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#ifndef LOCKFILE_H
#define LOCKFILE_H
* File write-locks as used by Git.
* For an overview of how to use the lockfile API, please see
* Documentation/technical/api-lockfile.txt
* This module keeps track of all locked files in lock_file_list for
* use at cleanup. This list and the lock_file objects that comprise
* it must be kept in self-consistent states at all time, because the
* program can be interrupted any time by a signal, in which case the
* signal handler will walk through the list attempting to clean up
* any open lock files.
* A lockfile is owned by the process that created it. The lock_file
* object has an "owner" field that records its owner. This field is
* used to prevent a forked process from closing a lockfile created by
* its parent.
* The possible states of a lock_file object are as follows:
* - Uninitialized. In this state the object's on_list field must be
* zero but the rest of its contents need not be initialized. As
* soon as the object is used in any way, it is irrevocably
* registered in the lock_file_list, and on_list is set.
* - Locked, lockfile open (after hold_lock_file_for_update(),
* hold_lock_file_for_append(), or reopen_lock_file()). In this
* state:
* - the lockfile exists
* - active is set
* - filename holds the filename of the lockfile
* - fd holds a file descriptor open for writing to the lockfile
* - fp holds a pointer to an open FILE object if and only if
* fdopen_lock_file() has been called on the object
* - owner holds the PID of the process that locked the file
* - Locked, lockfile closed (after successful close_lock_file()).
* Same as the previous state, except that the lockfile is closed
* and fd is -1.
* - Unlocked (after commit_lock_file(), commit_lock_file_to(),
* rollback_lock_file(), a failed attempt to lock, or a failed
* close_lock_file()). In this state:
* - active is unset
* - filename is empty (usually, though there are transitory
* states in which this condition doesn't hold). Client code should
* *not* rely on the filename being empty in this state.
* - fd is -1
* - the object is left registered in the lock_file_list, and
* on_list is set.
struct lock_file {
struct lock_file *volatile next;
volatile sig_atomic_t active;
volatile int fd;
FILE *volatile fp;
volatile pid_t owner;
char on_list;
struct strbuf filename;
/* String appended to a filename to derive the lockfile name: */
#define LOCK_SUFFIX ".lock"
#define LOCK_NO_DEREF 2
extern void unable_to_lock_message(const char *path, int err,
struct strbuf *buf);
extern NORETURN void unable_to_lock_die(const char *path, int err);
extern int hold_lock_file_for_update_timeout(
struct lock_file *lk, const char *path,
int flags, long timeout_ms);
static inline int hold_lock_file_for_update(
struct lock_file *lk, const char *path,
int flags)
return hold_lock_file_for_update_timeout(lk, path, flags, 0);
extern int hold_lock_file_for_append(struct lock_file *lk, const char *path,
int flags);
extern FILE *fdopen_lock_file(struct lock_file *, const char *mode);
extern char *get_locked_file_path(struct lock_file *);
extern int commit_lock_file_to(struct lock_file *, const char *path);
extern int commit_lock_file(struct lock_file *);
extern int reopen_lock_file(struct lock_file *);
extern int close_lock_file(struct lock_file *);
extern void rollback_lock_file(struct lock_file *);
#endif /* LOCKFILE_H */