Weak.c 3.94 KB
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/* -----------------------------------------------------------------------------
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 *
 * (c) The GHC Team, 1998-1999
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 *
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 * Weak pointers / finalizers
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 *
 * ---------------------------------------------------------------------------*/

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#include "PosixSource.h"
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#include "Rts.h"
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#include "RtsUtils.h"
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#include "SchedAPI.h"
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#include "RtsFlags.h"
#include "Weak.h"
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#include "Schedule.h"
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#include "Prelude.h"
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#include "RtsAPI.h"
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#include "Trace.h"
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// ForeignPtrs with C finalizers rely on weak pointers inside weak_ptr_list
// to always be in the same order.

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StgWeak *weak_ptr_list;

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// So that we can detect when a finalizer illegally calls back into Haskell
rtsBool running_finalizers = rtsFalse;

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void
runCFinalizer(StgVoid *fn, StgVoid *ptr, StgVoid *env, StgWord flag)
{
    if (flag)
	((void (*)(void *, void *))fn)(env, ptr);
    else
	((void (*)(void *))fn)(ptr);
}

void
runAllCFinalizers(StgWeak *list)
{
    StgWeak *w;

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    running_finalizers = rtsTrue;

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    for (w = list; w; w = w->link) {
	StgArrWords *farr;

	farr = (StgArrWords *)UNTAG_CLOSURE(w->cfinalizer);

	if ((StgClosure *)farr != &stg_NO_FINALIZER_closure)
	    runCFinalizer((StgVoid *)farr->payload[0],
	                  (StgVoid *)farr->payload[1],
	                  (StgVoid *)farr->payload[2],
	                  farr->payload[3]);
    }
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    running_finalizers = rtsFalse;
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}

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/*
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 * scheduleFinalizers() is called on the list of weak pointers found
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 * to be dead after a garbage collection.  It overwrites each object
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 * with DEAD_WEAK, and creates a new thread to run the pending finalizers.
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 *
 * This function is called just after GC.  The weak pointers on the
 * argument list are those whose keys were found to be not reachable,
 * however the value and finalizer fields have by now been marked live.
 * The weak pointer object itself may not be alive - i.e. we may be
 * looking at either an object in from-space or one in to-space.  It
 * doesn't really matter either way.
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 *
 * Pre-condition: sched_mutex _not_ held.
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 */

void
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scheduleFinalizers(Capability *cap, StgWeak *list)
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{
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    StgWeak *w;
    StgTSO *t;
    StgMutArrPtrs *arr;
    nat n;

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    running_finalizers = rtsTrue;

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    // count number of finalizers, and kill all the weak pointers first...
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    n = 0;
    for (w = list; w; w = w->link) { 
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	StgArrWords *farr;
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	// Better not be a DEAD_WEAK at this stage; the garbage
	// collector removes DEAD_WEAKs from the weak pointer list.
	ASSERT(w->header.info != &stg_DEAD_WEAK_info);

	if (w->finalizer != &stg_NO_FINALIZER_closure) {
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	    n++;
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	}

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	farr = (StgArrWords *)UNTAG_CLOSURE(w->cfinalizer);

	if ((StgClosure *)farr != &stg_NO_FINALIZER_closure)
	    runCFinalizer((StgVoid *)farr->payload[0],
	                  (StgVoid *)farr->payload[1],
	                  (StgVoid *)farr->payload[2],
	                  farr->payload[3]);

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#ifdef PROFILING
        // A weak pointer is inherently used, so we do not need to call
        // LDV_recordDead().
	//
        // Furthermore, when PROFILING is turned on, dead weak
        // pointers are exactly as large as weak pointers, so there is
        // no need to fill the slop, either.  See stg_DEAD_WEAK_info
        // in StgMiscClosures.hc.
#endif
	SET_HDR(w, &stg_DEAD_WEAK_info, w->header.prof.ccs);
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    }
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    running_finalizers = rtsFalse;

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    // No finalizers to run?
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    if (n == 0) return;

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    debugTrace(DEBUG_weak, "weak: batching %d finalizers", n);
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    arr = (StgMutArrPtrs *)allocateLocal(cap, sizeofW(StgMutArrPtrs) + n);
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    TICK_ALLOC_PRIM(sizeofW(StgMutArrPtrs), n, 0);
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    SET_HDR(arr, &stg_MUT_ARR_PTRS_FROZEN_info, CCS_SYSTEM);
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    arr->ptrs = n;

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    n = 0;
    for (w = list; w; w = w->link) {
	if (w->finalizer != &stg_NO_FINALIZER_closure) {
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	    arr->payload[n] = w->finalizer;
	    n++;
	}
    }

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    t = createIOThread(cap, 
		       RtsFlags.GcFlags.initialStkSize, 
		       rts_apply(cap,
			   rts_apply(cap,
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			       (StgClosure *)runFinalizerBatch_closure,
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			       rts_mkInt(cap,n)), 
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			   (StgClosure *)arr)
	);
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    scheduleThread(cap,t);
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}