转自：点击打开链接
1.最基础，进程同时创建5个线程，各自调用同一个函数
[html] view plain copy #include <iostream> #include <pthread.h> //多线程相关操作头文件，可移植众多平台 using namespace std; #define NUM_THREADS 5 //线程数 void* say_hello( void* args ) { cout << "hello..." << 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]; //线程id for( int i = 0; i < NUM_THREADS; ++i ) { int ret = pthread_create( &tids[i], NULL, say_hello, NULL ); //参数：创建的线程id，线程参数，线程运行函数的起始地址，运行函数的参数 if( ret != 0 ) //创建线程成功返回0 { cout << "pthread_create error:error_code=" << ret << endl; } } pthread_exit( NULL ); //等待各个线程退出后，进程才结束，否则进程强制结束，线程处于未终止的状态 } 输入命令：g++ -o muti_thread_test_1 muti_thread_test_1.cpp -lpthread
注意：
1）此为c++程序，故用g++来编译生成可执行文件，并且要调用处理多线程操作相关的静态链接库文件pthread。
2）-lpthread 编译选项到位置可任意，如g++ -lpthread -o muti_thread_test_1 muti_thread_test_1.cpp
3）注意gcc和g++的区别，转到此文：点击打开链接
测试结果：
[html] view plain copy wq@wq-desktop:~/coding/muti_thread$ ./muti_thread_test_1 hello...hello... hello... hello... hello... [html] view plain copy wq@wq-desktop:~/coding/muti_thread$ ./muti_thread_test_1 hello...hello...hello... hello... hello...
可知，两次运行的结果会有差别，这不是多线程的特点吧？这显然没有同步？还有待进一步探索...
2.线程调用到函数在一个类中，那必须将该函数声明为静态函数函数
因为静态成员函数属于静态全局区，线程可以共享这个区域，故可以各自调用。
[html] view plain copy #include <iostream> #include <pthread.h> using namespace std; #define NUM_THREADS 5 class Hello { public: static void* say_hello( void* args ) { cout << "hello..." << endl; } }; int main() { pthread_t tids[NUM_THREADS]; for( int i = 0; i < NUM_THREADS; ++i ) { int ret = pthread_create( &tids[i], NULL, Hello::say_hello, NULL ); if( ret != 0 ) { cout << "pthread_create error:error_code" << ret << endl; } } pthread_exit( NULL ); }
测试结果：
[html] view plain copy wq@wq-desktop:~/coding/muti_thread$ ./muti_thread_test_2 hello... hello... hello... hello... hello... [html] view plain copy wq@wq-desktop:~/coding/muti_thread$ ./muti_thread_test_2 hello...hello...hello... hello... hello...
两次运行的结果会有差别，这显然没有同步!
3.如何在线程调用函数时传入参数呢？
先看下面修改的代码，传入线程编号作为参数：
[html] view plain copy #include <iostream> #include <pthread.h> //多线程相关操作头文件，可移植众多平台 using namespace std; #define NUM_THREADS 5 //线程数 void* say_hello( 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 int main() { pthread_t tids[NUM_THREADS]; //线程id cout << "hello in main.." << endl; for( int i = 0; i < NUM_THREADS; ++i ) { int ret = pthread_create( &tids[i], NULL, say_hello, (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 cout << "Current pthread id = " << tids[i] << endl; //用tids数组打印创建的进程id信息 if( ret != 0 ) //创建线程成功返回0 { cout << "pthread_create error:error_code=" << ret << endl; } } pthread_exit( NULL ); //等待各个线程退出后，进程才结束，否则进程强制结束，线程处于未终止的状态 } 测试结果： [html] view plain copy wq@wq-desktop:~/coding/muti_thread$ ./muti_thread_test_3 hello in main.. Current pthread id = 3078458224 Current pthread id = 3070065520 hello in hello in 2 1 Current pthread id = hello in 2 3061672816 Current pthread id = 3053280112 hello in 4 Current pthread id = hello in 4 3044887408 显然不是想要的结果，调用顺序很乱，这是为什么呢？
这是因为多线程到缘故，主进程还没开始对i赋值，线程已经开始跑了...?
