io_error: "too many open files" on Mac

[volodg]

Source:

use std::rand;

fn main() {

    for _ in range(0u, 1000u) {

        do spawn {

            while (true) {

                println!("{}", rand::random::<uint>());
            }
        }
    }
}

Compilation and run: rustc main.rs; ./main

Result:

task '<unnamed>' failed at 'Unhandled condition: io_error: rt::io::IoError{kind: OtherIoError, desc: "too many open files", detail: None}

[alexcrichton]

This is an unfortunate consequence of using libuv right now. All println requests go through libuv, which requires a handle to stdout. Whenever we get a libuv handle, we must eventually close it, but this will close the underlying file descriptor of the handle. To get around this, we dup the stdout file descriptor, causing you to reach the file descriptor limit fairly quickly on osx.

That being said, libuv recently had a patch (joyent/libuv@359d6678) to not close stdio file descriptors on unix. Sadly they're still closed on windows, so we haven't been able to fix this just yet. We can special-case unix/windows right now, but I'd almost rather just wait until joyent/libuv#991 is fixed.

Thanks for the bug report though!

[hatahet]

@alexcrichton Are there plans to move away from libuv?

[alexcrichton]

No, but there are many plans to optimize our usage of libuv!

[alexcrichton]

This was closed by #10804 now that we're no longer calling dup on all the stdio file descriptors on linux/max. We're still required to do it on windows, but that's a libuv limitation. Next time libuv is updated, that's something to watch for.