USEMA(7M)							     USEMA(7M)

NAME    [Toc]    [Back]

     usema, usemaclone - software semaphore driver

DESCRIPTION    [Toc]    [Back]

     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    [Toc]    [Back]

     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    [Toc]    [Back]

     /dev/usema

     /dev/usemaclone

SEE ALSO    [Toc]    [Back]

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


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