buffer: add support for pools using caller data in allocation

This should allow using more complex allocators than simple malloc
wrappers.

doc/APIchanges

@@ -13,6 +13,9 @@ libavutil:     2015-08-28
 
 API changes, most recent first:
 
+2016-xx-xx - lavu 55.6.0
+  xxxxxxx buffer.h - Add av_buffer_pool_init2().
+
 2016-xx-xx - xxxxxxx - lavf 57.3.0 - avformat.h
   Add AVFormatContext.opaque, io_open and io_close, allowing custom IO
   for muxers and demuxers that open additional files.

libavutil/buffer.c

@@ -194,6 +194,26 @@ int av_buffer_realloc(AVBufferRef **pbuf, int size)
     return 0;
 }
 
+AVBufferPool *av_buffer_pool_init2(int size, void *opaque,
+                                   AVBufferRef* (*alloc)(void *opaque, int size),
+                                   void (*pool_free)(void *opaque))
+{
+    AVBufferPool *pool = av_mallocz(sizeof(*pool));
+    if (!pool)
+        return NULL;
+
+    ff_mutex_init(&pool->mutex, NULL);
+
+    pool->size      = size;
+    pool->opaque    = opaque;
+    pool->alloc2    = alloc;
+    pool->pool_free = pool_free;
+
+    avpriv_atomic_int_set(&pool->refcount, 1);
+
+    return pool;
+}
+
 AVBufferPool *av_buffer_pool_init(int size, AVBufferRef* (*alloc)(int size))
 {
     AVBufferPool *pool = av_mallocz(sizeof(*pool));
@@ -224,6 +244,10 @@ static void buffer_pool_free(AVBufferPool *pool)
         av_freep(&buf);
     }
     ff_mutex_destroy(&pool->mutex);
+
+    if (pool->pool_free)
+        pool->pool_free(pool->opaque);
+
     av_freep(&pool);
 }
 
@@ -261,7 +285,8 @@ static AVBufferRef *pool_alloc_buffer(AVBufferPool *pool)
     BufferPoolEntry *buf;
     AVBufferRef     *ret;
 
-    ret = pool->alloc(pool->size);
+    ret = pool->alloc2 ? pool->alloc2(pool->opaque, pool->size) :
+                         pool->alloc(pool->size);
     if (!ret)
         return NULL;
 

libavutil/buffer.h

@@ -241,6 +241,23 @@ typedef struct AVBufferPool AVBufferPool;
  */
 AVBufferPool *av_buffer_pool_init(int size, AVBufferRef* (*alloc)(int size));
 
+/**
+ * Allocate and initialize a buffer pool with a more complex allocator.
+ *
+ * @param size size of each buffer in this pool
+ * @param opaque arbitrary user data used by the allocator
+ * @param alloc a function that will be used to allocate new buffers when the
+ *              pool is empty.
+ * @param pool_free a function that will be called immediately before the pool
+ *                  is freed. I.e. after av_buffer_pool_can_uninit() is called
+ *                  by the pool and all the frames are returned to the pool and
+ *                  freed. It is intended to uninitialize the user opaque data.
+ * @return newly created buffer pool on success, NULL on error.
+ */
+AVBufferPool *av_buffer_pool_init2(int size, void *opaque,
+                                   AVBufferRef* (*alloc)(void *opaque, int size),
+                                   void (*pool_free)(void *opaque));
+
 /**
  * Mark the pool as being available for freeing. It will actually be freed only
  * once all the allocated buffers associated with the pool are released. Thus it

libavutil/buffer_internal.h

@@ -88,7 +88,10 @@ struct AVBufferPool {
     volatile int refcount;
 
     int size;
+    void *opaque;
     AVBufferRef* (*alloc)(int size);
+    AVBufferRef* (*alloc2)(void *opaque, int size);
+    void         (*pool_free)(void *opaque);
 };
 
 #endif /* AVUTIL_BUFFER_INTERNAL_H */

libavutil/version.h

@@ -54,7 +54,7 @@
  */
 
 #define LIBAVUTIL_VERSION_MAJOR 55
-#define LIBAVUTIL_VERSION_MINOR  5
+#define LIBAVUTIL_VERSION_MINOR  6
 #define LIBAVUTIL_VERSION_MICRO  0
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \