Linux环境进程间通信（一）：管道及有名管道

#include <unistd.h>
int pipe(int fd[2])

 /**************
 * readtest.c *
 **************/
#include <unistd.h>
#include <sys/types.h>
#include <errno.h>
main()
{
	int pipe_fd[2];
	pid_t pid;
	char r_buf[100];
	char w_buf[4];
	char* p_wbuf;
	int r_num;
	int cmd;
	
	memset(r_buf,0,sizeof(r_buf));
	memset(w_buf,0,sizeof(r_buf));
	p_wbuf=w_buf;
	if(pipe(pipe_fd)<0)
	{
		printf("pipe create error\n");
		return -1;
	}
	
	if((pid=fork())==0)
	{
		printf("\n");
		close(pipe_fd[1]);
		sleep(3);//确保父进程关闭写端
	    r_num=read(pipe_fd[0],r_buf,100);
printf(	"read num is %d   the data read from the pipe is %d\n",r_num,atoi(r_buf));
		
		close(pipe_fd[0]);
		exit();
	}
	else if(pid>0)
	{
	close(pipe_fd[0]);//read
	strcpy(w_buf,"111");
	if(write(pipe_fd[1],w_buf,4)!=-1)
		printf("parent write over\n");
	close(pipe_fd[1]);//write
		printf("parent close fd[1] over\n");
	sleep(10);
	}	
}
 /**************************************************
 * 程序输出结果：
 * parent write over
 * parent close fd[1] over
 * read num is 4   the data read from the pipe is 111
 * 附加结论：
 * 管道写端关闭后，写入的数据将一直存在，直到读出为止.
 ****************************************************/ 
 

#include <unistd.h>
#include <sys/types.h>
main()
{
	int pipe_fd[2];
	pid_t pid;
	char r_buf[4];
	char* w_buf;
	int writenum;
	int cmd;
	
	memset(r_buf,0,sizeof(r_buf));
	if(pipe(pipe_fd)<0)
	{
		printf("pipe create error\n");
		return -1;
	}
	
	if((pid=fork())==0)
	{
		close(pipe_fd[0]);
		close(pipe_fd[1]);
		sleep(10);	
		exit();
	}
	else if(pid>0)
	{
	sleep(1);  //等待子进程完成关闭读端的操作
	close(pipe_fd[0]);//write
	w_buf="111";
	if((writenum=write(pipe_fd[1],w_buf,4))==-1)
		printf("write to pipe error\n");
	else	
		printf("the bytes write to pipe is %d \n", writenum);
	
	close(pipe_fd[1]);
	}	
}

#include <unistd.h>
#include <sys/types.h>
#include <errno.h>
main(int argc,char**argv)
{
	int pipe_fd[2];
	pid_t pid;
	char r_buf[4096];
	char w_buf[4096*2];
	int writenum;
	int rnum;
	memset(r_buf,0,sizeof(r_buf));	
	if(pipe(pipe_fd)<0)
	{
		printf("pipe create error\n");
		return -1;
	}
	
	if((pid=fork())==0)
	{
		close(pipe_fd[1]);
		while(1)
		{
		sleep(1);	
		rnum=read(pipe_fd[0],r_buf,1000);
		printf("child: readnum is %d\n",rnum);
		}
		close(pipe_fd[0]);
		
		exit();
	}
	else if(pid>0)
	{
	close(pipe_fd[0]);//write
	memset(r_buf,0,sizeof(r_buf));	
	if((writenum=write(pipe_fd[1],w_buf,1024))==-1)
		printf("write to pipe error\n");
	else	
		printf("the bytes write to pipe is %d \n", writenum);
	writenum=write(pipe_fd[1],w_buf,4096);
	close(pipe_fd[1]);
	}	
}
输出结果：
the bytes write to pipe 1000
the bytes write to pipe 1000  //注意，此行输出说明了写入的非原子性
the bytes write to pipe 1000
the bytes write to pipe 1000
the bytes write to pipe 1000
the bytes write to pipe 120  //注意，此行输出说明了写入的非原子性
the bytes write to pipe 0
the bytes write to pipe 0
......

