Re-arm timer as necessary in MessageLoopFuchsia

Author: George Wright

fml/BUILD.gn

@@ -227,6 +227,7 @@ executable("fml_unittests") {
     "memory/weak_ptr_unittest.cc",
     "message_loop_task_queues_merge_unmerge_unittests.cc",
     "message_loop_task_queues_unittests.cc",
+    "message_loop_unittests.cc",
     "message_unittests.cc",
     "paths_unittests.cc",
     "platform/darwin/string_range_sanitization_unittests.mm",
@@ -243,10 +244,7 @@ executable("fml_unittests") {
 
   # TODO(gw280): Figure out why these tests don't work currently on Fuchsia
   if (!is_fuchsia) {
-    sources += [
-      "file_unittest.cc",
-      "message_loop_unittests.cc",
-    ]
+    sources += [ "file_unittest.cc" ]
   }
 
   deps = [

fml/message_loop_unittests.cc

@@ -10,6 +10,7 @@
 #include "flutter/fml/build_config.h"
 #include "flutter/fml/concurrent_message_loop.h"
 #include "flutter/fml/message_loop.h"
+#include "flutter/fml/message_loop_impl.h"
 #include "flutter/fml/synchronization/count_down_latch.h"
 #include "flutter/fml/synchronization/waitable_event.h"
 #include "flutter/fml/task_runner.h"
@@ -309,3 +310,32 @@ TEST(MessageLoop, CanCreateConcurrentMessageLoop) {
   latch.Wait();
   ASSERT_GE(thread_ids.size(), 1u);
 }
+
+TEST(MessageLoop, TIME_SENSITIVE(WakeUpTimersAreSingletons)) {
+  auto loop_impl = fml::MessageLoopImpl::Create();
+
+  const auto t1 = fml::TimeDelta::FromMilliseconds(10);
+  const auto t2 = fml::TimeDelta::FromMilliseconds(20);
+
+  const auto begin = fml::TimePoint::Now();
+
+  // Register a task scheduled for 10ms in the future. This schedules a
+  // WakeUp call on the MessageLoopImpl with that fml::TimePoint
+  loop_impl->PostTask(
+      [&]() {
+        auto delta = fml::TimePoint::Now() - begin;
+        auto ms = delta.ToMillisecondsF();
+        ASSERT_GE(ms, 18);
+        ASSERT_LE(ms, 22);
+
+        loop_impl->Terminate();
+      },
+      fml::TimePoint::Now() + t1);
+
+  // Call WakeUp manually to change the WakeUp time to the future. If the
+  // timer is correctly set up to be rearmed instead of a new timer scheduled,
+  // the above task will be executed at t2 instead of t1 now.
+  loop_impl->WakeUp(fml::TimePoint::Now() + t2);
+
+  loop_impl->Run();
+}

fml/platform/fuchsia/message_loop_fuchsia.cc

@@ -5,13 +5,16 @@
 #include "flutter/fml/platform/fuchsia/message_loop_fuchsia.h"
 
 #include <lib/async-loop/default.h>
-#include <lib/async/cpp/task.h>
 #include <lib/zx/time.h>
 
 namespace fml {
 
 MessageLoopFuchsia::MessageLoopFuchsia()
-    : loop_(&kAsyncLoopConfigAttachToCurrentThread) {}
+    : loop_(&kAsyncLoopConfigAttachToCurrentThread) {
+  auto handler = [this](async_dispatcher_t* dispatcher, async::Task* task,
+                        zx_status_t status) { RunExpiredTasksNow(); };
+  task_.set_handler(handler);
+}
 
 MessageLoopFuchsia::~MessageLoopFuchsia() = default;
 
@@ -30,8 +33,12 @@ void MessageLoopFuchsia::WakeUp(fml::TimePoint time_point) {
     due_time = zx::nsec((time_point - now).ToNanoseconds());
   }
 
-  auto status = async::PostDelayedTask(
-      loop_.dispatcher(), [this]() { RunExpiredTasksNow(); }, due_time);
+  std::scoped_lock lock(task_mutex_);
+
+  auto status = task_.Cancel();
+  FML_DCHECK(status == ZX_OK || status == ZX_ERR_NOT_FOUND);
+
+  status = task_.PostDelayed(loop_.dispatcher(), due_time);
   FML_DCHECK(status == ZX_OK);
 }
 

fml/platform/fuchsia/message_loop_fuchsia.h

@@ -6,6 +6,7 @@
 #define FLUTTER_FML_PLATFORM_FUCHSIA_MESSAGE_LOOP_FUCHSIA_H_
 
 #include <lib/async-loop/cpp/loop.h>
+#include <lib/async/cpp/task.h>
 
 #include "flutter/fml/macros.h"
 #include "flutter/fml/message_loop_impl.h"
@@ -25,6 +26,8 @@ class MessageLoopFuchsia : public MessageLoopImpl {
   void WakeUp(fml::TimePoint time_point) override;
 
   async::Loop loop_;
+  std::mutex task_mutex_;
+  async::Task task_;
 
   FML_FRIEND_MAKE_REF_COUNTED(MessageLoopFuchsia);
   FML_FRIEND_REF_COUNTED_THREAD_SAFE(MessageLoopFuchsia);