ghc/rts/win32/AwaitEvent.c

   1 /*
   2  * Wait/check for external events. Periodically, the
   3  * Scheduler checks for the completion of external operations,
   4  * like the expiration of timers, completion of I/O requests
   5  * issued by Haskell threads.
   6  *
   7  * If the Scheduler is otherwise out of work, it'll block
   8  * herein waiting for external events to occur.
   9  *
  10  * This file mirrors the select()-based functionality
  11  * for POSIX / Unix platforms in rts/Select.c, but for
  12  * Win32.
  13  *
  14  */
  15 #include "Rts.h"
  16 #include "Schedule.h"
  17 #include <windows.h>
  18 #include "win32/AsyncIO.h"
  19 #if defined(THREADED_RTS)
  20 #include "Capability.h"
  21 #endif
  22
  23 // Used to avoid calling abandonRequestWait() if we don't need to.
  24 // Protected by sched_mutex.
  25 static nat workerWaitingForRequests = 0;
  26
  27 void
  28 awaitEvent(rtsBool wait)
  29 {
  30   int ret;
  31
  32 #ifdef THREADED_RTS
  33   // Small optimisation: we don't want the waiting thread to wake
  34   // up straight away just because a previous returning worker has
  35   // called abandonRequestWait().  If the event is no longer needed,
  36   // reset it.  We must do this inside the sched_mutex.
  37   if (!needToYieldToReturningWorker()) {
  38       resetAbandonRequestWait();
  39   }
  40 #endif
  41
  42   do {
  43     /* Try to de-queue completed IO requests
  44      */
  45     workerWaitingForRequests = 1;
  46     RELEASE_LOCK(&sched_mutex);
  47     ret = awaitRequests(wait);
  48     ACQUIRE_LOCK(&sched_mutex);
  49     workerWaitingForRequests = 0;
  50     if (!ret) {
  51       return; /* still hold the lock */
  52     }
  53
  54     // Return to the scheduler if:
  55     //
  56     //  - we were interrupted
  57     //  - new threads have arrived
  58     //  - another worker wants to take over (THREADED_RTS)
  59
  60   } while (wait
  61            && !interrupted
  62            && run_queue_hd == END_TSO_QUEUE
  63 #ifdef THREADED_RTS
  64            && !needToYieldToReturningWorker()
  65 #endif
  66       );
  67 }
  68
  69 #ifdef THREADED_RTS
  70 void
  71 wakeBlockedWorkerThread()
  72 {
  73     if (workerWaitingForRequests) {
  74         abandonRequestWait();
  75     }
  76 }
  77 #endif