* gc.h, gc.c (SCM_FREECELL_P): Removed for good.

(scm_block_gc, scm_gc_heap_lock): Removed.  Removed all uses.
(scm_gc_running_p): Now a macro that refers to the scm_i_thread
field.
(scm_i_sweep_mutex): Now a non-recursive mutex.  GC can not happen
recursively.
(scm_igc, scm_i_gc): Renamed former to latter.  Changed all uses.
Do not lock scm_i_sweep_mutex, which is now non-recursive, or set
scm_gc_running_p.  Do not run the scm_after_gc_c_hook.
(scm_gc): Lock scm_i_sweep_mutex, set scm_gc_running_p and run the
scm_after_gc_c_hook here.
(scm_gc_for_new_cell): Set scm_gc_running_p here and run the
scm_after_gc_c_hook when a full GC has in fact been performed.
(scm_i_expensive_validation_check): Call scm_gc, not scm_i_gc.

* gc-segment.c (scm_i_get_new_heap_segment): Do not check
scm_gc_heap_lock.

* gc-malloc.c (scm_realloc, increase_mtrigger): Set
scm_gc_running_p while the scm_i_sweep_mutex is locked.

libguile/gc-malloc.c

@@ -111,19 +111,22 @@ scm_realloc (void *mem, size_t size)
     return ptr;
 
   scm_i_scm_pthread_mutex_lock (&scm_i_sweep_mutex);
+  scm_gc_running_p = 1;
 
   scm_i_sweep_all_segments ("realloc");
   
   SCM_SYSCALL (ptr = realloc (mem, size));
   if (ptr)
     { 
+      scm_gc_running_p = 0;
       scm_i_pthread_mutex_unlock (&scm_i_sweep_mutex);
       return ptr;
     }
 
-  scm_igc ("realloc");
+  scm_i_gc ("realloc");
   scm_i_sweep_all_segments ("realloc");
   
+  scm_gc_running_p = 0;
   scm_i_pthread_mutex_unlock (&scm_i_sweep_mutex);
   
   SCM_SYSCALL (ptr = realloc (mem, size));
@@ -219,9 +222,10 @@ increase_mtrigger (size_t size, const char *what)
       float yield;
       
       scm_i_scm_pthread_mutex_lock (&scm_i_sweep_mutex);
+      scm_gc_running_p = 1;
       
       prev_alloced  = mallocated;
-      scm_igc (what);
+      scm_i_gc (what);
       scm_i_sweep_all_segments ("mtrigger");
 
       yield = (((float) prev_alloced - (float) scm_mallocated)
@@ -263,6 +267,7 @@ increase_mtrigger (size_t size, const char *what)
 #endif
 	}
 
+      scm_gc_running_p = 0;
       scm_i_pthread_mutex_unlock (&scm_i_sweep_mutex);
     }
 }

libguile/gc-segment.c

@@ -89,7 +89,7 @@ scm_i_initialize_heap_segment_data (scm_t_heap_segment * segment, size_t request
   scm_t_cell *  memory = 0;
 
   /*
-    We use malloc to alloc the heap. On GNU libc this is 
+    We use calloc to alloc the heap. On GNU libc this is 
     equivalent to mmapping /dev/zero
    */
   SCM_SYSCALL (memory = (scm_t_cell * ) calloc (1, mem_needed));
@@ -458,19 +458,11 @@ scm_i_find_heap_segment_containing_object (SCM obj)
   RETURN: the index of the segment.
  */
 int 
-scm_i_get_new_heap_segment (scm_t_cell_type_statistics *freelist, policy_on_error error_policy)
+scm_i_get_new_heap_segment (scm_t_cell_type_statistics *freelist,
+			    policy_on_error error_policy)
 {
   size_t len;
 
-  if (scm_gc_heap_lock)
-    {
-      /* Critical code sections (such as the garbage collector) aren't
-       * supposed to add heap segments.
-       */
-      fprintf (stderr, "scm_i_get_new_heap_segment: Can not extend locked heap.\n");
-      abort ();
-    }
-
   {
     /* Assure that the new segment is predicted to be large enough.
      *

libguile/gc.c

@@ -67,13 +67,9 @@ extern unsigned long * __libc_ia64_register_backing_store_base;
 #include <unistd.h>
 #endif
 
