QSemaphore: Improve waking up on 64-bit Linux

By judiciously positioning of the bits, we can optimize for the case of
threads trying to acquire a single token, which is what QSemaphore
should be mostly used for, as it matches the POSIX Semaphore API
(sem_wait, sem_timedwait and sem_trywait). If there are only waiters
waiting for a single token, we know that adding n tokens means n threads
can wake up.

This optimizes for multi-token waiters too. For example, if we have 50
single-token waiters and 50 multi-token waiters, a sem.release(5) will
wake up 55 threads instead of 100.

Change-Id: I209fcd5dbc2b4e5381cffffd14de5550c75d2600
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

0 files changed, 0 insertions, 0 deletions