lavu: add support for atomic operations.

These could be used for reference counting, or for keeping track of
decoding progress in references in multithreaded decoders.

Support is provided by gcc/msvc/suncc intrinsics, with a fallback using
pthread mutexes.

Signed-off-by: Anton Khirnov <anton@khirnov.net>

configure

@@ -1285,9 +1285,11 @@ HAVE_LIST="
     loongson
     machine_ioctl_bt848_h
     machine_ioctl_meteor_h
+    machine_rw_barrier
     malloc_h
     MapViewOfFile
     memalign
+    MemoryBarrier
     mkstemp
     mm_empty
     mmap
@@ -1322,6 +1324,7 @@ HAVE_LIST="
     struct_v4l2_frmivalenum_discrete
     symver_asm_label
     symver_gnu_asm
+    sync_synchronize
     sysconf
     sysctl
     sys_mman_h
@@ -3453,6 +3456,9 @@ check_func  strerror_r
 check_func  strptime
 check_func  strtok_r
 check_func  sched_getaffinity
+check_builtin sync_synchronize "" "__sync_synchronize()"
+check_builtin machine_rw_barrier mbarrier.h "__machine_rw_barrier()"
+check_builtin MemoryBarrier windows.h "MemoryBarrier()"
 check_func  sysconf
 check_func  sysctl
 check_func  usleep

libavutil/Makefile

@@ -54,6 +54,7 @@ BUILT_HEADERS = avconfig.h
 
 OBJS = adler32.o                                                        \
        aes.o                                                            \
+       atomic.o                                                         \
        audio_fifo.o                                                     \
        avstring.o                                                       \
        base64.o                                                         \
@@ -100,6 +101,7 @@ SKIPHEADERS          = old_pix_fmts.h
 
 TESTPROGS = adler32                                                     \
             aes                                                         \
+            atomic                                                      \
             avstring                                                    \
             base64                                                      \
             blowfish                                                    \

libavutil/atomic.c

@@ -0,0 +1,123 @@
+/*
+ * Copyright (c) 2012 Ronald S. Bultje <rsbultje@gmail.com>
+ *
+ * This file is part of Libav.
+ *
+ * Libav is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * Libav is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with Libav; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "atomic.h"
+
+#if !HAVE_MEMORYBARRIER && !HAVE_SYNC_SYNCHRONIZE && !HAVE_MACHINE_RW_BARRIER
+
+#if HAVE_PTHREADS
+
+#include <pthread.h>
+
+static pthread_mutex_t atomic_lock = PTHREAD_MUTEX_INITIALIZER;
+
+int avpriv_atomic_int_get(volatile int *ptr)
+{
+    int res;
+
+    pthread_mutex_lock(&atomic_lock);
+    res = *ptr;
+    pthread_mutex_unlock(&atomic_lock);
+
+    return res;
+}
+
+void avpriv_atomic_int_set(volatile int *ptr, int val)
+{
+    pthread_mutex_lock(&atomic_lock);
+    *ptr = val;
+    pthread_mutex_unlock(&atomic_lock);
+}
+
+int avpriv_atomic_int_add_and_fetch(volatile int *ptr, int inc)
+{
+    int res;
+
+    pthread_mutex_lock(&atomic_lock);
+    *ptr += inc;
+    res = *ptr;
+    pthread_mutex_unlock(&atomic_lock);
+
+    return res;
+}
+
+void *avpriv_atomic_ptr_cas(void * volatile *ptr, void *oldval, void *newval)
+{
+    void *ret;
+    pthread_mutex_lock(&atomic_lock);
+    ret = *ptr;
+    if (*ptr == oldval)
+        *ptr = newval;
+    pthread_mutex_unlock(&atomic_lock);
+    return ret;
+}
+
+#elif !HAVE_THREADS
+
+int avpriv_atomic_int_get(volatile int *ptr)
+{
+    return *ptr;
+}
+
+void avpriv_atomic_int_set(volatile int *ptr, int val)
+{
+    *ptr = val;
+}
+
+int avpriv_atomic_int_add_and_fetch(volatile int *ptr, int inc)
+{
+    *ptr += inc;
+    return *ptr;
+}
+
+void *avpriv_atomic_ptr_cas(void * volatile *ptr, void *oldval, void *newval)
+{
+    if (*ptr == oldval) {
+        *ptr = newval;
+        return oldval;
+    }
+    return *ptr;
+}
+
+#else
+
+#error "Threading is enabled, but there is no implementation of atomic operations available"
+
+#endif /* HAVE_PTHREADS */
+
+#endif /* !HAVE_MEMORYBARRIER && !HAVE_SYNC_SYNCHRONIZE && !HAVE_MACHINE_RW_BARRIER */
+
+#ifdef TEST
+#include <assert.h>
+
+int main(void)
+{
+    volatile int val = 1;
+    int res;
+
+    res = avpriv_atomic_int_add_and_fetch(&val, 1);
+    assert(res == 2);
+    avpriv_atomic_int_set(&val, 3);
+    res = avpriv_atomic_int_get(&val);
+    assert(res == 3);
+
+    return 0;
+}
+#endif

