I still like Ara's idea
However--is something like this already possible if we redefine the
Thread#raise method? For example define it to be something like this.
class Thread
def raise_safe *args
# sorry, couldn't think of a better way than a mutex to prohibit
weirdness from occurring. So that's where a problem would occur--in the
ensure block of the synchronize function. Ahh well. If you re-aliased
raise to be this method, maybe avoided.
@raise_mutex.synchronize {
unless @currently_non_interruptible_section
raise *args
else
self.queued_interrupts << *args
end
}
end
def uninterruptible_block
return if @currently_non_interruptible_section # already within one.
Maybe should keep a count of how deep you are. Not sure
@currently_non_interruptible_section = true
begin
yield # might want to handle queued exceptions at the end of this
block
ensure
@raise_mutex.synchronize {@currently_non_interruptible_section =
false}
end
# after this point the thread is subject to interruptions again
end
end
Then you could have a thread do something like
uninterruptible_block do
# some stuff
# handle the queued interrupts if desired. Note that you could loop
and 'check if you've been interupted yet' once per loop or what not, if
desired
end
# handle queued interrupts, if desired
timeout would possibly become
def timeout(sec, exception=Error)
return yield if sec == nil or sec.zero?
raise ThreadError, "timeout within critical session"\
if Thread.critical
raise ThreadError, "called nested functions that want to use
uninterruptible and raise on it" if
Thread.current.currently_non_interruptible_section
# this is necessary since we do use 'real' raise this time
# to interrupt our block's yielding
# so if you had nested--ever--the raise of an uppermost one
# could interrupt a lower one in it ensure. Same problem would occur.
# we can only have one at a time.
# this is a hack that assumes we 'only' use uninterruptible_block for
calls to timeout.
death_mutex = Mutex.new
uninterruptible_block do
begin
x = Thread.current
y = Thread.start {
sleep sec
death_mutex.synchronize {
x.raise exception, "execution expired" if x.alive? # this is
not raise_safe, but real raise. Still unsafe as per some previous
comments...but is it safer than it used to be now?
}
}
yield sec # would this code be dampered somehow?
ensure
death_mutex.synchronize {
y.kill if y and y.alive?
}
end
end
for interrupt in Thread.current.queued_interrupts do; raise interrupt;
end # or something like that
end
now you could "replace" the use of raise with raise_safe. Would this
work?
This would prohibit 'other threads' from interrupting a thread that is
within a timeout block (obviously bad) until it timed out, but would it
be thread safe?
Thoughts?
Thank you for reading
Overall I'd say I'm in agreeance with the OP's call to deprecate
Thread#kill, Thread#raise, Thread#critical= as they can too easily hurt,
though something like this might help. This suggestion also seems far
less complete than Tanaka's somehow.
Still wishing for an ensure block that was somehow 'guaranteed' to run
all the way through, and delay interruptions or ignore them till it
ended.
Thanks.
-R
