TASKBLOCK(3P)							 TASKBLOCK(3P)

NAME    [Toc]    [Back]

     taskblock,	taskunblock, tasksetblockcnt - routines	to block/unblock tasks

C SYNOPSIS    [Toc]    [Back]

     #include <sys/types.h>
     #include <task.h>

     int taskblock (tid_t tid);

     int taskunblock (tid_t tid);

     int tasksetblockcnt (tid_t	tid, int count);

DESCRIPTION    [Toc]    [Back]

     These routines provide a complete set of blocking/unblocking capabilities
     for tasks.	 Blocking is implemented via a counting	semaphore in the
     system.  Each call	to taskblock decrements	the count and, if it goes
     negative, the task	is suspended.  When taskunblock	is called, the count
     is	incremented, and if it goes positive (or zero),	the task is restarted.
  This provides both a simple, race free synchronization ability
     between two tasks,	as well	as a much more powerful	capability to
     synchronize multiple tasks.

     In	order to guarantee a known starting place the tasksetblockcnt function
     may be called which will force the	semaphore count	to the value given by
     count. New	tasks have their semaphore zeroed.  Normally, count should be
     set to 0.	If the resulting block count is	greater	than or	equal to zero
     and the task is currently blocked,	it will	be unblocked.  If the
     resulting block count is less than	zero, the task will be blocked.	 Using
     this, a simple rendezvous mechanism can be	set up.	 If one	task wanted to
     wait for n	other tasks to complete, it could set its block	count to -n.
     This would	immediately force the task to block.  Then as each task
     finishes it unblocks the waiting task.  When the n'th task	finishes the
     waiting task will be woken.

     A task may	block another task provided that standard UNIX permissions are
     satisfied.

     These routines will fail and no operation will be performed if one	or
     more of the following are true:

     [EINVAL]
	  The tid specified is not a valid task	id.

     [EPERM]
	  The caller is	not operating on itself, its effective user ID is not
	  super-user, and its real or effective	user ID	does not match the
	  real or effective user ID of the to be acted on task.







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TASKBLOCK(3P)							 TASKBLOCK(3P)



SEE ALSO
     blockproc(2), taskdestroy(3P), taskctl(3P), taskcreate(3P).

DIAGNOSTICS    [Toc]    [Back]

     Upon successful completion, 0 is returned.	 Otherwise, a value of -1 is
     returned to the calling task, and errno is	set to indicate	the error.


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