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IO#each_line hangs when its #2461

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JoshCheek opened this issue Jan 15, 2015 · 5 comments
Closed

IO#each_line hangs when its #2461

JoshCheek opened this issue Jan 15, 2015 · 5 comments
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@headius
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core JRuby 1.7.x
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JRuby 9.0.0.0-pre1

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@JoshCheek
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Script below hangs. I don't expect this behaviour, but I do test it to make sure it handles it gracefully, but it's locking up the test suite.

# cat f.rb
read, write = IO.pipe
Thread.new do
  sleep 1
  read.close
end
read.each_line { |line| line }

# ruby -v
ruby 2.1.1p76 (2014-02-24 revision 45161) [x86_64-darwin13.0]

# ruby f.rb
f.rb:6:in `each_line': stream closed (IOError)
    from f.rb:6:in `<main>'

# chruby jruby
# ruby -v
jruby 1.7.16 (1.9.3p392) 2014-09-25 575b395 on Java HotSpot(TM) 64-Bit Server VM 1.7.0_51-b13 +jit [darwin-x86_64]

# ruby f.rb
....
@headius
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headius commented Jan 15, 2015

Works like in MRI on 9k.

On 1.7.x it appears that both threads are trying to acquire the same lock. each_line probably locks once around the whole operation while the other thread attempts to lock it on entry to read. However IO#close should trigger blocking threads to wake up, as in 9k...even if they're inside a synchronized bit of code.

May be possible to change the granularity of the locking or fix the interrupt.

@headius
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headius commented Jan 15, 2015

Correction: it is ChannelStream.getline that's synchronized and leading to the lock contention. So it's not locking around the whole loop, but it is locking while it waits for the next line.

@headius
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headius commented Jan 15, 2015

So it's a bit trickier to fix. The getline logic in 1.7 does not use any selector (just calls blocking read), so it doesn't have an easily-interruptible call (interrupting a blocking read on JVM closes that stream).

This may be a problem too large to solve given the way 1.7's IO is implemented, especially given that 9k appears to do it right.

@headius
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headius commented Jan 15, 2015

Going to call this fixed for 9k.

@headius headius closed this as completed Jan 15, 2015
@headius headius added this to the JRuby 9.0.0.0-pre1 milestone Jan 15, 2015
@headius headius self-assigned this Jan 15, 2015
@JoshCheek
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Thanks for looking into it :)

JoshCheek added a commit to JoshCheek/seeing_is_believing that referenced this issue Jan 16, 2015
@JoshCheek
Remove Rbx and JRuby from Travis build
fde70cd 
No need to waste Travis's computers on these since I know I expect them to fail for now.
And I'm not working on them as I'm putting #31 on hold for a bit.
Also removing it from things to do for #47.

JRuby has an IO bug at the moment, it's causing EventStream tests to lock up.
jruby/jruby#2461
I could probably get around it by commenting them out, it's not for a case that I actually expect anyway.
But 9k Fixes this anyway, so wait for that to be common.

Rbx had a bug with how it was handling mass assignment.
The "rest" variable on this line https://github.com/JoshCheek/seeing_is_believing/blob/2ddca5d42c693e3028d574dcb74bcc1f654b068c/lib/seeing_is_believing/binary/remove_annotations.rb#L79
is nil when thre is only one subarray.
I had started to open a bug report, but realized m Rbx was a bit older.
So was going to upgrade and see if its still there, maybe try and fix it.
But I couldn't get it to install. Couldn't find llvm-config.
I'm on an older OS (Lion) since everyone had issues going to Yosemite, and don't feel like
going through the headache of upgrading just to get a newer llvm, just to get Rbx.
Plus apparently Apple is now tracking a lot more data, and you have to run some Python script
to turn it off or something, and IDK, this one is working sufficiently fine for me.
Oh, but I wound up uninstalling Rbx while attempting to upgrade, so now I don't
even have one that I can test against.

I'll probably come back to these when I have more time and it takes less effort.
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