pthread简介
现在开始介入thread的初步知识。
创建pthread
直接上一个demo code:
#include <iostream>
#include <pthread.h>
using namespace std;
#define NUM_THREADS 5
// 綫程運行的函數
void* say_hello(void* args){
cout << "Hello, vimer" << endl;
return 0;
}
int main(){
// 定义线程的ID变量，多个变量使用数组
pthread_t tids[NUM_THREADS];
for (int i = 0; i < NUM_THREADS; i++){
// 参数依次是： 创建线程的id, 线程参数， 调用的函数，传入的函数args
int ret = pthread_create(&tids[i], NULL, say_hello, NULL);
if(ret != 0)
cout << "pthread_create error: error_code=" << ret << endl;
}
// 等各个线程退出后，进程才结束，否则进程强制结束了，线程可能还没有反应过来
pthread_exit(NULL);
}
编译命令:
g++ thread.cpp -lpthread -o test
其实，这里有意思的是，不同时间执行的输出是不一样的:
vimer@user-HP:~/test/thread$ ./test
Hello, vimer
Hello, vimerHello, vimer
Hello, vimer
Hello, vimer
vimer@user-HP:~/test/thread$ ./test
Hello, vimer
Hello, vimer
Hello, vimer
Hello, vimer
Hello, vimer
是这样的，目前还是有点难以理解。 看一下具体的api吧：
/* Create a new thread, starting with execution of START-ROUTINE
getting passed ARG. Creation attributed come from ATTR. The new
handle is stored in *NEWTHREAD. */
extern int pthread_create (pthread_t *__restrict __newthread,
const pthread_attr_t *__restrict __attr,
void *(*__start_routine) (void *),
void *__restrict __arg) __THROWNL __nonnull ((1, 3));
/* Terminate calling thread.
The registered cleanup handlers are called via exception handling
so we cannot mark this function with __THROW.*/
extern void pthread_exit (void *__retval) __attribute__ ((__noreturn__));
向线程传递参数
#include <iostream>
#include <pthread.h>
using namespace std;
#define NUM_THREADS 5
void *PrintHello(void *threadid){
// 对传入的参数进行强制类型转换，由无类型指针转化为整型指针
int tid = *((int*)threadid);
cout << "Hello vimer! thread id" << tid << endl;
pthread_exit(NULL);
}
int main()
{
pthread_t threads[NUM_THREADS];
int indexes[NUM_THREADS];
int rc;
int i;
for(i = 0; i < NUM_THREADS; i++){
cout << "main(): create thread," << i << endl;
indexes[i] = i; // 保存i的值
// 传入的时候必须强制转换为void *类型，即无类型指针
rc = pthread_create(&threads[i], NULL, PrintHello,
(void*)&(indexes[i]));
if (rc){
cout << "fail to create thread" << rc << endl;
exit(-1);
}
}
pthread_exit(NULL);
}
输出的结果如下:
vimer@user-HP:~/test$ ./test
main(): create thread,0
main(): create thread,1
Hello vimer! thread id0
main(): create thread,2
Hello vimer! thread id1
main(): create thread,3
Hello vimer! thread id2
Hello vimer! thread id3
main(): create thread,4
Hello vimer! thread id4
下面这个例子是传递结构体参数:
#include <iostream>
#include <pthread.h>
using namespace std;
#define NUM_THREADS 5
struct thread_data{
int thread_id;
char *message;
};
void *PrintHello(void *threadargs){
struct thread_data *my_data;
my_data = (struct thread_data *)threadargs;
cout << "Thread ID: " << my_data->thread_id;
cout << " Message:" << my_data->message << endl;
pthread_exit(NULL);
}
int main()
{
pthread_t threads[NUM_THREADS];
struct thread_data td[NUM_THREADS];
int rc, i;
for ( i = 0; i < NUM_THREADS; i++){
cout << "main(): create thread" << i << endl;
td[i].thread_id = i;
td[i].message = (char *)"this is message";
rc = pthread_create(&threads[i], NULL,
PrintHello, (void *)&td[i]);
if (rc) {
cout << "fail to create thread" << rc << endl;
exit(-1);
}
}
pthread_exit(NULL);
}
输出log :
vimer@user-HP:~/test$ ./test
main(): create thread0
main(): create thread1
Thread ID: 0 Message:this is message
main(): create thread2
Thread ID: 1 Message:this is message
main(): create thread3
Thread ID: 2 Message:this is message
Thread ID: 3 Message:this is message
main(): create thread4
Thread ID: 4 Message:this is message