[FFmpeg-devel] [PATCH 1/2] file: operate in blocks, check for interrupts

[Michael Niedermayer]

On Sun, Jul 07, 2013 at 08:56:35PM +0300, Andrey Utkin wrote:
> Interruptibility of file operations is strongly desirable in case of
> slow storage access, e.g. mounted network share.
> Note that file I/O operation still may block (or even freeze) inside of
> single read(2) or write(2) operation. There is no API for
> asynchronous file I/O, but hopefully it will appear in future.
> ---
>  libavformat/file.c | 36 ++++++++++++++++++++++++++++++++----
>  1 file changed, 32 insertions(+), 4 deletions(-)
> 
> diff --git a/libavformat/file.c b/libavformat/file.c
> index e09a64b..640fbdd 100644
> --- a/libavformat/file.c
> +++ b/libavformat/file.c
> @@ -49,10 +49,12 @@ typedef struct FileContext {
>      const AVClass *class;
>      int fd;
>      int trunc;
> +    int blocksize;
>  } FileContext;
>  
>  static const AVOption file_options[] = {
>      { "truncate", "Truncate existing files on write", offsetof(FileContext, trunc), AV_OPT_TYPE_INT, { .i64 = 1 }, 0, 1, AV_OPT_FLAG_ENCODING_PARAM },
> +    { "blocksize", "set I/O operation block size", offsetof(FileContext, blocksize), AV_OPT_TYPE_INT, { .i64 = 4*1024 }, 1, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM },
>      { NULL }
>  };
>  
> @@ -66,15 +68,41 @@ static const AVClass file_class = {
>  static int file_read(URLContext *h, unsigned char *buf, int size)
>  {
>      FileContext *c = h->priv_data;
> -    int r = read(c->fd, buf, size);
> -    return (-1 == r)?AVERROR(errno):r;
> +    int to_read = size;
> +    int blocksize;
> +    int r;
> +    while (to_read) {
> +      if (ff_check_interrupt(&h->interrupt_callback))
> +        return AVERROR_EXIT;
> +      blocksize = (c->blocksize < size) ? c->blocksize : size;
> +      r = read(c->fd, buf, blocksize);

isnt it sufficient to simply limit size without any loop ?

also, by how much does this patch improve reactiveness ?


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Democracy is the form of government in which you can choose your dictator
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