src: cancel pending delayed platform tasks on exit

Worker threads need an event loop without active libuv handles in
order to shut down. One source of handles that was previously
not accounted for were delayed V8 tasks; these create timers
that would be standing in the way of clearing the event loop.

To solve this, keep track of the scheduled tasks in a list
and close their timer handles before the corresponding isolate/loop
is removed from the platform.

It is not clear from the V8 documentation what the expectation is
with respect to pending background tasks at the end of the
isolate lifetime; however, an alternative approach of executing
these scheduled tasks when flushing them led to an infinite loop
of tasks scheduling each other; so it seems safe to assume that
the behaviour implemented in this patch is at least acceptable.

Original-PR-URL: https://github.com/ayojs/ayo/pull/120
Original-Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>
PR-URL: https://github.com/nodejs/node/pull/16700
Reviewed-By: James M Snell <jasnell@gmail.com>

1 files changed, 39 insertions, 15 deletions

diff --git a/src/node_platform.cc b/src/node_platform.cc
index ec2fca6c41..7cec43cbf4 100644
--- a/src/node_platform.cc
+++ b/src/node_platform.cc
@@ -4,6 +4,7 @@
 #include "env.h"
 #include "env-inl.h"
 #include "util.h"
+#include <algorithm>
 
 namespace node {
 
@@ -45,13 +46,17 @@ void PerIsolatePlatformData::CallOnForegroundThread(Task* task) {
 
 void PerIsolatePlatformData::CallDelayedOnForegroundThread(
     Task* task, double delay_in_seconds) {
-  auto pair = new std::pair<Task*, double>(task, delay_in_seconds);
-  foreground_delayed_tasks_.Push(pair);
+  auto delayed = new DelayedTask();
+  delayed->task = task;
+  delayed->platform_data = this;
+  delayed->timeout = delay_in_seconds;
+  foreground_delayed_tasks_.Push(delayed);
   uv_async_send(flush_tasks_);
 }
 
 PerIsolatePlatformData::~PerIsolatePlatformData() {
   FlushForegroundTasksInternal();
+  CancelPendingDelayedTasks();
 
   uv_close(reinterpret_cast<uv_handle_t*>(flush_tasks_),
            [](uv_handle_t* handle) {
@@ -120,7 +125,7 @@ size_t NodePlatform::NumberOfAvailableBackgroundThreads() {
   return threads_.size();
 }
 
-static void RunForegroundTask(Task* task) {
+void PerIsolatePlatformData::RunForegroundTask(Task* task) {
   Isolate* isolate = Isolate::GetCurrent();
   HandleScope scope(isolate);
   Environment* env = Environment::GetCurrent(isolate);
@@ -130,14 +135,29 @@ static void RunForegroundTask(Task* task) {
   delete task;
 }
 
-static void RunForegroundTask(uv_timer_t* handle) {
-  Task* task = static_cast<Task*>(handle->data);
-  RunForegroundTask(task);
-  uv_close(reinterpret_cast<uv_handle_t*>(handle), [](uv_handle_t* handle) {
-    delete reinterpret_cast<uv_timer_t*>(handle);
+void PerIsolatePlatformData::RunForegroundTask(uv_timer_t* handle) {
+  DelayedTask* delayed = static_cast<DelayedTask*>(handle->data);
+  auto& tasklist = delayed->platform_data->scheduled_delayed_tasks_;
+  auto it = std::find(tasklist.begin(), tasklist.end(), delayed);
+  CHECK_NE(it, tasklist.end());
+  tasklist.erase(it);
+  RunForegroundTask(delayed->task);
+  uv_close(reinterpret_cast<uv_handle_t*>(&delayed->timer),
+           [](uv_handle_t* handle) {
+    delete static_cast<DelayedTask*>(handle->data);
   });
 }
 
+void PerIsolatePlatformData::CancelPendingDelayedTasks() {
+  for (auto delayed : scheduled_delayed_tasks_) {
+    uv_close(reinterpret_cast<uv_handle_t*>(&delayed->timer),
+             [](uv_handle_t* handle) {
+      delete static_cast<DelayedTask*>(handle->data);
+    });
+  }
+  scheduled_delayed_tasks_.clear();
+}
+
 void NodePlatform::DrainBackgroundTasks(Isolate* isolate) {
   PerIsolatePlatformData* per_isolate = ForIsolate(isolate);
 
@@ -152,18 +172,18 @@ void NodePlatform::DrainBackgroundTasks(Isolate* isolate) {
 
 bool PerIsolatePlatformData::FlushForegroundTasksInternal() {
   bool did_work = false;
+
   while (auto delayed = foreground_delayed_tasks_.Pop()) {
     did_work = true;
     uint64_t delay_millis =
-        static_cast<uint64_t>(delayed->second + 0.5) * 1000;
-    uv_timer_t* handle = new uv_timer_t();
-    handle->data = static_cast<void*>(delayed->first);
-    uv_timer_init(loop_, handle);
+        static_cast<uint64_t>(delayed->timeout + 0.5) * 1000;
+    delayed->timer.data = static_cast<void*>(delayed);
+    uv_timer_init(loop_, &delayed->timer);
     // Timers may not guarantee queue ordering of events with the same delay if
     // the delay is non-zero. This should not be a problem in practice.
-    uv_timer_start(handle, RunForegroundTask, delay_millis, 0);
-    uv_unref(reinterpret_cast<uv_handle_t*>(handle));
-    delete delayed;
+    uv_timer_start(&delayed->timer, RunForegroundTask, delay_millis, 0);
+    uv_unref(reinterpret_cast<uv_handle_t*>(&delayed->timer));
+    scheduled_delayed_tasks_.push_back(delayed);
   }
   while (Task* task = foreground_tasks_.Pop()) {
     did_work = true;
@@ -199,6 +219,10 @@ void NodePlatform::FlushForegroundTasks(v8::Isolate* isolate) {
   ForIsolate(isolate)->FlushForegroundTasksInternal();
 }
 
+void NodePlatform::CancelPendingDelayedTasks(v8::Isolate* isolate) {
+  ForIsolate(isolate)->CancelPendingDelayedTasks();
+}
+
 bool NodePlatform::IdleTasksEnabled(Isolate* isolate) { return false; }
 
 double NodePlatform::MonotonicallyIncreasingTime() {