[Mesa-dev] [RFC PATCH v2] Evade very ugly system dependent code by replacing an flock

[Timothy Arceri]

On 21/05/18 00:47, Benedikt Schemmer wrote:
> There is exactly one flock in mesa and it caused mesa not to build
> on windows when shader cache was enabled.
> 
> It should be possible to revert 9f8dc3bf03ec825bae7041858dda6ca2e9a34363
> "utils: build sha1/disk cache only with Android/Autoconf" currently
> guarding the offending code with ENABLE_SHADER_CACHE
> 
> This would allow shader cache to work on windows I think.
> I dont have a test system with windows though.
> 
> This builds on linux and is tested with Deus Ex:MD and Metro 2033 Redux
> both with cold shader cache.
> 
> Really
> Fixes: d1efa09d342bff3e5def2978a0bef748d74f9c82
> 
> v2: make the patch ridiculously simple (Jan Vesely) needs testing though
> 
> CC: Tapani Pälli <tapani.palli at intel.com>
> CC: "Marek Olšák" <maraeo at gmail.com>
> CC: Emil Velikov <emil.l.velikov at gmail.com>
> CC: Timothy Arceri <tarceri at itsqueeze.com>
> CC: Samuel Pitoiset <samuel.pitoiset at gmail.com>
> CC: Jan Vesely <jan.vesely at rutgers.edu>
> ---
> This enables the patch
> [PATCH 1/3] mesa/main/shaderapi: Use generate_sha1() unconditionally
> 
>   src/util/disk_cache.c | 14 ++------------
>   1 file changed, 2 insertions(+), 12 deletions(-)
> 
> diff --git a/src/util/disk_cache.c b/src/util/disk_cache.c
> index 4a762eff20..35847af6a6 100644
> --- a/src/util/disk_cache.c
> +++ b/src/util/disk_cache.c
> @@ -28,7 +28,6 @@
>   #include <string.h>
>   #include <stdlib.h>
>   #include <stdio.h>
> -#include <sys/file.h>
>   #include <sys/types.h>
>   #include <sys/stat.h>
>   #include <sys/mman.h>
> @@ -876,7 +875,7 @@ cache_put(void *job, int thread_index)
>      if (asprintf(&filename_tmp, "%s.tmp", filename) == -1)
>         goto done;
>   
> -   fd = open(filename_tmp, O_WRONLY | O_CLOEXEC | O_CREAT, 0644);
> +   fd = open(filename_tmp, O_WRONLY | O_CLOEXEC | O_CREAT | O_EXCL, 0644);
>   
>      /* Make the two-character subdirectory within the cache as needed. */
>      if (fd == -1) {

There is another open call here that would need to be updated for this 
to work correctly. Although as I've said before there is more than this 
required for this to work on windows.

> @@ -890,16 +889,7 @@ cache_put(void *job, int thread_index)
>            goto done;
>      }
>   
> -   /* With the temporary file open, we take an exclusive flock on
> -    * it. If the flock fails, then another process still has the file
> -    * open with the flock held. So just let that file be responsible
> -    * for writing the file.
> -    */
> -   err = flock(fd, LOCK_EX | LOCK_NB);
> -   if (err == -1)
> -      goto done;
> -
> -   /* Now that we have the lock on the open temporary file, we can
> +   /* Now that we have the open temporary file, we can
>       * check to see if the destination file already exists. If so,
>       * another process won the race between when we saw that the file
>       * didn't exist and now. In this case, we don't do anything more,
>