USEMA(7M)                                                            USEMA(7M)


NAME
     usema, usemaclone - software semaphore driver

DESCRIPTION
     The usema driver manages the allocation and operation of counting
     semaphores that are used as the basis of spinlocks and semaphores.

     The usemaclone device allocates a new semaphore device, and returns a
     file handle to it.  Other processes can attach to that semaphore using an
     ioctl operation on the usema device.  The driver provides atomic blocking
     and unblocking services.  Blocking can be either interruptible or not.
     The driver also provides for asynchronous blocking and later polling to
     inquire whether a given semaphore is available.  This polling is
     available through the standard poll(2) and select(2) mechanisms.

CAVEATS
     The usema driver is intended to be used only by the standard library
     spinlock and semaphore routines.  Client programs should use these
     routines, rather than using usema directly.

FILES
     /dev/usema

     /dev/usemaclone

SEE ALSO
     poll(2), select(2), usinit(3P), usnewlock(3P), usnewsema(3P).


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