windows-osi-convertRToW-and-logging-optimizations-20080227

windows-osi-convertRToW-and-logging-optimizations-20080227

LICENSE MIT

Add lock_convertRToW which permits a read-lock to be upgraded to a
write lock.  If the caller is the only reader it permits a fast
transition otherwise it adds the caller to the waiters queue.

In the osi_Log macros, check to see if the log is enabled before making
the function call.  This avoids significant function call overhead.

In the cache manager, make use of the above.