linux的多线程,其实就是clone系统调用的实现的(共享文件等)
首先看个具体的例子:
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>
#include <string.h>
#include <sched.h>
#include <errno.h>
void *print_message_function( void *ptr );
int main()
{
pthread_t thread1, thread2;
const char *message1 = "Thread 1";
const char *message2 = "Thread 2";
int iret1, iret2;
/* Create independent threads each of which will execute function */
iret1 = pthread_create( &thread1, NULL, print_message_function, (void*) message1);
iret2 = pthread_create( &thread2, NULL, print_message_function, (void*) message2);
/* Wait till threads are complete before main continues. Unless we */
/* wait we run the risk of executing an exit which will terminate */
/* the process and all threads before the threads have completed. */
pthread_join( thread1, NULL);
pthread_join( thread2, NULL);
printf("Thread 1 returns: %d\n",iret1);
printf("Thread 2 returns: %d\n",iret2);
for(;;)
{
usleep(250*1000);
}
return 0;
}
void *print_message_function( void *ptr )
{
char *message;
for(;;)
{
message = (char *) ptr;
printf("%s \n", message);
usleep(3*250*1000);
}
return 0;
}
此时一共有三个进程在跑(相对于kernel来说,只有进程的概念)
一般情况是,一个进程在/proc 目录下就对应一个,以该进程ID号名字的
文件目录,该目录下保存着该进程的所有信息。
但是对应,所谓的多线程,它的目录结构该会这么样呢?
假如该程序名为:thread
$ top -t | grep thread
PID TID PR CPU% S VSS RSS PCY UID Thread Proc
31694 31694 0 0% S 3008K 416K root thread system/bin/thread
31694 31695 0 0% S 3008K 416K root thread system/bin/thread
31694 31696 0 0% S 3008K 416K root thread system/bin/thread
可知他们对应于一个进程ID号,而在此目录下,分别在有其他三个线程目录信息:
proc/31694/task # ls
31694
31695
31696