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src/master/http.cpp Lines 2433-2440 (patched) <https://reviews.apache.org/r/68903/#comment293537> The interesting scenario is when the only available working thread is the one currently attached to the master actor. In this scenario, is the expectation here that each `process::async(worker)` will be spawned and executed on this single worker thread before master actor proceeds to launching the last worker? - Alexander Rukletsov On Oct. 3, 2018, 12:07 a.m., Benjamin Mahler wrote: > > ----------------------------------------------------------- > This is an automatically generated e-mail. To reply, visit: > https://reviews.apache.org/r/68903/ > ----------------------------------------------------------- > > (Updated Oct. 3, 2018, 12:07 a.m.) > > > Review request for mesos, Alexander Rukletsov and Benno Evers. > > > Repository: mesos > > > Description > ------- > > The approach taken to serve endpoints in parallel was to call > `process::async` for each request and block until they finish. > Blocking in this case assumes that there will be enough additional > non-blocked worker threads to execute all the requests. When the > number of blocking Processes is equal or greater than the number > of worker threads, deadlock become possible. The parallel endpoint > serving approach added another blocking Process. > > While we could make blocking safe (see MESOS-8256) by, for example, > detaching a worker thread prior to blocking (a la golang), such a > change is more involved. > > In lieu of making blocking safe, this patch updates the Master to > block only when it's guaranteed to be safe. This is accomplished > by: > > (1) using a "work queue" (just a shared atomic "next index") and > having workers pop items from this "queue", > (2) we execute one of the workers on the master Process directly, > (3) when this worker completes, we then know that all requests > are either processed or being processed (i.e. the `async` > `Process` is executing on a worker thread), > (4) the master can then block on a count down latch, knowing > that it will unblock because of (3). > > > Diffs > ----- > > src/master/http.cpp d912789bcfdcf6eaefc29dba7b878fa4e02f9276 > > > Diff: https://reviews.apache.org/r/68903/diff/1/ > > > Testing > ------- > > > Thanks, > > Benjamin Mahler > >
