【Linux】线程创建/终止/等待/分离

业界资讯 2023-04-17 15:58:53 阅读次数: 0

目录

线程概念

线程创建

线程间共享全局变量

批量创建线程

多线程的局部变量

线程终止

线程等待

线程分离

线程概念

        线程：线程是进程内的执行流

        windows环境：线程有专门的数据结构，TCB

        linux环境：线程与进程一样用PCB描述

        进程是承担分配系统资源的基本实体，线程是cpu调用资源的基本单位

        创建线程需要链接pthread动态库

        线程间切换比进程间切换成本更低：cache在线程间上下文切换时不用再更新

线程的缺点：

        性能损失：cpu的核数决定线程的个数，cpu的个数决定进程的个数

        健壮性降低：一个线程挂掉会影响另一个线程

        缺乏访问控制：进程是访问控制的基本粒度，在一个线程中调用某个os函数会对整个进程造成影响

        编程难度提高：多线程的编程和调试难度提高

线程创建

        makefile

mythread: mythread.cc
	g++ -o $@ $^ -std=c++11 -lpthread

.PHONY:clean
clean:
	rm -rf mythread

        mythread.cc

#include <iostream>
#include <pthread.h>
#include <unistd.h>
#include <sys/types.h>
#include <cassert>
using namespace std;

void* thread_routine(void* args) {
     while (true) {
        cout << "我是子线程, 我正在运行..." << endl;
        sleep(1);
     }
}

int main() {
    pthread_t tid;
    pthread_create(&tid, NULL, thread_routine, (void*)"thread one");

    //主线程
    while (true) {
        cout << "我是主线程, 我正在运行..." << endl;
        sleep(1);
    }

    return 0;
}

         由运行结果可得，线程的LWP与PID有关，且主线程的LWP与PID相等

线程间共享全局变量

#include <iostream>
#include <pthread.h>
#include <unistd.h>
#include <sys/types.h>
#include <cassert>
using namespace std;

int g_val = 0;

void* thread_routine(void* args) {
    const char* name = (const char*)args;
     while (true) {
        cout << "我是子线程, " << name << " &g_val=" << &g_val << " g_val=" << g_val << endl;
        ++g_val;
        sleep(1);
     }
}

int main() {
    pthread_t tid;
    int n = pthread_create(&tid, NULL, thread_routine, (void*)"thread one");
    assert(n == 0);

    //主线程
    while (true) {
        char buffer[64];
        snprintf(buffer, sizeof(buffer), "0x%x", tid);
        cout << "我是主线程, 我创建的 tid=" << buffer << " &g_val=" << &g_val << " g_val=" << g_val << endl;
        ++g_val;
        sleep(1);
    }

    return 0;
}

线程私有的资源：

  1. PCB属性私有
  2. 私有上下文结构
  3. 私有栈结构

批量创建线程

// int pthread_create(pthread_t *thread, const pthread_attr_t *attr, void *(*start_routine)(void*), void arg)

// thread: 返回线程id
// attr: 设置线程的属性，attr为NULL表示使用默认值
// start_routine: 是个函数地址，线程启动后要执行的函数
// atg: 产给线程启动函数的参数
#include <iostream>
#include <pthread.h>
#include <unistd.h>
#include <sys/types.h>
#include <cassert>
#include <vector>
#include <string>
using namespace std;

class ThreadData {
public:
    pthread_t tid;
    char namebuffer[64];
};

void* start_routine(void* args) {
    ThreadData* td = static_cast<ThreadData*>(args);    //安全的进行强制类型转化
    int cnt = 3;
    while (cnt) {
        cout << "new thread create success, name : " << td->namebuffer << " cnt: " << cnt-- << endl;
        sleep(1);
    }
    delete td;
    return nullptr;
}

int main() {
    vector<ThreadData*> threads;
#define NUM 3
    for (int i = 0; i < NUM; ++i) {
        ThreadData* td = new ThreadData();
        snprintf(td->namebuffer, sizeof(td->namebuffer), "%s:%d", "thread", i + 1);
        pthread_create(&td->tid, nullptr, start_routine, td);
        threads.push_back(td);
    }

    for (auto& iter: threads) {
        cout << "create thread: " << iter->namebuffer << " : " << iter->tid << endl;
    }

    while (true) {
        cout << "new thread create success, name : main thread" << endl;
        sleep(1);
    }
}