-
-
-unsigned int scm_gc_running_p = 0;
-
 /* Lock this mutex before doing lazy sweeping.
  */
-scm_i_pthread_mutex_t scm_i_sweep_mutex = SCM_I_PTHREAD_RECURSIVE_MUTEX_INITIALIZER;
+scm_i_pthread_mutex_t scm_i_sweep_mutex = SCM_I_PTHREAD_MUTEX_INITIALIZER;
 
 /* Set this to != 0 if every cell that is accessed shall be checked:
  */
@@ -129,7 +125,7 @@ scm_i_expensive_validation_check (SCM cell)
       else
 	{
 	  counter = scm_debug_cells_gc_interval;
-	  scm_igc ("scm_assert_cell_valid");
+	  scm_gc ();
 	}
     }
 }
@@ -214,18 +210,6 @@ SCM_DEFINE (scm_set_debug_cell_accesses_x, "set-debug-cell-accesses!", 1, 0, 0,
  */
 unsigned long scm_mtrigger;
 
-/* scm_gc_heap_lock
- * If set, don't expand the heap.  Set only during gc, during which no allocation
- * is supposed to take place anyway.
- */
-int scm_gc_heap_lock = 0;
-
-/* GC Blocking
- * Don't pause for collection if this is set -- just
- * expand the heap.
- */
-int scm_block_gc = 1;
-
 /* During collection, this accumulates objects holding
  * weak references.
  */
@@ -456,7 +440,12 @@ SCM_DEFINE (scm_gc, "gc", 0, 0, 0,
 	    "no longer accessible.")
 #define FUNC_NAME s_scm_gc
 {
-  scm_igc ("call");
+  scm_i_scm_pthread_mutex_lock (&scm_i_sweep_mutex);
+  scm_gc_running_p = 1;
+  scm_i_gc ("call");
+  scm_gc_running_p = 0;
+  scm_i_pthread_mutex_unlock (&scm_i_sweep_mutex);
+  scm_c_hook_run (&scm_after_gc_c_hook, 0);
   return SCM_UNSPECIFIED;
 }
 #undef FUNC_NAME
@@ -464,16 +453,18 @@ SCM_DEFINE (scm_gc, "gc", 0, 0, 0,
 
 
 
-/* When we get POSIX threads support, the master will be global and
+/* The master is global and common while the freelist will be
- * common while the freelist will be individual for each thread.
+ * individual for each thread.
  */
 
 SCM
 scm_gc_for_newcell (scm_t_cell_type_statistics *freelist, SCM *free_cells)
 {
   SCM cell;
+  int did_gc = 0;
  
   scm_i_scm_pthread_mutex_lock (&scm_i_sweep_mutex);
+  scm_gc_running_p = 1;
 
   *free_cells = scm_i_sweep_some_segments (freelist);
   if (*free_cells == SCM_EOL && scm_i_gc_grow_heap_p (freelist))
@@ -482,10 +473,10 @@ scm_gc_for_newcell (scm_t_cell_type_statistics *freelist, SCM *free_cells)
       *free_cells = scm_i_sweep_some_segments (freelist);
     }
 
-  if (*free_cells == SCM_EOL && !scm_block_gc)
+  if (*free_cells == SCM_EOL)
     {
       /*
-	with the advent of lazy sweep, GC yield is only know just
+	with the advent of lazy sweep, GC yield is only known just
 	before doing the GC.
       */
       scm_i_adjust_min_yield (freelist);
@@ -494,7 +485,8 @@ scm_gc_for_newcell (scm_t_cell_type_statistics *freelist, SCM *free_cells)
 	out of fresh cells. Try to get some new ones.
        */
 
-      scm_igc ("cells");
+      did_gc = 1;
+      scm_i_gc ("cells");
 
       *free_cells = scm_i_sweep_some_segments (freelist);
     }
@@ -515,8 +507,12 @@ scm_gc_for_newcell (scm_t_cell_type_statistics *freelist, SCM *free_cells)
 
   *free_cells = SCM_FREE_CELL_CDR (cell);
 
+  scm_gc_running_p = 0;
   scm_i_pthread_mutex_unlock (&scm_i_sweep_mutex);
 
+  if (did_gc)
+    scm_c_hook_run (&scm_after_gc_c_hook, 0);
+
   return cell;
 }
 
@@ -527,18 +523,14 @@ scm_t_c_hook scm_before_sweep_c_hook;
 scm_t_c_hook scm_after_sweep_c_hook;
 scm_t_c_hook scm_after_gc_c_hook;
 
