em/use_sema_lock is a SAP Parameter attribute which is used to control Use OS semaphore for internal EM/ES locking information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
The parameter enables you to use a semaphore instead of a spinlock for
process synchronization in extended memory administration.
Although spinlocks are considerably faster than semaphores, they cause
certain problems upon recovery from work process crashes. The parameter
can also be used as a workaround if other problems with spinlocks occur.
Possible Values
TRUE - Operating system semaphore is used
FALSE - Spinlock is used
See SAP Parameter Documentation for full SAP documentation for this profile parameter.