libavutil/atomic.h

@@ -0,0 +1,74 @@
+/*
+ * Copyright (c) 2012 Ronald S. Bultje <rsbultje@gmail.com>
+ *
+ * This file is part of Libav.
+ *
+ * Libav is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * Libav is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with Libav; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef AVUTIL_ATOMIC_H
+#define AVUTIL_ATOMIC_H
+
+#include "config.h"
+
+#if HAVE_MEMORYBARRIER
+#include "atomic_win32.h"
+#elif HAVE_SYNC_SYNCHRONIZE
+#include "atomic_gcc.h"
+#elif HAVE_MACHINE_RW_BARRIER
+#include "atomic_suncc.h"
+#else
+
+/**
+ * Load the current value stored in an atomic integer.
+ *
+ * @param ptr atomic integer
+ * @return the current value of the atomic integer
+ * @note This acts as a memory barrier.
+ */
+int avpriv_atomic_int_get(volatile int *ptr);
+
+/**
+ * Store a new value in an atomic integer.
+ *
+ * @param ptr atomic integer
+ * @param val the value to store in the atomic integer
+ * @note This acts as a memory barrier.
+ */
+void avpriv_atomic_int_set(volatile int *ptr, int val);
+
+/**
+ * Add a value to an atomic integer.
+ *
+ * @param ptr atomic integer
+ * @param inc the value to add to the atomic integer (may be negative)
+ * @return the new value of the atomic integer.
+ * @note This does NOT act as a memory barrier. This is primarily
+ *       intended for reference counting.
+ */
+int avpriv_atomic_int_add_and_fetch(volatile int *ptr, int inc);
+
+/**
+ * Atomic pointer compare and swap.
+ *
+ * @param ptr pointer to the pointer to operate on
+ * @param oldval do the swap if the current value of *ptr equals to oldval
+ * @param newval value to replace *ptr with
+ * @return the value of *ptr before comparison
+ */
+void *avpriv_atomic_ptr_cas(void * volatile *ptr, void *oldval, void *newval);
+
+#endif /* HAVE_MEMORYBARRIER */
+#endif /* AVUTIL_ATOMIC_H */

