvoker invoker_;
   const std::string name_;
   const int component_;
   FakeIceTransport* dest_ RTC_GUARDED_BY(network_thread_) = nullptr;
@@ -420,6 +420,7 @@ class FakeIceTransport : public IceTransportInternal {
       RTC_GUARDED_BY(network_thread_);
   rtc::CopyOnWriteBuffer last_sent_packet_ RTC_GUARDED_BY(network_thread_);
   rtc::Thread* const network_thread_;
+  webrtc::ScopedTaskSafetyDetached task_safety_;
 };
 
 class FakeIceTransportWrapper : public webrtc::IceTransportInterface {

rtc_base/task_utils/pending_task_safety_flag.cc

@@ -19,6 +19,13 @@ rtc::scoped_refptr<PendingTaskSafetyFlag> PendingTaskSafetyFlag::Create() {
   return new rtc::RefCountedObject<PendingTaskSafetyFlag>();
 }
 
+rtc::scoped_refptr<PendingTaskSafetyFlag>
+PendingTaskSafetyFlag::CreateDetached() {
+  auto safety_flag = Create();
+  safety_flag->main_sequence_.Detach();
+  return safety_flag;
+}
+
 void PendingTaskSafetyFlag::SetNotAlive() {
   RTC_DCHECK_RUN_ON(&main_sequence_);
   alive_ = false;

rtc_base/task_utils/pending_task_safety_flag.h

@@ -58,10 +58,28 @@ 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();
 
   ~PendingTaskSafetyFlag() = default;
 
   void SetNotAlive();
+  // The SetAlive method is intended to support Start/Stop/Restart usecases.
+  // When a class has called SetNotAlive on a flag used for posted tasks, and
+  // decides it wants to post new tasks and have them run, there are two
+  // reasonable ways to do that:
+  //
+  // (i) Use the below SetAlive method. One subtlety is that any task posted
+  //     prior to SetNotAlive, and still in the queue, is resurrected and will
+  //     run.
+  //
+  // (ii) Create a fresh flag, and just drop the reference to the old one. This
+  //      avoids the above problem, and ensures that tasks poster prior to
+  //      SetNotAlive stay cancelled. Instead, there's a potential data race on
+  //      the flag pointer itself. Some synchronization is required between the
+  //      thread overwriting the flag pointer, and the threads that want to post
+  //      tasks and therefore read that same pointer.
   void SetAlive();
   bool alive() const;
 
@@ -103,6 +121,21 @@ class ScopedTaskSafety {
       PendingTaskSafetyFlag::Create();
 };
 
+// Like ScopedTaskSafety, but allows construction on a different thread than
+// where the flag will be used.
+class ScopedTaskSafetyDetached {
+ public:
+  ScopedTaskSafetyDetached() = default;
+  ~ScopedTaskSafetyDetached() { flag_->SetNotAlive(); }
+
+  // Returns a new reference to the safety flag.
+  rtc::scoped_refptr<PendingTaskSafetyFlag> flag() const { return flag_; }
+
+ private:
+  rtc::scoped_refptr<PendingTaskSafetyFlag> flag_ =
+      PendingTaskSafetyFlag::CreateDetached();
+};
+
 }  // namespace webrtc
 
 #endif  // RTC_BASE_TASK_UTILS_PENDING_TASK_SAFETY_FLAG_H_