std::defer_lock, std::try_to_lock, std::adopt_lock
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<tbody> </tbody> constexpr std::defer_lock_t defer_lock = std::defer_lock_t(); |
(seit C++11) | |
constexpr std::try_to_lock_t try_to_lock = std::try_to_lock_t(); |
(seit C++11) | |
constexpr std::adopt_lock_t adopt_lock = std::adopt_lock_t(); |
(seit C++11) | |
std::defer_lock, std::try_to_lock and std::adopt_lock are instances of empty struct tag types std::defer_lock_t, std::try_to_lock_t and std::adopt_lock_t respectively.
They are used to specify locking strategies for std::lock_guard and std::unique_lock.
Type
Original: Type The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. |
Effect(s) |
defer_lock_t
|
nicht erwerben Besitz des Mutex
Original: do not acquire ownership of the mutex The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. |
try_to_lock_t
|
versuchen Besitz des Mutex ohne Blockierung zu erwerben
Original: try to acquire ownership of the mutex without blocking The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. |
adopt_lock_t
|
nehmen den aufrufenden Thread hat bereits Besitz des Mutex
Original: assume the calling thread already has ownership of the mutex The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. |
Beispiel
#include <mutex>
#include <thread>
struct bank_account {
explicit bank_account(int balance) : balance(balance) {}
int balance;
std::mutex m;
};
void transfer(bank_account &from, bank_account &to, int amount)
{
// attempt to lock both mutexes without deadlock
std::lock(from.m, to.m);
// make sure both already-locked mutexes are unlocked when
// we're done; if we just used the lock_guard without std::lock
// and std::adopt_lock, we might deadlock with other calls to transfer
std::lock_guard lock1(from.m, std::adopt_lock);
std::lock_guard lock2(to.m, std::adopt_lock);
from.balance -= amount;
to.balance += amount;
}
int main()
{
bank_account my_account(100);
bank_account your_account(50);
std::thread t1(transfer, my_account, your_account, 10);
std::thread t2(transfer, your_account, my_account, 5);
t1.join();
t2.join();
}