std::shared_lock<Mutex>:: lock

以共享模式锁定关联的互斥锁。效果上调用 mutex ( ) - > lock_shared ( ) 。

参数

(无)

返回值

(无)

异常

• 由 mutex ( ) - > lock_shared ( ) 抛出的任何异常。

• 如果没有关联的互斥锁，将抛出 std::system_error ，其错误代码为 std::errc::operation_not_permitted 。

• 如果关联的互斥量已被此 shared_lock 锁定（即 owns_lock 返回 true ），将抛出 std::system_error 异常，其错误码为 std::errc::resource_deadlock_would_occur 。

示例

#include <iostream>
#include <mutex>
#include <shared_mutex>
#include <string>
#include <thread>
std::string file = "Original content."; // 模拟文件
std::mutex output_mutex; // 保护输出操作的互斥锁
std::shared_mutex file_mutex; // 读写互斥锁
void read_content(int id)
{
    std::string content;
    {
        std::shared_lock lock(file_mutex, std::defer_lock); // 先不锁定
        lock.lock(); // 在此处锁定
        content = file;
    }
    std::lock_guard lock(output_mutex);
    std::cout << "Contents read by reader #" << id << ": " << content << '\n';
}
void write_content()
{
    {
        std::lock_guard file_lock(file_mutex);
        file = "New content";
    }
    std::lock_guard output_lock(output_mutex);
    std::cout << "New content saved.\n";
}
int main()
{
    std::cout << "Two readers reading from file.\n"
              << "A writer competes with them.\n";
    std::thread reader1{read_content, 1};
    std::thread reader2{read_content, 2};
    std::thread writer{write_content};
    reader1.join();
    reader2.join();
    writer.join();
    std::cout << "The first few operations to file are done.\n";
    reader1 = std::thread{read_content, 3};
    reader1.join();
}

Two readers reading from file.
A writer competes with them.
Contents read by reader #1: Original content.
Contents read by reader #2: Original content.
New content saved.
The first few operations to file are done.
Contents read by reader #3: New content

参见