Add ephemeron-table-clear!; ephemeron key can be immediate

* libguile/ephemerons.c (scm_make_ephemeron): Relax restriction that key
be a heap object.  It's too annoying otherwise.
(scm_c_ephemeron_table_clear_x):
(scm_ephemeron_table_clear_x): New interface.
* module/ice-9/ephemerons.scm: Expose ephemeron-table-clear!.
* test-suite/tests/ephemerons.test ("ephemerons"): Update tests.

libguile/atomics-internal.h

@@ -57,6 +57,12 @@ scm_atomic_ref_pointer (void **loc)
   atomic_uintptr_t *a_loc = (atomic_uintptr_t *) loc;
   return (void *) atomic_load (a_loc);
 }
+static inline void *
+scm_atomic_swap_pointer (void **loc, void *new_val)
+{
+  atomic_uintptr_t *a_loc = (atomic_uintptr_t *) loc;
+  return (void *) atomic_exchange (a_loc, (uintptr_t) new_val);
+}
 static inline void
 scm_atomic_set_bits (scm_t_bits *loc, scm_t_bits val)
 {
@@ -141,6 +147,16 @@ scm_atomic_ref_pointer (void **loc)
   scm_i_pthread_mutex_unlock (&atomics_lock);
   return ret;
 }
+static inline void *
+scm_atomic_swap_pointer (void **loc, void *new_val)
+{
+  void *ret;
+  scm_i_pthread_mutex_lock (&atomics_lock);
+  ret = *loc;
+  *loc = new_val;
+  scm_i_pthread_mutex_unlock (&atomics_lock);
+  return ret;
+}
 
 static inline void
 scm_atomic_set_bits (scm_t_bits *loc, scm_t_bits val)

libguile/ephemerons.c

@@ -30,6 +30,7 @@
 #include <stdio.h>
 #include <unistd.h>
 
+#include "atomics-internal.h"
 #include "extensions.h"
 #include "gc-internal.h"
 #include "gsubr.h"
@@ -147,7 +148,6 @@ SCM_DEFINE_STATIC (scm_make_ephemeron, "make-ephemeron", 2, 0, 0,
                    "as @var{key} and the ephemeron itself are alive.")
 #define FUNC_NAME s_scm_make_ephemeron
 {
-  SCM_MAKE_VALIDATE (1, key, HEAP_OBJECT_P);
   return PTR2SCM (scm_c_make_ephemeron (key, val));
 }
 #undef FUNC_NAME
@@ -299,6 +299,15 @@ scm_c_ephemeron_table_try_push_x (struct scm_ephemeron_table *et, size_t idx,
   return prev;
 }
 
+static struct gc_ephemeron*
+scm_c_ephemeron_table_clear_x (struct scm_ephemeron_table *et, size_t idx)
+{
+  if (idx >= et->size)
+    abort();
+
+  return scm_atomic_swap_pointer ((void**) &et->contents[idx], NULL);
+}
+
 struct scm_ephemeron_table*
 scm_c_ephemeron_table_copy (struct scm_ephemeron_table *et)
 {
@@ -408,6 +417,23 @@ SCM_DEFINE_STATIC (scm_ephemeron_table_try_push_x, "ephemeron-table-try-push!",
 }
 #undef FUNC_NAME
 
+SCM_DEFINE_STATIC (scm_ephemeron_table_clear_x, "ephemeron-table-clear!",
+                   2, 0, 0, (SCM et, SCM idx),
+                   "Clear the slot @var{idx} of the ephemeron table @var{et} "
+                   "and return its previous value.")
+#define FUNC_NAME s_scm_ephemeron_table_clear_x
+{
+  SCM_VALIDATE_EPHEMERON_TABLE (1, et);
+  SCM_ASSERT_RANGE (2, idx,
+                    scm_to_size_t (idx) < scm_as_ephemeron_table (et)->size);
+
+  struct gc_ephemeron *prev =
+    scm_c_ephemeron_table_clear_x (scm_as_ephemeron_table (et),
+                                   scm_to_size_t (idx));
+  return prev ? PTR2SCM (prev) : SCM_BOOL_F;
+}
+#undef FUNC_NAME
+
 int
 scm_i_print_ephemeron_table (SCM exp, SCM port, scm_print_state *pstate SCM_UNUSED)
 {

module/ice-9/ephemerons.scm

@@ -35,7 +35,8 @@
 
             ephemeron-table-ref
             ephemeron-table-push!
-            ephemeron-table-try-push!))
+            ephemeron-table-try-push!
+            ephemeron-table-clear!))
 
 (eval-when (expand load eval)
   (load-extension (string-append "libguile-" (effective-version))

test-suite/tests/ephemerons.test

@@ -27,14 +27,10 @@
   (pass-if (ephemeron? (make-ephemeron (cons 42 42) 42)))
 
   (with-test-prefix "ephemeron key not heap object"
-    (pass-if-exception "fixnum" exception:wrong-type-arg
+    (pass-if "fixnum" (ephemeron? (make-ephemeron 42 42)))
-      (make-ephemeron 42 42))
+    (pass-if "char" (ephemeron? (make-ephemeron #\a 42)))
-    (pass-if-exception "char" exception:wrong-type-arg
+    (pass-if "bool" (ephemeron? (make-ephemeron #f 42)))
-      (make-ephemeron #\a 42))
+    (pass-if "bool" (ephemeron? (make-ephemeron #t 42))))
-    (pass-if-exception "bool" exception:wrong-type-arg
-      (make-ephemeron #f 42))
-    (pass-if-exception "bool" exception:wrong-type-arg
-      (make-ephemeron #t 42)))
 
   (let ((x (cons 42 69)))
     (define e (make-ephemeron x 100))