lavu: add a new API for reference-counted data buffers.

4 files changed, 453 insertions, 0 deletions

diff --git a/libavutil/Makefile b/libavutil/Makefile
index 4406b1386d..ef29d5c4b5 100644
--- a/libavutil/Makefile
+++ b/libavutil/Makefile
@@ -11,6 +11,7 @@ HEADERS = adler32.h                                                     \
           base64.h                                                      \
           blowfish.h                                                    \
           bswap.h                                                       \
+          buffer.h                                                      \
           channel_layout.h                                              \
           common.h                                                      \
           cpu.h                                                         \
@@ -59,6 +60,7 @@ OBJS = adler32.o                                                        \
        avstring.o                                                       \
        base64.o                                                         \
        blowfish.o                                                       \
+       buffer.o                                                         \
        channel_layout.o                                                 \
        cpu.o                                                            \
        crc.o                                                            \
diff --git a/libavutil/buffer.c b/libavutil/buffer.c
new file mode 100644
index 0000000000..b5e92c9f14
--- /dev/null
+++ b/libavutil/buffer.c
@@ -0,0 +1,194 @@
+/*
+ * 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 <stdint.h>
+#include <string.h>
+
+#include "atomic.h"
+#include "buffer_internal.h"
+#include "common.h"
+#include "mem.h"
+
+AVBufferRef *av_buffer_create(uint8_t *data, int size,
+                              void (*free)(void *opaque, uint8_t *data),
+                              void *opaque, int flags)
+{
+    AVBufferRef *ref = NULL;
+    AVBuffer    *buf = NULL;
+
+    buf = av_mallocz(sizeof(*buf));
+    if (!buf)
+        return NULL;
+
+    buf->data     = data;
+    buf->size     = size;
+    buf->free     = free ? free : av_buffer_default_free;
+    buf->opaque   = opaque;
+    buf->refcount = 1;
+
+    if (flags & AV_BUFFER_FLAG_READONLY)
+        buf->flags |= BUFFER_FLAG_READONLY;
+
+    ref = av_mallocz(sizeof(*ref));
+    if (!ref) {
+        av_freep(&buf);
+        return NULL;
+    }
+
+    ref->buffer = buf;
+    ref->data   = data;
+    ref->size   = size;
+
+    return ref;
+}
+
+void av_buffer_default_free(void *opaque, uint8_t *data)
+{
+    av_free(data);
+}
+
+AVBufferRef *av_buffer_alloc(int size)
+{
+    AVBufferRef *ret = NULL;
+    uint8_t    *data = NULL;
+
+    data = av_malloc(size);
+    if (!data)
+        return NULL;
+
+    ret = av_buffer_create(data, size, av_buffer_default_free, NULL, 0);
+    if (!ret)
+        av_freep(&data);
+
+    return ret;
+}
+
+AVBufferRef *av_buffer_allocz(int size)
+{
+    AVBufferRef *ret = av_buffer_alloc(size);
+    if (!ret)
+        return NULL;
+
+    memset(ret->data, 0, size);
+    return ret;
+}
+
+AVBufferRef *av_buffer_ref(AVBufferRef *buf)
+{
+    AVBufferRef *ret = av_mallocz(sizeof(*ret));
+
+    if (!ret)
+        return NULL;
+
+    *ret = *buf;
+
+    avpriv_atomic_int_add_and_fetch(&buf->buffer->refcount, 1);
+
+    return ret;
+}
+
+void av_buffer_unref(AVBufferRef **buf)
+{
+    AVBuffer *b;
+
+    if (!buf || !*buf)
+        return;
+    b = (*buf)->buffer;
+    av_freep(buf);
+
+    if (!avpriv_atomic_int_add_and_fetch(&b->refcount, -1)) {
+        b->free(b->opaque, b->data);
+        av_freep(&b);
+    }
+}
+
+int av_buffer_is_writable(const AVBufferRef *buf)
+{
+    if (buf->buffer->flags & AV_BUFFER_FLAG_READONLY)
+        return 0;
+
+    return avpriv_atomic_int_add_and_fetch(&buf->buffer->refcount, 0) == 1;
+}
+
+int av_buffer_make_writable(AVBufferRef **pbuf)
+{
+    AVBufferRef *newbuf, *buf = *pbuf;
+
+    if (av_buffer_is_writable(buf))
+        return 0;
+
+    newbuf = av_buffer_alloc(buf->size);
+    if (!newbuf)
+        return AVERROR(ENOMEM);
+
+    memcpy(newbuf->data, buf->data, buf->size);
+    av_buffer_unref(pbuf);
+    *pbuf = newbuf;
+
+    return 0;
+}
+
+int av_buffer_realloc(AVBufferRef **pbuf, int size)
+{
+    AVBufferRef *buf = *pbuf;
+    uint8_t *tmp;
+
+    if (!buf) {
