Replace the reader concurrency semaphores for user reads and view
updates with the newly introduced reader concurrency semaphore group,
which assigns a semaphore for each service level.
Each group is statically assigned to some pool of memory on startup and
dynamically distribute this memory between the semaphores, relative to
the number of shares of the corresponding scheduling group.
The intent of having a separate reader concurrency semaphore for each
scheduling group is to prevent priority inversion issues due to reads
with different priorities waiting on the same semaphore, as well as make
memory allocation more fair between service levels due to the adjusted
number of shares.
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