Atomic vars implemented in a more general way.

We have them into zmalloc.c, but this is going to replace that
implementation, so that it's possible to use the same idea everywhere
inside the code base.

Author: antirez

src/atomicvar.h

@@ -0,0 +1,94 @@
+/* This file implements atomic counters using __atomic or __sync macros if
+ * available, otherwise synchronizing different threads using a mutex.
+ *
+ * The exported interaface is composed of three macros:
+ *
+ * atomicIncr(var,count,mutex) -- Increment the atomic counter
+ * atomicDecr(var,count,mutex) -- Decrement the atomic counter
+ * atomicGet(var,dstvar,mutex) -- Fetch the atomic counter value
+ *
+ * If atomic primitives are availble (tested in config.h) the mutex
+ * is not used.
+ *
+ * Never use return value from the macros. To update and get use instead:
+ *
+ *  atomicIncr(mycounter,...);
+ *  atomicGet(mycounter,newvalue);
+ *  doSomethingWith(newvalue);
+ *
+ * ----------------------------------------------------------------------------
+ *
+ * Copyright (c) 2015, Salvatore Sanfilippo <antirez at gmail dot com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   * Redistributions of source code must retain the above copyright notice,
+ *     this list of conditions and the following disclaimer.
+ *   * Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *   * Neither the name of Redis nor the names of its contributors may be used
+ *     to endorse or promote products derived from this software without
+ *     specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <pthread.h>
+
+#ifndef __ATOMIC_VAR_H
+#define __ATOMIC_VAR_H
+
+#if defined(__ATOMIC_RELAXED)
+/* Implementation using __atomic macros. */
+
+#define atomicIncr(var,count,mutex) __atomic_add_fetch(&var,(count),__ATOMIC_RELAXED)
+#define atomicDecr(var,count,mutex) __atomic_sub_fetch(&var,(count),__ATOMIC_RELAXED)
+#define atomicGet(var,dstvar,mutex) do { \
+    dstvar = __atomic_load_n(&var,__ATOMIC_RELAXED); \
+} while(0)
+
+#elif defined(HAVE_ATOMIC)
+/* Implementation using __sync macros. */
+
+#define atomicIncr(var,count,mutex) __sync_add_and_fetch(&var,(count))
+#define atomicDecr(var,count,mutex) __sync_sub_and_fetch(&var,(count))
+#define atomicGet(var,dstvar,mutex) do { \
+    dstvar = __sync_sub_and_fetch(&var,0); \
+} while(0)
+
+#else
+/* Implementation using pthread mutex. */
+
+#define atomicIncr(var,count,mutex) do { \
+    pthread_mutex_lock(&mutex); \
+    var += (count); \
+    pthread_mutex_unlock(&mutex); \
+} while(0)
+
+#define atomicDecr(var,count,mutex) do { \
+    pthread_mutex_lock(&mutex); \
+    var -= (count); \
+    pthread_mutex_unlock(&mutex); \
+} while(0)
+
+#define atomicGet(var,dstvar,mutex) do { \
+    pthread_mutex_lock(&mutex); \
+    dstvar = var; \
+    pthread_mutex_unlock(&mutex); \
+} while(0)
+#endif
+
+#endif /* __ATOMIC_VAR_H */