100% CPU with ExtEventLoop

[kelunik]

See https://gist.github.com/kelunik/79f843c541aceb3927c5463cc643d502 for a reproduction script.

While the child process runs, php test.php consumes 100% CPU when running on the ExtEventLoop. Additionally, the connection is closed directly instead of one second later if there's currently a child process running.

See also https://twitter.com/kelunik/status/917757971790286848 and replies.

[clue]

Thank you for filing this issue! I think it serves as a valid reference that suggests reactphp/child-process#51 may actually be an issue for some use cases.

Given that it's related to this known issue in another component, I don't see much that we could do here in this component.

I believe this has been answered, so I'm closing this for now. Please come back with more details if this problem persists and we can reopen this 👍

[kelunik]

@clue It works fine with the StreamSelectLoop. While it might be related to the linked issue, it probably shouldn't result in 100% CPU usage. The only expected issue with reactphp/child-process#51 is connections being kept open, but stream_socket_shutdown seems to solve that. Without stream_socket_shutdown, I get the expected hanging behavior with the StreamSelectLoop. I believe this is a separate issue.

[clue]

Can you send in a gist to reproduce this issue without the known issue linked above? Thank you.

[kelunik]

Please re-open the issue, so I don't forget about it.

[clue]

No worries, I'll make sure to ping you if nothing changes about this issue in a few days and will reopen if you send a gist to reproduce this! 👍 Thank you.

[clue]

Ping @kelunik, I suppose this is still resolved? 👍

[kelunik]

It's weird. If I try to look into it with phpdbg and pause the execution and continue it again, the 100% CPU usage is gone. Seems to be a Heisenbug. Haven't found another reproduction case, because I'm not sure what causes it. So no, it's not resolved as stated previously. It's not the expected misbehavior that reactphp/child-process#51 might cause, as previously stated.

[clue]

@kelunik Thanks for trying to dig into this. If you happen to find a way to reproduce this, I'm happy to re-open this so we can look into this 👍

[lajosbencz]

I've ran into this issue aswell, i'm installing react/child-process:0.6.1 from composer, and the default event loop (React\EventLoop\ExtUvLoop) consumes 100% of the CPU.
If i explicitly set it to StreamSelectLoop, the process works as expected at around 5-10% CPU usage.

The project im using it in: https://github.com/lajosbencz/phrocman

Could it be purely related to the loop implementation, and nothing to do with the component itself?

[clue]

@lajosbencz We're not aware of any such issues at the moment. Can you provide a minimal test script to reproduce this locally?

If this is related to spawning child-processes, can you take a look at one of the possible work-arounds for reactphp/child-process#51, such as clue/reactphp-sqlite#7?