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std::condition_variable::wait_for

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Tema Biblioteca de ayuda
Threads
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Threads
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thread(C++11)
this_thread espacio de nombres
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this_thread namespace
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get_id(C++11)
yield(C++11)
sleep_for(C++11)
sleep_until(C++11)
Exclusión mutua
Original:
Mutual exclusion
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mutex(C++11)
timed_mutex(C++11)
Gestión de bloqueos genérico
Original:
Generic lock management
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lock_guard(C++11)
unique_lock(C++11)
defer_lock_t
try_to_lock_t
adopt_lock_t
(C++11)
(C++11)
(C++11)
lock(C++11)
try_lock(C++11)
defer_lock
try_to_lock
adopt_lock
(C++11)
(C++11)
(C++11)
Las variables de condición
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Condition variables
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condition_variable(C++11)
condition_variable_any(C++11)
notify_all_at_thread_exit(C++11)
cv_status(C++11)
Futuros
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Futures
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promise(C++11)
future(C++11)
shared_future(C++11)
packaged_task(C++11)
async(C++11)
launch(C++11)
future_status(C++11)
future_error(C++11)
future_category(C++11)
future_errc(C++11)
 
std::condition_variable
Las funciones miembro
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Member functions
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condition_variable::condition_variable
condition_variable::~condition_variable
Notificación
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Notification
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condition_variable::notify_one
condition_variable::notify_all
Espera
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Waiting
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condition_variable::wait
condition_variable::wait_for
condition_variable::wait_until
Identificador nativo
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Native handle
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condition_variable::native handle
 
template< class Rep, class Period >

std::cv_status wait_for( std::unique_lock<std::mutex>& lock,

                         const std::chrono::duration<Rep, Period>& rel_time);
(1) (desde C++11)
template< class Rep, class Period, class Predicate >

bool wait_for( std::unique_lock<std::mutex>& lock,
               const std::chrono::duration<Rep, Period>& rel_time,

               Predicate pred);
(2) (desde C++11)
1)
Atómicamente libera lock, bloquea el hilo de ejecución actual y lo agrega a la lista de temas que esperan en *this. El hilo se desbloqueará cuando notify_all() o notify_one() se ejecuta, o cuando expira el tiempo de espera rel_time relativa. También puede ser desbloqueado falsamente. Cuando se desbloquea, sin importar la razón, lock es readquirido y sale wait_for(). Si esta función sale a través de una excepción, también se volvió a adquirir lock .
Original:
Atomically releases lock, blocks the current executing thread, and adds it to the list of threads waiting on *this. The thread will be unblocked when notify_all() or notify_one() is executed, or when the relative timeout rel_time expires. It may also be unblocked spuriously. When unblocked, regardless of the reason, lock is reacquired and wait_for() exits. If this function exits via exception, lock is also reacquired.
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2)
Equivalente a
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Equivalent to
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while (!pred())
    if (wait_for(lock, rel_time) == std::cv_status::timeout)
        return pred();
return true;

Esta sobrecarga puede usarse para ignorar despertares espurias .
Original:
This overload may be used to ignore spurious awakenings.
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Contenido

[editar] Parámetros

lock -
un objeto de std::unique_lock<std::mutex> tipo, que debe ser bloqueado por el flujo actual
Original:
an object of type std::unique_lock<std::mutex>, which must be locked by the current thread
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rel_time -
un objeto de tipo std::chrono::duration que representa el tiempo máximo de espera para pasar
Original:
an object of type std::chrono::duration representing the maximum time to spend waiting
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pred - predicate which returns ​false
si la espera debe continuar
Original:
if the waiting should be continued
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.

The signature of the predicate function should be equivalent to the following:

 bool pred();

[editar] Valor de retorno

1)
std::cv_status::timeout si el tiempo de espera relativa especificada por rel_time expirado, std::cv_status::no_timeout overwise .
Original:
std::cv_status::timeout if the relative timeout specified by rel_time expired, std::cv_status::no_timeout overwise.
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2)
false si el predicado pred aún evalúa false tras el tiempo de espera caducado rel_time, de lo contrario true .
Original:
false if the predicate pred still evaluates to false after the rel_time timeout expired, otherwise true.
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[editar] Excepciones

Puede lanzar std::system_error, también pueden propagar excepciones producidas por lock.lock() o lock.unlock() .
Original:
May throw std::system_error, may also propagate exceptions thrown by lock.lock() or lock.unlock().
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[editar] Notas

Llamar a esta función si lock.mutex() no está bloqueado por el flujo actual es un comportamiento indefinido .
Original:
Calling this function if lock.mutex() is not locked by the current thread is undefined behavior.
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Llamar a esta función si lock.mutex() no es el mutex mismo que el utilizado por todos los otros subprocesos que están a la espera de la variable misma condición es un comportamiento no definido .
Original:
Calling this function if lock.mutex() is not the same mutex as the one used by all other threads that are currently waiting on the same condition variable is undefined behavior.
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[editar] Ejemplo

#include <iostream>
#include <atomic>
#include <condition_variable>
#include <thread>
#include <chrono>
 
std::condition_variable cv;
std::mutex cv_m;
std::atomic<int> i = ATOMIC_VAR_INIT(0);
 
void waits(int idx)
{
    std::unique_lock<std::mutex> lk(cv_m);
    if(cv.wait_for(lk, std::chrono::milliseconds(idx*100), [](){return i == 1;})) 
        std::cerr << "Thread " << idx << " finished waiting. i == " << i << '\n';
    else
        std::cerr << "Thread " << idx << " timed out. i == " << i << '\n';
}
 
void signals()
{
    std::this_thread::sleep_for(std::chrono::milliseconds(120));
    std::cerr << "Notifying...\n";
    cv.notify_all();
    std::this_thread::sleep_for(std::chrono::milliseconds(100));
    i = 1;
    std::cerr << "Notifying again...\n";
    cv.notify_all();
}
 
int main()
{
    std::thread t1(waits, 1), t2(waits, 2), t3(waits, 3), t4(signals);
    t1.join(); t2.join(), t3.join(), t4.join();
}

Output:

Thread 1 timed out. i == 0
Notifying...
Thread 2 timed out. i == 0
Notifying again...
Thread 3 finished waiting. i == 1

[editar] Ver también

Bloquea el subproceso actual hasta que la variable condición es despertado
Original:
blocks the current thread until the condition variable is woken up
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(miembro público función) [edit]
Bloquea el subproceso actual hasta que la variable condición es despertado o hasta que punto se especifica el tiempo ha sido alcanzada
Original:
blocks the current thread until the condition variable is woken up or until specified time point has been reached
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(miembro público función) [edit]