修改代码如下：
[html] view plain copy #include <iostream> #include <pthread.h> //多线程相关操作头文件，可移植众多平台 using namespace std; #define NUM_THREADS 5 //线程数 void* say_hello( void* args ) { cout << "hello in thread " << *( (int *)args ) << 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]; //线程id int indexes[NUM_THREADS]; //用来保存i的值避免被修改 for( int i = 0; i < NUM_THREADS; ++i ) { indexes[i] = i; int ret = pthread_create( &tids[i], NULL, say_hello, (void*)&(indexes[i]) ); if( ret != 0 ) //创建线程成功返回0 { cout << "pthread_create error:error_code=" << ret << endl; } } for( int i = 0; i < NUM_THREADS; ++i ) pthread_join( tids[i], NULL ); //pthread_join用来等待一个线程的结束，是一个线程阻塞的函数 } 测试结果：
[html] view plain copy wq@wq-desktop:~/coding/muti_thread$ ./muti_thread_test_3 hello in thread hello in thread hello in thread hello in thread hello in thread 30124
这是正常的吗？感觉还是有问题...待续
代码中如果没有pthread_join主线程会很快结束从而使整个进程结束，从而使创建的线程没有机会开始执行就结束了。加入pthread_join后，主线程会一直等待直到等待的线程结束自己才结束，使创建的线程有机会执行。
4.线程创建时属性参数的设置pthread_attr_t及join功能的使用
线程的属性由结构体pthread_attr_t进行管理。
typedef struct { int detachstate; 线程的分离状态 int schedpolicy; 线程调度策略 struct sched_param schedparam; 线程的调度参数 int inheritsched; 线程的继承性 int scope; 线程的作用域 size_t guardsize; 线程栈末尾的警戒缓冲区大小 int stackaddr_set; void * stackaddr; 线程栈的位置 size_t stacksize; 线程栈的大小 }pthread_attr_t;
[html] view plain copy #include <iostream> #include <pthread.h> using namespace std; #define NUM_THREADS 5 void* say_hello( void* args ) { cout << "hello in thread " << *(( int * )args) << endl; int status = 10 + *(( int * )args); //线程退出时添加退出的信息，status供主程序提取该线程的结束信息 pthread_exit( ( void* )status ); } int main() { pthread_t tids[NUM_THREADS]; int indexes[NUM_THREADS]; pthread_attr_t attr; //线程属性结构体，创建线程时加入的参数 pthread_attr_init( &attr ); //初始化 pthread_attr_setdetachstate( &attr, PTHREAD_CREATE_JOINABLE ); //是设置你想要指定线程属性参数，这个参数表明这个线程是可以join连接的，join功能表示主程序可以等线程结束后再去做某事，实现了主程序和线程同步功能 for( int i = 0; i < NUM_THREADS; ++i ) { indexes[i] = i; int ret = pthread_create( &tids[i], &attr, say_hello, ( void* )&( indexes[i] ) ); if( ret != 0 ) { cout << "pthread_create error:error_code=" << ret << endl; } } pthread_attr_destroy( &attr ); //释放内存 void *status; for( int i = 0; i < NUM_THREADS; ++i ) { int ret = pthread_join( tids[i], &status ); //主程序join每个线程后取得每个线程的退出信息status if( ret != 0 ) { cout << "pthread_join error:error_code=" << ret << endl; } else { cout << "pthread_join get status:" << (long)status << endl; } } } 测试结果：
[html] view plain copy wq@wq-desktop:~/coding/muti_thread$ ./muti_thread_test_4 hello in thread hello in thread hello in thread hello in thread 0hello in thread 321 4 pthread_join get status:10 pthread_join get status:11 pthread_join get status:12 pthread_join get status:13 pthread_join get status:14 5.互斥锁的实现 互斥锁是实现线程同步的一种机制，只要在临界区前后对资源加锁就能阻塞其他进程的访问。
[html] view plain copy #include <iostream> #include <pthread.h> using namespace std; #define NUM_THREADS 5 int sum = 0; //定义全局变量，让所有线程同时写，这样就需要锁机制 pthread_mutex_t sum_mutex; //互斥锁 void* say_hello( void* args ) { cout << "hello in thread " << *(( int * )args) << endl; pthread_mutex_lock( &sum_mutex ); //先加锁，再修改sum的值，锁被占用就阻塞，直到拿到锁再修改sum; cout << "before sum is " << sum << " in thread " << *( ( int* )args ) << endl; sum += *( ( int* )args ); cout << "after sum is " << sum << " in thread " << *( ( int* )args ) << endl; pthread_mutex_unlock( &sum_mutex ); //释放锁，供其他线程使用 pthread_exit( 0 ); } int main() { pthread_t tids[NUM_THREADS]; int indexes[NUM_THREADS]; pthread_attr_t attr; //线程属性结构体，创建线程时加入的参数 pthread_attr_init( &attr ); //初始化 pthread_attr_setdetachstate( &attr, PTHREAD_CREATE_JOINABLE ); //是设置你想要指定线程属性参数，这个参数表明这个线程是可以join连接的，join功能表示主程序可以等线程结束后再去做某事，实现了主程序和线程同步功能 pthread_mutex_init( &sum_mutex, NULL ); //对锁进行初始化 for( int i = 0; i < NUM_THREADS; ++i ) { indexes[i] = i; int ret = pthread_create( &tids[i], &attr, say_hello, ( void* )&( indexes[i] ) ); //5个进程同时去修改sum if( ret != 0 ) { cout << "pthread_create error:error_code=" << ret << endl; } } pthread_attr_destroy( &attr ); //释放内存 