Varianti

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

    Da cppreference.com.

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    <metanoindex/>

     
    C++
     
    Discussione libreria di supporto
    Threads
    Original:
    Threads
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    thread(C++11)
    this_thread spazio dei nomi
    Original:
    this_thread namespace
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    get_id(C++11)
    yield(C++11)
    sleep_for(C++11)
    sleep_until(C++11)
    Mutua esclusione
    Original:
    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
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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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    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)
     
    <tbody> </tbody>
    constexpr std::defer_lock_t defer_lock = std::defer_lock_t();
    		 (dal C++11)
    constexpr std::try_to_lock_t try_to_lock = std::try_to_lock_t();
    		 (dal C++11)
    constexpr std::adopt_lock_t adopt_lock = std::adopt_lock_t();
    		 (dal 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.

    Tipo
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    Type
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    		 Effect(s)
    defer_lock_t
    non acquisire la proprietà del mutex
    Original:
    do not acquire ownership of the mutex
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    try_to_lock_t
    cercare di acquisire la proprietà del mutex senza bloccare
    Original:
    try to acquire ownership of the mutex without blocking
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    adopt_lock_t
    assumere il thread chiamante ha già la proprietà del mutex
    Original:
    assume the calling thread already has ownership of the mutex
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    Esempio

    [edit]
    #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();
}


    Vedi anche
    tipo di tag utilizzato per specificare strategia di blocco
    Original:
    tag type used to specify locking strategy
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    (classe) [modifica]
    costruisce un lock_guard, opzionalmente bloccare il mutex dato
    Original:
    constructs a lock_guard, optionally locking the given mutex
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    (metodo pubblico) [modifica]
    costruisce un unique_lock, eventualmente bloccare il mutex in dotazione
    Original:
    constructs a unique_lock, optionally locking the supplied mutex
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    (metodo pubblico) [modifica]