Add Task.yield and usage example #97
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art-w
commented
Nov 28, 2022
| @@ -139,7 +139,7 @@ let rec recv_poll_loop mchan dls cur_offset = | |||
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| let recv_poll_with_dls mchan dls = | |||
| try | |||
| Ws_deque.pop (Array.unsafe_get mchan.channels dls.id) | |||
| Ws_deque.steal (Array.unsafe_get mchan.channels dls.id) | |||
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Ws_deque.pop returns the latest pushed item (like a stack ocaml-multicore/saturn#38 ), and as such doesn't allow yield to be run after we had a chance to go through the other tasks from the deque :/
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(This PR is more of a question mark, there's an unpleasant change to make this POC work, and perhaps
domainslibshouldn't provide this primitive?)When using a lockfree datastructure to communicate between tasks, I didn't find a way to write the basic strategy "failed to make progress, retry later". With standard domains, we can use
Domain.cpu_relax ()to spinlock a bit... but with tasks this can deadlock the current domain (if we are waiting on a task scheduled on the same domain, we'll never give it a chance to run). Of course it (slowly) works if another domain steals our pending tasks, but all the domains may actually be stuck and unable to help.I've included a small artificial example to demonstrate the issue :)