std::defer_lock, std::try_to_lock, std::adopt_lock, std::defer_lock_t, std::try_to_lock_t, std::adopt_lock_t
来自cppreference.com
在标头 <mutex> 定义 | ||
struct defer_lock_t {explicit defer_lock_t()=default;}; | (1) | (C++11 起) |
constexprstd::defer_lock_t defer_lock {}; | (2) | (C++11 起) (C++17 起 inline) |
struct try_to_lock_t {explicit try_to_lock_t()=default;}; | (3) | (C++11 起) |
constexprstd::try_to_lock_t try_to_lock {}; | (4) | (C++11 起) (C++17 起 inline) |
struct adopt_lock_t {explicit adopt_lock_t()=default;}; | (5) | (C++11 起) |
constexprstd::adopt_lock_t adopt_lock {}; | (6) | (C++11 起) (C++17 起 inline) |
1,3,5) 空类标签类型
std::defer_lock_t、std::try_to_lock_t 和 std::adopt_lock_t 可在 std::unique_lock 和 std::shared_lock 的构造函数形参列表中使用，以指定锁定策略。2,4,6)(1,3,5) 的相应实例
std::defer_lock、std::try_to_lock 和 std::adopt_lock 可以用于传递给构造函数以标明锁定策略的类型。类模板 std::lock_guard 仅有一个构造函数接受标签 std::adopt_lock。
| 类型 | 效果 |
defer_lock_t | 不获得互斥体的所有权 |
try_to_lock_t | 尝试获得互斥体的所有权而不阻塞 |
adopt_lock_t | 假设调用方线程已拥有互斥体的所有权 |
[编辑]示例
运行此代码
#include <iostream>#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){if(&from ==&to)// 避免自我转账情况中的死锁return; // 锁定两个互斥体而不死锁std::lock(from.m, to.m);// 保证两个已锁定互斥体在作用域结尾解锁std::lock_guard<std::mutex> lock1(from.m, std::adopt_lock);std::lock_guard<std::mutex> lock2(to.m, std::adopt_lock); // 等价方法：// std::unique_lock<std::mutex> lock1(from.m, std::defer_lock);// std::unique_lock<std::mutex> lock2(to.m, std::defer_lock);// std::lock(lock1, lock2); 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(); std::cout<<"my_account.balance = "<< my_account.balance<<"\n""your_account.balance = "<< your_account.balance<<'\n';}
输出：
my_account.balance = 95 your_account.balance = 55
[编辑]参阅
构造 lock_guard，可选地锁定给定的互斥体 ( std::lock_guard<Mutex> 的公开成员函数) | |
构造 unique_lock，可选地锁定提供的互斥体 ( std::unique_lock<Mutex> 的公开成员函数) |
