[hackers] [ubase] Implement fifo listener mode for respawn || sin

[git]

commit 0e6d7ca2864634a9aecf7c03e40e1fcd046f826b
Author: sin <s...@2f30.org>
Date:   Mon Apr 21 11:48:09 2014 +0100

    Implement fifo listener mode for respawn

diff --git a/respawn.1 b/respawn.1
index f9d68a1..05ad86b 100644
--- a/respawn.1
+++ b/respawn.1
@@ -2,7 +2,7 @@
 .SH NAME
 BrespawnR - Spawn the given command repeatedly
 .SH SYNOPSIS
-BrespawnR [B-dI NR] IcmdR [Iargs...R]
+BrespawnR [B-lI fifoR] [B-dI NR] IcmdR [Iargs...R]
 .SH DESCRIPTION
 BrespawnR spawns the given IcmdR in a new session
 repeatedly.
@@ -10,3 +10,9 @@ repeatedly.
 .TP
 B-dR
 Set the delay between invocations of IcmdR.  It defaults to 0.
+.TP
+B-lR
+Listen on the specified IfifoR for writes.  For each write
+spawn a new instance of IcmdR.  This can be used in conjunction
+with a process supervisor to restart a particular program.  The B-lR
+and B-dR options are incompatible.  All writes are discarded.
diff --git a/respawn.c b/respawn.c
index 453c534..4f65e04 100644
--- a/respawn.c
+++ b/respawn.c
@@ -1,6 +1,11 @@
 /* See LICENSE file for copyright and license details. */
+#include <fcntl.h>
 #include <errno.h>
+#include <stdio.h>
 #include <stdlib.h>
+#include <sys/select.h>
+#include <sys/time.h>
+#include <sys/stat.h>
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <unistd.h>
@@ -9,20 +14,28 @@
 static void
 usage(void)
 {
-       eprintf("usage: respawn [-d N] cmd [args...]
");
+       eprintf("usage: respawn [-l fifo] [-d N] cmd [args...]
");
 }
 
 int
 main(int argc, char *argv[])
 {
+       char *fifo = NULL;
+       unsigned int delay = 0;
        pid_t pid;
+       char buf[BUFSIZ];
        int savederrno;
-       unsigned int delay = 0;
+       int fd;
+       ssize_t n;
+       fd_set rdfd;
 
        ARGBEGIN {
        case 'd':
                delay = estrtol(EARGF(usage()), 0);
                break;
+       case 'l':
+               fifo = EARGF(usage());
+               break;
        default:
                usage();
        } ARGEND;
@@ -30,7 +43,30 @@ main(int argc, char *argv[])
        if(argc < 1)
                usage();
 
+       if (fifo && delay > 0)
+               usage();
+
+       if (fifo) {
+               fd = open(fifo, O_RDWR | O_NONBLOCK);
+               if (fd < 0)
+                       eprintf("open %s:", fifo);
+       }
+
        while (1) {
+               if (fifo) {
+                       FD_ZERO(&rdfd);
+                       FD_SET(fd, &rdfd);
+                       n = select(fd + 1, &rdfd, NULL, NULL, NULL);
+                       if (n < 0)
+                               eprintf("select:");
+                       if (n == 0 || FD_ISSET(fd, &rdfd) == 0)
+                               continue;
+                       while ((n = read(fd, buf, sizeof(buf))) > 0)
+                               ;
+                       if (n < 0)
+                               if (errno != EAGAIN)
+                                       eprintf("read %s:", fifo);
+               }
                pid = fork();
                if (pid < 0)
                        eprintf("fork:");
@@ -47,7 +83,8 @@ main(int argc, char *argv[])
                        waitpid(pid, NULL, 0);
                        break;
                }
-               sleep(delay);
+               if (!fifo)
+                       sleep(delay);
        }
        /* not reachable */
        return EXIT_SUCCESS;