* Added a config hook for secret key into the app.
the server first looks in an environment variable,
then looks in a config file.
For the cellxgene launch app, a default key is used if none is provided.
For the eb app, a secret key must be provided.
* Improved fix for matrix cache handling.
During the MatrixDataCacheItem acquire function there was a
time when the write lock was released and the read lock was taken.
During that time, the dataset could have been deleted, later
result in the MatrixDataCacheManageri data adaptor returning None.
The solution is to demote the writer lock to a reader lock instead
of unlocking and relocking.
Also, when a the cache needs to delete an entry, the delete
is done outside the MatrixDataCacheManager lock. This operation
only requires the write lock for the MatrixDataCacheItem.
Fixes#1255
* Introduce a config file to cellxgene
The config file format is in yaml. The default config is located
in server/common/default_config.py. A user may create a yaml file
that contains a subset of these fields. It can be used during cellxgene
launch, or for hosted cellxgene.
The code has also been refactored. Much of the logic to check arguments
has moved from launch to app config.
It is now possible to set the tiledb context parameters using the config
file. Other feature will soon be handled in a similar way.
Bruce Martin