rts/TopHandler.c

   1 #include "Rts.h"
   2 #include "StablePtr.h"
   3 #include "TopHandler.h"
   4
   5 #if defined(THREADED_RTS)
   6 static Mutex m; // Protects the operations on topHandlerPtr,
   7                 // which aren't atomic
   8 #endif
   9 static StgStablePtr topHandlerPtr;
  10
  11 void rts_setMainThread(StgWeak *weak) {
  12     ACQUIRE_LOCK(&m);
  13     if (topHandlerPtr != NULL) {
  14         freeStablePtr(topHandlerPtr); // OK to do under the lock
  15     }
  16     topHandlerPtr = getStablePtr((StgPtr)weak);
  17     // referent is a Weak#
  18     ASSERT(weak->header.info == &stg_WEAK_info);
  19
  20     // See Note [rts_setMainThread has an unsound type] in
  21     // libraries/base/GHC/TopHandler.hs.
  22     ASSERT(weak->key->header.info == &stg_TSO_info);
  23
  24     RELEASE_LOCK(&m);
  25 }
  26
  27 StgTSO *getTopHandlerThread(void) {
  28     ACQUIRE_LOCK(&m);
  29     StgWeak *weak = (StgWeak*)deRefStablePtr(topHandlerPtr);
  30     RELEASE_LOCK(&m);
  31     if (weak == NULL) {
  32         // topHandlerPtr was never initialised
  33         return NULL;
  34     }
  35     const StgInfoTable *info = ACQUIRE_LOAD(&weak->header.info);
  36     if (info == &stg_WEAK_info) {
  37         StgClosure *key = ((StgWeak*)weak)->key;
  38
  39         // See Note [rts_setMainThread has an unsound type] in
  40         // libraries/base/GHC/TopHandler.hs.
  41         ASSERT(key->header.info == &stg_TSO_info);
  42
  43         return (StgTSO *)key;
  44     } else if (info == &stg_DEAD_WEAK_info) {
  45         return NULL;
  46     } else {
  47         barf("getTopHandlerThread: neither a WEAK nor a DEAD_WEAK: %p %p %d",
  48              weak, info, info->type);
  49         return NULL;
  50     }
  51 }
  52
  53 void initTopHandler(void) {
  54 #if defined(THREADED_RTS)
  55     initMutex(&m);
  56 #endif
  57     topHandlerPtr = NULL;
  58 }
  59
  60 void exitTopHandler(void) {
  61     freeStablePtr(topHandlerPtr);
  62     topHandlerPtr = NULL;
  63 #if defined(THREADED_RTS)
  64     closeMutex(&m);
  65 #endif
  66 }