Fix finalizer resuscitation causing excessive GC

* libguile/finalizers.c (async_gc_finalizer):
  (scm_i_register_async_gc_callback): Replace "weak gc callback"
  mechanism with "async gc callback" mechanism.  Very similar but the
  new API is designed to be called a bounded number of times, to avoid
  running afoul of libgc heuristics.
* libguile/weak-list.h: New internal header.
* libguile/Makefile.am (noinst_HEADERS): Add weak-list.h.
* libguile/weak-set.c (vacuum_all_weak_sets):
  (scm_c_make_weak_set, scm_init_weak_set):
* libguile/weak-table.c (vacuum_all_weak_tables):
  (scm_c_make_weak_table, scm_init_weak_table): Arrange to vacuum all
  weak sets from a single async GC callback, and likewise for weak
  tables.

Thanks to Ludovic Courtès for tracking this bug down!

1 files changed, 17 insertions, 1 deletions

diff --git a/libguile/weak-table.c b/libguile/weak-table.c
index 1bb513b17..599c4cf0e 100644
--- a/libguile/weak-table.c
+++ b/libguile/weak-table.c
@@ -33,6 +33,7 @@
 #include "libguile/ports.h"
 
 #include "libguile/validate.h"
+#include "libguile/weak-list.h"
 #include "libguile/weak-table.h"
 
 
@@ -832,6 +833,17 @@ do_vacuum_weak_table (SCM table)
   return;
 }
 
+static scm_i_pthread_mutex_t all_weak_tables_lock = SCM_I_PTHREAD_MUTEX_INITIALIZER;
+static SCM all_weak_tables = SCM_EOL;
+
+static void
+vacuum_all_weak_tables (void)
+{
+  scm_i_pthread_mutex_lock (&all_weak_tables_lock);
+  scm_i_visit_weak_list (&all_weak_tables, do_vacuum_weak_table);
+  scm_i_pthread_mutex_unlock (&all_weak_tables_lock);
+}
+
 SCM
 scm_c_make_weak_table (unsigned long k, scm_t_weak_table_kind kind)
 {
@@ -839,7 +851,9 @@ scm_c_make_weak_table (unsigned long k, scm_t_weak_table_kind kind)
 
   ret = make_weak_table (k, kind);
 
-  scm_i_register_weak_gc_callback (ret, do_vacuum_weak_table);
+  scm_i_pthread_mutex_lock (&all_weak_tables_lock);
+  all_weak_tables = scm_i_weak_cons (ret, all_weak_tables);
+  scm_i_pthread_mutex_unlock (&all_weak_tables_lock);
 
   return ret;
 }
@@ -1155,6 +1169,8 @@ void
 scm_init_weak_table ()
 {
 #include "libguile/weak-table.x"
+
+  scm_i_register_async_gc_callback (vacuum_all_weak_tables);
 }
 
 /*