std::try_lock_C++中文网

C++ 参考手册

定义于头文件 `<mutex>`
template< class Lockable1, class Lockable2, class... LockableN> int try_lock( Lockable1& lock1, Lockable2& lock2, LockableN&... lockn);		(C++11 起)

尝试锁定每个给定的可锁定 (Lockable) 对象 lock1 、 lock2 、 ... 、 lockn ，通过以从头开始的顺序调用 try_lock 。

若调用 try_lock 失败，则不再进一步调用 try_lock ，并对任何已锁对象调用 unlock ，返回锁定失败对象的 0 底下标。

若调用 try_lock 抛出异常，则在重抛前对任何已锁对象调用 unlock 。

参数

lock1, lock2, ... , lockn	-	要锁定的可锁定 (Lockable) 对象

返回值

成功时为 -1 ，否则为锁定失败对象的 0 底下标值。

示例

下列示例用 std::try_lock 周期地记录并重置运行于分离线程的计数器。

运行此代码

#include <mutex>
#include <vector>
#include <thread>
#include <iostream>
#include <functional>
#include <chrono>
 
int main()
{
    int foo_count = 0;
    std::mutex foo_count_mutex;
    int bar_count = 0;
    std::mutex bar_count_mutex;
    int overall_count = 0;
    bool done = false;
    std::mutex done_mutex;
 
    auto increment = [](int &counter, std::mutex &m,  const char *desc) {
        for (int i = 0; i < 10; ++i) {
            std::unique_lock<std::mutex> lock(m);
            ++counter;
            std::cout << desc << ": " << counter << '\n';
            lock.unlock();
            std::this_thread::sleep_for(std::chrono::seconds(1));
        }
    };
 
    std::thread increment_foo(increment, std::ref(foo_count), 
        std::ref(foo_count_mutex), "foo");
    std::thread increment_bar(increment, std::ref(bar_count), 
        std::ref(bar_count_mutex), "bar");
 
    std::thread update_overall([&]() {
        done_mutex.lock();
        while (!done) {
            done_mutex.unlock();
            int result = std::try_lock(foo_count_mutex, bar_count_mutex);
            if (result == -1) {
                overall_count += foo_count + bar_count;
                foo_count = 0;
                bar_count = 0;
                std::cout << "overall: " << overall_count << '\n';
                foo_count_mutex.unlock();
                bar_count_mutex.unlock();
            }
            std::this_thread::sleep_for(std::chrono::seconds(2));
            done_mutex.lock();
        }
        done_mutex.unlock();
    });
 
    increment_foo.join();
    increment_bar.join();
    done_mutex.lock();
    done = true;
    done_mutex.unlock();
    update_overall.join();
 
    std::cout << "Done processing\n"
              << "foo: " << foo_count << '\n'
              << "bar: " << bar_count << '\n'
              << "overall: " << overall_count << '\n';
}

可能的输出：

bar: 1
foo: 1
foo: 2
bar: 2
foo: 3
overall: 5
bar: 1
foo: 1
bar: 2
foo: 2
bar: 3
overall: 10
bar: 1
foo: 1
bar: 2
foo: 2
overall: 14
bar: 1
foo: 1
bar: 2
overall: 17
foo: 1
bar: 1
foo: 2
overall: 20
Done processing
foo: 0
bar: 0
overall: 20

参阅

lock (C++11)	锁定指定的互斥体，若任何一个不可用则阻塞 (函数模板)