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/*
* nq CMD... - run CMD... in background and in order, saving output to ,* files
*
* - requires POSIX.1-2008
* - enforcing order works like this:
* - every job has a flock(2)ed file ala ",TIMESTAMP.PID"
* - every job starts only after all earlier flock(2)ed files finished
* - the lock is released when job terminates
* - no sub-second file system time stamps are required, jobs are started
* with millisecond precision
* - we try hard to make the currently running ,* file have +x bit
* - you can re-queue jobs using "sh ,jobid"
*
* To the extent possible under law,
* Christian Neukirchen <chneukirchen@gmail.com>
* has waived all copyright and related or neighboring rights to this work.
* http://creativecommons.org/publicdomain/zero/1.0/
*/
#define _POSIX_C_SOURCE 200809L
#include <sys/file.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
void
swrite(int fd, char *str)
{
size_t l = strlen(str);
if (write(fd, str, l) != l) {
perror("write");
exit(222);
}
}
void
write_execline(int fd, int argc, char *argv[])
{
int i;
char *s;
swrite(fd, "exec");
for (i = 0; i < argc; i++) {
swrite(fd, " '");
for (s = argv[i]; *s; s++) {
if (*s == '\'')
swrite(fd, "'\\''");
else
write(fd, s, 1);
}
swrite(fd, "'");
}
}
int
main(int argc, char *argv[])
{
int dirfd, lockfd;
int pipefd[2];
char lockfile[32];
pid_t child;
struct timeval started;
struct dirent *ent;
/* timestamp is milliseconds since epoch. */
gettimeofday(&started, NULL);
int64_t ms = started.tv_sec*1000 + started.tv_usec/1000;
if (argc <= 1) {
swrite(2, "usage: nq CMD...\n");
exit(1);
}
char *path = getenv("NQDIR");
if (!path)
path = ".";
dirfd = open(path, O_RDONLY);
if (dirfd < 0) {
perror("dir open");
exit(111);
}
pipe(pipefd);
/* first fork, parent exits to run in background. */
child = fork();
if (child == -1) {
perror("fork");
exit(111);
}
else if (child > 0) {
char c;
/* wait until child has backgrounded. */
close(pipefd[1]);
read(pipefd[0], &c, 1);
exit(0);
}
close(pipefd[0]);
/* second fork, child later execs the job, parent collects status. */
child = fork();
if (child == -1) {
perror("fork");
exit(111);
}
else if (child > 0) {
int status;
/* output expected lockfile name. */
sprintf(lockfile, ",%011lx.%d", ms, child);
dprintf(1, "%s\n", lockfile);
close(0);
close(1);
/* signal parent to exit. */
close(pipefd[1]);
wait(&status);
lockfd = openat(dirfd, lockfile, O_RDWR | O_APPEND);
if (lockfd < 0) {
perror("open");
exit(222);
}
fchmod(lockfd, 0600);
if (WIFEXITED(status))
dprintf(lockfd, "\n[exited with status %d.]\n",
WEXITSTATUS(status));
else
dprintf(lockfd, "\n[killed by signal %d.]\n",
WTERMSIG(status));
exit(0);
}
close(pipefd[1]);
/* create and lock lockfile. since this cannot be done in one step,
use a different filename first. */
sprintf(lockfile, ".,%011lx.%d", ms, getpid());
lockfd = openat(dirfd, lockfile,
O_CREAT | O_EXCL | O_RDWR | O_APPEND, 0600);
if (lockfd < 0) {
perror("open");
exit(222);
}
if (flock(lockfd, LOCK_EX) < 0) {
perror("flock");
exit(222);
}
/* drop leading '.' */
renameat(dirfd, lockfile, dirfd, lockfile+1);
write_execline(lockfd, argc, argv);
DIR *dir = fdopendir(dirfd);
if (!dir) {
perror("fdopendir");
exit(111);
}
again:
while ((ent = readdir(dir))) {
if (ent->d_name[0] == ',' &&
strcmp(ent->d_name, lockfile+1) < 0) {
int f = openat(dirfd, ent->d_name, O_RDWR);
if (flock(f, LOCK_EX | LOCK_NB) == -1 &&
errno == EWOULDBLOCK) {
flock(f, LOCK_EX); /* sit it out. */
close(f);
rewinddir(dir);
goto again;
}
fchmod(f, 0600);
close(f);
}
}
closedir(dir); /* closes dirfd too. */
/* ready to run. */
swrite(lockfd, "\n\n");
fchmod(lockfd, 0700);
dup2(lockfd, 2);
dup2(lockfd, 1);
close(lockfd);
execvp(argv[1], argv+1);
perror("execvp");
return 222;
}
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