select example

// C program to illustrate 
// non I/O blocking calls 
#include <string.h> 
#include <stdio.h> 
#include <stdlib.h>
#include <unistd.h> 
#include <fcntl.h> // library for fcntl function 
#define MSGSIZE 16 
char* msg1 ="hello"; 
char* msg2 ="bye !!"; 

void parent_read(int p[]);
void child_write(int p[]);

int main() 
{ 
	int p[2], i; 

	// error checking for pipe 
	if (pipe(p) < 0) 
		exit(1); 

	// error checking for fcntl 
	//if (fcntl(p[0], F_SETFL, fcntl(p[0], F_GETFL, 0) & ~O_NONBLOCK) < 0) 
	if (fcntl(p[0], F_SETFL, O_NONBLOCK) < 0) 
		exit(2); 

	// continued 
	switch (fork()) { 

	// error 
	case -1: 
		exit(3); 

	// 0 for child process 
	case 0: 
		child_write(p); 
		break; 

	default: 
		parent_read(p); 
		break; 
	} 
	return 0; 
} 
void parent_read(int p[]) 
{ 
	int nread; 
	char buf[MSGSIZE];

	
	struct timeval master_tv, temp_tv;
	master_tv.tv_sec = 5;
    master_tv.tv_usec = 0;

	fd_set master_readfds, temp_readfds;
	FD_ZERO(&master_readfds);
	FD_SET(p[0], &master_readfds);
	FD_SET(STDIN_FILENO, &master_readfds);
	

	// write link 
	//close(p[1]); 
    
	while (1) {
		memcpy(&temp_readfds, &master_readfds, sizeof(master_readfds));
	    memcpy(&temp_tv, &master_tv, sizeof(master_tv));
	    memset(buf, '\0', MSGSIZE * sizeof(char));

		nread = select(FD_SETSIZE, &temp_readfds, NULL, NULL, &temp_tv);
		printf("nread:%d\n",nread);
		if(nread == 0){
			printf("Timeout\n");
		}
		if (FD_ISSET(p[0], &temp_readfds)){
			nread = read(p[0], buf, MSGSIZE);
			printf("buf:%s\n", buf);
		}
		if (FD_ISSET(STDIN_FILENO, &temp_readfds)){
			nread = read(STDIN_FILENO, buf, MSGSIZE - 1);
			buf[strcspn(buf, "\n")] = '\0';
			printf("klavyeden %s girildi\n", buf);
		}
		// // read call if return -1 then pipe is 
		// // empty because of fcntl 
		// nread = read(p[0], buf, MSGSIZE); 
		// switch (nread) { 
		// case -1: 

		// 		printf("(pipe empty)\n"); 
		// 		//sleep(1); 
		// 		break; 

		// // case 0 means all bytes are read and EOF(end of conv.) 
		// case 0: 
		// 	printf("End of conversation\n"); 

		// 	// read link 
		// 	close(p[0]); 

		// 	exit(0); 
		// default: 

		// 	// text read 
		// 	// by default return no. of bytes 
		// 	// which read call read at that time 
		// 	printf("MSG = % s\n", buf); 
		// }
	}
} 
void child_write(int p[]) 
{ 
	int i; 

	// read link 
	// close(p[0]); 

	// write 3 times "hello" in 3 second interval 
	for (i = 0; i < 3; i++) { 
		write(p[1], msg1, MSGSIZE); 
		sleep(3); 
	} 

	// write "bye" one times 
	write(p[1], msg2, MSGSIZE); 

	// here after write all bytes then write end 
	// doesn't close so read end block but 
	// because of fcntl block doesn't happen.. 
	exit(0); 
}