Add infrastructure for reference counts.
OpenSSL has traditionally done reference counting with |int|s and the
|CRYPTO_add| function. Unless a special callback is installed (rare),
this is implemented by doing the reference count operations under a
lock.
This change adds infrastructure for handling reference counts and uses
atomic operations when C11 support is available.
Change-Id: Ia023ce432319efd00f77a7340da27d16ee4b63c3
Reviewed-on: https://boringssl-review.googlesource.com/4771
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/crypto/refcount_c11.c b/crypto/refcount_c11.c
new file mode 100644
index 0000000..a77473f
--- /dev/null
+++ b/crypto/refcount_c11.c
@@ -0,0 +1,65 @@
+/* Copyright (c) 2015, Google Inc.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
+
+#include "internal.h"
+
+
+#if defined(OPENSSL_C11_ATOMIC)
+
+#include <assert.h>
+#include <stdalign.h>
+#include <stdatomic.h>
+#include <stdlib.h>
+
+#include <openssl/type_check.h>
+
+
+/* See comment above the typedef of CRYPTO_refcount_t about these tests. */
+static_assert(alignof(CRYPTO_refcount_t) == alignof(_Atomic CRYPTO_refcount_t),
+ "_Atomic alters the needed alignment of a reference count");
+static_assert(sizeof(CRYPTO_refcount_t) == sizeof(_Atomic CRYPTO_refcount_t),
+ "_Atomic alters the size of a reference count");
+
+static_assert((CRYPTO_refcount_t)-1 == CRYPTO_REFCOUNT_MAX,
+ "CRYPTO_REFCOUNT_MAX is incorrect");
+
+void CRYPTO_refcount_inc(CRYPTO_refcount_t *count) {
+ uint32_t expected = atomic_load(count);
+
+ while (expected != CRYPTO_REFCOUNT_MAX) {
+ uint32_t new_value = expected + 1;
+ if (atomic_compare_exchange_weak(count, &expected, new_value)) {
+ break;
+ }
+ }
+}
+
+int CRYPTO_refcount_dec_and_test_zero(CRYPTO_refcount_t *count) {
+ uint32_t expected = atomic_load(count);
+
+ for (;;) {
+ if (expected == 0) {
+ abort();
+ } else if (expected == CRYPTO_REFCOUNT_MAX) {
+ return 0;
+ } else {
+ const uint32_t new_value = expected - 1;
+ if (atomic_compare_exchange_weak(count, &expected, new_value)) {
+ return new_value == 0;
+ }
+ }
+ }
+}
+
+#endif /* OPENSSL_C11_ATOMIC */