Changes between Version 82 and Version 83 of LightweightConcurrency

May 22, 2012 10:05:30 PM (4 years ago)



  • LightweightConcurrency

    v82 v83  
    366366== Safe-foreign Calls ==
     368A safe foreign call does not impede the execution of other Haskell threads on the same scheduler, if the foreign call blocks. Before performing the foreign call, the task, say `T1`, releases the capability that it currently owns. This might wake up other tasks which are waiting to acquire a free capability. After the foreign call has completed, `T1` tries to reacquire the last owned capability. In the fast path, the foreign call quickly completes and `T1` reacquires the capability. In the slow path, some other task, say `T2`, acquires the capability.
     370=== Slow-path in Vanilla RTS ===
     372In the vanilla RTS, `T2` will pick the next available thread from the current capability's run queue and resume execution. When `T1` eventually completes the foreign call, it tries to reacquire the capability. Thus, performing a safe-foreign call does not block all the threads on that capability.
     374=== Slow-path in LWC RTS ===
     376The fast path in the LWC implementation is the same as vanilla implementation. However, in the slow path, we need a way for `T2` to resume the scheduler, and a way for `T1` to join the scheduler when the foreign call execution eventually completes. Assume that the Haskell thread that is running on the task `T1` is `t1`. We utilize the yieldContrlAction of `t1` to enable `T2` to resume execution of other threads on the scheduler. When `T1` eventually resumes execution after the foreign call, it finds that it has lost the race to acquire the capability to T2. At this point, `T1` executes `t1`'s scheduleSContAction to join the scheduler.
    368378== Asynchronous Exceptions ==