lavfi: add a generic API for buffer queues.

libavfilter/bufferqueue.h

+/*
+ * Generic buffer queue
+ * Copyright (c) 2012 Nicolas George
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg 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.
+ *
+ * FFmpeg 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 FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef AVFILTER_BUFFERQUEUE_H
+#define AVFILTER_BUFFERQUEUE_H
+
+/**
+ * FFBufQueue: simple AVFilterBufferRef queue API
+ *
+ * Note: this API is not thread-safe. Concurrent access to the same queue
+ * must be protected by a mutex or any synchronization mechanism.
+ */
+
+/**
+ * Maximum size of the queue.
+ *
+ * This value can be overridden by definying it before including this
+ * header.
+ * Powers of 2 are recommended.
+ */
+#ifndef FF_BUFQUEUE_SIZE
+#define FF_BUFQUEUE_SIZE 32
+#endif
+
+#include "avfilter.h"
+#include "libavutil/avassert.h"
+
+/**
+ * Structure holding the queue
+ */
+struct FFBufQueue {
+    AVFilterBufferRef *queue[FF_BUFQUEUE_SIZE];
+    unsigned short head;
+    unsigned short available; /**< number of available buffers */
+};
+
+#define BUCKET(i) queue->queue[(queue->head + (i)) % FF_BUFQUEUE_SIZE]
+
+/**
+ * Add a buffer to the queue.
+ *
+ * If the queue is already full, then the current last buffer is dropped
+ * (and unrefed) with a warning before adding the new buffer.
+ */
+static inline void ff_bufqueue_add(void *log, struct FFBufQueue *queue,
+                                   AVFilterBufferRef *buf)
+{
+    if (queue->available == FF_BUFQUEUE_SIZE) {
+        av_log(log, AV_LOG_WARNING, "Buffer queue overflow, dropping.\n");
+        avfilter_unref_buffer(BUCKET(--queue->available));
+    }
+    BUCKET(queue->available++) = buf;
+}
+
+/**
+ * Get a buffer from the queue without altering it.
+ *
+ * Buffer with index 0 is the first buffer in the queue.
+ * Return NULL if the queue has not enough buffers.
+ */
+static inline AVFilterBufferRef *ff_bufqueue_peek(struct FFBufQueue *queue,
+                                                  unsigned index)
+{
+    return index < queue->available ? BUCKET(index) : NULL;
+}
+
+/**
+ * Get the first buffer from the queue and remove it.
+ *
+ * Do not use on an empty queue.
+ */
+static inline AVFilterBufferRef *ff_bufqueue_get(struct FFBufQueue *queue)
+{
+    AVFilterBufferRef *ret = queue->queue[queue->head];
+    av_assert0(queue->available);
+    queue->available--;
+    queue->queue[queue->head] = NULL;
+    queue->head = (queue->head + 1) % FF_BUFQUEUE_SIZE;
+    return ret;
+}
+
+/**
+ * Unref and remove all buffers from the queue.
+ */
+static inline void ff_bufqueue_discard_all(struct FFBufQueue *queue)
+{
+    while (queue->available)
+        avfilter_unref_buffer(ff_bufqueue_get(queue));
+}
+
+#undef BUCKET
+
+#endif /* AVFILTER_BUFFERQUEUE_H */