[FFmpeg-devel] [PATCH 09/35] lavu/fifo: add a flag for automatically growing the FIFO as needed

[Anton Khirnov <anton@khirnov.net>]

This will not increase the FIFO beyond 1MB, unless the caller explicitly
specifies otherwise.
---
 doc/APIchanges   |  3 ++-
 libavutil/fifo.c | 41 +++++++++++++++++++++++++++++++++++++++--
 libavutil/fifo.h | 15 ++++++++++++++-
 3 files changed, 55 insertions(+), 4 deletions(-)

diff --git a/doc/APIchanges b/doc/APIchanges
index f64759d69d..52b42762ea 100644
--- a/doc/APIchanges
+++ b/doc/APIchanges
@@ -20,7 +20,8 @@ API changes, most recent first:
   rather than bytes.
   Add av_fifo_elem_size(), av_fifo_can_read(), av_fifo_can_write(),
   av_fifo_grow2(), av_fifo_drain2(), av_fifo_write(), av_fifo_write_from_cb(),
-  av_fifo_read(), av_fifo_read_to_cb(), av_fifo_peek(), av_fifo_peek_to_cb().
+  av_fifo_read(), av_fifo_read_to_cb(), av_fifo_peek(), av_fifo_peek_to_cb(),
+  av_fifo_auto_grow_limit().
 
 2022-01-xx - xxxxxxxxxx - lavu fifo.h
   Access to all AVFifoBuffer members is deprecated. The struct will
diff --git a/libavutil/fifo.c b/libavutil/fifo.c
index ea944bc936..2c15df5d5c 100644
--- a/libavutil/fifo.c
+++ b/libavutil/fifo.c
@@ -34,6 +34,9 @@
 # define CTX_STRUCT_NAME AVFifoBuffer
 #endif
 
+// by default the FIFO can be auto-grown to 1MB
+#define AUTO_GROW_DEFAULT_BYTES (1024 * 1024)
+
 typedef struct CTX_STRUCT_NAME {
     // These fields must match then contents of AVFifoBuffer in fifo.h
     // until FF_API_FIFO_PUBLIC is removed
@@ -48,6 +51,9 @@ typedef struct CTX_STRUCT_NAME {
     size_t offset_r, offset_w;
     // distinguishes the ambigous situation offset_r == offset_w
     int    is_empty;
+
+    unsigned int flags;
+    size_t       auto_grow_limit;
 } FifoBuffer;
 
 AVFifoBuffer *av_fifo_alloc2(size_t nb_elems, size_t elem_size,
@@ -75,10 +81,19 @@ AVFifoBuffer *av_fifo_alloc2(size_t nb_elems, size_t elem_size,
     f->nb_elems  = nb_elems;
     f->elem_size = elem_size;
 
+    f->flags           = flags;
+    f->auto_grow_limit = FFMAX(AUTO_GROW_DEFAULT_BYTES / elem_size, 1);
+
     av_fifo_reset((AVFifoBuffer*)f);
     return (AVFifoBuffer*)f;
 }
 
+void av_fifo_auto_grow_limit(AVFifoBuffer *f, size_t max_elems)
+{
+    FifoBuffer *fb = (FifoBuffer*)f;
+    fb->auto_grow_limit = max_elems;
+}
+
 AVFifoBuffer *av_fifo_alloc_array(size_t nmemb, size_t size)
 {
     if (nmemb > SIZE_MAX / size)
@@ -207,6 +222,27 @@ void av_fifo_drain2(AVFifoBuffer *f, size_t size)
 #endif
 }
 
+static int fifo_check_space(AVFifoBuffer *f, size_t to_write)
+{
+    FifoBuffer         *fb = (FifoBuffer*)f;
+    const size_t can_write = av_fifo_can_write(f);
+    const size_t need_grow = to_write > can_write ? to_write - can_write : 0;
+    size_t can_grow;
+
+    if (!need_grow)
+        return 0;
+
+    can_grow = fb->auto_grow_limit > fb->nb_elems ?
+               fb->auto_grow_limit - fb->nb_elems : 0;
+    if ((fb->flags & AV_FIFO_FLAG_AUTO_GROW) && need_grow <= can_grow) {
+        // allocate a bit more than necessary, if we can
+        const size_t inc = (need_grow < can_grow / 2 ) ? need_grow * 2 : can_grow;
+        return av_fifo_grow2(f, inc);
+    }
+
+    return AVERROR(ENOSPC);
+}
+
 static int fifo_write_common(AVFifoBuffer *f, const uint8_t *buf, size_t *nb_elems,
                              AVFifoCB read_cb, void *opaque)
 {
@@ -218,8 +254,9 @@ static int fifo_write_common(AVFifoBuffer *f, const uint8_t *buf, size_t *nb_ele
     uint32_t wndx= f->wndx;
 #endif
 
-    if (to_write > av_fifo_can_write(f))
-        return AVERROR(ENOSPC);
+    ret = fifo_check_space(f, to_write);
+    if (ret < 0)
+        return ret;
 
     do {
         size_t    len = FFMIN(fb->nb_elems - offset_w, to_write);
diff --git a/libavutil/fifo.h b/libavutil/fifo.h
index c7be5e8f7d..11eb36944a 100644
--- a/libavutil/fifo.h
+++ b/libavutil/fifo.h
@@ -83,6 +83,13 @@ AVFifoBuffer *av_fifo_alloc(unsigned int size);
  */
 AVFifoBuffer *av_fifo_alloc_array(size_t nmemb, size_t size);
 
+/**
+ * Automatically resize the FIFO on writes, so that the data fits. This
+ * automatic resizing happens up to a limit that can be modified with
+ * av_fifo_auto_grow_limit().
+ */
+#define AV_FIFO_FLAG_AUTO_GROW      (1 << 0)
+
 /**
  * Allocate and initialize an AVFifoBuffer with a given element size.
  *
@@ -90,7 +97,7 @@ AVFifoBuffer *av_fifo_alloc_array(size_t nmemb, size_t size);
  * @param nb_elems initial number of elements that can be stored in the FIFO
  * @param elem_size Size in bytes of a single element. Further operations on
  *                  the returned FIFO will implicitly use this element size.
- * @param flags currently unused, must be 0
+ * @param flags a combination of AV_FIFO_FLAG_*
  *
  * @return newly-allocated AVFifoBuffer on success, a negative error code on failure
  */
@@ -115,6 +122,12 @@ void av_fifo_freep(AVFifoBuffer **f);
  */
 size_t av_fifo_elem_size(const AVFifoBuffer *f);
 
+/**
+ * Set the maximum size (in elements) to which the FIFO can be resized
+ * automatically. Has no effect unless AV_FIFO_FLAG_AUTO_GROW is used.
+ */
+void av_fifo_auto_grow_limit(AVFifoBuffer *f, size_t max_elems);
+
 /**
  * Reset the AVFifoBuffer to the state right after av_fifo_alloc, in particular it is emptied.
  * @param f AVFifoBuffer to reset
-- 
2.33.0

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