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 pipeline cache contains three separate hash tables, one for the
state affecting the vertex shaders, one for the fragment shaders and
one for the resulting combined program. Previously these hash tables
had a fair bit of duplicated code to calculate the hashes, check for
equality and copy the pipeline when it is added. This patch moves the
common bits of code to a new type called CoglPipelineHashTable which
just wraps a GHashTable with a given set of state flags to use for
hashing and checking for equality.
Reviewed-by: Robert Bragg <robert@linux.intel.com>
(cherry picked from commit 402796430c839038339e531363b8c2463f9b2a9e)
Conflicts:
cogl/Makefile.am
