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Commit f2e845bb authored by Simon Marlow's avatar Simon Marlow
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[project @ 1999-02-26 13:36:12 by simonm] 

Change the semantics of weak pointers - now weak pointer objects
aren't automatically considered reachable, so a weak pointer to a weak
pointer object is now meaningful.
parent a59148d1
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ghc/rts/GC.c
+ 74
− 24
View file @ f2e845bb
/* -----------------------------------------------------------------------------
* $Id: GC.c,v 1.43 1999/02/26 12:46:46 simonm Exp $
* $Id: GC.c,v 1.44 1999/02/26 13:36:12 simonm Exp $
*
* (c) The GHC Team 1998-1999
*
......@@ -100,21 +100,23 @@ lnat g0s0_pcnt_kept = 30; /* percentage of g0s0 live at last minor GC */
Static function declarations
-------------------------------------------------------------------------- */
static StgClosure *evacuate(StgClosure *q);
static void zeroStaticObjectList(StgClosure* first_static);
static rtsBool traverse_weak_ptr_list(void);
static void zeroMutableList(StgMutClosure *first);
static void revertDeadCAFs(void);
static StgClosure * evacuate ( StgClosure *q );
static void zero_static_object_list ( StgClosure* first_static );
static void zero_mutable_list ( StgMutClosure *first );
static void revert_dead_CAFs ( void );
static void scavenge_stack(StgPtr p, StgPtr stack_end);
static void scavenge_large(step *step);
static void scavenge(step *step);
static void scavenge_static(void);
static void scavenge_mutable_list(generation *g);
static void scavenge_mut_once_list(generation *g);
static rtsBool traverse_weak_ptr_list ( void );
static void cleanup_weak_ptr_list ( void );
static void scavenge_stack ( StgPtr p, StgPtr stack_end );
static void scavenge_large ( step *step );
static void scavenge ( step *step );
static void scavenge_static ( void );
static void scavenge_mutable_list ( generation *g );
static void scavenge_mut_once_list ( generation *g );
#ifdef DEBUG
static void gcCAFs(void);
static void gcCAFs ( void );
#endif
/* -----------------------------------------------------------------------------
......@@ -196,10 +198,10 @@ void GarbageCollect(void (*get_roots)(void))
scavenged_static_objects = END_OF_STATIC_LIST;
/* zero the mutable list for the oldest generation (see comment by
* zeroMutableList below).
* zero_mutable_list below).
*/
if (major_gc) {
zeroMutableList(generations[RtsFlags.GcFlags.generations-1].mut_once_list);
zero_mutable_list(generations[RtsFlags.GcFlags.generations-1].mut_once_list);
}
/* Save the old to-space if we're doing a two-space collection
......@@ -337,7 +339,6 @@ void GarbageCollect(void (*get_roots)(void))
/* Mark the weak pointer list, and prepare to detect dead weak
* pointers.
*/
markWeakList();
old_weak_ptr_list = weak_ptr_list;
weak_ptr_list = NULL;
weak_done = rtsFalse;
......@@ -360,7 +361,7 @@ void GarbageCollect(void (*get_roots)(void))
*/
scavengeEverything();
/* revert dead CAFs and update enteredCAFs list */
revertDeadCAFs();
revert_dead_CAFs();
#endif
markHugsObjects();
#if 0
......@@ -427,7 +428,12 @@ void GarbageCollect(void (*get_roots)(void))
}
}
/* Now see which stable names are still alive
/* Final traversal of the weak pointer list (see comment by
* cleanUpWeakPtrList below).
*/
cleanup_weak_ptr_list();
/* Now see which stable names are still alive.
*/
gcStablePtrTable(major_gc);
......@@ -660,7 +666,7 @@ void GarbageCollect(void (*get_roots)(void))
}
/* revert dead CAFs and update enteredCAFs list */
revertDeadCAFs();
revert_dead_CAFs();
/* mark the garbage collected CAFs as dead */
#ifdef DEBUG
......@@ -669,7 +675,7 @@ void GarbageCollect(void (*get_roots)(void))
/* zero the scavenged static object list */
if (major_gc) {
zeroStaticObjectList(scavenged_static_objects);
zero_static_object_list(scavenged_static_objects);
}
/* Reset the nursery
......@@ -745,6 +751,17 @@ traverse_weak_ptr_list(void)
last_w = &old_weak_ptr_list;
for (w = old_weak_ptr_list; w; w = next_w) {
/* First, this weak pointer might have been evacuated. If so,
* remove the forwarding pointer from the weak_ptr_list.
