Namespace
Varianti

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

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
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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)
 
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
Original:
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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[modifica] 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();
}


[modifica] Vedi anche

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