void *status; for( int i = 0; i < NUM_THREADS; ++i ) { int ret = pthread_join( tids[i], &status ); //主程序join每个线程后取得每个线程的退出信息status if( ret != 0 ) { cout << "pthread_join error:error_code=" << ret << endl; } } cout << "finally sum is " << sum << endl; pthread_mutex_destroy( &sum_mutex ); //注销锁 } 测试结果： [html] view plain copy wq@wq-desktop:~/coding/muti_thread$ ./muti_thread_test_5 hello in thread hello in thread hello in thread 410 before sum is hello in thread 0 in thread 4 after sum is 4 in thread 4hello in thread 2 3 before sum is 4 in thread 1 after sum is 5 in thread 1 before sum is 5 in thread 0 after sum is 5 in thread 0 before sum is 5 in thread 2 after sum is 7 in thread 2 before sum is 7 in thread 3 after sum is 10 in thread 3 finally sum is 10 可知，sum的访问和修改顺序是正常的，这就达到了多线程的目的了，但是线程的运行顺序是混乱的，混乱就是正常？
6.信号量的实现 信号量是线程同步的另一种实现机制，信号量的操作有signal和wait，本例子采用条件信号变量pthread_cond_t tasks_cond; 信号量的实现也要给予锁机制。
[html] view plain copy #include <iostream> #include <pthread.h> #include <stdio.h> using namespace std; #define BOUNDARY 5 int tasks = 10; pthread_mutex_t tasks_mutex; //互斥锁 pthread_cond_t tasks_cond; //条件信号变量，处理两个线程间的条件关系，当task>5，hello2处理，反之hello1处理，直到task减为0 void* say_hello2( void* args ) { pthread_t pid = pthread_self(); //获取当前线程id cout << "[" << pid << "] hello in thread " << *( ( int* )args ) << endl; bool is_signaled = false; //sign while(1) { pthread_mutex_lock( &tasks_mutex ); //加锁 if( tasks > BOUNDARY ) { cout << "[" << pid << "] take task: " << tasks << " in thread " << *( (int*)args ) << endl; --tasks; //modify } else if( !is_signaled ) { cout << "[" << pid << "] pthread_cond_signal in thread " << *( ( int* )args ) << endl; pthread_cond_signal( &tasks_cond ); //signal:向hello1发送信号，表明已经>5 is_signaled = true; //表明信号已发送，退出此线程 } pthread_mutex_unlock( &tasks_mutex ); //解锁 if( tasks == 0 ) break; } } void* say_hello1( void* args ) { pthread_t pid = pthread_self(); //获取当前线程id cout << "[" << pid << "] hello in thread " << *( ( int* )args ) << endl; while(1) { pthread_mutex_lock( &tasks_mutex ); //加锁 if( tasks > BOUNDARY ) { cout << "[" << pid << "] pthread_cond_signal in thread " << *( ( int* )args ) << endl; pthread_cond_wait( &tasks_cond, &tasks_mutex ); //wait:等待信号量生效，接收到信号，向hello2发出信号，跳出wait,执行后续 } else { cout << "[" << pid << "] take task: " << tasks << " in thread " << *( (int*)args ) << endl; --tasks; } pthread_mutex_unlock( &tasks_mutex ); //解锁 if( tasks == 0 ) break; } } int main() { pthread_attr_t attr; //线程属性结构体，创建线程时加入的参数 pthread_attr_init( &attr ); //初始化 pthread_attr_setdetachstate( &attr, PTHREAD_CREATE_JOINABLE ); //是设置你想要指定线程属性参数，这个参数表明这个线程是可以join连接的，join功能表示主程序可以等线程结束后再去做某事，实现了主程序和线程同步功能 pthread_cond_init( &tasks_cond, NULL ); //初始化条件信号量 pthread_mutex_init( &tasks_mutex, NULL ); //初始化互斥量 pthread_t tid1, tid2; //保存两个线程id int index1 = 1; int ret = pthread_create( &tid1, &attr, say_hello1, ( void* )&index1 ); if( ret != 0 ) { cout << "pthread_create error:error_code=" << ret << endl; } int index2 = 2; ret = pthread_create( &tid2, &attr, say_hello2, ( void* )&index2 ); if( ret != 0 ) { cout << "pthread_create error:error_code=" << ret << endl; } pthread_join( tid1, NULL ); //连接两个线程 pthread_join( tid2, NULL ); pthread_attr_destroy( &attr ); //释放内存 pthread_mutex_destroy( &tasks_mutex ); //注销锁 pthread_cond_destroy( &tasks_cond ); //正常退出 } 测试结果： 先在线程2中执行say_hello2，再跳转到线程1中执行say_hello1，直到tasks减到0为止。
[html] view plain copy wq@wq-desktop:~/coding/muti_thread$ ./muti_thread_test_6 [3069823856] hello in thread 2 [3078216560] hello in thread 1[3069823856] take task: 10 in thread 2 [3069823856] take task: 9 in thread 2 [3069823856] take task: 8 in thread 2 [3069823856] take task: 7 in thread 2 [3069823856] take task: 6 in thread 2 [3069823856] pthread_cond_signal in thread 2 [3078216560] take task: 5 in thread 1 [3078216560] take task: 4 in thread 1 [3078216560] take task: 3 in thread 1 [3078216560] take task: 2 in thread 1 [3078216560] take task: 1 in thread 1 到此，对多线程编程有了一个初步的了解，当然还有其他实现线程同步的机制，有待进一步探索。
