pthread_cond_init man page on Ultrix

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pthread_cond_init(3thr)				       pthread_cond_init(3thr)

Name
       pthread_cond_init - Creates a condition variable.

Syntax
       #include <pthread.h>

       int pthread_cond_init (ond, attr)
       pthread_cond_t *cond;
       pthread_condattr_t attr;

Arguments
       cond    Condition variable that is created.

       attr    Condition  variable  attributes object that defines the charac‐
	       teristics of the condition variable created.   If  you  specify
	       pthread_condattr_default, default attributes are used.

Description
       This  routine creates and initializes a condition variable. A condition
       variable is a synchronization object used in conjunction with a	mutex.
       A  mutex	 controls  access  to shared data; a condition variable allows
       threads to wait for that data to enter a defined state.	The  state  is
       defined by a Boolean expression called a predicate.

       A condition variable is signaled or broadcast to indicate that a predi‐
       cate might have become true. The broadcast operation indicates that all
       waiting	threads should resume and reevaluate the predicate. The signal
       operation is used when any one waiting thread can continue.

       If a thread that holds a mutex determines that the shared data  is  not
       in the correct state for it to proceed (the associated predicate is not
       true), it waits on a condition variable	associated  with  the  desired
       state.  Waiting	on  the	 condition variable automatically releases the
       mutex so that other threads can modify or examine the shared data. When
       a  thread  modifies  the	 state	of the shared data so that a predicate
       might be true, it signals or broadcasts on  the	appropriate  condition
       variable so that threads waiting for that predicate can continue.

       It  is  important  that	all  threads waiting on a particular condition
       variable at any time hold the same mutex.  If they do not, the behavior
       of  the	wait operation is unpredictable (an implementation can use the
       mutex to control internal access to  the	 condition  variable  object).
       However,	 it  is	 legal	for  a client to store condition variables and
       mutexes and later reuse them in different combinations. The client must
       ensure  that  no threads use the condition variable with the old mutex.
       At any time, an arbitrary number of condition variables can be  associ‐
       ated  with  a  single mutex, each representing a different predicate of
       the shared data protected by that mutex.

       Condition variables are not owned by a particular thread.  Any  associ‐
       ated  storage is not automatically deallocated when the creating thread
       terminates.

Return Values
       If an error condition occurs, this routine returns  -1,	the  condition
       variable	 is  not  initialized, and the contents of cond are undefined.
       This routine sets errno to  the	corresponding  error  value.  Possible
       return values are as follows.

       Return	Error	   Description

       0		   Successful  comple‐
			   tion.

       -1	[EAGAIN]   The	system	 lacks
			   the	     necessary
			   resources  to  ini‐
			   tialize     another
			   condition variable.

			   The	system-imposed
			   limit  on the total
			   number of condition
			   variables	 under
			   execution by a sin‐
			   gle	   user	    is
			   exceeded.

       -1	[ENOMEM]   Insufficient memory
			   exists  to initial‐
			   ize	the  condition
			   variable.

						       pthread_cond_init(3thr)
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