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Diffstat (limited to 'lockfile.h')
| -rw-r--r-- | lockfile.h | 87 |
1 files changed, 87 insertions, 0 deletions
diff --git a/lockfile.h b/lockfile.h new file mode 100644 index 0000000..cd2ec95 --- /dev/null +++ b/lockfile.h @@ -0,0 +1,87 @@ +#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_SUFFIX_LEN 5 + +#define LOCK_DIE_ON_ERROR 1 +#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(struct lock_file *, const char *path, int); +extern int hold_lock_file_for_append(struct lock_file *, const char *path, int); +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 */ |