libavutil/atomic_gcc.h

@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2012 Ronald S. Bultje <rsbultje@gmail.com>
+ *
+ * This file is part of Libav.
+ *
+ * Libav is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * Libav is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with Libav; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "atomic.h"
+
+#define avpriv_atomic_int_get atomic_int_get_gcc
+static inline int atomic_int_get_gcc(volatile int *ptr)
+{
+    __sync_synchronize();
+    return *ptr;
+}
+
+#define avpriv_atomic_int_set atomic_int_set_gcc
+static inline void atomic_int_set_gcc(volatile int *ptr, int val)
+{
+    *ptr = val;
+    __sync_synchronize();
+}
+
+#define avpriv_atomic_int_add_and_fetch atomic_int_add_and_fetch_gcc
+static inline int atomic_int_add_and_fetch_gcc(volatile int *ptr, int inc)
+{
+    return __sync_add_and_fetch(ptr, inc);
+}
+
+#define avpriv_atomic_ptr_cas atomic_ptr_cas_gcc
+static inline void *atomic_ptr_cas_gcc(void * volatile *ptr,
+                                       void *oldval, void *newval)
+{
+    return __sync_val_compare_and_swap(ptr, oldval, newval);
+}

libavutil/atomic_suncc.h

@@ -0,0 +1,51 @@
+/*
+ *
+ * This file is part of Libav.
+ *
+ * Libav is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * Libav is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with Libav; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <atomic.h>
+#include <mbarrier.h>
+
+#include "atomic.h"
+
+#define avpriv_atomic_int_get atomic_int_get_suncc
+static inline int atomic_int_get_suncc(volatile int *ptr)
+{
+    __machine_rw_barrier();
+    return *ptr;
+}
+
+#define avpriv_atomic_int_set atomic_int_set_suncc
+static inline void atomic_int_set_suncc(volatile int *ptr, int val)
+{
+    *ptr = val;
+    __machine_rw_barrier();
+}
+
+#define avpriv_atomic_int_add_and_fetch atomic_int_add_and_fetch_suncc
+static inline int atomic_int_add_and_fetch_suncc(volatile int *ptr, int inc)
+{
+    return atomic_add_int_nv(ptr, inc);
+}
+
+#define avpriv_atomic_ptr_cas atomic_ptr_cas_suncc
+static inline void *atomic_ptr_cas_suncc(void * volatile *ptr,
+                                         void *oldval, void *newval)
+{
+    return atomic_cas_ptr(ptr, oldval, newval);
+}
+

libavutil/atomic_win32.h

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2012 Ronald S. Bultje <rsbultje@gmail.com>
+ *
+ * This file is part of Libav.
+ *
+ * Libav is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * Libav is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with Libav; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <windows.h>
+
+#include "atomic.h"
+
+#define avpriv_atomic_int_get atomic_int_get_win32
+static inline int atomic_int_get_win32(volatile int *ptr)
+{
+    MemoryBarrier();
+    return *ptr;
+}
+
+#define avpriv_atomic_int_set atomic_int_set_win32
+static inline void atomic_int_set_win32(volatile int *ptr, int val)
+{
+    *ptr = val;
+    MemoryBarrier();
+}
+
+#define avpriv_atomic_int_add_and_fetch atomic_int_add_and_fetch_win32
+static inline int atomic_int_add_and_fetch_win32(volatile int *ptr, int inc)
+{
+    return inc + InterlockedExchangeAdd(ptr, inc);
+}
+
+#define avpriv_atomic_ptr_cas atomic_ptr_cas_win32
+static inline void *atomic_ptr_cas_win32(void * volatile *ptr,
+                                         void *oldval, void *newval)
+{
+    return InterlockedCompareExchangePointer(ptr, newval, oldval);
+}

tests/fate/libavutil.mak

@@ -8,6 +8,11 @@ fate-aes: libavutil/aes-test$(EXESUF)
 fate-aes: CMD = run libavutil/aes-test
 fate-aes: REF = /dev/null
 
+FATE_LIBAVUTIL += fate-atomic
+fate-atomic: libavutil/atomic-test$(EXESUF)
+fate-atomic: CMD = run libavutil/atomic-test
+fate-atomic: REF = /dev/null
+
 FATE_LIBAVUTIL += fate-avstring
 fate-avstring: libavutil/avstring-test$(EXESUF)
 fate-avstring: CMD = run libavutil/avstring-test