Bug #4284
closed
Timeout.timeout may cause application exit unintetionally, again
Description
=begin
This issue was discovered during [Bug#4266] discussion.
Current timeout is racy.
Now, timeout module has following code.¶
def timeout()
begin
x = Thread.current
y = Thread.start {
begin
sleep sec
rescue => e
x.raise e
else
x.raise exception, "execution expired" if x.alive?
end
}
return yield(sec)
rescue exception => e
raise Error, e.message, e.backtrace
ensure
if y and y.alive?
y.kill
y.join # make sure y is dead.
end
end
end
Unfortunatelly,
y = Thread.start {}
is not an atomic operation. Then, A following race can occur.
CPU0(thread x) CPU1(thread y) remark¶
enter begin block
[thread construct] but no assign y yet
sleep sec
wakeup from sleep
x.raise
if y return false. (see above)
Therefore, CPU0 don't call y.join and leak y's thread resource. C# have solved
this two-step-construction vs asynchrounous exception race by RAII.
But unfortunately, Ruby don't have such language feature. So, We can't write
async-exception-safe code. One of solution is to move timeout module from ruby code
into c code as JRuby does. But I don't think timeout is only asynchrounos exception user.
we also have Interrupt class (for Ctrl-C) and I think we need to allow to write async
exception safe code by ruby.
Or, Am I missing something?
=end
Updated by