Bryan O'Sullivan wrote:
Simon Marlow wrote:
I'm sure, yes. The non-blocking flag is part of the "open file description" (see [1], [2]), not the file descriptor.
Ah, yes indeed. I had misunderstood what runProcess was trying to do. Given that, the patch I believed would help was not, in fact, going to do so.
If there's a way to work around this behaviour, it's not obvious to me. Had you any thoughts in mind?
We use O_NONBLOCK to do multithreaded I/O with our lightweight threads. If you're prepared to use OS threads, then you don't need O_NONBLOCK, you can just make a non-blocking foreign call to do the I/O: e.g foreign import safe "read", this makes the call in a separate OS thread, so other Haskell threads aren't blocked. Only the threaded RTS supports OS threads, though. The idea in my patch (not my idea, I think it's been used elsewhere) is to allow both kinds of FDs: non-blocking I/O for FDs that we are sure are local to the current process, and ordinary blocking I/O with OS threads for FDs that might be shared with another process. In the non-threaded RTS you have two options: continue to use O_NONBLOCK and keep the tee bug, or use blocking I/O for the standard FDs (all other threads will be blocked while you do I/O on a std FD). Cheers, Simon