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lockfile.c: Adding mechanism to take a lock of a file after a given amount on time. even if the file is locked.

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This commit is contained in:
Henrik Hautakoski 2013-10-17 15:47:10 +02:00
parent d779db6715
commit 61cad77a0c
1 changed files with 41 additions and 8 deletions
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49
lockfile.c
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@ -22,6 +22,7 @@
*/
#include <stdio.h>
#include <string.h>
#include <time.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
@ -31,6 +32,11 @@
#include "error.h"
#include "lockfile.h"
/* Maximum time a lockfile can be uhm.. locked (in seconds)
Used to prevent deadlocks when processes "forgets" to unlock. */
#define MAX_LOCK_TIME (15 * 60) /* 15 min is fine. */
static struct lockfile *active_locks;
static void release_all_locks() {
@ -94,28 +100,55 @@ static inline void init(void) {
is_init = 1;
}
static double get_lock_time(const char *path) {
struct stat st;
if (stat(path, &st) < 0)
return -1;
return difftime(time(NULL), st.st_ctime);
}
static int open_lock(const char *path, int force) {
int fd, mask = O_WRONLY | O_TRUNC | O_CREAT | O_EXCL;
if (force)
mask &= ~O_EXCL;
fd = open(path, mask, 0600);
if (fd < 0) {
/* Force open if lockfile exists
and MAX_LOCK_TIME is exceeded */
if (errno == EEXIST
&& get_lock_time(path) > MAX_LOCK_TIME) {
mask &= ~O_EXCL;
return open(path, mask, 0600);
}
}
return fd;
}
int hold_lock(struct lockfile *lock, const char *filename, int force) {
int rc, mask = O_WRONLY | O_CREAT | O_TRUNC;
int rc;
init();
if (is_locked(lock))
return -1;
if (!force)
mask |= O_EXCL;
rc = snprintf(lock->name, sizeof(lock->name), "%s.lock", filename);
if (rc > sizeof(lock->name))
return -1;
lock->fd = open(lock->name, mask, 0600);
lock->fd = open_lock(lock->name, force);
if (lock->fd < 0) {
return error(errno == EEXIST ?
"'%s' is locked" : "unable to create lockfile '%s'",
lock->name);
return error(errno == EEXIST ? "'%s' is locked" :
"unable to create lockfile '%s'", lock->name);
}
lock->next = active_locks;
active_locks = lock;
return lock->fd;