Comments on: Command Input/Output and blocking http://ivanmiljenovic.wordpress.com/2009/12/10/command-inputoutput-and-blocking/ Getting into blogging before it's too late Sun, 16 Jun 2013 06:28:36 +0000 hourly 1 http://wordpress.com/ By: Ivan Miljenovic http://ivanmiljenovic.wordpress.com/2009/12/10/command-inputoutput-and-blocking/#comment-139 Thu, 10 Dec 2009 23:22:20 +0000 http://ivanmiljenovic.wordpress.com/?p=84#comment-139 Hmmm…. maybe…

From memory, the reason I need to have strict stdout is to ensure dot fully finishes, so I didn’t think of it as being a problem with the stdin and stdout “clashing” in a sense.

]]> By: ToRA http://ivanmiljenovic.wordpress.com/2009/12/10/command-inputoutput-and-blocking/#comment-138 Thu, 10 Dec 2009 14:50:16 +0000 http://ivanmiljenovic.wordpress.com/?p=84#comment-138 No, dot output stuffs after the first digraph/graph {} is closed, (it may well be using line buffering so it looks like you need to eof when you actually need to newline). Either way, you block on stdout being closed (strict hGetContents), which it doesn’t close until stdin closes (and there is no more work to do).
try:

$ cat | dot
digraph {
}
digraph {
}

dot will output something back, after the first , but leave stdin open for you to enter more stuff…

T

]]> By: Ivan Miljenovic http://ivanmiljenovic.wordpress.com/2009/12/10/command-inputoutput-and-blocking/#comment-137 Thu, 10 Dec 2009 14:33:26 +0000 http://ivanmiljenovic.wordpress.com/?p=84#comment-137 Close: dot won’t start doing anything until the stdin handle closes; as such, it just hangs waiting for an EOF that never comes :s

(What makes it even more fun is that I had to keep closing ghci to kill off the zombie processes that it spawned…)

]]> By: ToRA http://ivanmiljenovic.wordpress.com/2009/12/10/command-inputoutput-and-blocking/#comment-136 Thu, 10 Dec 2009 14:25:21 +0000 http://ivanmiljenovic.wordpress.com/?p=84#comment-136 On a guess, you use the bracket to close stdin, and dot won’t close stdout or stderr until stdin closes (you can give dot multiple graphs one after another). Stdin/stdout not closing means your signal mvars never get written, and thus you end up blocking…?

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