30) SIGPWR	31) SIGSYS	32) SIGRTMIN	33) SIGRTMIN+1
34) SIGRTMIN+2	35) SIGRTMIN+3	36) SIGRTMIN+4	37) SIGRTMIN+5
38) SIGRTMIN+6	39) SIGRTMIN+7	40) SIGRTMIN+8	41) SIGRTMIN+9
42) SIGRTMIN+10	43) SIGRTMIN+11	44) SIGRTMIN+12	45) SIGRTMIN+13
46) SIGRTMIN+14	47) SIGRTMIN+15	48) SIGRTMAX-15	49) SIGRTMAX-14

#include <unistd.h>
#include <sys/types.h>
main()
{
	int pipe_fd[2];
	pid_t pid;
	char r_buf[4];
	char** w_buf[256];
	int childexit=0;
	int i;
	int cmd;
	
	memset(r_buf,0,sizeof(r_buf));
	if(pipe(pipe_fd)<0)
	{
		printf("pipe create error\n");
		return -1;
	}
	if((pid=fork())==0)
	//子进程：解析从管道中获取的命令，并作相应的处理
	{
		printf("\n");
		close(pipe_fd[1]);
		sleep(2);
		
		while(!childexit)
		{	
			read(pipe_fd[0],r_buf,4);
			cmd=atoi(r_buf);
			if(cmd==0)
			{
printf("child: receive command from parent over\n now child process exit\n");
				childexit=1;
			}
			
		       else if(handle_cmd(cmd)!=0)
				return;
			sleep(1);
		}
		close(pipe_fd[0]);
		exit();
	}
	else if(pid>0)
	//parent: send commands to child
	{
	close(pipe_fd[0]);
	w_buf[0]="003";
	w_buf[1]="005";
	w_buf[2]="777";
	w_buf[3]="000";
	for(i=0;i<4;i++)
		write(pipe_fd[1],w_buf[i],4);
	close(pipe_fd[1]);
	}	
}
//下面是子进程的命令处理函数（特定于应用）：
int handle_cmd(int cmd)
{
if((cmd<0)||(cmd>256))
//suppose child only support 256 commands
	{
	printf("child: invalid command \n");
	return -1;
	}
printf("child: the cmd from parent is %d\n", cmd);
return 0;
}

#include <sys/types.h>
#include <sys/stat.h>
int mkfifo(const char * pathname, mode_t mode)

#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <fcntl.h>
#define FIFO_SERVER "/tmp/fifoserver"
main(int argc,char** argv)
//参数为即将写入的字节数
{
	int fd;
	char w_buf[4096*2];
	int real_wnum;
	memset(w_buf,0,4096*2);
	if((mkfifo(FIFO_SERVER,O_CREAT|O_EXCL)<0)&&(errno!=EEXIST))
		printf("cannot create fifoserver\n");
	if(fd==-1)
		if(errno==ENXIO)
			printf("open error; no reading process\n");
		
     	fd=open(FIFO_SERVER,O_WRONLY|O_NONBLOCK,0);
	//设置非阻塞标志
	//fd=open(FIFO_SERVER,O_WRONLY,0);
	//设置阻塞标志
	real_wnum=write(fd,w_buf,2048);
	if(real_wnum==-1)
	{
		if(errno==EAGAIN)
			printf("write to fifo error; try later\n");
	}
	else 
		printf("real write num is %d\n",real_wnum);
	real_wnum=write(fd,w_buf,5000);
	//5000用于测试写入字节大于4096时的非原子性
	//real_wnum=write(fd,w_buf,4096);
	//4096用于测试写入字节不大于4096时的原子性
	
	if(real_wnum==-1)
		if(errno==EAGAIN)
			printf("try later\n");
}

#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <fcntl.h>
#define FIFO_SERVER "/tmp/fifoserver"
main(int argc,char** argv)
{
	char r_buf[4096*2];
	int  fd;
	int  r_size;
	int  ret_size;
	r_size=atoi(argv[1]);
	printf("requred real read bytes %d\n",r_size);
	memset(r_buf,0,sizeof(r_buf));
	fd=open(FIFO_SERVER,O_RDONLY|O_NONBLOCK,0);
	//fd=open(FIFO_SERVER,O_RDONLY,0);
	//在此处可以把读程序编译成两个不同版本：阻塞版本及非阻塞版本
	if(fd==-1)
	{
		printf("open %s for read error\n");
		exit();	
	}
	while(1)
	{
		
		memset(r_buf,0,sizeof(r_buf));
		ret_size=read(fd,r_buf,r_size);
		if(ret_size==-1)
			if(errno==EAGAIN)
				printf("no data avlaible\n");
		printf("real read bytes %d\n",ret_size);
		sleep(1);
	}	
	pause();
	unlink(FIFO_SERVER);
}