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src: limit foreground tasks draining loop #19987

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src: limit foreground tasks draining loop #19987

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66a7421
src: limit foreground tasks draining loop
ulan Apr 12, 2018
4dbc4aa
[squash] clarify the comment of flushing
ulan Apr 13, 2018
c435401
[squash] fix the repost count in the new test.
ulan Apr 16, 2018
167ae0e
[squash] drain all tasks in inspector-agent.
ulan Apr 20, 2018
f46763b
[squash] fix comment s/iff/if/.
ulan Apr 20, 2018
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2 changes: 1 addition & 1 deletion src/inspector_agent.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -316,7 +316,7 @@ class NodeInspectorClient : public V8InspectorClient {
terminated_ = false;
running_nested_loop_ = true;
while (!terminated_ && channel_->waitForFrontendMessage()) {
platform_->FlushForegroundTasks(env_->isolate());
while (platform_->FlushForegroundTasks(env_->isolate())) {}
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Doesn't this line preserve the bug? Because, even though you swap the queue before draining it, you're still running this loop forever if new tasks are constantly added to the original queue

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The inspector posts foreground tasks and requires that they are all processed before going to the outer loop.

AFAIK this code runs only when the inspector is active and the program is paused. The normal libuv tasks are not processed here. Latency shouldn't be an issue.

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My understanding is that the original bug this is trying to fix (#19937) is that there are cases where foreground tasks can add additional tasks to the queue. The bug was fixed by freezing the queue inside of FlushForegroundTasks, but this line of code I'm commenting on appears to loop THAT CALL so that the freeze fix doesn't actually help anything. It still will run forever, if foreground tasks add themselves.

Unless there's more than one place where FlushForegroundTasks is being called, and that's not an issue for this line?

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There is certainly more than one place. This particular line addresses a very specific interaction.

}
terminated_ = false;
running_nested_loop_ = false;
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4 changes: 2 additions & 2 deletions src/node_platform.cc
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Expand Up @@ -260,8 +260,8 @@ void NodePlatform::CallDelayedOnForegroundThread(Isolate* isolate,
std::unique_ptr<Task>(task), delay_in_seconds);
}

void NodePlatform::FlushForegroundTasks(v8::Isolate* isolate) {
ForIsolate(isolate)->FlushForegroundTasksInternal();
bool NodePlatform::FlushForegroundTasks(v8::Isolate* isolate) {
return ForIsolate(isolate)->FlushForegroundTasksInternal();
}

void NodePlatform::CancelPendingDelayedTasks(v8::Isolate* isolate) {
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11 changes: 7 additions & 4 deletions src/node_platform.h
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Expand Up @@ -66,9 +66,9 @@ class PerIsolatePlatformData :
void ref();
int unref();

// Returns true iff work was dispatched or executed.
// New tasks that are posted during flushing of the queue are postponed until
// the next flushing.
// Returns true iff work was dispatched or executed. New tasks that are
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Nit: s/iff/if.

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@apapirovski I guess these were intentional?

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@apapirovski apapirovski Apr 20, 2018 •
edited
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Yeah but I know the meaning and I didn't even think of it until you mentioned it... but maybe that just reflects badly on me... 🤔 😆

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@apapirovski apapirovski Apr 20, 2018 •
edited
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I guess what I'm saying: I don't think this is the place for iff. It doesn't make it clearer.

But I'm not going to object if someone prefers this. It's a low priority thing for me.

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Done. The iff was there before my change. I agree that if seems slightly better.

// posted during flushing of the queue are postponed until the next
// flushing.
bool FlushForegroundTasksInternal();
void CancelPendingDelayedTasks();

Expand Down Expand Up @@ -133,7 +133,10 @@ class NodePlatform : public MultiIsolatePlatform {
double CurrentClockTimeMillis() override;
v8::TracingController* GetTracingController() override;

void FlushForegroundTasks(v8::Isolate* isolate);
// Returns true iff work was dispatched or executed. New tasks that are
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Same here, s/iff/if

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Done.

// posted during flushing of the queue are postponed until the next
// flushing.
bool FlushForegroundTasks(v8::Isolate* isolate);

void RegisterIsolate(IsolateData* isolate_data, uv_loop_t* loop) override;
void UnregisterIsolate(IsolateData* isolate_data) override;
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7 changes: 4 additions & 3 deletions test/cctest/test_platform.cc
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Expand Up @@ -45,10 +45,11 @@ TEST_F(PlatformTest, SkipNewTasksInFlushForegroundTasks) {
int run_count = 0;
platform->CallOnForegroundThread(
isolate_, new RepostingTask(2, &run_count, isolate_, platform.get()));
platform->FlushForegroundTasks(isolate_);
EXPECT_TRUE(platform->FlushForegroundTasks(isolate_));
EXPECT_EQ(1, run_count);
platform->FlushForegroundTasks(isolate_);
EXPECT_TRUE(platform->FlushForegroundTasks(isolate_));
EXPECT_EQ(2, run_count);
platform->FlushForegroundTasks(isolate_);
EXPECT_TRUE(platform->FlushForegroundTasks(isolate_));
EXPECT_EQ(3, run_count);
EXPECT_FALSE(platform->FlushForegroundTasks(isolate_));
}