std::lock
来自 cppreference.cn
| 定义于头文件 <mutex> |
||
| template< class Lockable1, class Lockable2, class... LockableN > void lock( Lockable1& lock1, Lockable2& lock2, LockableN&... lockn ); |
(C++11 起) | |
使用死锁避免算法锁定给定的 Lockable 对象 lock1、lock2、...、lockn 以避免死锁。
这些对象通过一系列未指定的 lock、try_lock 和 unlock 调用来锁定。如果对 lock 或 unlock 的调用导致异常，则在重新抛出之前，会对所有已锁定的对象调用 unlock。
目录 |
[编辑] 参数
| lock1, lock2, ... , lockn | - | 要锁定的 Lockable 对象 |
[编辑] 返回值
(无)
[编辑] 注意
Boost 提供此函数的一个版本，它接受一对迭代器定义的 Lockable 对象序列。
std::scoped_lock 为此函数提供了 RAII 包装器，通常优于直接调用 std::lock。
[编辑] 示例
以下示例使用 std::lock 锁定成对的互斥量而不会发生死锁。
运行此代码
#include <chrono> #include <functional> #include <iostream> #include <mutex> #include <string> #include <thread> #include <vector> struct Employee { Employee(std::string id) : id(id) {} std::string id; std::vector<std::string> lunch_partners; std::mutex m; std::string output() const { std::string ret = "Employee " + id + " has lunch partners: "; for (auto n{lunch_partners.size()}; const auto& partner : lunch_partners) ret += partner + (--n ? ", " : ""); return ret; } }; void send_mail(Employee&, Employee&) { // Simulate a time-consuming messaging operation std::this_thread::sleep_for(std::chrono::milliseconds(696)); } void assign_lunch_partner(Employee& e1, Employee& e2) { static std::mutex io_mutex; { std::lock_guard<std::mutex> lk(io_mutex); std::cout << e1.id << " and " << e2.id << " are waiting for locks" << std::endl; } // Use std::lock to acquire two locks without worrying about // other calls to assign_lunch_partner deadlocking us { std::lock(e1.m, e2.m); std::lock_guard<std::mutex> lk1(e1.m, std::adopt_lock); std::lock_guard<std::mutex> lk2(e2.m, std::adopt_lock); // Equivalent code (if unique_locks are needed, e.g. for condition variables) // std::unique_lock<std::mutex> lk1(e1.m, std::defer_lock); // std::unique_lock<std::mutex> lk2(e2.m, std::defer_lock); // std::lock(lk1, lk2); // Superior solution available in C++17 // std::scoped_lock lk(e1.m, e2.m); { std::lock_guard<std::mutex> lk(io_mutex); std::cout << e1.id << " and " << e2.id << " got locks" << std::endl; } e1.lunch_partners.push_back(e2.id); e2.lunch_partners.push_back(e1.id); } send_mail(e1, e2); send_mail(e2, e1); } int main() { Employee alice("Alice"), bob("Bob"), christina("Christina"), dave("Dave"); // Assign in parallel threads because mailing users about lunch assignments // takes a long time std::vector<std::thread> threads; threads.emplace_back(assign_lunch_partner, std::ref(alice), std::ref(bob)); threads.emplace_back(assign_lunch_partner, std::ref(christina), std::ref(bob)); threads.emplace_back(assign_lunch_partner, std::ref(christina), std::ref(alice)); threads.emplace_back(assign_lunch_partner, std::ref(dave), std::ref(bob)); for (auto& thread : threads) thread.join(); std::cout << alice.output() << '\n' << bob.output() << '\n' << christina.output() << '\n' << dave.output() << '\n'; }
可能的输出
Alice and Bob are waiting for locks Alice and Bob got locks Christina and Bob are waiting for locks Christina and Bob got locks Christina and Alice are waiting for locks Dave and Bob are waiting for locks Dave and Bob got locks Christina and Alice got locks Employee Alice has lunch partners: Bob, Christina Employee Bob has lunch partners: Alice, Christina, Dave Employee Christina has lunch partners: Bob, Alice Employee Dave has lunch partners: Bob
[编辑] 参阅
| (C++11) |
实现可移动的互斥体所有权包装器 (类模板) |
| (C++11) |
尝试通过重复调用 try_lock 来获取互斥体的所有权(函数模板) |
| (C++17) |
用于多个互斥体的死锁避免 RAII 包装器 (类模板) |