+        /* allocate a new buffer with av_realloc(), so it will be reallocatable
+         * later */
+        uint8_t *data = av_realloc(NULL, size);
+        if (!data)
+            return AVERROR(ENOMEM);
+
+        buf = av_buffer_create(data, size, av_buffer_default_free, NULL, 0);
+        if (!buf) {
+            av_freep(&data);
+            return AVERROR(ENOMEM);
+        }
+
+        buf->buffer->flags |= BUFFER_FLAG_REALLOCATABLE;
+        *pbuf = buf;
+
+        return 0;
+    } else if (buf->size == size)
+        return 0;
+
+    if (!(buf->buffer->flags & BUFFER_FLAG_REALLOCATABLE) ||
+        !av_buffer_is_writable(buf)) {
+        /* cannot realloc, allocate a new reallocable buffer and copy data */
+        AVBufferRef *new = NULL;
+
+        av_buffer_realloc(&new, size);
+        if (!new)
+            return AVERROR(ENOMEM);
+
+        memcpy(new->data, buf->data, FFMIN(size, buf->size));
+
+        av_buffer_unref(pbuf);
+        *pbuf = new;
+        return 0;
+    }
+
+    tmp = av_realloc(buf->buffer->data, size);
+    if (!tmp)
+        return AVERROR(ENOMEM);
+
+    buf->buffer->data = buf->data = tmp;
+    buf->buffer->size = buf->size = size;
+    return 0;
+}
diff --git a/libavutil/buffer.h b/libavutil/buffer.h
new file mode 100644
index 0000000000..843dfbe24a
--- /dev/null
+++ b/libavutil/buffer.h
@@ -0,0 +1,197 @@
+/*
+ * 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
+ */
+
+/**
+ * @file
+ * @ingroup lavu_buffer
+ * refcounted data buffer API
+ */
+
+#ifndef AVUTIL_BUFFER_H
+#define AVUTIL_BUFFER_H
+
+#include <stdint.h>
+
+/**
+ * @defgroup lavu_buffer AVBuffer
+ * @ingroup lavu_data
+ *
+ * @{
+ * AVBuffer is an API for reference-counted data buffers.
+ *
+ * There are two core objects in this API -- AVBuffer and AVBufferRef. AVBuffer
+ * represents the data buffer itself; it is opaque and not meant to be accessed
+ * by the caller directly, but only through AVBufferRef. However, the caller may
+ * e.g. compare two AVBuffer pointers to check whether two different references
+ * are describing the same data buffer. AVBufferRef represents a single
+ * reference to an AVBuffer and it is the object that may be manipulated by the
+ * caller directly.
+ *
+ * There are two functions provided for creating a new AVBuffer with a single
+ * reference -- av_buffer_alloc() to just allocate a new buffer, and
+ * av_buffer_create() to wrap an existing array in an AVBuffer. From an existing
+ * reference, additional references may be created with av_buffer_ref().
+ * Use av_buffer_unref() to free a reference (this will automatically free the
+ * data once all the references are freed).
+ *
+ * The convention throughout this API and the rest of Libav is such that the
+ * buffer is considered writable if there exists only one reference to it (and
+ * it has not been marked as read-only). The av_buffer_is_writable() function is
+ * provided to check whether this is true and av_buffer_make_writable() will
+ * automatically create a new writable buffer when necessary.
+ * Of course nothing prevents the calling code from violating this convention,
+ * however that is safe only when all the existing references are under its
+ * control.
+ *
+ * @note Referencing and unreferencing the buffers is thread-safe and thus
+ * may be done from multiple threads simultaneously without any need for
+ * additional locking.
+ *
+ * @note Two different references to the same buffer can point to different
+ * parts of the buffer (i.e. their AVBufferRef.data will not be equal).
+ */
+
+/**
+ * A reference counted buffer type. It is opaque and is meant to be used through
+ * references (AVBufferRef).
+ */
+typedef struct AVBuffer AVBuffer;
+
+/**
+ * A reference to a data buffer.
+ *
+ * The size of this struct is not a part of the public ABI and it is not meant
+ * to be allocated directly.
+ */
+typedef struct AVBufferRef {
+    AVBuffer *buffer;
+
+    /**
+     * The data buffer. It is considered writable if and only if
+     * this is the only reference to the buffer, in which case
+     * av_buffer_is_writable() returns 1.
+     */
+    uint8_t *data;
+    /**
+     * Size of data in bytes.
+     */
+    int      size;
+} AVBufferRef;
+
+/**
+ * Allocate an AVBuffer of the given size using av_malloc().
+ *
+ * @return an AVBufferRef of given size or NULL when out of memory
+ */
+AVBufferRef *av_buffer_alloc(int size);
+
+/**
+ * Same as av_buffer_alloc(), except the returned buffer will be initialized
+ * to zero.
