Ensure "can_work" flag gets set/unset from inside a mutex

reclaim.c

@@ -24,6 +24,7 @@
 #ifdef GC_PTHREADS
 static pthread_mutex_t flzr_mtx = PTHREAD_MUTEX_INITIALIZER;
 static pthread_cond_t flzr_t_has_work = PTHREAD_COND_INITIALIZER;
+static int flzr_can_work = 0;
 #elif
 #error "This fork of BDWGC only supports POSIX threads"
 #endif
@@ -888,11 +889,15 @@ static void* init_finalize_thread(void *arg)
 {
   while(1) {
     pthread_mutex_lock(&flzr_mtx);
-    while (GC_should_invoke_finalizers() == 0) {
+    flzr_can_work = GC_should_invoke_finalizers();
+    while (flzr_can_work == 0) {
       pthread_cond_wait(&flzr_t_has_work, &flzr_mtx);
     }
     pthread_mutex_unlock(&flzr_mtx);
     GC_invoke_finalizers();
+    pthread_mutex_lock(&flzr_mtx);
+    flzr_can_work = 0;
+    pthread_mutex_unlock(&flzr_mtx);
   }
   return arg;
 }
@@ -910,6 +915,7 @@ GC_INNER void GC_maybe_wake_finalizer_thread()
     return;
 
   pthread_mutex_lock(&flzr_mtx);
+  flzr_can_work = 1;
   pthread_cond_signal(&flzr_t_has_work);
   pthread_mutex_unlock(&flzr_mtx);
 }