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cache_file: add a mode that creates a temporary file

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Since we have to be portable, our options for creating temporary files
are somewhat limited. tmpfile() happens to be available everywhere, so
use that. This function doesn't allow having a "visible" filename or
location, so we use the magic string "TMP" for this.
This commit is contained in:
wm4 2014-08-30 20:03:31 +02:00
parent 829fdef219
commit c80adac077
2 changed files with 38 additions and 16 deletions
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51
DOCS/man/options.rst
View File

@ -2767,31 +2767,52 @@ Cache
on the situation, either of these might be slower than the other method.
This option allows control over this.
``--cache-file=<path>``
Create a cache file on the filesystem with the given name. The file is
always overwritten. When the general cache is enabled, this file cache
will be used to store whatever is read from the source stream.
``--cache-file=<TMP|path>``
Create a cache file on the filesystem.
This will always overwrite the cache file, and you can't use an existing
cache file to resume playback of a stream. (Technically, mpv wouldn't
even know which blocks in the file are valid and which not.)
There are two ways of using this:
The resulting file will not necessarily contain all data of the source
stream. For example, if you seek, the parts that were skipped over are
never read and consequently are not written to the cache. The skipped over
parts are filled with zeros. This means that the cache file doesn't
necessarily correspond to a full download of the source stream.
1. Passing a path (a filename). The file will always be overwritten. When
the general cache is enabled, this file cache will be used to store
whatever is read from the source stream.
Both of these issues could be improved if there is any user interest.
This will always overwrite the cache file, and you can't use an existing
cache file to resume playback of a stream. (Technically, mpv wouldn't
even know which blocks in the file are valid and which not.)
The resulting file will not necessarily contain all data of the source
stream. For example, if you seek, the parts that were skipped over are
never read and consequently are not written to the cache. The skipped over
parts are filled with zeros. This means that the cache file doesn't
necessarily correspond to a full download of the source stream.
Both of these issues could be improved if there is any user interest.
.. warning:: Causes random corruption when used with ordered chapters or
with ``--audio-file``.
2. Passing the string ``TMP``. This will not be interpreted as filename.
Instead, an invisible temporary file is created. It depends on your
C library where this file is created (usually ``/tmp/``), and whether
filename is visible (the ``tmpfile()`` function is used). On some
systems, automatic deletion of the cache file might not be guaranteed
(like on MS Windows).
If you want to use a file cache, this mode is recommended, because it
doesn't break ordered chapters or ``--audio-file``. These modes open
multiple cache streams, and using the same file for them obviously
clashes.
Also see ``--cache-file-size``.
.. warning:: Causes random corruption when used with ordered chapters.
``--cache-file-size=<kBytes>``
Maximum size of the file created with ``--cache-file``. For read accesses
above this size, the cache is simply not used.
Keep in mind that some use-cases, like playing ordered chapters with cache
enabled, will actually create multiple cache files, each of which will
use up to this much disk space.
(Default: 1048576, 1 GB.)
``--no-cache``

3
stream/cache_file.c
View File

@ -127,7 +127,8 @@ int stream_file_cache_init(stream_t *cache, stream_t *stream,
if (!opts->file || !opts->file[0] || opts->file_max < 1)
return 0;
FILE *file = fopen(opts->file, "wb+");
bool use_anon_file = strcmp(opts->file, "TMP") == 0;
FILE *file = use_anon_file ? tmpfile() : fopen(opts->file, "wb+");
if (!file) {
MP_ERR(cache, "can't open cache file '%s'\n", opts->file);
return -1;