+ */
+AVBufferRef *av_buffer_allocz(int size);
+
+/**
+ * Always treat the buffer as read-only, even when it has only one
+ * reference.
+ */
+#define AV_BUFFER_FLAG_READONLY (1 << 0)
+
+/**
+ * Create an AVBuffer from an existing array.
+ *
+ * If this function is successful, data is owned by the AVBuffer. The caller may
+ * only access data through the returned AVBufferRef and references derived from
+ * it.
+ * If this function fails, data is left untouched.
+ * @param data   data array
+ * @param size   size of data in bytes
+ * @param free   a callback for freeing data
+ * @param opaque parameter to be passed to free
+ * @param flags  a combination of AV_BUFFER_FLAG_*
+ *
+ * @return an AVBufferRef referring to data on success, NULL on failure.
+ */
+AVBufferRef *av_buffer_create(uint8_t *data, int size,
+                              void (*free)(void *opaque, uint8_t *data),
+                              void *opaque, int flags);
+
+/**
+ * Default free callback, which calls av_free() on the buffer data.
+ * This function is meant to be passed to av_buffer_create(), not called
+ * directly.
+ */
+void av_buffer_default_free(void *opaque, uint8_t *data);
+
+/**
+ * Create a new reference to an AVBuffer.
+ *
+ * @return a new AVBufferRef referring to the same AVBuffer as buf or NULL on
+ * failure.
+ */
+AVBufferRef *av_buffer_ref(AVBufferRef *buf);
+
+/**
+ * Free a given reference and automatically free the buffer if there are no more
+ * references to it.
+ *
+ * @param buf the reference to be freed. The pointer is set to NULL on return.
+ */
+void av_buffer_unref(AVBufferRef **buf);
+
+/**
+ * @return 1 if the caller may write to the data referred to by buf (which is
+ * true if and only if buf is the only reference to the underlying AVBuffer).
+ * Return 0 otherwise.
+ * A positive answer is valid until av_buffer_ref() is called on buf.
+ */
+int av_buffer_is_writable(const AVBufferRef *buf);
+
+/**
+ * Create a writable reference from a given buffer reference, avoiding data copy
+ * if possible.
+ *
+ * @param buf buffer reference to make writable. On success, buf is either left
+ *            untouched, or it is unreferenced and a new writable AVBufferRef is
+ *            written in its place. On failure, buf is left untouched.
+ * @return 0 on success, a negative AVERROR on failure.
+ */
+int av_buffer_make_writable(AVBufferRef **buf);
+
+/**
+ * Reallocate a given buffer.
+ *
+ * @param buf  a buffer reference to reallocate. On success, buf will be
+ *             unreferenced and a new reference with the required size will be
+ *             written in its place. On failure buf will be left untouched. *buf
+ *             may be NULL, then a new buffer is allocated.
+ * @param size required new buffer size.
+ * @return 0 on success, a negative AVERROR on failure.
+ *
+ * @note the buffer is actually reallocated with av_realloc() only if it was
+ * initially allocated through av_buffer_realloc(NULL) and there is only one
+ * reference to it (i.e. the one passed to this function). In all other cases
+ * a new buffer is allocated and the data is copied.
+ */
+int av_buffer_realloc(AVBufferRef **buf, int size);
+
+/**
+ * @}
+ */
+
+#endif /* AVUTIL_BUFFER_H */
diff --git a/libavutil/buffer_internal.h b/libavutil/buffer_internal.h
new file mode 100644
index 0000000000..677c341d64
--- /dev/null
+++ b/libavutil/buffer_internal.h
@@ -0,0 +1,60 @@
+/*
+ * 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_BUFFER_INTERNAL_H
+#define AVUTIL_BUFFER_INTERNAL_H
+
+#include <stdint.h>
+
+#include "buffer.h"
+
+/**
+ * The buffer is always treated as read-only.
+ */
+#define BUFFER_FLAG_READONLY      (1 << 0)
+/**
+ * The buffer was av_realloc()ed, so it is reallocatable.
+ */
+#define BUFFER_FLAG_REALLOCATABLE (1 << 1)
+
+struct AVBuffer {
+    uint8_t *data; /**< data described by this buffer */
+    int      size; /**< size of data in bytes */
+
+    /**
+     *  number of existing AVBufferRef instances referring to this buffer
+     */
+    volatile int refcount;
+
+    /**
+     * a callback for freeing the data
+     */
+    void (*free)(void *opaque, uint8_t *data);
+
+    /**
+     * an opaque pointer, to be used by the freeing callback
+     */
+    void *opaque;
+
+    /**
+     * A combination of BUFFER_FLAG_*
+     */
+    int flags;
+};
+
+#endif /* AVUTIL_BUFFER_INTERNAL_H */