多线程的局部变量

        每个线程都有独立的栈结构，线程内部定义的变量并不共享

#include <iostream>
#include <pthread.h>
#include <unistd.h>
#include <sys/types.h>
#include <cassert>
#include <vector>
#include <string>
using namespace std;

class ThreadData {
public:
    pthread_t tid;
    char namebuffer[64];
};

void* start_routine(void* args) {
    sleep(1);
    ThreadData* td = static_cast<ThreadData*>(args);    //安全的进行强制类型转化
    int cnt = 3;
    while (cnt) {
        cout << "cnt: " << cnt << " &cnt: " << &cnt << endl;
        cnt--;
        sleep(1);
    }
    delete td;
    return nullptr;
}

int main() {
    vector<ThreadData*> threads;
#define NUM 3
    for (int i = 0; i < NUM; ++i) {
        ThreadData* td = new ThreadData();
        snprintf(td->namebuffer, sizeof(td->namebuffer), "%s:%d", "thread", i + 1);
        pthread_create(&td->tid, nullptr, start_routine, td);
        threads.push_back(td);
    }

    for (auto& iter: threads) {
        cout << "create thread: " << iter->namebuffer << " : " << iter->tid << endl;
    }

    while (true) {
        cout << "new thread create success, name : main thread" << endl;
        sleep(1);
    }
}

        __thread 内置类型

#include <iostream>
#include <pthread.h>
#include <unistd.h>
#include <sys/types.h>
#include <cassert>
using namespace std;

// 添加 __thread ，可以将一个内置类型设置为线程局部存储
__thread int g_val = 0;

void* thread_routine(void* args) {
    const char* name = (const char*)args;
     while (true) {
        cout << "我是子线程, " << name << " &g_val=" << &g_val << " g_val=" << g_val << endl;
        ++g_val;
        sleep(1);
     }
}

int main() {
    pthread_t tid;
    int n = pthread_create(&tid, NULL, thread_routine, (void*)"thread one");
    assert(n == 0);

    //主线程
    while (true) {
        char buffer[64];
        snprintf(buffer, sizeof(buffer), "0x%x", tid);
        cout << "我是主线程, 我创建的 tid=" << buffer << " &g_val=" << &g_val << " g_val=" << g_val << endl;
        sleep(1);
    }

    return 0;
}

线程终止

        1. return ：线程对应的函数返回了，线程也就终止了

        2. pthread_exit() ：线程终止信号，exit信号是进程终止信号

        3. pthread_cance() ：线程取消

#include <iostream>
#include <pthread.h>
#include <unistd.h>
#include <sys/types.h>
#include <cassert>
#include <vector>
#include <string>
#include <cstdlib>
using namespace std;

class ThreadData {
public:
    int number;
    pthread_t tid;
    char namebuffer[64];
};

class ThreadReturn {
public:
    int exit_code;
    int exit_result;
};

void* start_routine(void* args) {
    ThreadData* td = static_cast<ThreadData*>(args);    //安全的进行强制类型转化
    int cnt = 3;
    while (cnt) {
        cout << "cnt: " << cnt << " &cnt: " << &cnt << endl;
        cnt--;
        sleep(1);
    }
    // delete td;
    //return nullptr;
    //pthread_exit(nullptr);
    //return (void*)td->number;   
    //pthread_exit((void*)td->number);

    // ThreadReturn* tr = new ThreadReturn();
    // tr->exit_code = 1;
    // tr->exit_result = td->number;
    // return (void*)tr;

    return (void*)100;
}

int main() {
    vector<ThreadData*> threads;
#define NUM 3
    for (int i = 0; i < NUM; ++i) {
        ThreadData* td = new ThreadData();
        td->number = i + 1;
        snprintf(td->namebuffer, sizeof(td->namebuffer), "%s:%d", "thread", i + 1);
        pthread_create(&td->tid, nullptr, start_routine, td);
        threads.push_back(td);
    }

    for (auto& iter: threads) {
        cout << "create thread: " << iter->namebuffer << " : " << iter->tid << endl;
    }

    sleep(2);
    for (int i = 0; i <= threads.size() / 2; ++i) {
        pthread_cancel(threads[i]->tid);
        cout << "pthread_cancel: " << threads[i]->namebuffer << " success " << endl;
        //取消线程的线程的前提是线程还在运行
        //如果线程被取消，退出码为 -1
    }

    for (auto& iter: threads) {
        void* ret = nullptr;    
        //ThreadReturn* ret = nullptr;
        // int n = pthread_join(iter->tid, nullptr);
        int n = pthread_join(iter->tid, &ret);  // void** pret;
        assert(n == 0);
        // cout << "join " << iter->namebuffer << " success, number: " << (long long)ret << endl;
        cout << "join " << iter->namebuffer << " success, exit_code: " << (long long)ret << endl;
        delete iter;
    }

    cout << "main thread quit" << endl;
    return 0;
}

线程等待

int pthread_join(pthread_t thread, void** retval);

