Bug #7917: Can't write to a Logger in a signal handler

• Status: Rejected
• Assignee: kosaki (Motohiro KOSAKI)
• Target version: 2.1.0
• ruby -v: 2.0.0-rc2
• Backport: 2.3: UNKNOWN, 2.4: UNKNOWN

[mperham (Mike Perham)]

Looks like Ruby 2.0 does not allow Mutex#lock within a signal handler. This prevents Logger from working since it uses an underlying mutex.

log writing failed. can't be called from trap context
log writing failed. can't be called from trap context
log writing failed. can't be called from trap context
log writing failed. can't be called from trap context

Here's Ruby code which reproduces the problem:

require 'logger'

LOG = Logger.new(STDOUT)
LOG.info "Now logging!"

trap 'INT' do
LOG.info "Hello"
end

sleep
LOG.info "Done"

Run it and hit Ctrl-C.

[kosaki (Motohiro KOSAKI)]

Because your example is deadlockable when using 1.9.3 or earlier. 2.0 detect your mistake and tell you.

[mame (Yusuke Endoh)]

• Status changed from Open to Assigned
• Assignee set to kosaki (Motohiro KOSAKI)
• Target version set to 2.1.0

This issue is arguable, but anyway I don't consider it a showstopper.
I postpone it to 2.1.0.

It is very arguable if the fault is in the code, or in the design of Ruby core.

--
Yusuke Endoh [e-mail]

[normalperson (Eric Wong)]

"mperham (Mike Perham)" [e-mail] wrote:

trap 'INT' do
LOG.info "Hello"
end

An ugly workaround I use is to spawn a thread inside trap:

trap 'INT' do
Thread.new do
LOG.info "Hello"
end
end

[kosaki (Motohiro KOSAKI)]

On Sat, Feb 23, 2013 at 3:06 AM, Eric Wong [e-mail] wrote:

"mperham (Mike Perham)" [e-mail] wrote:

trap 'INT' do
LOG.info "Hello"
end

An ugly workaround I use is to spawn a thread inside trap:

trap 'INT' do
Thread.new do
LOG.info "Hello"
end
end

Um. this is safe.

btw, following is unsafe when 1.9.x. because trap safe th.join is a
new feature of 2.0.

trap 'INT' do
t = Thread.new do
LOG.info "Hello"
end
t.join
end

see http://bugs.ruby-lang.org/issues/6416

Hm.
Should we backport this fix to 1.9.3 too?

[kosaki (Motohiro KOSAKI)]

trap 'INT' do
t = Thread.new do
LOG.info "Hello"
end
t.join
end

Oops, no. This code is completely wrong. Sorry for confusing.
Please don't mind my previous mail. This code is deadlockable and
should never be used.

[kosaki (Motohiro KOSAKI)]

• Status changed from Assigned to Rejected

Closed. because it's not a bug.

[hkmaly (Honza Maly)]

What IS the recommended way to fix this if Mutex nor Thread are safe in signal handler? Also created question for what is safe in signal handler in general as #14222

[normalperson (Eric Wong)]

[e-mail] wrote:

What IS the recommended way to fix this if Mutex nor Thread
are safe in signal handler? Also created question for what is
safe in signal handler in general as #14222

See my response for [ruby-core:84410] [Misc #14222] :>
https://bugs.ruby-lang.org/issues/14222