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std::condition_variable

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Thema Support-Bibliothek
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)
Gegenseitigen Ausschluss
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Mutual exclusion
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mutex(C++11)
timed_mutex(C++11)
Generische Sperrverwaltung
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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)
Zustand Variablen
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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)
Futures
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Futures
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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
Member-Funktionen
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Member functions
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condition_variable::condition_variable
condition_variable::~condition_variable
Notification
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Notification
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condition_variable::notify_one
condition_variable::notify_all
Warten
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Waiting
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condition_variable::wait
condition_variable::wait_for
condition_variable::wait_until
Ureinwohner Griff
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Native handle
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condition_variable::native handle
 
Defined in header <condition_variable>
class condition_variable;
(seit C++11)

Die condition_variable Klasse ist ein grundlegendes Synchronisierungsmittel das verwendet werden kann, um einen Thread oder mehrere Threads gleichzeitig zu blockieren, bis:

  • eine Benachrichtigung von einem anderen Thread empfangen wird
  • es zu einer Zeitüberschreitung kommt, oder
  • ein spurious wakeup auftritt

Jeder Thread, der auf einer std::condition_variable warten möchte, muss zuerst ein std::unique_lock erwerben. Die wait-Operationen geben den gelockten Mutex atomar frei und pausieren den aktuellen Thread. Wenn die condition-Variable benachrichtigt wird, wird der Thread geweckt, und der Mutex wieder gelockt.

Die Klasse std::condition_variable ist ein StandardLayoutType. Sie ist nicht CopyConstructible, MoveConstructible, CopyAssignable, MoveAssignable.

Inhaltsverzeichnis

[Bearbeiten] Member-Typen

Member-Typ Definition
native_handle_type implementierungsabhängig

[Bearbeiten] Member-Funktionen

Baut das Objekt
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constructs the object
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(öffentliche Elementfunktion) [edit]
zerstört sich das Objekt
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destructs the object
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(öffentliche Elementfunktion) [edit]
operator=
[gelöscht]
nicht kopieren übertragbar
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not copy-assignable
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(öffentliche Elementfunktion) [edit]
Benachrichtigen
Informiert einen wartenden Thread
(öffentliche Elementfunktion) [edit]
Benachrichtigt alle wartenden Threads
(öffentliche Elementfunktion) [edit]
Warten
Blockiert den aktuellen Thread, bis die condition variable geweckt wird
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blocks the current thread until the condition variable is woken up
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(öffentliche Elementfunktion) [edit]
Blockiert den aktuellen Thread, bis die condition variable geweckt wird oder die angegebenene Zeitspanne abgelaufen ist
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blocks the current thread until the condition variable is woken up or after the specified timeout duration
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(öffentliche Elementfunktion) [edit]
Blockiert den aktuellen Thread, bis die condition variable geweckt wird oder bis der angegebenene Zeitpunkt erreicht wurde
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blocks the current thread until the condition variable is woken up or until specified time point has been reached
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(öffentliche Elementfunktion) [edit]
Native Handle
gibt das systemeigene Handle zurück
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returns the native handle
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(öffentliche Elementfunktion) [edit]

[Bearbeiten] Beispiel

#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;
        notified = 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