Namespace
Varianti

std::condition_variable

Da cppreference.com.
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Discussione libreria di supporto
Threads
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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
 
Defined in header <condition_variable>
class condition_variable;
(dal C++11)
La classe condition_variable è una primitiva di sincronizzazione che può essere utilizzato per bloccare un filo, o più thread contemporaneamente, fino:
Original:
The condition_variable class is a synchronization primitive that can be used to block a thread, or multiple threads at the same time, until:
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  • una notifica viene ricevuta da un altro thread
    Original:
    a notification is received from another thread
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  • un timeout scade, o
    Original:
    a timeout expires, or
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  • un wakeup spurie verifica
    Original:
    a wakeup spurie occurs
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Qualsiasi thread che intende aspettare std::condition_variable deve acquisire una std::unique_lock prima. Le operazioni di attesa atomicamente rilasciare il mutex e sospendere l'esecuzione del thread. Quando la variabile di condizione è notificato, il filo si risveglia, e il mutex viene riacquisito.
Original:
Any thread that intends to wait on std::condition_variable has to acquire a std::unique_lock first. The wait operations atomically release the mutex and suspend the execution of the thread. When the condition variable is notified, the thread is awakened, and the mutex is reacquired.
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La classe è un std::condition_variable StandardLayoutType. Non è CopyConstructible, MoveConstructible, CopyAssignable, MoveAssignable.
Original:
The class std::condition_variable is a StandardLayoutType. It is not CopyConstructible, MoveConstructible, CopyAssignable, MoveAssignable.
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Indice

[modifica] Membri tipi

Membro tipo
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Member type
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Definition
native_handle_type
Implementazione definita
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implementation-defined
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[modifica] Membri funzioni

Costruisce l'oggetto
Original:
constructs the object
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(membro pubblico funzione) [edit]
distrugge l'oggetto
Original:
destructs the object
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(membro pubblico funzione) [edit]
operator=
[cancellato]
non copia-assegnabile
Original:
not copy-assignable
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(membro pubblico funzione) [edit]
Notifica
Original:
Notification
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segnala un thread in attesa
Original:
notifies one waiting thread
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(membro pubblico funzione) [edit]
informa tutti i thread in attesa
Original:
notifies all waiting threads
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(membro pubblico funzione) [edit]
In attesa
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Waiting
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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 dopo la durata del timeout specificato
Original:
blocks the current thread until the condition variable is woken up or after the specified timeout duration
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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]
Maniglia nativo
Original:
Native handle
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restituisce l'handle nativo
Original:
returns the native handle
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(membro pubblico funzione) [edit]

[modifica] Esempio

#include <condition_variable>
#include <mutex>
#include <thread>
#include <iostream>
#include <queue>
#include <chrono>
 
int main()
{
    std::queue<int> produced_nums;
    std::mutex m;
    std::condition_variable cond_var;
    bool done = false;
    bool notified = false;
 
    std::thread producer([&]() {
        for (int i = 0; i < 5; ++i) {
            std::this_thread::sleep_for(std::chrono::seconds(1));
            std::unique_lock<std::mutex> lock(m);
            std::cout << "producing " << i << '\n';
            produced_nums.push(i);
            notified = true;
            cond_var.notify_one();
        }   
 
        done = true;
        cond_var.notify_one();
    }); 
 
    std::thread consumer([&]() {
        std::unique_lock<std::mutex> lock(m);
        while (!done) {
            while (!notified) {  // loop to avoid spurious wakeups
                cond_var.wait(lock);
            }   
            while (!produced_nums.empty()) {
                std::cout << "consuming " << produced_nums.front() << '\n';
                produced_nums.pop();
            }   
            notified = false;
        }   
    }); 
 
    producer.join();
    consumer.join();
}

Possible output:

producing 0
consuming 0
producing 1
consuming 1
producing 2
consuming 2
producing 3
consuming 3
producing 4
consuming 4