进程、线程与协程

进程、线程与协程 | Processes, Threads, and Coroutines

进程 | Processes

定义 | Definition

进程是操作系统中运行的一个独立的程序实例，具有自己的内存空间和系统资源。

A process is an independent program instance running in an operating system, with its own memory space and system resources.

特点 | Characteristics

• 独立性 | Independence：每个进程独立运行，互不干扰。 Each process runs independently, without interfering with others.
• 资源分配 | Resource Allocation：进程拥有独立的资源，如内存、文件句柄等。 Processes have their own resources, such as memory and file handles.
• 上下文切换 | Context Switching：进程切换开销大，需要保存和恢复 CPU 上下文。 Context switching between processes is costly, requiring saving and restoring the CPU context.

创建和销毁 | Creation and Termination

• 创建 | Creation：通过系统调用（如 fork）创建新进程。 Created using system calls like fork.
• 销毁 | Termination：进程完成任务或被终止后，系统回收其资源。 Terminated when it completes its task or is killed, with the system reclaiming its resources.

示例 | Example

// Example in C
#include <stdio.h>
#include <unistd.h>
 
int main() {
    pid_t pid = fork();
    if (pid == 0) {
        // Child process
        printf("This is the child process\n");
    } else {
        // Parent process
        printf("This is the parent process\n");
    }
    return 0;
}

线程 | Threads

定义 | Definition

线程是进程内的一个执行单元，共享进程的资源，但具有独立的执行路径。

A thread is an execution unit within a process, sharing the process’s resources but having an independent execution path.

特点 | Characteristics

• 共享资源 | Resource Sharing：线程共享进程的内存空间和资源。 Threads share the process’s memory space and resources.
• 轻量级 | Lightweight：线程比进程更轻量级，创建和切换开销较小。 Threads are more lightweight than processes, with lower creation and switching costs.
• 并发执行 | Concurrent Execution：同一进程内的多个线程可以并发执行。 Multiple threads within the same process can execute concurrently.

创建和销毁 | Creation and Termination

• 创建 | Creation：通过库函数（如 pthread_create）创建新线程。 Created using library functions like pthread_create.
• 销毁 | Termination：线程完成任务或被终止后，线程的资源被回收。 Terminated when it completes its task or is killed, with its resources being reclaimed.

示例 | Example

// Example in C using pthreads
#include <pthread.h>
#include <stdio.h>
 
void* thread_func(void* arg) {
    printf("This is a thread\n");
    return NULL;
}
 
int main() {
    pthread_t thread;
    pthread_create(&thread, NULL, thread_func, NULL);
    pthread_join(thread, NULL);
    return 0;
}

协程 | Coroutines

定义 | Definition

协程是一种比线程更轻量级的用户级任务调度方式，允许在单个线程内暂停和恢复执行。

A coroutine is a user-level task scheduling method that is more lightweight than threads, allowing pausing and resuming execution within a single thread.

特点 | Characteristics

• 轻量级 | Lightweight：协程切换开销极小，不涉及内核态切换。 Coroutines have minimal switching overhead and do not involve kernel-mode switching.
• 协作式多任务 | Cooperative Multitasking：协程通过显式调用让出控制权，实现多任务调度。 Coroutines use cooperative multitasking by explicitly yielding control to achieve multitasking.
• 共享同一线程的执行上下文 | Shared Execution Context：协程在同一线程内共享执行上下文和栈空间。 Coroutines share the execution context and stack space within the same thread.

创建和销毁 | Creation and Termination

• 创建 | Creation：通过语言级支持或库（如 Python 的 asyncio）创建协程。 Created using language-level support or libraries like Python’s asyncio.
• 销毁 | Termination：协程完成任务后由调度器回收。 Reclaimed by the scheduler after the coroutine completes its task.

示例 | Example

# Example in Python using asyncio
import asyncio
 
async def coroutine_func():
    print("This is a coroutine")
    await asyncio.sleep(1)
    print("Coroutine done")
 
async def main():
    await coroutine_func()
 
asyncio.run(main())

比较 | Comparison

特性	进程	线程	协程
独立性	独立的内存空间和资源	共享进程的内存空间和资源	共享线程的执行上下文
创建开销	高	低	最低
切换开销	高	低	最低
并发性	是	是	否（通常在单线程内协作）
适用场景	多任务并行，资源隔离	多任务并行，资源共享	高效的任务切换和并发处理

进程适用于需要资源隔离和稳定性的场景，线程适用于需要高效并发执行的场景，而协程则适用于需要极高并发且开销极低的场景。 Processes are suitable for scenarios requiring resource isolation and stability, threads for efficient concurrent execution, and coroutines for scenarios requiring extremely high concurrency with minimal overhead.