rts/Weak.c

   1 /* -----------------------------------------------------------------------------
   2  *
   3  * (c) The GHC Team, 1998-1999
   4  *
   5  * Weak pointers / finalizers
   6  *
   7  * ---------------------------------------------------------------------------*/
   8
   9 #include "PosixSource.h"
  10 #include "Rts.h"
  11 #include "RtsAPI.h"
  12
  13 #include "RtsUtils.h"
  14 #include "Weak.h"
  15 #include "Schedule.h"
  16 #include "Prelude.h"
  17 #include "Trace.h"
  18
  19 void
  20 runCFinalizers(StgCFinalizerList *list)
  21 {
  22     StgCFinalizerList *head;
  23     for (head = list;
  24         (StgClosure *)head != &stg_NO_FINALIZER_closure;
  25         head = (StgCFinalizerList *)head->link)
  26     {
  27         if (head->flag)
  28             ((void (*)(void *, void *))head->fptr)(head->eptr, head->ptr);
  29         else
  30             ((void (*)(void *))head->fptr)(head->ptr);
  31     }
  32 }
  33
  34 void
  35 runAllCFinalizers(StgWeak *list)
  36 {
  37     StgWeak *w;
  38     Task *task;
  39
  40     task = myTask();
  41     if (task != NULL) {
  42         task->running_finalizers = rtsTrue;
  43     }
  44
  45     for (w = list; w; w = w->link) {
  46         runCFinalizers((StgCFinalizerList *)w->cfinalizers);
  47     }
  48
  49     if (task != NULL) {
  50         task->running_finalizers = rtsFalse;
  51     }
  52 }
  53
  54 /*
  55  * scheduleFinalizers() is called on the list of weak pointers found
  56  * to be dead after a garbage collection.  It overwrites each object
  57  * with DEAD_WEAK, and creates a new thread to run the pending finalizers.
  58  *
  59  * This function is called just after GC.  The weak pointers on the
  60  * argument list are those whose keys were found to be not reachable,
  61  * however the value and finalizer fields have by now been marked live.
  62  * The weak pointer object itself may not be alive - i.e. we may be
  63  * looking at either an object in from-space or one in to-space.  It
  64  * doesn't really matter either way.
  65  *
  66  * Pre-condition: sched_mutex _not_ held.
  67  */
  68
  69 void
  70 scheduleFinalizers(Capability *cap, StgWeak *list)
  71 {
  72     StgWeak *w;
  73     StgTSO *t;
  74     StgMutArrPtrs *arr;
  75     StgWord size;
  76     nat n, i;
  77     Task *task;
  78
  79     task = myTask();
  80     if (task != NULL) {
  81         task->running_finalizers = rtsTrue;
  82     }
  83
  84     // count number of finalizers, and kill all the weak pointers first...
  85     n = 0;
  86     for (w = list; w; w = w->link) {
  87         // Better not be a DEAD_WEAK at this stage; the garbage
  88         // collector removes DEAD_WEAKs from the weak pointer list.
  89         ASSERT(w->header.info != &stg_DEAD_WEAK_info);
  90
  91         if (w->finalizer != &stg_NO_FINALIZER_closure) {
  92             n++;
  93         }
  94
  95         runCFinalizers((StgCFinalizerList *)w->cfinalizers);
  96
  97 #ifdef PROFILING
  98         // A weak pointer is inherently used, so we do not need to call
  99         // LDV_recordDead().
 100         //
 101         // Furthermore, when PROFILING is turned on, dead weak
 102         // pointers are exactly as large as weak pointers, so there is
 103         // no need to fill the slop, either.  See stg_DEAD_WEAK_info
 104         // in StgMiscClosures.hc.
 105 #endif
 106         SET_HDR(w, &stg_DEAD_WEAK_info, w->header.prof.ccs);
 107     }
 108
 109     if (task != NULL) {
 110         task->running_finalizers = rtsFalse;
 111     }
 112
 113     // No finalizers to run?
 114     if (n == 0) return;
 115
 116     debugTrace(DEBUG_weak, "weak: batching %d finalizers", n);
 117
 118     size = n + mutArrPtrsCardTableSize(n);
 119     arr = (StgMutArrPtrs *)allocate(cap, sizeofW(StgMutArrPtrs) + size);
 120     TICK_ALLOC_PRIM(sizeofW(StgMutArrPtrs), n, 0);
 121     SET_HDR(arr, &stg_MUT_ARR_PTRS_FROZEN_info, CCS_SYSTEM);
 122     arr->ptrs = n;
 123     arr->size = size;
 124
 125     n = 0;
 126     for (w = list; w; w = w->link) {
 127         if (w->finalizer != &stg_NO_FINALIZER_closure) {
 128             arr->payload[n] = w->finalizer;
 129             n++;
 130         }
 131     }
 132     // set all the cards to 1
 133     for (i = n; i < size; i++) {
 134         arr->payload[i] = (StgClosure *)(W_)(-1);
 135     }
 136
 137     t = createIOThread(cap,
 138                        RtsFlags.GcFlags.initialStkSize,
 139                        rts_apply(cap,
 140                            rts_apply(cap,
 141                                (StgClosure *)runFinalizerBatch_closure,
 142                                rts_mkInt(cap,n)),
 143                            (StgClosure *)arr)
 144         );
 145     scheduleThread(cap,t);
 146 }