Timeouts leave threads hanging

[massenz]

I believe I've come across an issue when running requests in many threads (one thread per request) and some (but not all) of them time out.

The timeouts seem to be "honored" but the thread that initiated the request is left waiting for a semaphore: doing some debugging in Xcode's thread view, I noticed all the threads were stuck on this line:

dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER)

when I changed it to something like:

                        let NSEC: Int64 = {
                            var base: Int64 = 1
                            for _ in 1...9 {
                                base *= 10
                            }
                            return base
                        }()

                        let tint: Int64 = Int64(timeout ?? 10.0)
                        let how_long = dispatch_time(DISPATCH_TIME_NOW, tint * NSEC)

                        dispatch_semaphore_wait(semaphore, how_long)

my code now runs without problem, I can see threads being created then destroyed, and it's now been running for > 1 hour without any issue (it used to just crash and die with a hundred or so of hung threads in a couple of minutes).

If you want, I'd be happy to polish the fix and push a PR?

[dduan]

Hi @massenz, thanks for reporting this. I think we need to look into it more carefully. I don't know how you manage your threads. But in general, I would use a separate Just instance per thread:

// threaded branch
let just = JustOf<HTTP>()
// do work with this instance

[massenz]

My code doesn't actually create/manage threads: we simply use the dispatch_async(backgroundQueue, { // block of code } so the threads are managed by iOS.

I think in total it must have created approx 1,000 threads during the last run, but only a handful were active at any time, after the fix.

I completely agree that the code pasted above was as "quick and dirty" as it gets :) and needs more careful review: in particular, I am not sure where that Semaphore gets set/reset, but I suspect that when the request times out, it just gets "abandoned" without ever resetting the state.

Since I last posted the earlier message, I've run my code for > 1 hour, and had 200 "rounds" (that would be a few 1,000's requests) and the app is still happily running; also Memory consumption (which was ballooning) was extremely low all the time.

BTW (and I realize I should have said this earlier :) ) I totally love Just - I am a beginner in Swift and it made my life so much easier! Thanks!

[massenz]

Forgot to say - yes, we have an instance of Just per thread.

[dduan]

Released! https://github.com/JustHTTP/Just/releases/tag/v0.4.6