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std::adopt_lock_t
struct adopt_lock_t {};
constexpr adopt_lock_t adopt_lock {};
是一个空类，作为adopt_lock类型
对unique_lock or lock_guard的建造含糊，将adopt_lock作为参数传递，使object不要锁互斥量，并且假定互斥量已经被
当前线程锁住
std::defer_lock_t
struct defer_lock_t {};
是一个空类，used as the type of defer_lock
constexpr defer_lock_t defer_lock {};
对unique_lock的构造函数传递defer_lock，使它不要在构建阶段自动的锁定metex lock，
初始化对象as not owning a lock
std::try_to_lock_t
struct try_to_lock_t {};
是一个空类，used as the tyep of tyr_to_lock
constexpr try_to_lock_t try_to_lock {};
向unique_lock传递try_to_lock参数，使得它调用try_lock成员函数，而不是lock函数图lock the mutex object;
std::mutex foo, bar;void TaskA() {std::lock (foo, bar); //simultaneous lock prevent deadlockunique_lock<std::mutex> lck1(foo, std::adopt_lock);unique_lock<std::mutex> lck2 (bar, std::adopt_lock);std::cout<<"TaskA"<<std::endl;//unlock automatically on destruction of lck1, lck2;
}
void TaskB() { // foo.lock(); bar.lock();unique_lock<mutex> lck1, lck2;lck1 = unique_lock<mutex>(foo, std::defer_lock);lck2 = unique_lock<mutex> (bar, std::defer_lock);std::lock(lck1, lck2); // simultaneous lock prevent deadlockcout<<"TaskB"<<endl;
}| value | description |
|---|---|
| (no tag) | Lock on construction by calling member lock. |
| try_to_lock | Attempt to lock on construction by calling member try_lock |
| defer_lock | Do not lock on construction (and assume it is not already locked by thread) |
| adopt_lock | Adopt current lock (assume it is already locked by thread). |
try_to_lock_t, defer_lock_t and adopt_lock_t are the types of objects try_to_lock, defer_lock and adopt_lock, respectively.
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