*/
if (get_itbl(w)->type == EVACUATED) {
w = (StgWeak *)((StgEvacuated *)w)->evacuee;
*last_w = w;
}
ASSERT(get_itbl(w)->type == WEAK);
/* Now, check whether the key is reachable.
*/
if ((new = isAlive(w->key))) {
w->key = new;
/* evacuate the value and finalizer */
......@@ -782,6 +799,39 @@ traverse_weak_ptr_list(void)
return rtsTrue;
}
/* -----------------------------------------------------------------------------
After GC, the live weak pointer list may have forwarding pointers
on it, because a weak pointer object was evacuated after being
moved to the live weak pointer list. We remove those forwarding
pointers here.
Also, we don't consider weak pointer objects to be reachable, but
we must nevertheless consider them to be "live" and retain them.
Therefore any weak pointer objects which haven't as yet been
evacuated need to be evacuated now.
-------------------------------------------------------------------------- */
static void
cleanup_weak_ptr_list ( void )
{
StgWeak *w, **last_w;
last_w = &weak_ptr_list;
for (w = weak_ptr_list; w; w = w->link) {
if (get_itbl(w)->type == EVACUATED) {
w = (StgWeak *)((StgEvacuated *)w)->evacuee;
*last_w = w;
}
if (Bdescr((P_)w)->evacuated == 0) {
(StgClosure *)w = evacuate((StgClosure *)w);
*last_w = w;
}
last_w = &(w->link);
}
}
/* -----------------------------------------------------------------------------
isAlive determines whether the given closure is still alive (after
a garbage collection) or not. It returns the new address of the
......@@ -2432,7 +2482,7 @@ scavenge_large(step *step)
}
static void
zeroStaticObjectList(StgClosure* first_static)
zero_static_object_list(StgClosure* first_static)
{
StgClosure* p;
StgClosure* link;
......@@ -2454,7 +2504,7 @@ zeroStaticObjectList(StgClosure* first_static)
* mutable list.
*/
static void
zeroMutableList(StgMutClosure *first)
zero_mutable_list( StgMutClosure *first )
{
StgMutClosure *next, *c;
......@@ -2481,7 +2531,7 @@ void RevertCAFs(void)
}
}
void revertDeadCAFs(void)
void revert_dead_CAFs(void)
{
StgCAF* caf = enteredCAFs;
enteredCAFs = END_CAF_LIST;
......@@ -2505,7 +2555,7 @@ void revertDeadCAFs(void)
break;
}
default:
barf("revertDeadCAFs: enteredCAFs list corrupted");
barf("revert_dead_CAFs: enteredCAFs list corrupted");
}
caf = next;
}
......
ghc/rts/Weak.c
+ 8
− 15
View file @ f2e845bb
/* -----------------------------------------------------------------------------
* $Id: Weak.c,v 1.9 1999/02/26 12:43:58 simonm Exp $
* $Id: Weak.c,v 1.10 1999/02/26 13:36:14 simonm Exp $
*
* (c) The GHC Team, 1998-1999
*
......@@ -44,6 +44,13 @@ finalizeWeakPointersNow(void)
* scheduleFinalizers() is called on the list of weak pointers found
* to be dead after a garbage collection. It overwrites each object
* with DEAD_WEAK, and creates a new thread for the finalizer.
*
* 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.
*/
void
......@@ -63,17 +70,3 @@ scheduleFinalizers(StgWeak *list)
w->header.info = &DEAD_WEAK_info;
}
}
void
markWeakList(void)
{
StgWeak *w, **last_w;
last_w = &weak_ptr_list;
for (w = weak_ptr_list; w; w = w->link) {
w = (StgWeak *)MarkRoot((StgClosure *)w);
*last_w = w;
last_w = &(w->link);
}
}
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