From e11f3655fb3bbedc29e496db26a25e6c83d25baf Mon Sep 17 00:00:00 2001 From: erw7 Date: Sun, 3 Jul 2022 01:14:08 +0900 Subject: fix(jobs): deadlock in channel.c:exit_event #19082 In the rare case that exit_event is called from process_close_handles, it stalls waiting for the process to exit (the routine is currently underway to do just that). This causes `job_spec.lua` to sometimes stall. REJECTED IDEAS: ============================================================== 1. Currently `exit_event` is placed on `main_loop.fast_events`. Would the problem be solved by using `main_loop.events` instead? - A: Maybe, but it will cause other problems, such as queuing exit_event() during "Press Enter..." prompt which may result in the event not being processed, leading to another stall. 2. Can we avoid the timer? - A: Using a timer is just the easiest way to queue a delayed event without causing an infinite loop in the queue currently being processed. 3. Can we avoid the new `exit_need_delay` global... 1. by using `process_is_tearing_down` instead? - A: Can't use `process_is_tearing_down` because its semantics are different. 2. by checking a similar condition as `process_teardown`? https://github.com/neovim/neovim/blob/f50135a32e11c535e1dc3a8e9460c5b4e640ee86/src/nvim/event/process.c#L141-L142 ``` if (!process_is_tearing_down || (kl_empty(main_loop.children) && multiqueue_empty(main_loop.events))) { uv_timer_start(&main_loop.exit_delay_timer, exit_delay_cb, 0, 0); return; } ``` - A: Tried but it did not work (other stalls occurred). Maybe exit_event() is called from a source other than process_close_handles() and is delayed, the delayed exit_event() will be executed before main_loop.events is processed, resulting in an infinite loop. --- src/nvim/msgpack_rpc/channel.c | 11 +++++++++++ 1 file changed, 11 insertions(+) (limited to 'src/nvim/msgpack_rpc/channel.c') diff --git a/src/nvim/msgpack_rpc/channel.c b/src/nvim/msgpack_rpc/channel.c index 388fa2584c..de01443313 100644 --- a/src/nvim/msgpack_rpc/channel.c +++ b/src/nvim/msgpack_rpc/channel.c @@ -532,8 +532,19 @@ void rpc_close(Channel *channel) } } +static void exit_delay_cb(uv_timer_t *handle) +{ + uv_timer_stop(&main_loop.exit_delay_timer); + multiqueue_put(main_loop.fast_events, exit_event, 0); +} + static void exit_event(void **argv) { + if (exit_need_delay) { + uv_timer_start(&main_loop.exit_delay_timer, exit_delay_cb, 0, 0); + return; + } + if (!exiting) { os_exit(0); } -- cgit