pthread_cond_init(3-thr) pthread_cond_init(3-thr)
NAME
pthreadcondinit - creates a condition variable
SYNOPSIS
#include <pthread.h>
int pthreadcondinit(
pthreadcondt *cond,
pthreadcondattrt attr);
PARAMETERS
cond Condition variable that is created.
attr Condition variable attributes object that defines the
characteristics of the condition variable created. If you
specify pthreadcondattrdefault, default attributes are
used.
DESCRIPTION
The pthreadcondinit() 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
predicate might have become true. The broadcast operation indicates
that all waiting threads need to 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 predi-
cate 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
associated with a single mutex, each representing a different predi-
cate of the shared data protected by that mutex.
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pthread_cond_init(3-thr) pthread_cond_init(3-thr)
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 the function fails, errno may be set to one of the following
values:
EAGAIN The system lacks the necessary resources to initialize
another condition variable.
EINVAL Invalid attributes object.
ENOMEM Insufficient memory exists to initialize the condition vari-
able.
SEE ALSO
pthreadcondbroadcast(3-thr), pthreadconddestroy(3-thr),
pthreadcondsignal(3-thr), pthreadcondtimedwait(3-thr),
pthreadcondwait(3-thr).
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