rts: Unglobalize dead_weak_ptr_list and resurrected_threads

In the concurrent nonmoving collector we will need the ability to call
`traverseWeakPtrList` concurrently with minor generation collections.
This global state stands in the way of this. However, refactoring it
away is straightforward since this list only persists the length of a
single GC.

rts/sm/Compact.c

@@ -940,7 +940,7 @@ update_bkwd_compact( generation *gen )
 }
 
 void
-compact(StgClosure *static_objects)
+compact(StgClosure *static_objects, StgWeak *dead_weak_ptr_list, StgTSO *resurrected_threads)
 {
     W_ n, g, blocks;
     generation *gen;

rts/sm/Compact.h

@@ -45,6 +45,8 @@ is_marked(StgPtr p, bdescr *bd)
     return (*bitmap_word & bit_mask);
 }
 
-void compact (StgClosure *static_objects);
+void compact (StgClosure *static_objects,
+              StgWeak *dead_weak_ptr_list,
+              StgTSO *resurrected_threads);
 
 #include "EndPrivate.h"

rts/sm/GC.c

@@ -416,15 +416,20 @@ GarbageCollect (uint32_t collect_gen,
    * Repeatedly scavenge all the areas we know about until there's no
    * more scavenging to be done.
    */
+
+  StgWeak *dead_weak_ptr_list = NULL;
+  StgTSO *resurrected_threads = END_TSO_QUEUE;
+
   for (;;)
   {
       scavenge_until_all_done();
+
       // The other threads are now stopped.  We might recurse back to
       // here, but from now on this is the only thread.
 
       // must be last...  invariant is that everything is fully
       // scavenged at this point.
-      if (traverseWeakPtrList()) { // returns true if evaced something
+      if (traverseWeakPtrList(&dead_weak_ptr_list, &resurrected_threads)) { // returns true if evaced something
           inc_running();
           continue;
       }
@@ -468,7 +473,7 @@ GarbageCollect (uint32_t collect_gen,
   // Finally: compact or sweep the oldest generation.
   if (major_gc && oldest_gen->mark) {
       if (oldest_gen->compact)
-          compact(gct->scavenged_static_objects);
+          compact(gct->scavenged_static_objects, dead_weak_ptr_list, resurrected_threads);
       else
           sweep(oldest_gen);
   }

rts/sm/MarkWeak.c

@@ -77,15 +77,9 @@
 typedef enum { WeakPtrs, WeakThreads, WeakDone } WeakStage;
 static WeakStage weak_stage;
 
-// List of weak pointers whose key is dead
-StgWeak *dead_weak_ptr_list;
-
-// List of threads found to be unreachable
-StgTSO *resurrected_threads;
-
-static void    collectDeadWeakPtrs (generation *gen);
+static void    collectDeadWeakPtrs (generation *gen, StgWeak **dead_weak_ptr_list);
 static bool tidyWeakList (generation *gen);
-static bool resurrectUnreachableThreads (generation *gen);
+static bool resurrectUnreachableThreads (generation *gen, StgTSO **resurrected_threads);
 static void    tidyThreadList (generation *gen);
 
 void
@@ -100,12 +94,10 @@ initWeakForGC(void)
     }
 
     weak_stage = WeakThreads;
-    dead_weak_ptr_list = NULL;
-    resurrected_threads = END_TSO_QUEUE;
 }
 
 bool
-traverseWeakPtrList(void)
+traverseWeakPtrList(StgWeak **dead_weak_ptr_list, StgTSO **resurrected_threads)
 {
   bool flag = false;
 
@@ -140,7 +132,7 @@ traverseWeakPtrList(void)
 
       // Resurrect any threads which were unreachable
       for (g = 0; g <= N; g++) {
-          if (resurrectUnreachableThreads(&generations[g])) {
+          if (resurrectUnreachableThreads(&generations[g], resurrected_threads)) {
               flag = true;
           }
       }
@@ -175,7 +167,7 @@ traverseWeakPtrList(void)
        */
       if (flag == false) {
           for (g = 0; g <= N; g++) {
-              collectDeadWeakPtrs(&generations[g]);
+              collectDeadWeakPtrs(&generations[g], dead_weak_ptr_list);
           }
 
           weak_stage = WeakDone;  // *now* we're done,
@@ -190,7 +182,7 @@ traverseWeakPtrList(void)
   }
 }
 
-static void collectDeadWeakPtrs (generation *gen)
+static void collectDeadWeakPtrs (generation *gen, StgWeak **dead_weak_ptr_list)
 {
     StgWeak *w, *next_w;
     for (w = gen->old_weak_ptr_list; w != NULL; w = next_w) {
@@ -201,12 +193,12 @@ static void collectDeadWeakPtrs (generation *gen)
         }
         evacuate(&w->finalizer);
         next_w = w->link;
-        w->link = dead_weak_ptr_list;
-        dead_weak_ptr_list = w;
+        w->link = *dead_weak_ptr_list;
+        *dead_weak_ptr_list = w;
     }
 }
 
-static bool resurrectUnreachableThreads (generation *gen)
+static bool resurrectUnreachableThreads (generation *gen, StgTSO **resurrected_threads)
 {
     StgTSO *t, *tmp, *next;
     bool flag = false;
@@ -225,8 +217,8 @@ static bool resurrectUnreachableThreads (generation *gen)
         default:
             tmp = t;
             evacuate((StgClosure **)&tmp);
-            tmp->global_link = resurrected_threads;
-            resurrected_threads = tmp;
+            tmp->global_link = *resurrected_threads;
+            *resurrected_threads = tmp;
             flag = true;
         }
     }

rts/sm/MarkWeak.h

@@ -19,7 +19,7 @@ extern StgTSO *resurrected_threads;
 
 void    collectFreshWeakPtrs   ( void );
 void    initWeakForGC          ( void );
-bool    traverseWeakPtrList    ( void );
+bool    traverseWeakPtrList    ( StgWeak **dead_weak_ptr_list, StgTSO **resurrected_threads );
 void    markWeakPtrList        ( void );
 void    scavengeLiveWeak       ( StgWeak * );