1. 28 Mar, 2017 1 commit
  2. 12 Sep, 2016 1 commit
    • Simon Marlow's avatar
      Add hs_try_putmvar() · 454033b5
      Simon Marlow authored
      Summary:
      This is a fast, non-blocking, asynchronous, interface to tryPutMVar that
      can be called from C/C++.
      
      It's useful for callback-based C/C++ APIs: the idea is that the callback
      invokes hs_try_putmvar(), and the Haskell code waits for the callback to
      run by blocking in takeMVar.
      
      The callback doesn't block - this is often a requirement of
      callback-based APIs.  The callback wakes up the Haskell thread with
      minimal overhead and no unnecessary context-switches.
      
      There are a couple of benchmarks in
      testsuite/tests/concurrent/should_run.  Some example results comparing
      hs_try_putmvar() with using a standard foreign export:
      
          ./hs_try_putmvar003 1 64 16 100 +RTS -s -N4     0.49s
          ./hs_try_putmvar003 2 64 16 100 +RTS -s -N4     2.30s
      
      hs_try_putmvar() is 4x faster for this workload (see the source for
      hs_try_putmvar003.hs for details of the workload).
      
      An alternative solution is to use the IO Manager for this.  We've tried
      it, but there are problems with that approach:
      * Need to create a new file descriptor for each callback
      * The IO Manger thread(s) become a bottleneck
      * More potential for things to go wrong, e.g. throwing an exception in
        an IO Manager callback kills the IO Manager thread.
      
      Test Plan: validate; new unit tests
      
      Reviewers: niteria, erikd, ezyang, bgamari, austin, hvr
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D2501
      454033b5