--- /dev/null
+/* lckdo.c: run a program with a lock held,
+ * to prevent multiple processes running in parallel.
+ * Use just like `nice' or `nohup'.
+ * Written by Michael Tokarev <mjt@tls.msk.ru>
+ * Public domain.
+ */
+
+#define _GNU_SOURCE
+#define _BSD_SOURCE
+#include <unistd.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <sysexits.h>
+#include <sys/file.h>
+#include <sys/wait.h>
+#include <signal.h>
+
+/* compile with -DUSE_FLOCK to use flock() instead of fcntl() */
+
+#if !defined(USE_FLOCK) && !defined(F_SETLKW)
+# define USE_FLOCK
+#endif
+
+#ifndef __GNUC__
+# ifndef __attribute__
+# define __attribute__(x)
+# endif
+#endif
+
+static char *progname;
+static void
+__attribute__((format(printf,3,4)))
+__attribute__((noreturn))
+error(int errnum, int exitcode, const char *fmt, ...) {
+ va_list ap;
+ fprintf(stderr, "%s: ", progname);
+ va_start(ap, fmt); vfprintf(stderr, fmt, ap); va_end(ap);
+ if (errnum) fprintf(stderr, ": %s\n", strerror(errnum));
+ else fputs("\n", stderr);
+ exit(exitcode);
+}
+
+static const char *lckfile;
+static int quiet;
+
+static void sigalarm(int sig) {
+ if (quiet)
+ _exit(EX_TEMPFAIL);
+ error(0, EX_TEMPFAIL,
+ "lock file `%s' is already locked (timeout waiting)", lckfile);
+ sig = sig;
+}
+
+int main(int argc, char **argv) {
+ int fd;
+ int c;
+ int create = O_CREAT;
+ int dofork = 1;
+ int waittime = 0;
+ int shared = 0;
+ int test = 0;
+ int fdn = -1;
+#ifndef USE_FLOCK
+ struct flock fl;
+#endif
+
+ if ((progname = strrchr(argv[0], '/')) == NULL) progname = argv[0];
+ else argv[0] = ++progname;
+
+ if (argc == 1) {
+ printf(
+"%s: execute a program with a lock set.\n"
+"Usage: %s [options] lockfile program [arguments]\n"
+"where options are:\n"
+" -w - if the lock is already held by another process,\n"
+" wait for it to complete instead of failing immediately\n"
+" -W sec - the same as -w but wait not more than sec seconds\n"
+" -e - execute the program directly, no fork/wait\n"
+" (keeps extra open file descriptor)\n"
+" -E nnn - set the fd# to keep open in -e case (implies -e)\n"
+" -n - do not create the lock file if it does not exist\n"
+" -q - produce no output if lock is already held\n"
+" -s - lock in shared (read) mode\n"
+" -x - lock in exclusive (write) mode (default)\n"
+" -t - test for lock existence"
+#ifndef USE_FLOCK
+ " (just prints pid if any with -q)\n"
+#endif
+" (implies -n)\n"
+ , progname, progname);
+ return 0;
+ }
+
+ while((c = getopt(argc, argv, "+wW:neE:sxtq")) != EOF)
+ switch(c) {
+ case 'w':
+ if (!waittime)
+ waittime = -1;
+ break;
+ case 'W':
+ if ((waittime = atoi(optarg)) < 1)
+ error(0, EX_USAGE, "invalid wait time `%s'", optarg);
+ break;
+ case 't':
+ test = 1;
+ /* fall */
+ case 'n':
+ create = 0;
+ break;
+ case 'E':
+ if ((fdn = atoi(optarg)) < 0 || fdn == 2)
+ error(0, EX_USAGE, "invalid fd# `%s'", optarg);
+ /* fall */
+ case 'e':
+ dofork = 0;
+ break;
+ case 's':
+ shared = 1;
+ break;
+ case 'x':
+ shared = 0;
+ break;
+ case 'q':
+ quiet = 1;
+ break;
+ default:
+ return EX_USAGE;
+ }
+
+ argc -= optind; argv += optind;
+ if (!argc || (!test && argc < 2))
+ error(0, EX_USAGE, "too few arguments given");
+
+ lckfile = *argv++;
+
+#ifdef USE_FLOCK
+ create |= O_RDONLY;
+#else
+ if (!test)
+ create |= shared ? O_RDONLY : O_WRONLY;
+#endif
+ fd = open(lckfile, create, 0666);
+ if (fd < 0) {
+ if (test && errno == ENOENT) {
+ if (!quiet)
+ printf("lockfile `%s' is not locked\n", lckfile);
+ return 0;
+ }
+ error(errno, EX_CANTCREAT, "unable to open `%s'", lckfile);
+ }
+
+ if (!test && fdn >= 0) {
+ /* dup it early to comply with stupid POSIX fcntl locking semantics */
+ if (dup2(fd, fdn) < 0)
+ error(errno, EX_OSERR, "dup2(%d,%d) failed", fd, fdn);
+ close(fd);
+ fd = fdn;
+ }
+
+ if (test)
+ waittime = 0;
+ else if (waittime > 0) {
+ alarm(waittime);
+ signal(SIGALRM, sigalarm);
+ }
+#ifdef USE_FLOCK
+ c = flock(fd, (shared ? LOCK_SH : LOCK_EX) | (waittime ? 0 : LOCK_NB));
+ if (test && c < 0 &&
+ (errno == EWOULDBLOCK || errno == EAGAIN || errno == EACCES)) {
+ if (!quiet)
+ printf("lockfile `%s' is locked\n", lckfile);
+ else
+ printf("locked\n");
+ return EX_TEMPFAIL;
+ }
+#else
+ memset(&fl, 0, sizeof(fl));
+ fl.l_type = shared ? F_RDLCK : F_WRLCK;
+ c = fcntl(fd, test ? F_GETLK : waittime ? F_SETLKW : F_SETLK, &fl);