#include <iostream>
#include <pthread.h>
#include <unistd.h>
#include <sys/types.h>
#include <cassert>
#include <vector>
#include <string>
#include <cstdlib>
using namespace std;

class ThreadData {
public:
    pthread_t tid;
    char namebuffer[64];
};

void* start_routine(void* args) {
    ThreadData* td = static_cast<ThreadData*>(args);    //安全的进行强制类型转化
    int cnt = 3;
    while (cnt) {
        cout << "cnt: " << cnt << " &cnt: " << &cnt << endl;
        cnt--;
        sleep(1);
    }
    // delete td;
    pthread_exit(nullptr);
}

int main() {
    vector<ThreadData*> threads;
#define NUM 3
    for (int i = 0; i < NUM; ++i) {
        ThreadData* td = new ThreadData();
        snprintf(td->namebuffer, sizeof(td->namebuffer), "%s:%d", "thread", i + 1);
        pthread_create(&td->tid, nullptr, start_routine, td);
        threads.push_back(td);
    }

    for (auto& iter: threads) {
        cout << "create thread: " << iter->namebuffer << " : " << iter->tid << endl;
    }

    for (auto& iter: threads) {
        int n = pthread_join(iter->tid, nullptr);
        assert(n == 0);
        cout << "join " << iter->namebuffer << " success " << endl;
        delete iter;
    }

    while (true) {
        cout << "new thread create success, name : main thread" << endl;
        sleep(1);
    }
}

        线程等待返回值

#include <iostream>
#include <pthread.h>
#include <unistd.h>
#include <sys/types.h>
#include <cassert>
#include <vector>
#include <string>
#include <cstdlib>
using namespace std;

class ThreadData {
public:
    int number;
    pthread_t tid;
    char namebuffer[64];
};

class ThreadReturn {
public:
    int exit_code;
    int exit_result;
};

void* start_routine(void* args) {
    ThreadData* td = static_cast<ThreadData*>(args);    //安全的进行强制类型转化
    int cnt = 3;
    while (cnt) {
        cout << "cnt: " << cnt << " &cnt: " << &cnt << endl;
        cnt--;
        sleep(1);
    }
    // delete td;
    //return nullptr;
    //pthread_exit(nullptr);
    //return (void*)td->number;   
    //pthread_exit((void*)td->number);
    ThreadReturn* tr = new ThreadReturn();
    tr->exit_code = 1;
    tr->exit_result = td->number;
    return (void*)tr;
}

int main() {
    vector<ThreadData*> threads;
#define NUM 3
    for (int i = 0; i < NUM; ++i) {
        ThreadData* td = new ThreadData();
        td->number = i + 1;
        snprintf(td->namebuffer, sizeof(td->namebuffer), "%s:%d", "thread", i + 1);
        pthread_create(&td->tid, nullptr, start_routine, td);
        threads.push_back(td);
    }

    for (auto& iter: threads) {
        cout << "create thread: " << iter->namebuffer << " : " << iter->tid << endl;
    }

    // sleep(5);
    // for (int i = 0; i < threads.size() / 2; ++i) {
    //     pthread_cancel(threads[i]->tid);
    //     cout << "pthread_cancel: " << threads[i]->namebuffer << " success " << endl;
    //     //如果线程被取消，退出码为i-1
    // }

    for (auto& iter: threads) {
        //void* ret = nullptr;    
        ThreadReturn* ret = nullptr;
        // int n = pthread_join(iter->tid, nullptr);
        int n = pthread_join(iter->tid, (void**)&ret);  // void** pret;
        assert(n == 0);
        // cout << "join " << iter->namebuffer << " success, number: " << (long long)ret << endl;
        cout << "join " << iter->namebuffer << " success, code: " << ret->exit_code << ", result: " << ret->exit_result << endl;
        delete iter;
    }

    cout << "main thread quit" << endl;
    return 0;
}

线程分离

        pthread_self() 获得线程ID

         pthread_detach() 线程分离

        线程分离状态，主线程无法等待

#include <iostream>
#include <thread>
#include <unistd.h>
#include <cstdio>
#include <string>
#include <cerrno>
#include <cstring>
using namespace std;

string changeID(const pthread_t& thread_id) {
    char tid[128];
    snprintf(tid, sizeof(tid), "0x%x", thread_id);
    return tid;
}

void* start_routine(void* args) {
    string name = static_cast<const char*>(args);
    //pthread_detach(pthread_self());     //设置自己为分离状态
    int cnt = 5;
    while (cnt--) { 
        cout << name <<" running ... : " << changeID(pthread_self()) << endl;
        sleep(1);
    }
    return nullptr;
}

int main() {
    pthread_t tid;
    pthread_create(&tid, nullptr, start_routine, (void*)"thread one");
    string main_id = changeID(pthread_self());  
    cout << "main thread run ... new thread id : " << changeID(tid) << " main thread id: " << main_id << endl;
    //pthread_join(tid, nullptr);
    pthread_detach(tid);    //主线程分离新线程

    //sleep(1);
    //一个线程默认是joinable的，如果设置了分离状态，不能够再进行等待了
    int n = pthread_join(tid, nullptr);
    cout << "result: " << n << " : " << strerror(n) << endl;
    return 0;
}

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