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std::defer_lock, std::try_to_lock, std::adopt_lock

提供: cppreference.com
< cpp‎ | thread

constexpr std::defer_lock_t defer_lock = std::defer_lock_t();
(C++11およびそれ以降)
constexpr std::try_to_lock_t try_to_lock = std::try_to_lock_t();
(C++11およびそれ以降)
constexpr std::adopt_lock_t adopt_lock = std::adopt_lock_t();
(C++11およびそれ以降)

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.

タイプ
Original:
Type
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Effect(s)
defer_lock_t
ミューテックスの所有権を取得するものではありません
Original:
do not acquire ownership of the mutex
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try_to_lock_t
ブロックせずに、ミューテックスの所有権を取得しよう
Original:
try to acquire ownership of the mutex without blocking
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adopt_lock_t
呼び出し元のスレッドが既にミューテックスの所有権を持っていると仮定する
Original:
assume the calling thread already has ownership of the mutex
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[編集]

#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();
}


[編集] も参照してください

ロック·ストラテジーを指定するために使用されるタグの種類
Original:
tag type used to specify locking strategy
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(クラス) [edit]
オプションで、任意のミューテックスをロックして、lock_guardを構築します
Original:
constructs a lock_guard, optionally locking the given mutex
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(パブリックメンバ関数of std::lock_guard) [edit]
必要に応じて付属のミューテックスをロックして、unique_lockを構築します
Original:
constructs a unique_lock, optionally locking the supplied mutex
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(パブリックメンバ関数of std::unique_lock) [edit]