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src: UV_RUN_ONCE in a loop is inefficient #8496
Description
src/node.cc calls uv_run(loop, UV_RUN_ONCE) in a loop:
do {
v8_platform.PumpMessageLoop(isolate);
more = uv_run(env.event_loop(), UV_RUN_ONCE);
if (more == false) {
v8_platform.PumpMessageLoop(isolate);
EmitBeforeExit(&env);
// Emit `beforeExit` if the loop became alive either after emitting
// event, or after running some callbacks.
more = uv_loop_alive(env.event_loop());
if (uv_run(env.event_loop(), UV_RUN_NOWAIT) != 0)
more = true;
}
} while (more == true);uv_run() looks like this:
int uv_run(uv_loop_t* loop, uv_run_mode mode) {
// ...
while (r != 0 && loop->stop_flag == 0) {
uv__update_time(loop);
uv__run_timers(loop);
// ...
uv__io_poll(loop, timeout);
uv__run_check(loop);
uv__run_closing_handles(loop);
if (mode == UV_RUN_ONCE) {
uv__update_time(loop);
uv__run_timers(loop);
}
r = uv__loop_alive(loop);
if (mode == UV_RUN_ONCE || mode == UV_RUN_NOWAIT)
break;
}
// ...
}The way we use UV_RUN_ONCE is:
- Inefficient.
uv__update_time()is called twice. It's expensive on systems where querying the system time is expensive (e.g. virtualized systems.) - Arguably incorrect. Timers are effectively dispatched twice per look tick.
Branched off #8460 (comment).
Activity
Fishrock123 commentedon Sep 13, 2016
This sounds like it has an awfully good chance of being related to #3665
Trott commentedon Jul 10, 2017
@bnoordhuis Any new information to add to this? If no one's actively working on it, maybe we can add a
help wantedlabel?bnoordhuis commentedon Jul 10, 2017
Good idea. Label added.
src: Node implementation of v8::Platform
src: Node implementation of v8::Platform
src: Node implementation of v8::Platform
src: Node implementation of v8::Platform