多线程代码实例

例1 多线程及参数传递

#include<iostream>
#include<cstdlib>
#include<pthread.h>

using namespace std;

#define NUM_THREADS 5

void *say_hello1(void *args)
{
    int i = *( (int *)args );  //对传入的参数进行强制类型转换，由无类型指针转变为整形指针，再用*读取其指向到内容
    cout << "hello in " << i << endl;
} //函数返回的是函数指针，便于后面作为参数
/********************************************************************/

void *say_hello2(void *args)
{
    int i = (long)args;  //对传入的参数进行强制类型转换，由无类型指针转变为整形指针，再用*读取其指向到内容
    cout << "hello in " << i << endl;
} //函数返回的是函数指针，便于后面作为参数
/*****************************************************************************/

int main()
{
    pthread_t tids[NUM_THREADS];
    cout << "hello in main..." << endl;
    for(int i = 0 ; i < NUM_THREADS; ++ i){
        //int ret = pthread_create( &tids[i], NULL, say_hello1, (void*)&i);//传入到参数必须强转为void*类型，即无类型指针，&i表示取i的地址，即指向i的指针
        int ret = pthread_create( &tids[i], NULL, say_hello2, (void*)i);
        cout << "Current pthread id = " << tids[i] << endl;
        if(ret != 0){
            cout << "pthread_create error: error_code = " << ret << endl;
        }
    }
    pthread_exit(NULL);
}

调用void *say_hello1(void *args)输出结果：

hello in main...
Current pthread id = 139639619233536
Current pthread id = 139639610840832
Current pthread id = 139639602448128
hello in hello in 3
hello in 3
3hello in 3

Current pthread id = 139639594055424
Current pthread id = 139639585662720
hello in 5

调用void *say_hello2(void *args)输出结果：

hello in main...
Current pthread id = 139654340855552
hello in 0
Current pthread id = 139654332462848
hello in 1
Current pthread id = 139654324070144
hello in 2
Current pthread id = 139654315677440
hello in 3
Current pthread id = 139654307284736
hello in 4

例2 结构体传递多个参数

#include<iostream>
#include<cstdlib>
#include<pthread.h>

using namespace std;

#define NUM_THREADS 5

struct  thread_data{
    int thread_id;
    char *message;
};

void *PrintHello(void *threadarg){
    struct thread_data *may_data;
    may_data = (struct thread_data *) threadarg;
    cout << "thread ID: " << may_data->thread_id;
    cout << "message: " << may_data->message << endl;

    pthread_exit(NULL);
}
int main()
{
    pthread_t threads[NUM_THREADS];
    struct thread_data td[NUM_THREADS];
    int rc;
    int i;
    for(i = 0; i < NUM_THREADS; ++ i){
        cout << "main(): creating thread, " << i << endl;
        td[i].thread_id = i;
        td[i].message = "this is message";
        rc = pthread_create(&threads[i], NULL, PrintHello, (void*)&td[i]);
        if(rc){
            cout << "error" << rc << endl;
        }
    }
    pthread_exit(NULL);
}

输出结果：

main(): creating thread, 0
main(): creating thread, 1
main(): creating thread, 2
thread ID: 0message: this is message
thread ID: 1message: this is message
thread ID: 2message: this is message
main(): creating thread, 3
main(): creating thread, 4
thread ID: 3message: this is message
thread ID: 4message: this is message

例3 pthread_join等待线程结束

#include<iostream>
#include<cstdlib>
#include<pthread.h>
#include<unistd.h> //sleep(1)

using namespace std;

#define NUM_THREADS 5

void *wait(void *t)
{
    int i;
    long tid;

    tid = (long)t;

    sleep(1);
    cout << "Sleeping in thread" << endl;
    cout << "Thread with id: " << tid << "...exiting" << endl;
    pthread_exit(NULL);
}

int main()
{
    int rc;
    int i;
    pthread_t threads[NUM_THREADS];
    pthread_attr_t attr;
    void *status;

    //Initialize and set thread joinable
    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);

    for(i = 0; i < NUM_THREADS; ++ i){
        cout << "main(): creating thread, " << i << endl;
        rc = pthread_create(&threads[i], NULL, wait, (void*)i);
        if(rc){
            cout << "error: " << rc << endl;
        }
    }

    //free attribute and wait for the other threads
    pthread_attr_destroy(&attr);
    for(i = 0; i < NUM_THREADS; ++ i){
        rc = pthread_join(threads[i], &status);
        if(rc){
            cout << "error: " << rc << endl;
        }
        cout << "Main: completed thread id: " << i;
        cout << "exiting with status: " << status << endl;
    }

    cout << "Main: program exiting." << endl;
    pthread_exit(NULL);
}

输出结果：

main(): creating thread, 0
main(): creating thread, 1
main(): creating thread, 2
main(): creating thread, 3
main(): creating thread, 4
Sleeping in threadSleeping in thread
Thread with id: 1...exiting

Thread with id: 4...exiting
Sleeping in threadSleeping in thread
Thread with id: 2...exiting

Thread with id: 0...exiting
Sleeping in thread
Thread with id: 3...exiting
Main: completed thread id: 0exiting with status: 0
Main: completed thread id: 1exiting with status: 0
Main: completed thread id: 2exiting with status: 0
Main: completed thread id: 3exiting with status: 0
Main: completed thread id: 4exiting with status: 0
Main: program exiting.

例4 pthread_exit() and pthread_join()

#define debug_Msg(fmt, arg...)\
    do{\
        printf("%s %d : ", __FILE__, __LINE__);\
        printf(fmt, ##arg);\
    }while(0)

void * doPrint(void *arg)
{
    debug_Msg("%s\n", (char*)arg);
    char *p = "thread is over";
    pthread_exit(p);
}

int main()
{
    pthread_t pid;
    char * pt = "hello pthread";
    pthread_create(&pid, NULL, doPrint, pt);
    void * p = NULL;
    pthread_join(pid, &p);
    debug_Msg("return of thread : [%s]\n", (char*)p);

    return 0;
}

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