Fix overflow in TaskRunnerWindow. (#182822) (#5)

knopp · web-flow · commit 3997067aabde · 2026-02-25T18:21:58.000+01:00
Fixes flutter/flutter#182501 Right now empty `TaskRunner::ProcessTasks()` returns `TaskTimePoint::max() - now` (relative time). This causes problems, because the value is later used in `TaskRunnerWindow` to schedule timer at `std::chrono::high_resolution_clock::now() + relative_time`). This of course overflows, because the new `now()` in `TaskRunnerWindow` is higher than the value used to calculate original delta inside `TaskRunner`. `TaskRunnerWindow` already had special case where it checks for `std::chrono::nanoseconds::max()`. In this PR the behavior of `TaskRunnerWindow::SetTimer` has been updated to check for overflow rather than excepcting a special value. *If you had to change anything in the [flutter/tests] repo, include a link to the migration guide as per the [breaking change policy].* ## Pre-launch Checklist - [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [x] I read the [Tree Hygiene] wiki page, which explains my responsibilities. - [x] I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement]. - [x] I signed the [CLA]. - [x] I listed at least one issue that this PR fixes in the description above. - [x] I updated/added relevant documentation (doc comments with `///`). - [x] I added new tests to check the change I am making, or this PR is [test-exempt]. - [x] I followed the [breaking change policy] and added [Data Driven Fixes] where supported. - [x] All existing and new tests are passing. 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An issue is not required if the PR fixes something trivial like a typo.* *If you had to change anything in the [flutter/tests] repo, include a link to the migration guide as per the [breaking change policy].* ## Pre-launch Checklist - [ ] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [ ] I read the [Tree Hygiene] wiki page, which explains my responsibilities. - [ ] I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement]. - [ ] I signed the [CLA]. - [ ] I listed at least one issue that this PR fixes in the description above. - [ ] I updated/added relevant documentation (doc comments with `///`). - [ ] I added new tests to check the change I am making, or this PR is [test-exempt]. - [ ] I followed the [breaking change policy] and added [Data Driven Fixes] where supported. - [ ] All existing and new tests are passing. 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diff --git a/engine/src/flutter/shell/platform/windows/task_runner.cc b/engine/src/flutter/shell/platform/windows/task_runner.cc
@@ -63,10 +63,11 @@ std::chrono::nanoseconds TaskRunner::ProcessTasks() {
   // Calculate duration to sleep for on next iteration.
   {
     std::lock_guard<std::mutex> lock(task_queue_mutex_);
-    const auto next_wake = task_queue_.empty() ? TaskTimePoint::max()
-                                               : task_queue_.top().fire_time;
-
-    return std::min(next_wake - now, std::chrono::nanoseconds::max());
+    if (task_queue_.empty()) {
+      return std::chrono::nanoseconds::max();
+    } else {
+      return task_queue_.top().fire_time - now;
+    }
   }
 }
 
diff --git a/engine/src/flutter/shell/platform/windows/task_runner_unittests.cc b/engine/src/flutter/shell/platform/windows/task_runner_unittests.cc
@@ -121,6 +121,12 @@ class TestTaskRunnerWindow : public TaskRunnerWindow {
   TestTaskRunnerWindow() : TaskRunnerWindow() {}
 };
 
+TEST(TaskRunnerTest, EmptyTaskRunnerReturnsNanoSecondsMax) {
+  TaskRunner runner(MockGetCurrentTime, [](const FlutterTask*) {});
+  auto res = runner.ProcessTasks();
+  EXPECT_EQ(res, std::chrono::nanoseconds::max());
+}
+
 TEST(TaskRunnerTest, TaskRunnerWindowCoalescesWakeUpMessages) {
   class Delegate : public TaskRunnerWindow::Delegate {
    public:
diff --git a/engine/src/flutter/shell/platform/windows/task_runner_window.cc b/engine/src/flutter/shell/platform/windows/task_runner_window.cc
@@ -185,12 +185,11 @@ void TaskRunnerWindow::ProcessTasks() {
 }
 
 void TaskRunnerWindow::SetTimer(std::chrono::nanoseconds when) {
-  if (when == std::chrono::nanoseconds::max()) {
-    timer_thread_.ScheduleAt(
-        std::chrono::time_point<std::chrono::high_resolution_clock>::max());
-  } else {
-    timer_thread_.ScheduleAt(std::chrono::high_resolution_clock::now() + when);
-  }
+  auto now = std::chrono::high_resolution_clock::now();
+  auto remaining_to_max =
+      std::chrono::nanoseconds::max() - now.time_since_epoch();
+  when = std::min(when, remaining_to_max);
+  timer_thread_.ScheduleAt(now + when);
 }
 
 WNDCLASS TaskRunnerWindow::RegisterWindowClass() {

Original file line number	Diff line number	Diff line change
`@@ -63,10 +63,11 @@ std::chrono::nanoseconds TaskRunner::ProcessTasks() {`
`63`	`63`	`// Calculate duration to sleep for on next iteration.`
`64`	`64`	`{`
`65`	`65`	`std::lock_guard<std::mutex> lock(task_queue_mutex_);`
`66`		`- const auto next_wake = task_queue_.empty() ? TaskTimePoint::max()`
`67`		`- : task_queue_.top().fire_time;`
`68`		`-`
`69`		`- return std::min(next_wake - now, std::chrono::nanoseconds::max());`
	`66`	`+ if (task_queue_.empty()) {`
	`67`	`+ return std::chrono::nanoseconds::max();`
	`68`	`+ } else {`
	`69`	`+ return task_queue_.top().fire_time - now;`
	`70`	`+ }`
`70`	`71`	`}`
`71`	`72`	`}`
`72`	`73`