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So for a coding test I had to make a chat client-server pair in ocaml. Done, based on a select loop. Well, mostly done, I didn't address blocking writes. I decided to redo the thing with threads, for the practice. Getting the basic functionality wasn't hard: synchronized queue for communication, simpler buffered socket readers than the first version had, and such.
Getting the threads to quit gracefully, though, that took a lot longer. I think part is due to ocaml's POSIX threads implentation: I'm told that "no one" uses it, they all use LWT (lightweight threads) instead. I can confirm some deficiencies: no Thread.detach functionality, for example, which was a big roadblock. And Thread.kill is in the API documentation, but when I tried to use it, got
Throwing an exception from the worker threads to notify the main program to join() them didn't work either, though I'm told I shouldn't expect that to work anyway. I think it works now, with a fair bit of polling -- not busy wait spinning, but reads timing out every 0.1 seconds to check for changes of state -- but that feels messy. As for whether it's simpler... well, it is fewer lines than the select() version, and should handle large (potentially blocking) messages better, so I guess so. Hmm, well, the core chat module is slightly shorter, but main is longer, and there's an extra SQueue module. Still, being more correct is good.
Getting the threads to quit gracefully, though, that took a lot longer. I think part is due to ocaml's POSIX threads implentation: I'm told that "no one" uses it, they all use LWT (lightweight threads) instead. I can confirm some deficiencies: no Thread.detach functionality, for example, which was a big roadblock. And Thread.kill is in the API documentation, but when I tried to use it, got
Thread 2 killed on uncaught exception Invalid_argument("Thread.kill: not
implemented")
Throwing an exception from the worker threads to notify the main program to join() them didn't work either, though I'm told I shouldn't expect that to work anyway. I think it works now, with a fair bit of polling -- not busy wait spinning, but reads timing out every 0.1 seconds to check for changes of state -- but that feels messy. As for whether it's simpler... well, it is fewer lines than the select() version, and should handle large (potentially blocking) messages better, so I guess so. Hmm, well, the core chat module is slightly shorter, but main is longer, and there's an extra SQueue module. Still, being more correct is good.