+ if (test && c == 0) {
+ if (fl.l_type == F_UNLCK) {
+ if (!quiet)
+ printf("lockfile `%s' is not locked\n", lckfile);
+ return 0;
+ }
+ if (!quiet)
+ printf("lockfile `%s' is locked by process %d\n", lckfile, fl.l_pid);
+ else
+ printf("%d\n", fl.l_pid);
+ return EX_TEMPFAIL;
+ }
+#endif
+ if (waittime > 0)
+ alarm(0);
+ if (c < 0) {
+ if (errno != EWOULDBLOCK && errno != EAGAIN && errno != EACCES)
+ error(errno, EX_OSERR, "unable to lock `%s'", lckfile);
+ else if (quiet)
+ return EX_TEMPFAIL;
+ else
+ error(0, EX_TEMPFAIL, "lockfile `%s' is already locked", lckfile);
+ }
+
+ if (dofork) {
+ pid_t pid;
+ int flags = fcntl(fd, F_GETFD, 0);
+ if (flags < 0)
+ error(errno, EX_OSERR, "fcntl() failed");
+ fcntl(fd, F_SETFD, flags | FD_CLOEXEC);
+ pid = fork();
+ if (pid < 0)
+ error(errno, EX_OSERR, "unable to fork");
+ else if (pid) {
+ if (wait(&c) < 0)
+ error(errno, EX_OSERR, "wait() failed");
+ if (WIFSIGNALED(c))
+ error(0, EX_SOFTWARE, "%s: %s", *argv, strsignal(WTERMSIG(c)));
+ return WEXITSTATUS(c);
+ }
+ }
+ execvp(*argv, argv);
+ error(errno, EX_OSERR, "unable to execute %s", *argv);
+}
--- /dev/null
+<?xml version="1.0" encoding="utf-8"?>
+
+<!--
+
+Written by Michael Tokarev <mjt@tls.msk.ru>
+Public domain.
+
+-->
+
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook V4.4//EN"
+"file:///usr/share/xml/docbook/schema/dtd/4.4/docbookx.dtd"
+[]>
+
+<refentry>
+ <refentryinfo>
+ <address>
+ <email>mjt@tls.msk.ru</email>
+ </address>
+ <author>
+ <firstname>Michael</firstname>
+ <surname>Tokarev</surname>
+ </author>
+ <date>2007-08-15</date>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>lckdo</refentrytitle>
+ <manvolnum>1</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>lckdo</refname>
+ <refpurpose>run a program with a lock held</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <cmdsynopsis>
+ <command>lckdo</command>
+ <arg>options</arg>
+ <arg choice="req">lockfile</arg>
+ <arg choice="req">program</arg>
+ <arg>arguments</arg>
+ </cmdsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>DESCRIPTION</title>
+
+ <para><command>lckdo</command> runs a program with a lock
+ held, in order to prevent multiple processes from running in
+ parallel. Use just like <command>nice</command> or
+ <command>nohup</command>.</para>
+
+ </refsect1>
+
+ <refsect1>
+ <title>OPTIONS</title>
+
+ <variablelist>
+
+ <varlistentry>
+ <term><option>-w</option></term>
+ <listitem>
+ <para>If the lock is already held by another process,
+ wait for it to complete instead of failing
+ immediately.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>-W {sec}</option></term>
+ <listitem>
+ <para>The same as -w but wait not more than sec
+ seconds.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>-e</option></term>
+ <listitem>
+ <para>Execute the program directly without forking and
+ waiting (keeps an extra file descriptor open).</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>-E {nnn}</option></term>
+ <listitem>
+ <para>Set the file descriptor number to keep open when
+ exec()ing (implies -e).</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>-n</option></term>
+ <listitem>
+ <para>Do not create the lock file if it does not
+ exist.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>-q</option></term>
+ <listitem>
+ <para>Produce no output if lock is already held.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>-s</option></term>
+ <listitem>
+ <para>Lock in shared (read) mode.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>-x</option></term>
+ <listitem>
+ <para>Lock in exclusive (write) mode (default).</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><option>-t</option></term>
+ <listitem>
+ <para>Test for lock existence.</para>
+ </listitem>
+ </varlistentry>
+
+ </variablelist>
+
+ </refsect1>
+
+ <refsect1>
+ <title>EXIT STATUS</title>
+
+ <para>If the lock was successfully acquired, the return value is that
+ of the program invoked by <command>lckdo</command>. If the lock
+ couldn't be acquired, EX_TEMPFAIL is returned. If there was a problem
+ opening/creating or locking the lock file, EX_CANTCREAT or EX_OSERR
+ will be returned.</para>
+
+ </refsect1>
+
+</refentry>
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