进程基本概念—创建以及管道通信



1:进程的创建

fork创建进程(ubuntu14.04 CodeBlock13.12)

#include<stdio.h>

#include<unistd.h>

#include<sys/types.h>

 

int main(void)

{

int local_int = 8;

pid_t pid;

pid = fork();

if(pid == 0)

{

printf("This is the child process\n");

local_int = 1;

printf("Child num is %d\n",local_int);

}

else

{

sleep(2);

printf("This is the parent process\n");

printf("Parent num is %d\n",local_int);

}

printf("==================\n");

return 0;

}

 

有以上可以看出，子继承将父进程的数据空间、堆、栈复制，只是一个副本；

 

另外fork下所有代码复制各个进程空间之下，fork效率比较高，采用的是写时拷贝，也就是

也就是只有进程空间的各段的内容要发生变化时，才会将父进程的内容复制一份给子进程。

Pastedfrom <http://www.cnblogs.com/biyeymyhjob/archive/2012/07/20/2601655.html>

 

2：进程间的通信

管道(有名管道和无名管道)共享内存信号信号量 消息队列

 

2.1管道

#include<stdio.h>

#include<stdlib.h>

#include<unistd.h>

#include<sys/types.h>

#include<string.h>

 

int main()

{

int  pipe_fd[2];

char r_buf[10];

char w_buf[10];

int local_int = 8;

pid_t pid;

memset(r_buf,0,sizeof(r_buf));

memset(w_buf,0,sizeof(w_buf));

pipe(pipe_fd);

pid = fork();

if(pid == 0)

{

printf("This is the child process\n");

local_int = 1;

int r_num;

printf("Child num is %d\n",local_int);

sleep(1);

//r_num=read(pipe_fd[0],r_buf,sizeof(r_buf)/sizeof(r_buf[0]));

r_num=read(pipe_fd[0],r_buf,100);

printf("read num is %d,and the data is%d\n",r_num,atoi(r_buf));

close(pipe_fd[0]);

}

else

{

close(pipe_fd[0]);

strcpy(w_buf,"111");

write(pipe_fd[1],w_buf,strlen(w_buf));

close(pipe_fd[1]);

printf("parent write is over\n");

sleep(3);

printf("This is the parent process\n");

printf("Parent num is %d\n",local_int);

}

printf("==================\n");

return 0;

}

Pipe_fd[0]为读端，pipe_fd[1]为写端。

注意：

1)读完之后管道的数据就不存在，最好放到一个变量中

2)如果读进程不读走管道缓冲区中的数据，那么写操作将一直阻塞。

3)如果写进程不向管道缓冲区中的写数据，那么读操作将一直阻塞。

有名管道

intmkfifo(const char * pathname, mode_t mode)

 

#include<stdio.h>

#include<unistd.h>

#include<sys/types.h>

#include<errno.h>

#include<fcntl.h>

#include<string.h>

#defineFIFO_SERVER "/tmp/fifoserver"

int main(void)

{

int local_int = 8;

pid_t pid;

char w_buf[20];

char r_buf[20];

int fd;

memset(w_buf,2,sizeof(w_buf));

memset(r_buf,0,sizeof(r_buf));

if((mkfifo(FIFO_SERVER,O_CREAT|O_EXCL)<0)&&(errno!=EEXIST))

printf("cannot create fifoserver\n");

fd=open(FIFO_SERVER,O_RDWR,0);

pid = fork();

if(pid == 0)

{

int real_wnum=0;

printf("This is the child process\n");

local_int = 1;

strcpy(w_buf,"111");

 

real_wnum=write(fd,w_buf,strlen(w_buf));

printf("real_wnum= %d\n",real_wnum);

printf("Child num is %d\n",local_int);

}

else

{

int real_rnum = 0;

sleep(2);

printf("This is the parent process\n");

real_rnum = read(fd,r_buf,sizeof(r_buf));

printf("real_rnum= %d\n",real_rnum);

printf("real_rnum %d,and the data is%d\n",real_rnum,atoi(r_buf));

printf("Parent num is %d\n",local_int);

close(fd);

}

printf("==================\n");

return 0;

}

管道的区别：

1)无名管道没有名字，只能用于亲缘关系的进程间通信

2)有名管道是以文件形式存在在文件系统中，只要访问该路径，就可以相互通信

Pastedfrom <http://www.ibm.com/developerworks/cn/linux/l-ipc/part1/>