std::defer_lock, std::try_to_lock, std::adopt_lock
来自cppreference.com
定义于头文件 <mutex>
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constexpr std::defer_lock_t defer_lock {}; |
(C++11 起) (C++17 前) |
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inline constexpr std::defer_lock_t defer_lock {}; |
(C++17 起) | |
constexpr std::try_to_lock_t try_to_lock {}; |
(C++11 起) (C++17 前) |
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inline constexpr std::try_to_lock_t try_to_lock {}; |
(C++17 起) | |
constexpr std::adopt_lock_t adopt_lock {}; |
(C++11 起) (C++17 前) |
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inline constexpr std::adopt_lock_t adopt_lock {}; |
(C++17 起) | |
std::defer_lock
、 std::try_to_lock
和 std::adopt_lock
分别是空结构体标签类型 std::defer_lock_t 、 std::try_to_lock_t 和 std::adopt_lock_t 的实例。
它们用于为 std::lock_guard 、 std::unique_lock 及 std::shared_lock 指定锁定策略。
类型 | 效果 |
defer_lock_t
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不获得互斥的所有权 |
try_to_lock_t
|
尝试获得互斥的所有权而不阻塞 |
adopt_lock_t
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假设调用方线程已拥有互斥的所有权 |
示例
运行此代码
#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) { // 锁定两个互斥而不死锁 std::lock(from.m, to.m); // 保证二个已锁定互斥在作用域结尾解锁 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(); }
参阅
(C++11)(C++11)(C++11) |
用于指定锁定策略的标签类型 (类) |
构造 lock_guard ,可选地锁定给定的互斥 ( 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 ( std::unique_lock<Mutex> 的公开成员函数) |