线程编程全攻略：从入门到精通

线程的概念

线程是操作系统能够进行运算调度的最小单位，它被包含在进程之中，是进程中的实际运作单位。一个进程中可以并发多个线程，每条线程并行执行不同的任务。线程是轻量级的进程，创建和销毁的开销较小，切换速度更快。

线程共享进程的资源，如内存空间、文件描述符等。每个线程拥有独立的执行堆栈和程序计数器。多线程编程可以提高程序的并发性和响应性，尤其在多核处理器上能显著提升性能。

线程的控制

线程创建

线程的创建通常通过调用操作系统或编程语言提供的API实现。例如在Java中可以通过继承Thread类或实现Runnable接口创建线程。

class MyThread extends Thread {
    public void run() {
        System.out.println("Thread running");
    }
}

在C++中可以使用std::thread：

#include <thread>
void threadFunction() {
    // 线程执行的代码
}
std::thread t(threadFunction);

线程同步

当多个线程访问共享资源时，需要使用同步机制防止竞态条件。常见的同步机制包括：

互斥锁(Mutex)：

std::mutex mtx;
mtx.lock();
// 临界区代码
mtx.unlock();

信号量(Semaphore)用于控制对多个资源的访问：

Semaphore sem = new Semaphore(3);
sem.acquire();
// 使用资源
sem.release();

条件变量(Condition Variable)用于线程间通信：

import threading
cond = threading.Condition()
cond.wait()  # 等待通知
cond.notify()  # 发送通知

线程通信

线程间通信可以通过共享内存或消息传递实现。共享内存需要同步机制保护，消息传递则更安全但开销较大。

在Go语言中使用channel进行线程通信：

ch := make(chan int)
go func() { ch <- 42 }()  // 发送
value := <-ch  // 接收

线程终止

线程终止应遵循安全原则，避免资源泄漏。通常线程执行完任务后自动终止，也可以显式终止：

在Python中：

import threading
def worker():
    while not threading.current_thread().stopped:
        # 工作代码
thread = threading.Thread(target=worker)
thread.stopped = False
thread.stopped = True  # 请求终止
thread.join()  # 等待线程结束

线程池管理

线程池可以避免频繁创建销毁线程的开销。Java中的Executor框架提供了线程池实现：

ExecutorService executor = Executors.newFixedThreadPool(4);
executor.submit(() -> {
    // 任务代码
});
executor.shutdown();

线程最佳实践

避免过度使用线程，线程数量应与处理器核心数相匹配。注意线程安全问题，优先使用线程安全的数据结构。合理处理异常，防止线程意外终止影响程序稳定性。

性能敏感场景考虑无锁编程或原子操作。调试多线程程序时使用专门的工具分析竞态条件和死锁问题。

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