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-rw-r--r--libguile/gc.c84
1 files changed, 76 insertions, 8 deletions
diff --git a/libguile/gc.c b/libguile/gc.c
index 48f688b93..29eee3392 100644
--- a/libguile/gc.c
+++ b/libguile/gc.c
@@ -108,11 +108,19 @@ scm_bits_t scm_tc16_allocated;
*/
unsigned int scm_debug_cell_accesses_p = 1;
+/* Set this to 0 if no additional gc's shall be performed, otherwise set it to
+ * the number of cell accesses after which a gc shall be called.
+ */
+static unsigned int debug_cells_gc_interval = 0;
+
/* Assert that the given object is a valid reference to a valid cell. This
* test involves to determine whether the object is a cell pointer, whether
* this pointer actually points into a heap segment and whether the cell
- * pointed to is not a free cell.
+ * pointed to is not a free cell. Further, additional garbage collections may
+ * get executed after a user defined number of cell accesses. This helps to
+ * find places in the C code where references are dropped for extremely short
+ * periods.
*/
void
scm_assert_cell_valid (SCM cell)
@@ -146,6 +154,24 @@ scm_assert_cell_valid (SCM cell)
(unsigned long) SCM_UNPACK (cell));
abort ();
}
+
+ /* If desired, perform additional garbage collections after a user
+ * defined number of cell accesses.
+ */
+ if (debug_cells_gc_interval)
+ {
+ static unsigned int counter = 0;
+
+ if (counter != 0)
+ {
+ --counter;
+ }
+ else
+ {
+ counter = debug_cells_gc_interval;
+ scm_igc ("scm_assert_cell_valid");
+ }
+ }
}
already_running = 0; /* re-enable */
}
@@ -155,7 +181,11 @@ scm_assert_cell_valid (SCM cell)
SCM_DEFINE (scm_set_debug_cell_accesses_x, "set-debug-cell-accesses!", 1, 0, 0,
(SCM flag),
"If @var{flag} is @code{#f}, cell access checking is disabled.\n"
- "If @var{flag} is @code{#t}, cell access checking is enabled.\n"
+ "If @var{flag} is @code{#t}, cell access checking is enabled,\n"
+ "but no additional calls to garbage collection are issued.\n"
+ "If @var{flag} is a number, cell access checking is enabled,\n"
+ "with an additional garbage collection after the given\n"
+ "number of cell accesses.\n"
"This procedure only exists when the compile-time flag\n"
"@code{SCM_DEBUG_CELL_ACCESSES} was set to 1.")
#define FUNC_NAME s_scm_set_debug_cell_accesses_x
@@ -163,6 +193,12 @@ SCM_DEFINE (scm_set_debug_cell_accesses_x, "set-debug-cell-accesses!", 1, 0, 0,
if (SCM_FALSEP (flag)) {
scm_debug_cell_accesses_p = 0;
} else if (SCM_EQ_P (flag, SCM_BOOL_T)) {
+ debug_cells_gc_interval = 0;
+ scm_debug_cell_accesses_p = 1;
+ } else if (SCM_INUMP (flag)) {
+ long int f = SCM_INUM (flag);
+ if (f <= 0) SCM_OUT_OF_RANGE (1, flag);
+ debug_cells_gc_interval = f;
scm_debug_cell_accesses_p = 1;
} else {
SCM_WRONG_TYPE_ARG (1, flag);
@@ -824,7 +860,7 @@ SCM_DEFINE (scm_gc_stats, "gc-stats", 0, 0, 0,
static void
-gc_start_stats (const char *what)
+gc_start_stats (const char *what SCM_UNUSED)
{
t_before_gc = scm_c_get_internal_run_time ();
scm_gc_cells_swept = 0;
@@ -2449,19 +2485,19 @@ alloc_some_heap (scm_freelist_t *freelist, policy_on_error error_policy)
*/
void
-scm_remember_upto_here_1 (SCM obj)
+scm_remember_upto_here_1 (SCM obj SCM_UNUSED)
{
/* Empty. Protects a single object from garbage collection. */
}
void
-scm_remember_upto_here_2 (SCM obj1, SCM obj2)
+scm_remember_upto_here_2 (SCM obj1 SCM_UNUSED, SCM obj2 SCM_UNUSED)
{
/* Empty. Protects two objects from garbage collection. */
}
void
-scm_remember_upto_here (SCM obj, ...)
+scm_remember_upto_here (SCM obj SCM_UNUSED, ...)
{
/* Empty. Protects any number of objects from garbage collection. */
}
@@ -2828,9 +2864,41 @@ gc_async_thunk (void)
* gc_async_thunk).
*/
static void *
-mark_gc_async (void * hook_data, void *func_data, void *data)
-{
+mark_gc_async (void * hook_data SCM_UNUSED,
+ void *func_data SCM_UNUSED,
+ void *data SCM_UNUSED)
+{
+ /* If cell access debugging is enabled, the user may choose to perform
+ * additional garbage collections after an arbitrary number of cell
+ * accesses. We don't want the scheme level after-gc-hook to be performed
+ * for each of these garbage collections for the following reason: The
+ * execution of the after-gc-hook causes cell accesses itself. Thus, if the
+ * after-gc-hook was performed with every gc, and if the gc was performed
+ * after a very small number of cell accesses, then the number of cell
+ * accesses during the execution of the after-gc-hook will suffice to cause
+ * the execution of the next gc. Then, guile would keep executing the
+ * after-gc-hook over and over again, and would never come to do other
+ * things.
+ *
+ * To overcome this problem, if cell access debugging with additional
+ * garbage collections is enabled, the after-gc-hook is never run by the
+ * garbage collecter. When running guile with cell access debugging and the
+ * execution of the after-gc-hook is desired, then it is necessary to run
+ * the hook explicitly from the user code. This has the effect, that from
+ * the scheme level point of view it seems that garbage collection is
+ * performed with a much lower frequency than it actually is. Obviously,
+ * this will not work for code that depends on a fixed one to one
+ * relationship between the execution counts of the C level garbage
+ * collection hooks and the execution count of the scheme level
+ * after-gc-hook.
+ */
+#if (SCM_DEBUG_CELL_ACCESSES == 1)
+ if (debug_cells_gc_interval == 0)
+ scm_system_async_mark (gc_async);
+#else
scm_system_async_mark (gc_async);
+#endif
+
return NULL;
}