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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 <stdio.h>
#include <string.h> #include <string.h>
#include <time.h>
#include <stdlib.h> #include <stdlib.h>
#include <unistd.h> #include <unistd.h>
#include <signal.h> #include <signal.h>
@ -31,6 +32,11 @@
#include "error.h" #include "error.h"
#include "lockfile.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 struct lockfile *active_locks;
static void release_all_locks() { static void release_all_locks() {
@ -94,28 +100,55 @@ static inline void init(void) {
is_init = 1; 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 hold_lock(struct lockfile *lock, const char *filename, int force) {
int rc, mask = O_WRONLY | O_CREAT | O_TRUNC; int rc;
init(); init();
if (is_locked(lock)) if (is_locked(lock))
return -1; return -1;
if (!force)
mask |= O_EXCL;
rc = snprintf(lock->name, sizeof(lock->name), "%s.lock", filename); rc = snprintf(lock->name, sizeof(lock->name), "%s.lock", filename);
if (rc > sizeof(lock->name)) if (rc > sizeof(lock->name))
return -1; return -1;
lock->fd = open(lock->name, mask, 0600); lock->fd = open_lock(lock->name, force);
if (lock->fd < 0) { if (lock->fd < 0) {
return error(errno == EEXIST ? return error(errno == EEXIST ? "'%s' is locked" :
"'%s' is locked" : "unable to create lockfile '%s'", "unable to create lockfile '%s'", lock->name);
lock->name);
} }
lock->next = active_locks; lock->next = active_locks;
active_locks = lock; active_locks = lock;
return lock->fd; return lock->fd;