Thwait

Ruby
1

i’m unsure if this should be expected to cause deadlock or not?

ruby -r thwait -e’ ThWait.all_waits(*Array.new(42){
Thread.new{Thread.stop} }) ’

for 1.8.1 - 1.8.4 it does.

thoughts?

-a

2

Ara.T.Howard wrote:

-a
Seems like it would. You create a bunch of threads, tell them not to
run, then tell the main thread to wait on all the stopped threads.

There’s no way for this program to complete or continue.

-Justin

3

On Tue, 22 Aug 2006, Justin C. wrote:

-a

Seems like it would. You create a bunch of threads, tell them not to run,
then tell the main thread to wait on all the stopped threads.

There’s no way for this program to complete or continue.

it seems like it should just hang then. otherwise this program wouldn’t
be
able to work

harp:~ > cat a.rb
require ‘thwait’

loop{
stopped = Thread.new{ Thread.stop }

 notify = Thread.new{ stopped.wakeup }

 ThWait.all_waits stopped

}

this code should be able to run - but it won’t. the docs say:

harp:~ > ri ThreadsWait
----------------------------------------------------- Class:
ThreadsWait
This class watches for termination of multiple threads. Basic
functionality (wait until specified threads have terminated) can
be
accessed through the class method ThreadsWait::all_waits. Finer
control can be gained using instance methods.

a sleeping thread has not terminated, but whose to say it won’t at some
point
in the future?

for instance. this is valid ruby

ruby -e’ Thread.new{ sleep }.join ’

it just hangs forever. similarly i feel that

ThWait.all_waits Thread.new{ sleep }

should also hang - not deadlock.

regards.

-a

4

Ara.T.Howard wrote:

i’m unsure if this should be expected to cause deadlock or not?

ruby -r thwait -e’ ThWait.all_waits(*Array.new(42){
Thread.new{Thread.stop} }) ’

for 1.8.1 - 1.8.4 it does.

thoughts?

Ruby has a pretty happy-go-lucky thread introspection
methodology although it seems to always be correct. It
can detect potential deadlocks pretty easily and will
just bow out. Ran into it just using plain Threads some
time back.

-a

5

[email protected] wrote:

wouldn’t be
ThWait.all_waits stopped
}

this code should be able to run - but it won’t. the docs say:

It does run. Try putting in an output statement in the loop. However,
what happens (I’m guessing) is something like this:

stopped = Thread.new { #=> context change

notify = Thread.new { stopped.wakeup } #=> okay, stopped can run

Now, Thread.stop runs for stopped

ThWait.all_waits stopped #=> now it will never be able to complete

a sleeping thread has not terminated, but whose to say it won’t at
some point
in the future?

In some instances, like these examples, you can say that it won’t
terminate. (I’m not sure if Ruby also detects deadlocks in more complex
examples incorrectly.)

for instance. this is valid ruby

ruby -e’ Thread.new{ sleep }.join ’

it just hangs forever. similarly i feel that

ThWait.all_waits Thread.new{ sleep }

should also hang - not deadlock.

Well, I think what’s happening is that Ruby can detect that, in the
second instance, there is no way for it not to deadlock. How could it
not? I’m not sure about the first instance, though.

-Justin

6

Justin C. wrote:

In some instances, like these examples, you can say that it won’t
terminate. (I’m not sure if Ruby also detects deadlocks in more
complex examples incorrectly.)

Uh, I didn’t mean Ruby is detecting these incorrectly - it is correct.
But there may be more complex situations in which it Ruby says
“Deadlock!” without there actually being a deadlock, I don’t know.

-Justin