уничтожить и инициализировать переменные условия (destroy and initialize condition variables)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
pthread_cond_destroy, pthread_cond_init — destroy and initialize
condition variables
Синопсис (Synopsis)
#include <pthread.h>
int pthread_cond_destroy(pthread_cond_t *cond);
int pthread_cond_init(pthread_cond_t *restrict cond,
const pthread_condattr_t *restrict attr);
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
Описание (Description)
The pthread_cond_destroy() function shall destroy the given
condition variable specified by cond; the object becomes, in
effect, uninitialized. An implementation may cause
pthread_cond_destroy() to set the object referenced by cond to an
invalid value. A destroyed condition variable object can be
reinitialized using pthread_cond_init(); the results of otherwise
referencing the object after it has been destroyed are undefined.
It shall be safe to destroy an initialized condition variable
upon which no threads are currently blocked. Attempting to
destroy a condition variable upon which other threads are
currently blocked results in undefined behavior.
The pthread_cond_init() function shall initialize the condition
variable referenced by cond with attributes referenced by attr.
If attr is NULL, the default condition variable attributes shall
be used; the effect is the same as passing the address of a
default condition variable attributes object. Upon successful
initialization, the state of the condition variable shall become
initialized.
See Section 2.9.9, Synchronization Object Copies and Alternative
Mappings for further requirements.
Attempting to initialize an already initialized condition
variable results in undefined behavior.
In cases where default condition variable attributes are
appropriate, the macro PTHREAD_COND_INITIALIZER can be used to
initialize condition variables. The effect shall be equivalent to
dynamic initialization by a call to pthread_cond_init() with
parameter attr specified as NULL, except that no error checks are
performed.
The behavior is undefined if the value specified by the cond
argument to pthread_cond_destroy() does not refer to an
initialized condition variable.
The behavior is undefined if the value specified by the attr
argument to pthread_cond_init() does not refer to an initialized
condition variable attributes object.
Возвращаемое значение (Return value)
If successful, the pthread_cond_destroy() and pthread_cond_init()
functions shall return zero; otherwise, an error number shall be
returned to indicate the error.
Ошибки (Error)
The pthread_cond_init() function shall fail if:
EAGAIN The system lacked the necessary resources (other than
memory) to initialize another condition variable.
ENOMEM Insufficient memory exists to initialize the condition
variable.
These functions shall not return an error code of [EINTR].
The following sections are informative.
Примеры (Examples)
A condition variable can be destroyed immediately after all the
threads that are blocked on it are awakened. For example,
consider the following code:
struct list {
pthread_mutex_t lm;
...
}
struct elt {
key k;
int busy;
pthread_cond_t notbusy;
...
}
/* Find a list element and reserve it. */
struct elt *
list_find(struct list *lp, key k)
{
struct elt *ep;
pthread_mutex_lock(&lp->lm);
while ((ep = find_elt(l, k) != NULL) && ep->busy)
pthread_cond_wait(&ep->notbusy, &lp->lm);
if (ep != NULL)
ep->busy = 1;
pthread_mutex_unlock(&lp->lm);
return(ep);
}
delete_elt(struct list *lp, struct elt *ep)
{
pthread_mutex_lock(&lp->lm);
assert(ep->busy);
... remove ep from list ...
ep->busy = 0; /* Paranoid. */
(A) pthread_cond_broadcast(&ep->notbusy);
pthread_mutex_unlock(&lp->lm);
(B) pthread_cond_destroy(&ep->notbusy);
free(ep);
}
In this example, the condition variable and its list element may
be freed (line B) immediately after all threads waiting for it
are awakened (line A), since the mutex and the code ensure that
no other thread can touch the element to be deleted.
Использование в приложениях (Application usage)
None.
Обоснование (Rationale)
If an implementation detects that the value specified by the cond
argument to pthread_cond_destroy() does not refer to an
initialized condition variable, it is recommended that the
function should fail and report an [EINVAL] error.
If an implementation detects that the value specified by the cond
argument to pthread_cond_destroy() or pthread_cond_init() refers
to a condition variable that is in use (for example, in a
pthread_cond_wait() call) by another thread, or detects that the
value specified by the cond argument to pthread_cond_init()
refers to an already initialized condition variable, it is
recommended that the function should fail and report an [EBUSY]
error.
If an implementation detects that the value specified by the attr
argument to pthread_cond_init() does not refer to an initialized
condition variable attributes object, it is recommended that the
function should fail and report an [EINVAL] error.
See also pthread_mutex_destroy(3p).
Будущие направления (Future directions)
None.
Смотри также (See also)
pthread_cond_broadcast(3p), pthread_cond_timedwait(3p),
pthread_mutex_destroy(3p)
The Base Definitions volume of POSIX.1‐2017, pthread.h(0p)
