std::defer_lock_t, std::try_to_lock_t, std::adopt_lock_t
From cppreference.com
struct defer_lock_t { };
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(since C++11) | |
struct try_to_lock_t { };
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(since C++11) | |
struct adopt_lock_t { };
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(since C++11) | |
std::defer_lock_t
, std::try_to_lock_t
and std::adopt_lock_t
are empty struct tag types used to specify locking strategy for std::lock_guard, std::unique_lock and std::shared_lock.
Type | Effect(s) |
defer_lock_t
|
do not acquire ownership of the mutex |
try_to_lock_t
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try to acquire ownership of the mutex without blocking |
adopt_lock_t
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assume the calling thread already has ownership of the mutex |
[edit] Example
Run this code
#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<std::mutex> lock1(from.m, std::adopt_lock); std::lock_guard<std::mutex> 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, std::ref(my_account), std::ref(your_account), 10); std::thread t2(transfer, std::ref(your_account), std::ref(my_account), 5); t1.join(); t2.join(); }
[edit] See also
(C++11)(C++11)(C++11)
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tag constants used to specify locking strategy (constant) |
constructs a lock_guard, optionally locking the given mutex (public member function of std::lock_guard )
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constructs a unique_lock , optionally locking the supplied mutex (public member function of std::unique_lock )
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