+/* Must be called while holding scm_i_sweep_mutex.
+ */
+
 void
-scm_igc (const char *what)
+scm_i_gc (const char *what)
 {
-  if (scm_block_gc)
-    return;
-
-  scm_i_scm_pthread_mutex_lock (&scm_i_sweep_mutex);
-
-  /* During the critical section, only the current thread may run. */
   scm_i_thread_put_to_sleep ();
 
-  ++scm_gc_running_p;
   scm_c_hook_run (&scm_before_gc_c_hook, 0);
 
 #ifdef DEBUGINFO
@@ -552,22 +544,13 @@ scm_igc (const char *what)
 
   gc_start_stats (what);
 
-
-  
-  if (scm_gc_heap_lock)
-    /* We've invoked the collector while a GC is already in progress.
-       That should never happen.  */
-    abort ();
-
   /*
     Set freelists to NULL so scm_cons() always triggers gc, causing
-    the above abort() to be triggered.
+    the assertion above to fail.
   */
   *SCM_FREELIST_LOC (scm_i_freelist) = SCM_EOL;
   *SCM_FREELIST_LOC (scm_i_freelist2) = SCM_EOL;
   
-  ++scm_gc_heap_lock;
-
   /*
     Let's finish the sweep. The conservative GC might point into the
     garbage, and marking that would create a mess.
@@ -589,28 +572,17 @@ scm_igc (const char *what)
   scm_mallocated -= scm_i_deprecated_memory_return;
 
   
+  /* Mark */
 
   scm_c_hook_run (&scm_before_mark_c_hook, 0);
-
   scm_mark_all ();
-  
   scm_gc_mark_time_taken += (scm_c_get_internal_run_time () - t_before_gc);
 
-  scm_c_hook_run (&scm_before_sweep_c_hook, 0);
+  /* Sweep
 
-  /*
+    TODO: the after_sweep hook should probably be moved to just before
-    Moved this lock upwards so that we can alloc new heap at the end of a sweep.
+    the mark, since that's where the sweep is finished in lazy
-
+    sweeping.
-    DOCME: why should the heap be locked anyway?
-   */
-  --scm_gc_heap_lock;
-
-  scm_gc_sweep ();
-
-
-  /*
-    TODO: this hook should probably be moved to just before the mark,
-    since that's where the  sweep is finished in lazy sweeping.
 
     MDJ 030219 <djurfeldt@nada.kth.se>: No, probably not.  The
     original meaning implied at least two things: that it would be
@@ -631,18 +603,15 @@ scm_igc (const char *what)
     distinct classes of hook functions since this can prevent some
     bad interference when several modules adds gc hooks.
    */
+
+  scm_c_hook_run (&scm_before_sweep_c_hook, 0);
+  scm_gc_sweep ();
   scm_c_hook_run (&scm_after_sweep_c_hook, 0);
+
   gc_end_stats ();
 
-  --scm_gc_running_p;
   scm_i_thread_wake_up ();
 
-  /*
-    See above.
-   */
-  scm_i_pthread_mutex_unlock (&scm_i_sweep_mutex);
-  scm_c_hook_run (&scm_after_gc_c_hook, 0);
-
   /*
     For debugging purposes, you could do
     scm_i_sweep_all_segments("debug"), but then the remains of the
@@ -916,7 +885,6 @@ scm_init_storage ()
   j = SCM_NUM_PROTECTS;
   while (j)
     scm_sys_protects[--j] = SCM_BOOL_F;
-  scm_block_gc = 1;
 
   scm_gc_init_freelist();
   scm_gc_init_malloc ();
@@ -1046,8 +1014,6 @@ scm_gc_sweep (void)
    */
   scm_i_reset_segments ();
   
-  /* When we move to POSIX threads private freelists should probably
-     be GC-protected instead. */
   *SCM_FREELIST_LOC (scm_i_freelist) = SCM_EOL;
   *SCM_FREELIST_LOC (scm_i_freelist2) = SCM_EOL;
 

libguile/gc.h

@@ -29,6 +29,34 @@
 
 
 
