/*
* File locker
*
- * Usage: with-lock-ex -<mode> <lockfile> <command> <args>...
+ * Usage:
+ * with-lock-ex -<mode> [-t <secs>] <lockfile> <command> <args>...
+ * with-lock-ex -l <lockfile>
*
* modes are
* w wait for the lock
* f fail if the lock cannot be acquired
* q silently do nothing if the lock cannot be acquired
+ * l show who is waiting (print "none" or "read <pid>"
+ * or "write <pid>"; lockfile opened for reading;
+ * no command may be specified)
+ *
+ * If -t is specified, then with-lock-ex will wait for up to <secs>
+ * seconds to acquire the lock, and then fail or silently do nothing
+ * (depending on whether -f or -q is specified). You cannot specify
+ * a timeout for modes l or w.
*
* with-lock-ex will open and lock the lockfile for writing and
* then feed the remainder of its arguments to exec(2); when
* compatibility with an earlier version).
*
* This file written by me, Ian Jackson, in 1993, 1994, 1995, 1996,
- * 1998, 1999. I hereby place it in the public domain.
+ * 1998, 1999, 2016.
+ *
+ * Copyright 1993-2016 Ian Jackson in some jurisdictions
+ * Copyright 2017 Ian Jackson in all jurisdictions
+ * Copyright 2017 Genome Research Ltd
+ *
+ * (MIT licence:)
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * SOFTWARE IN THE PUBLIC INTEREST, INC. BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
*/
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <sys/stat.h>
+#include <limits.h>
+#include <signal.h>
+#include <sys/time.h>
static const char *cmd;
exit(255);
}
+static void badusage(void) __attribute__((noreturn));
+
+static void badusage(void) {
+ fputs("usage: with-lock-ex -w|-q|-f [-t <secs>] <lockfile> <command> <args>...\n"
+ " with-lock-ex -l <lockfile>\n"
+ " with-lock-ex <lockfile> <command> <args>...\n",
+ stderr);
+ exit(255);
+}
+
+static int mode;
+
+/* This signal handler uses unsafe functions, so MUST NOT be callable
+ * during an unsafe function, as that is Undefined Behaviour
+ */
+static void alrm_handler(int signum) {
+ if (mode=='q') {
+ exit(0);
+ } else {
+ fprintf(stderr,
+ "with-lock-ex %s: timer expired while trying to acquire lock\n",
+ cmd);
+ exit(255);
+ }
+}
+
int main(int argc, char **argv) {
- int fd, mode, um;
+ int fd, um, c, r;
struct stat stab, fstab;
- long cloexec;
+ long cloexec, secs=0;
struct flock fl;
- const char *p;
-
- if (argc >= 3 && !strcmp((p= strrchr(argv[0],'/')) ? ++p : argv[0], "with-lock")) {
- mode= 'f';
- } else if (argc < 4 || argv[1][0] != '-' || argv[1][2] ||
- ((mode= argv[1][1]) != 'w' && mode != 'q' && mode != 'f')) {
- fputs("usage: with-lock-ex -w|-q|-f <lockfile> <command> <args>...\n"
- " with-lock <lockfile> <command> <args>...\n",
- stderr);
+ char *endptr;
+ sigset_t sigs, oldsigs;
+ struct sigaction siga;
+ struct itimerval itv;
+
+ mode= 'x';
+ while ((c= getopt(argc,argv,"+wfqlt:")) != -1) {
+ switch(c) {
+ case 'l':
+ case 'w':
+ case 'f':
+ case 'q':
+ if (mode != 'x') badusage();
+ mode= c;
+ break;
+ case 't':
+ errno = 0;
+ secs = strtol(optarg, &endptr, 0);
+ if (*endptr || endptr==optarg || errno==ERANGE)
+ fail("parsing timeout value");
+ if (secs < 0) {
+ fprintf(stderr,"timeout value must be >=0\n");
+ exit(255);
+ }
+ break;
+ default:
+ badusage();
+ }
+ }
+
+ if (secs && (mode=='l' || mode=='w')) {
+ fputs("-t only allowed with -q or -f.\n", stderr);
exit(255);
- } else {
- argv++; argc--;
}
+
+ argv += optind-1; argc -= optind-1;
+ if (argc < 2) badusage();
+
+ if (secs) {
+ if (sigemptyset(&sigs)) fail("Initialising signal set");
+ if (sigaddset(&sigs,SIGALRM)) fail("Adding SIGALRM to signal set");
+ if (sigprocmask(SIG_BLOCK,&sigs,&oldsigs)) fail("Blocking SIGALRM");
+ memset(&siga,0,sizeof(siga));
+ siga.sa_handler=alrm_handler;
+ if (sigaction(SIGALRM,&siga,NULL)) fail("Installing SIGALRM handler");
+ memset(&itv,0,sizeof(itv));
+ itv.it_value.tv_sec=secs;
+ if (setitimer(ITIMER_REAL,&itv,NULL)) fail("Setting timer");
+ }
+
cmd= argv[2];
um= umask(0777); if (um==-1) fail("find umask");
if (umask(um)==-1) fail("reset umask");
for (;;) {
-
- fd= open(argv[1],O_RDWR|O_CREAT,0666&~(um|((um&0222)<<1)));
+
+ int openmode = mode=='l' ? O_RDONLY : O_RDWR|O_CREAT;
+
+ fd= open(argv[1],openmode,0666&~(um|((um&0222)<<1)));
if (fd<0) fail(argv[1]);
for (;;) {
fl.l_type= F_WRLCK;
fl.l_whence= SEEK_SET;
fl.l_start= 0;
- fl.l_len= 1;
- if (fcntl(fd, mode=='w' ? F_SETLKW : F_SETLK, &fl) != -1) break;
+ fl.l_len= mode=='l' ? 0 : 1;
+ if (secs) sigprocmask(SIG_UNBLOCK,&sigs,NULL);
+ r = fcntl(fd,
+ mode=='l' ? F_GETLK :
+ mode=='w' || secs > 0 ? F_SETLKW :
+ F_SETLK,
+ &fl);
+ if (secs) sigprocmask(SIG_BLOCK,&sigs,NULL);
+ if (!r) {
+ break;
+ }
if (mode=='q' &&
(errno == EAGAIN || errno == EWOULDBLOCK || errno == EBUSY))
exit(0);
if (errno != EINTR) fail("could not acquire lock");
}
+ if (mode=='l') {
+ if (fl.l_pid) {
+ printf("%s %lu\n",
+ fl.l_type == F_WRLCK ? "write" :
+ fl.l_type == F_RDLCK ? "read" : "unknown",
+ (unsigned long)fl.l_pid);
+ } else {
+ printf("none\n");
+ }
+ if (ferror(stdout)) fail("print to stdout\n");
+ exit(0);
+ }
if (fstat(fd, &fstab)) fail("could not fstat lock fd");
if (stat(argv[1], &stab)) {
close(fd);
}
+ if (secs) {
+ itv.it_value.tv_sec=0;
+ if (setitimer(ITIMER_REAL,&itv,NULL)) fail("Clearing timer");
+ sigprocmask(SIG_SETMASK,&oldsigs,NULL);
+ siga.sa_handler=SIG_DFL;
+ sigaction(SIGALRM,&siga,NULL);
+ }
+
cloexec= fcntl(fd, F_GETFD); if (cloexec==-1) fail("fcntl F_GETFD");
cloexec &= ~1;
if (fcntl(fd, F_SETFD, cloexec)==-1) fail("fcntl F_SETFD");
~ian / chiark-utils.git / blobdiff