From 71d82d06d17f0205ccf5bb72ea11d3fd3e9eb363 Mon Sep 17 00:00:00 2001
From: Joshua Haberman <joshua@reverberate.org>
Date: Sat, 15 Aug 2009 20:20:28 -0700
Subject: Add refcounting and thread-safety to message definitions.

---
 src/upb_atomic.h | 162 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 162 insertions(+)
 create mode 100644 src/upb_atomic.h

(limited to 'src/upb_atomic.h')

diff --git a/src/upb_atomic.h b/src/upb_atomic.h
new file mode 100644
index 0000000..b3995e4
--- /dev/null
+++ b/src/upb_atomic.h
@@ -0,0 +1,162 @@
+/*
+ * upb - a minimalist implementation of protocol buffers.
+ *
+ * Copyright (c) 2009 Joshua Haberman.  See LICENSE for details.
+ *
+ * Only a very small part of upb is thread-safe.  Notably, individual
+ * messages, arrays, and strings are *not* thread safe for mutating.
+ * However, we do make message *metadata* such as upb_msgdef and
+ * upb_context thread-safe, and their ownership is tracked via atomic
+ * refcounting.  This header implements the small number of atomic
+ * primitives required to support this.  The primitives we implement
+ * are:
+ *
+ * - a reader/writer lock (wrappers around platform-provided mutexes).
+ * - an atomic refcount.
+ */
+
+#ifndef UPB_ATOMIC_H_
+#define UPB_ATOMIC_H_
+
+#include <stdbool.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* inline if possible, emit standalone code if required. */
+#ifndef INLINE
+#define INLINE static inline
+#endif
+
+#ifdef UPB_THREAD_UNSAFE
+
+/* Non-thread-safe implementations. ******************************************/
+
+typedef struct {
+  int val;
+} upb_atomic_refcount_t;
+
+INLINE void upb_atomic_refcount_init(upb_atomic_refcount_t *a, int val) {
+  a->val = val;
+}
+
+INLINE bool upb_atomic_ref(upb_atomic_refcount_t *a) {
+  return a->val++ == 0;
+}
+
+INLINE bool upb_atomic_unref(upb_atomic_refcount_t *a) {
+  return --a->val == 0;
+}
+
+typedef struct {
+} upb_rwlock_t;
+
+INLINE void upb_rwlock_init(upb_rwlock_t *l) { (void)l; }
+INLINE void upb_rwlock_destroy(upb_rwlock_t *l) { (void)l; }
+INLINE void upb_rwlock_rdlock(upb_rwlock_t *l) { (void)l; }
+INLINE void upb_rwlock_wrlock(upb_rwlock_t *l) { (void)l; }
+INLINE void upb_rwlock_unlock(upb_rwlock_t *l) { (void)l; }
+
+#endif
+
+/* Atomic refcount ************************************************************/
+
+#ifdef UPB_THREAD_UNSAFE
+
+/* Already defined above. */
+
+#elif (__GNUC__ == 4 && __GNUC_MINOR__ >= 1) || __GNUC__ > 4
+
+/* GCC includes atomic primitives. */
+
+typedef struct {
+  volatile int val;
+} upb_atomic_refcount_t;
+
+INLINE void upb_atomic_refcount_init(upb_atomic_refcount_t *a, int val) {
+  a->val = val;
+  __sync_synchronize();   /* Ensure the initialized value is visible. */
+}
+
+INLINE void upb_atomic_ref(upb_atomic_refcount_t *a) {
+  return __sync_fetch_and_add(&a->val) == 0;
+}
+
+INLINE bool upb_atomic_unref(upb_atomic_refcount_t *a) {
+  return __sync_sub_and_fetch(&a->val) == 0;
+}
+
+#elif defined(WIN32)
+
+/* Windows defines atomic increment/decrement. */
+#include <Windows.h>
+
+typedef struct {
+  volatile LONG val;
+} upb_atomic_refcount_t;
+
+INLINE void upb_atomic_refcount_init(upb_atomic_refcount_t *a, int val) {
+  InterlockedExchange(&a->val, val);
+}
+
+INLINE bool upb_atomic_ref(upb_atomic_refcount_t *a) {
+  return InterlockedIncrement(&a->val) == 1;
+}
+
+INLINE bool upb_atomic_unref(upb_atomic_refcount_t *a) {
+  return InterlockedDecrement(&a->val) == 0;
+}
+
+#else
+#error Atomic primitives not defined for your platform/CPU.  \
+       Implement them or compile with UPB_THREAD_UNSAFE.
+#endif
+
+/* Reader/Writer lock. ********************************************************/
+
+#ifdef UPB_THREAD_UNSAFE
+
+/* Already defined. */
+
+#elif defined(_POSIX_THREADS)
+
+typedef struct {
+  pthread_rwlock_t lock;
+} upb_rwlock_t;
+
+INLINE void upb_rwlock_init(upb_rwlock_t *l) {
+  /* TODO: check return value. */
+  pthread_rwlock_init(&l->lock);
+}
+
+INLINE void upb_rwlock_destroy(upb_rwlock_t *l) {
+  /* TODO: check return value. */
+  pthread_rwlock_destroy(&l->lock);
+}
+
+INLINE void upb_rwlock_rdlock(upb_rwlock_t *l) {
+  /* TODO: check return value. */
+  pthread_rwlock_rdlock(&l->lock);
+}
+
+INLINE void upb_rwlock_wrlock(upb_rwlock_t *l) {
+  /* TODO: check return value. */
+  pthread_rwlock_wrlock(&l->lock);
+}
+
+INLINE void upb_rwlock_unlock(upb_rwlock_t *l) {
+  /* TODO: check return value. */
+  pthread_rwlock_unlock(&l->lock);
+}
+
+#else
+#error Reader/writer lock is not defined for your platform/CPU.  \
+       Implement it or compile with UPB_THREAD_UNSAFE.
+#endif
+
+#ifdef __cplusplus
+}  /* extern "C" */
+#endif
+
+#endif  /* UPB_ATOMIC_H_ */
-- 
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