[ruby-core:75029] [Ruby trunk Bug#12298][Rejected] Indeterministic ruby behavior when another thread is killed

Issue #12298 has been updated by Eric Hodel.

File a.txt added
File b.txt added
File 12998.rb added
Status changed from Open to Rejected

This is not a ruby bug.  Thread scheduling is inherently non-deterministic.

Sometimes you'll switch to the work thread before reaching rb_thread_terminate_all which allows the ensure to run, sometimes you won't.

I've attached a reduced test case and logs from ruby built with THREAD_DEBUG=1

Honeybadger should probably not sleep in ensure as a way to reduce thrashing when work finishes (I'm guessing that's what they use the sleep for) and should use a different mechanism instead.



----------------------------------------
Bug #12298: Indeterministic ruby behavior when another thread is killed
https://bugs.ruby-lang.org/issues/12298#change-58155

* Author: Robert Pankowecki
* Status: Rejected
* Priority: Normal
* Assignee: 
* ruby -v: ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-linux]
* Backport: 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN
----------------------------------------
```
#!ruby
require 'securerandom'
class MyThread < ::Thread; end

def delay
  15
end

def run
  loop { work }
rescue Exception => e
  puts "#{Time.now} Exception"
ensure
  puts "#{Time.now} stopping agent"
end


def work
  puts "#{Time.now} start work"
  10_000_000.times { SecureRandom.hex }
  puts "finished work"
rescue StandardError => e
  puts "#{Time.now} Error"
ensure
  puts "#{Time.now} start sleep"
  sleep(delay)
  puts "#{Time.now} finished sleep"
end

t = MyThread.new{ run }

at_exit do
  puts "#{Time.now} killing thread"
  Thread.kill(t)
  puts "#{Time.now} killed thread"
end

sleep(10)
exit
```

I tried running this script multiple times in ruby 2.1.10, 2.2.4, 2.3.0 and I get inconsistent behavior. Sometimes the main thread does not wait for the second thread.

```
2016-04-15 11:07:09 +0200 start work
2016-04-15 11:07:19 +0200 killing thread
2016-04-15 11:07:19 +0200 killed thread
2016-04-15 11:07:19 +0200 stopping agent
```

And sometimes it does.

```
2016-04-15 11:07:26 +0200 start work
2016-04-15 11:07:36 +0200 killing thread
2016-04-15 11:07:36 +0200 killed thread
2016-04-15 11:07:36 +0200 start sleep
2016-04-15 11:07:51 +0200 finished sleep
2016-04-15 11:07:51 +0200 stopping agent
```

I appears that under higher CPU usage the 2nd scenario is more likely. In normal conditions the 1st happens more often probably.

I described [the whole story in my blogpost](http://blog.arkency.com/2016/04/how-i-hunted-the-most-odd-ruby-bug/)

I am not sure which behavior is ruby default (I assume not waiting for other threads) but sometimes apparently ruby does wait for other threads to finish.

---Files--------------------------------
a.txt (3.09 KB)
b.txt (3.58 KB)
12998.rb (508 Bytes)


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