test/select/test11.c

   1 /*
   2  * Test name: test11.c
   3  *
   4  * Objetive: The purpose of this test is to make sure that select works
   5  * with pipes.
   6  *
   7  * Description:  The select checks are divided in checks on writing for the
   8  * parent process, which has the writing end of the pipe, and checks on reading
   9  * and exception on the child process, which has the reading end of pipe. So
  10  * when the first process is ready to write to the pipe it will request a string
  11  * from the terminal and send it through the pipe. If the string is 'exit' then
  12  * the pipe is closed. The child process is blocked in a select checking for read
  13  * and exception. If there is data to be read then it will perform the read and
  14  * prints the read data. If the pipe is closed (user typed 'exit'), the child
  15  * process finishes.
  16  *
  17  * Jose M. Gomez
  18  */
  19
  20 #include <time.h>
  21 #include <sys/types.h>
  22 #include <sys/wait.h>
  23 #include <sys/asynchio.h>
  24 #include <fcntl.h>
  25 #include <unistd.h>
  26 #include <sys/select.h>
  27 #include <stdio.h>
  28 #include <stdlib.h>
  29 #include <limits.h>
  30 #include <string.h>
  31 #include <signal.h>
  32
  33 void pipehandler(int sig)
  34 {
  35
  36 }
  37
  38 void do_child(int data_pipe[])
  39 {
  40         /* reads from pipe and prints out the data */
  41         char data[2048];
  42         int retval;
  43         fd_set fds_read;
  44         fd_set fds_exception;
  45         struct timeval timeout;
  46
  47         signal(SIGPIPE, pipehandler);
  48         signal(SIGUSR1, pipehandler);
  49
  50         /* first, close the write part of the pipe, since it is not needed */
  51         close(data_pipe[1]);
  52
  53         while(1) {
  54                 FD_ZERO(&fds_read);
  55                 FD_ZERO(&fds_exception);
  56                 FD_SET(data_pipe[0], &fds_read);
  57                 FD_SET(data_pipe[0], &fds_exception);
  58                 timeout.tv_sec = 5;
  59                 timeout.tv_usec = 0;
  60                 retval = select(data_pipe[0]+1,  &fds_read, NULL, &fds_exception, &timeout);
  61                 if (retval == -1) {
  62                         perror("select");
  63                         fprintf(stderr, "child: Error in select\n");
  64                         continue;
  65                 } else printf("child select: %d\n", retval);
  66                 if (FD_ISSET(data_pipe[0], &fds_exception)) {
  67                         printf("child: exception fd set. quitting.\n");
  68                         break;
  69                 }
  70                 if (FD_ISSET(data_pipe[0], &fds_read)) {
  71                         printf("child: read fd set. reading.\n");
  72                         if ((retval = read(data_pipe[0], data, sizeof(data))) < 0) {
  73                                 perror("read");
  74                                 fprintf(stderr, "child: couldn't read from pipe\n");
  75                                 exit(-1);
  76                         }
  77                         if(retval == 0) {
  78                                 fprintf(stderr, "child: eof on pipe\n");
  79                                 break;
  80                         }
  81                         data[retval] = '\0';
  82                         printf("pid %d Pipe reads (%d): %s\n", getpid(), retval, data);
  83                 } else printf("child: no fd set\n");
  84         }
  85
  86         /* probably pipe was broken, or got EOF via the pipe. */
  87         exit(0);
  88 }
  89
  90 void do_parent(int data_pipe[])
  91 {
  92         char data[1024];
  93         int retval;
  94         fd_set fds_write;
  95
  96         signal(SIGPIPE, pipehandler);
  97         signal(SIGUSR1, pipehandler);
  98
  99         /* first, close the read part of pipe, since it is not needed */
 100         close(data_pipe[0]);
 101
 102         /* now enter a loop of read user input, and writing it to the pipe */
 103         while (1) {
 104                 FD_ZERO(&fds_write);
 105                 FD_SET(data_pipe[1], &fds_write);
 106                 printf("pid %d Waiting for pipe ready to write...\n", getpid());
 107                 retval = select(data_pipe[1]+1, NULL, &fds_write, NULL, NULL);
 108                 if (retval == -1) {
 109                         perror("select");
 110                         fprintf(stderr, "Parent: Error in select\n");
 111                         exit(-1);
 112                 }
 113
 114                 printf("Input data: ");
 115                 if(!gets(data)) {
 116                         printf("parent: eof; exiting\n");
 117                         break;
 118                 }
 119                 if (!strcmp(data, "exit"))
 120                         break;
 121                 if (!FD_ISSET(data_pipe[1], &fds_write)) {
 122                         fprintf(stderr, "parent: write fd not set?! retrying\n");
 123                         continue;
 124                 }
 125                 retval = write(data_pipe[1], &data, 1024);
 126                 if (retval == -1) {
 127                         perror("write");
 128                         fprintf(stderr, "Error writing on pipe\n");
 129                         exit(-1);
 130                 }
 131         }
 132
 133         /* got exit from user */
 134         close(data_pipe[1]);    /* close pipe, let child know we're done */
 135         wait(&retval);
 136         printf("Child exited with status: %d\n", retval);
 137         exit(0);
 138 }
 139
 140 void main(void) {
 141         int pipes[2];
 142         int retval;
 143         int pid;
 144
 145         /* create the pipe */
 146         retval = pipe(pipes);
 147         if (retval == -1) {
 148                 perror("pipe");
 149                 fprintf(stderr, "Error creating the pipe\n");
 150                 exit(-1);
 151         }
 152         pid = fork();
 153         if (pid == -1) {
 154                 fprintf(stderr, "Error forking\n");
 155                 exit(-1);
 156         }
 157
 158         if (pid == 0) /* child proc */
 159                 do_child(pipes);
 160         else
 161                 do_parent(pipes);
 162 }