c++多线程，adopt_lock_t/defer_lock_t/try_to_lock_t

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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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