+/* Cell allocation and garbage collection work rouhgly in the
+   following manner:
+
+   Each thread has a 'freelist', which is a list of available cells.
+   (It actually has two freelists, one for single cells and one for
+   double cells.  Everything works analogous for double cells.)
+
+   When a thread wants to allocate a cell and the freelist is empty,
+   it refers to a global list of unswept 'cards'.  A card is a small
+   block of cells that are contigous in memory, together with the
+   corresponding mark bits.  A unswept card is one where the mark bits
+   are set for cells that have been in use during the last global mark
+   phase, but the unmarked cells of the card have not been scanned and
+   freed yet.
+
+   The thread takes one of the unswept cards and sweeps it, thereby
+   building a new freelist that it then uses.  Sweeping a card will
+   call the smob free functions of unmarked cells, for example, and
+   thus, these free functions can run at any time, in any thread.
+
+   When there are no more unswept cards available, the thread performs
+   a global garbage collection.  For this, all other threads are
+   stopped.  A global mark is performed and all cards are put into the
+   global list of unswept cards.  Whennecessary, new cards are
+   allocated and initialized at this time.  The other threads are then
+   started again.
+*/
+
 typedef struct scm_t_cell
 {
   SCM word_0;
@@ -187,6 +215,10 @@ typedef unsigned long scm_t_c_bvec_long;
 #define SCM_SET_CELL_OBJECT_2(x, v) SCM_SET_CELL_OBJECT ((x), 2, (v))
 #define SCM_SET_CELL_OBJECT_3(x, v) SCM_SET_CELL_OBJECT ((x), 3, (v))
 
+#define SCM_CELL_OBJECT_LOC(x, n) (SCM_VALIDATE_CELL((x), &SCM_GC_CELL_OBJECT ((x), (n))))
+#define SCM_CARLOC(x)             (SCM_CELL_OBJECT_LOC ((x), 0))
+#define SCM_CDRLOC(x)             (SCM_CELL_OBJECT_LOC ((x), 1))
+
 #define SCM_CELL_TYPE(x) SCM_CELL_WORD_0 (x)
 #define SCM_SET_CELL_TYPE(x, t) SCM_SET_CELL_WORD_0 ((x), (t))
 
@@ -195,27 +227,11 @@ typedef unsigned long scm_t_c_bvec_long;
  * the freelist.  Due to this structure, freelist cells are not cons cells
  * and thus may not be accessed using SCM_CAR and SCM_CDR.  */
 
-/*
-  SCM_FREECELL_P removed ; the semantics are ambiguous with lazy
-  sweeping. Could mean "this cell is no longer in use (will be swept)"
-  or "this cell has just been swept, and is not yet in use".
- */
-
-#define SCM_FREECELL_P  this_macro_has_been_removed_see_gc_header_file
-
 #define SCM_FREE_CELL_CDR(x) \
   (SCM_GC_CELL_OBJECT ((x), 1))
 #define SCM_SET_FREE_CELL_CDR(x, v) \
   (SCM_GC_SET_CELL_OBJECT ((x), 1, (v)))
 
-
-#define SCM_CELL_OBJECT_LOC(x, n) (SCM_VALIDATE_CELL((x), &SCM_GC_CELL_OBJECT ((x), (n))))
-#define SCM_CARLOC(x)             (SCM_CELL_OBJECT_LOC ((x), 0))
-#define SCM_CDRLOC(x)             (SCM_CELL_OBJECT_LOC ((x), 1))
-
-
-
-
 #if (SCM_DEBUG_CELL_ACCESSES == 1)
 /* Set this to != 0 if every cell that is accessed shall be checked:
  */
@@ -227,10 +243,9 @@ void scm_i_expensive_validation_check (SCM cell);
 
 SCM_API scm_i_pthread_mutex_t scm_i_gc_admin_mutex;
 
-SCM_API int scm_block_gc;
+#define scm_gc_running_p (SCM_I_CURRENT_THREAD->gc_running_p)
-SCM_API int scm_gc_heap_lock;
-SCM_API unsigned int scm_gc_running_p;
 SCM_API scm_i_pthread_mutex_t scm_i_sweep_mutex;
+
 
 
 #if (SCM_ENABLE_DEPRECATED == 1)
@@ -305,7 +320,7 @@ SCM_API SCM scm_gc_live_object_stats (void);
 SCM_API SCM scm_gc (void);
 SCM_API void scm_gc_for_alloc (struct scm_t_cell_type_statistics *freelist);
 SCM_API SCM scm_gc_for_newcell (struct scm_t_cell_type_statistics *master, SCM *freelist);
-SCM_API void scm_igc (const char *what);
+SCM_API void scm_i_gc (const char *what);
 SCM_API void scm_gc_mark (SCM p);
 SCM_API void scm_gc_mark_dependencies (SCM p);
 SCM_API void scm_mark_locations (SCM_STACKITEM x[], unsigned long n);