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std::condition_variable::wait_for

Da cppreference.com.

 
 
Discussione libreria di supporto
Threads
Original:
Threads
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thread(C++11)
this_thread spazio dei nomi
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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)
Mutua esclusione
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Mutual exclusion
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mutex(C++11)
timed_mutex(C++11)
Blocco di gestione generico
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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)
Condizioni variabili
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)
Futures
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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
Membri funzioni
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Member functions
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condition_variable::condition_variable
condition_variable::~condition_variable
Notifica
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Notification
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condition_variable::notify_one
condition_variable::notify_all
In attesa
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Waiting
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condition_variable::wait
condition_variable::wait_for
condition_variable::wait_until
Maniglia 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) (dal 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) (dal C++11)
1)
Rilascia atomico lock, blocca il thread corrente di esecuzione, e lo aggiunge alla lista di thread in attesa su *this. Il filo sarà sbloccato quando notify_all() o notify_one() viene eseguito, o quando il timeout rel_time relativa scadenza. Essa può anche essere sbloccato spurio. Quando sbloccato, indipendentemente dal motivo, lock è riacquisito ed esce wait_for(). Se questa funzione termina via eccezionale, lock anche riacquistata.
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
Original:
Equivalent to
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while (!pred())
    if (wait_for(lock, rel_time) == std::cv_status::timeout)
        return pred();
return true;

Questo sovraccarico può essere utilizzato per ignorare risvegli spurie.
Original:
This overload may be used to ignore spurious awakenings.
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Indice

[modifica] Parametri

lock -
un oggetto di std::unique_lock<std::mutex> tipo, che deve essere bloccato dal thread corrente
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 oggetto di std::chrono::duration tipo che rappresenta il tempo massimo di attesa di spendere
Original:
an object of type std::chrono::duration representing the maximum time to spend waiting
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pred - predicate which returns ​false
se l'attesa deve essere continuato
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();

[modifica] Valore di ritorno

1)
std::cv_status::timeout se il timeout relativo specificato da rel_time scaduto, 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 se il pred predicato restituisce ancora false dopo il timeout rel_time scaduto, altrimenti true.
Original:
false if the predicate pred still evaluates to false after the rel_time timeout expired, otherwise true.
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[modifica] Eccezioni

Può lanciare std::system_error, può anche propagare eccezioni generate dal 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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[modifica] Note

Chiamare questa funzione se lock.mutex() non è bloccato dal thread corrente è un comportamento indefinito.
Original:
Calling this function if lock.mutex() is not locked by the current thread is undefined behavior.
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Chiamare questa funzione se lock.mutex() non è lo stesso mutex come quello utilizzato da tutti gli altri thread che sono attualmente in attesa sulla variabile stessa condizione è un comportamento indefinito.
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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[modifica] Esempio

#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

[modifica] Vedi anche

blocca il thread corrente fino a quando la variabile di condizione è svegliato
Original:
blocks the current thread until the condition variable is woken up
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(membro pubblico funzione) [edit]
blocca il thread corrente fino a quando la variabile di condizione è svegliato o fino a che punto nel tempo specificato è stato raggiunto
Original:
blocks the current thread until the condition variable is woken up or until specified time point has been reached
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(membro pubblico funzione) [edit]