timers/timed_read.c

+/* timed_read.c
+
+   Demonstrate the use of a timer to place a timeout on a blocking system call
+   (read(2) in this case).
+*/
 #include <signal.h>
 #include "tlpi_hdr.h"
 
 #define BUF_SIZE 200
 
 static void     /* SIGALRM handler: interrupts blocked system call */
 handler(int sig)
 {
     printf("Caught signal\n");          /* UNSAFE (see Section 21.1.2) */
 }
 
 int
 main(int argc, char *argv[])
 {
     struct sigaction sa;
     char buf[BUF_SIZE];
     ssize_t numRead;
     int savedErrno;
 
     if (argc > 1 && strcmp(argv[1], "--help") == 0)
         usageErr("%s [num-secs [restart-flag]]\n", argv[0]);
 
     /* Set up handler for SIGALRM. Allow system calls to be interrupted,
        unless second command-line argument was supplied. */
 
     sa.sa_flags = (argc > 2) ? SA_RESTART : 0;
     sigemptyset(&sa.sa_mask);
     sa.sa_handler = handler;
     if (sigaction(SIGALRM, &sa, NULL) == -1)
         errExit("sigaction");
 
     alarm((argc > 1) ? getInt(argv[1], GN_NONNEG, "num-secs") : 10);
 
     numRead = read(STDIN_FILENO, buf, BUF_SIZE);
 
     savedErrno = errno;                 /* In case alarm() changes it */
     alarm(0);                           /* Ensure timer is turned off */
     errno = savedErrno;
 
     /* Determine result of read() */
 
     if (numRead == -1) {
         if (errno == EINTR)
             printf("Read timed out\n");
         else
             errMsg("read");
     } else {
         printf("Successful read (%ld bytes): %.*s",
                 (long) numRead, (int) numRead, buf);
     }
 
     exit(EXIT_SUCCESS);
 }