From: nobu@...
Date: 2014-12-12T08:26:04+00:00
Subject: [ruby-core:66798] [ruby-trunk - Bug #10583] Process.spawn stalls forever opening named pipes (fifo)

Issue #10583 has been updated by Nobuyoshi Nakada.


Justin Greer wrote:
> While the reduced testcase I attached previously sounds like a rare usage, it's actually pretty common any time you're tying together multiple programs and one of them only knows how to work with a file/fifo instead of stdin/stdout.  Our actual usage is more along the lines of this pattern:

I have never used a fifo for such purpose, rather would use a normal pipe directly or `open3`.

> Either that, or it should use a non-blocking open when it tries to open files, so that the stall doesn't happen. 

And just fails with `ENXIO`.


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Bug #10583: Process.spawn stalls forever opening named pipes (fifo)
https://bugs.ruby-lang.org/issues/10583#change-50372

* Author: Justin Greer
* Status: Feedback
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
* ruby -v: ruby 2.1.5p273 (2014-11-13 revision 48405) [x86_64-darwin14.0]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN
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Ruby's implementation of Process.spawn seems to attempt to send error/success information from the spawned process back to the parent, and the parent won't continue until it gets this information.  However, a named pipe (fifo) is mapped to the spawned process' IO, it will stall opening the IO stream, and never be able to send the error/success status back to the parent.

While stalled, the parent process is sitting here: https://github.com/ruby/ruby/blob/ruby_2_1/process.c#L3403  This prevents spawning multiple commands that communicate through a named pipe.

Example testcase is attached.

---Files--------------------------------
spawn_bug_example.rb (486 Bytes)


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