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std::condition_variable::wait

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Biblioteca de suporte a discussão
Threads
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Threads
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thread(C++11)
this_thread namespace
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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)
Exclusão mútua
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Mutual exclusion
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mutex(C++11)
timed_mutex(C++11)
Gestão de bloqueio 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)
Variáveis ​​de condição
Original:
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
Funções de membro
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Member functions
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condition_variable::condition_variable
condition_variable::~condition_variable
Notificação
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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
 
void wait( std::unique_lock<std::mutex>& lock );
(1) (a partir do C++ 11)
template< class Predicate >
void wait( std::unique_lock<std::mutex>& lock, Predicate pred );
(2) (a partir do C++ 11)
wait faz com que o thread atual para bloquear até que a variável de condição é notificado ou um despertar espúria ocorre, opcionalmente looping até que algum predicado é satisfeito.
Original:
wait causes the current thread to block until the condition variable is notified or a spurious wakeup occurs, optionally looping until some predicate is satisfied.
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1)
Atomicamente libera lock, bloqueia a thread atual em execução, e acrescenta-lo à lista de espera da thread em *this. A discussão será desbloqueado quando notify_all() ou notify_one() é executado. Também pode ser desbloqueado spuriously. Quando desbloqueado, independentemente do motivo, lock é readquirido e sai wait. Se esta função saídas via de exceção, lock também é readquirida.
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. It may also be unblocked spuriously. When unblocked, regardless of the reason, lock is reacquired and wait exits. If this function exits via exception, lock is also reacquired.
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2)
Equivalente a
Original:
Equivalent to
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while (!pred()) {
  wait(lock);
}

Essa sobrecarga pode ser usada para ignorar despertares espúrias enquanto espera por uma condição específica a ser verdade.
Original:
This overload may be used to ignore spurious awakenings while waiting for a specific condition to become true.
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Índice

[editar] Parâmetros

lock -
um objeto de std::unique_lock<std::mutex> tipo, que deve ser bloqueado pelo thread atual
Original:
an object of type std::unique_lock<std::mutex>, which must be locked by the current thread
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pred - predicate which returns ​false
se o tempo de espera deve ser continuado
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

(Nenhum)
Original:
(none)
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[editar] Exceções

Pode lançar std::system_error, também podem propagar exceções lançadas por lock.lock() ou 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

Chamar essa função se lock.mutex() não está bloqueada pelo atual segmento é um comportamento indefinido.
Original:
Calling this function if lock.mutex() is not locked by the current thread is undefined behavior.
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Chamar essa função se lock.mutex() não é o mesmo mutex como o utilizado por todos os outros segmentos que estão aguardando na variável mesma condição é um comportamento indefinido.
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] Exemplo

[edit]
#include <iostream>
#include <condition_variable>
#include <thread>
#include <chrono>
 
std::condition_variable cv;
std::mutex cv_m;
int i = 0;
 
void waits()
{
    std::unique_lock<std::mutex> lk(cv_m);
    std::cerr << "Waiting... \n";
    cv.wait(lk, [](){return i == 1;});
    std::cerr << "...finished waiting. i == 1\n";
}
 
void signals()
{
    std::this_thread::sleep_for(std::chrono::seconds(1));
    std::cerr << "Notifying...\n";
    cv.notify_all();
    std::this_thread::sleep_for(std::chrono::seconds(1));
    i = 1;
    std::cerr << "Notifying again...\n";
    cv.notify_all();
}
 
int main()
{
    std::thread t1(waits), t2(waits), t3(waits), t4(signals);
    t1.join(); 
    t2.join(); 
    t3.join();
    t4.join();
}

Output:

Waiting...
Waiting...
Waiting...
Notifying...
Notifying again...
...finished waiting. i == 1
...finished waiting. i == 1
...finished waiting. i == 1

[editar] Veja também

Bloqueia o segmento atual até que a variável de condição é acordado ou após o período de tempo limite especificado
Original:
blocks the current thread until the condition variable is woken up or after the specified timeout duration
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(função pública membro) [edit]
bloqueia o segmento atual até que a variável de condição é acordado ou até ponto de tempo especificado foi alcançado
Original:
blocks the current thread until the condition variable is woken up or until specified time point has been reached
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(função pública membro) [edit]