在多线程编程中，互斥锁（mutex）是确保线程安全、避免数据竞争的重要工具。C++标准库提供了多种互斥锁，每种都有其特定的应用场景和特点。
主要有以下几种互斥锁（Mutex）：
这些是C++标准库中提供的几种主要的互斥锁类型。每种锁都有其特定的应用场景和使用方法，选择合适的互斥锁类型对于实现高效、安全的多线程程序非常重要。
std::mutex是最基本的互斥锁，主要用于保护临界区，确保同一时间只有一个线程可以访问共享资源。
特点：
示例代码：
#include <iostream>#include <thread>#include <mutex>std::mutex mtx;void print_thread_id(int id) { std::lock_guard<std::mutex> lock(mtx); // 自动管理锁的获取和释放 std::cout << "Thread ID: " << id << std::endl;}int main() { std::thread t1(print_thread_id, 1); std::thread t2(print_thread_id, 2); t1.join(); t2.join(); return 0;}std::timed_mutex在std::mutex的基础上增加了超时功能，允许线程在指定时间内尝试获取锁，如果在超时时间内未成功获取锁，则返回失败。
特点：
示例代码：
#include <iostream>#include <thread>#include <mutex>#include <chrono>std::timed_mutex tmtx;void try_to_lock(int id) { if(tmtx.try_lock_for(std::chrono::milliseconds(100))) { std::cout << "Thread " << id << " locked the mutex" << std::endl; std::this_thread::sleep_for(std::chrono::milliseconds(200)); tmtx.unlock(); } else { std::cout << "Thread " << id << " could not lock the mutex" << std::endl; }}int main() { std::thread t1(try_to_lock, 1); std::thread t2(try_to_lock, 2); t1.join(); t2.join(); return 0;}std::recursive_mutex允许同一线程多次获取锁而不会发生死锁，这对于递归函数或需要多次锁定的场景非常有用。
特点：
示例代码：
#include <iostream>#include <thread>#include <mutex>std::recursive_mutex rmtx;void recursive_function(int depth) { rmtx.lock(); std::cout << "Depth: " << depth << std::endl; if (depth > 0) { recursive_function(depth - 1); } rmtx.unlock();}int main() { std::thread t(recursive_function, 5); t.join(); return 0;}std::recursive_timed_mutex结合了std::recursive_mutex和std::timed_mutex的特性，支持递归锁定和超时机制。
特点：
示例代码：
#include <iostream>#include <thread>#include <mutex>#include <chrono>std::recursive_timed_mutex rtmmtx;void try_recursive_lock(int id, int depth) { if (rtmmtx.try_lock_for(std::chrono::milliseconds(100))) { std::cout << "Thread " << id << " locked at depth " << depth << std::endl; std::this_thread::sleep_for(std::chrono::milliseconds(50)); if (depth > 0) { try_recursive_lock(id, depth - 1); } rtmmtx.unlock(); } else { std::cout << "Thread " << id << " could not lock at depth " << depth << std::endl; }}int main() { std::thread t1(try_recursive_lock, 1, 3); std::thread t2(try_recursive_lock, 2, 3); t1.join(); t2.join(); return 0;}std::shared_mutex允许多个线程同时读取，但只有一个线程可以写入。这在读多写少的场景下非常有用。
特点：
示例代码：
#include <iostream>#include <thread>#include <shared_mutex>std::shared_mutex shmtx;void read_shared(int id) { std::shared_lock<std::shared_mutex> lock(shmtx); // 共享锁 std::cout << "Thread " << id << " is reading" << std::endl; std::this_thread::sleep_for(std::chrono::milliseconds(100));}void write_shared(int id) { std::unique_lock<std::shared_mutex> lock(shmtx); // 独占锁 std::cout << "Thread " << id << " is writing" << std::endl; std::this_thread::sleep_for(std::chrono::milliseconds(100));}int main() { std::thread readers[5], writer(write_shared, 1); for (int i = 0; i < 5; ++i) { readers[i] = std::thread(read_shared, i + 2); } writer.join(); for (auto& reader : readers) { reader.join(); } return 0;}std::shared_timed_mutex结合了std::shared_mutex和std::timed_mutex的特性，支持超时机制。
特点：
示例代码：
#include <iostream>#include <thread>#include <shared_mutex>#include <chrono>std::shared_timed_mutex shtmmtx;void try_read_shared(int id) { if (shtmmtx.try_lock_shared_for(std::chrono::milliseconds(100))) { std::cout << "Thread " << id << " is reading" << std::endl; std::this_thread::sleep_for(std::chrono::milliseconds(50)); shtmmtx.unlock_shared(); } else { std::cout << "Thread " << id << " could not read" << std::endl; }}void try_write_shared(int id) { if (shtmmtx.try_lock_for(std::chrono::milliseconds(100))) { std::cout << "Thread " << id << " is writing" << std::endl; std::this_thread::sleep_for(std::chrono::milliseconds(50)); shtmmtx.unlock(); } else { std::cout << "Thread " << id << " could not write" << std::endl; }}int main() { std::thread readers[5], writer(try_write_shared, 1); for (int i = 0; i < 5; ++i) { readers[i] = std::thread(try_read_shared, i + 2); } writer.join(); for (auto& reader : readers) { reader.join(); } return 0;}C++标准库提供了多种类型的互斥锁，每种锁都有其特定的用途和特点。选择合适的互斥锁类型可以有效提高程序的并发性能和安全性。
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