Previously when a pipeline is added to the cache it would never be
removed. If the application is generating a lot of unique pipelines
this can end up effectively leaking a large number of resources
including the GL program objects. Arguably this isn't really a problem
because if the application is generating that many unique pipelines
then it is doing something wrong anyway. It also implies that it will
be recompiling shaders very often so the cache leaking will likely be
the least of the problems.
This patch makes it keep track of which pipelines in the cache are in
use. The cache now returns a struct representing the entry instead of
directly returning the pipeline. This entry contains a usage counter
which the pipeline backends can use to mark when there is a pipeline
alive that is using the cache entry. When the hash table decides that
it's a good time to prune some entries, it will make a list of all of
the pipelines that are not in use and then remove the least recently
used half of the pipelines. That way it is less likely to remove
pipelines that the application is actually regenerating often even if
they aren't in use all of the time.
When the cache is pruned the hash table makes a note of how small the
cache could be if it removed all of the unused pipelines. The hash
table starts pruning when there are more entries than twice this
minimum expected size. The idea is that if that case it hit then the
hash table is more than half full of useless pipelines so the
application is generating lots of redundant pipelines and it is a good
time to remove them.
Reviewed-by: Robert Bragg <robert@linux.intel.com>
(cherry picked from commit c21aac22992bb7fef5a8d0913130b8245e67f2eb)
Conflicts:
cogl/driver/gl/cogl-pipeline-fragend-glsl.c
cogl/driver/gl/cogl-pipeline-progend-glsl.c
cogl/driver/gl/cogl-pipeline-vertend-glsl.c
cogl/driver/gl/gl/cogl-pipeline-fragend-arbfp.c
The CoglPipelineCache is now extended to store templates for state
affecting vertex shaders and combined programs. The GLSL fragend,
vertend and progend now uses this to get cached shaders and a program.
When a new pipeline is created it will now get hashed three times if
the GLSL backends are in use (once for the fragend, once for the
vertend and once for the progend). Ideally we should add some way for
the progend to check its cache before the fragends and vertends are
checked so that it can bypass them entirely if it can find a cached
combined program.
The pipeline cache is now handled in CoglPipelineCache instead of
directly in the ARBfp fragend. The flags needed to hash a pipeline
should be exactly the same for the ARBfp and GLSL fragends so it's
convenient to share the code. The hash table now stores the actual
pipeline as the value instead of the private data so that the two
fragends can attach their data to it. That way it's possible to use
the same pipeline key with ancestors that are using different
fragends.
The hash table is created with g_hash_table_new_full to set a
destructor for the key and value and there is a destructor for
CoglPipelineCache that gets called when the CoglContext is
destroyed. That way we no longer leak the pipelines and shader state
when the context is desroyed.
