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Diffstat (limited to 'Documentation/technical/api-lockfile.txt')
| -rw-r--r-- | Documentation/technical/api-lockfile.txt | 74 |
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diff --git a/Documentation/technical/api-lockfile.txt b/Documentation/technical/api-lockfile.txt deleted file mode 100644 index dd89404..0000000 --- a/Documentation/technical/api-lockfile.txt +++ /dev/null @@ -1,74 +0,0 @@ -lockfile API -============ - -The lockfile API serves two purposes: - -* Mutual exclusion. When we write out a new index file, first - we create a new file `$GIT_DIR/index.lock`, write the new - contents into it, and rename it to the final destination - `$GIT_DIR/index`. We try to create the `$GIT_DIR/index.lock` - file with O_EXCL so that we can notice and fail when somebody - else is already trying to update the index file. - -* Automatic cruft removal. After we create the "lock" file, we - may decide to `die()`, and we would want to make sure that we - remove the file that has not been committed to its final - destination. This is done by remembering the lockfiles we - created in a linked list and cleaning them up from an - `atexit(3)` handler. Outstanding lockfiles are also removed - when the program dies on a signal. - - -The functions -------------- - -hold_lock_file_for_update:: - - Take a pointer to `struct lock_file`, the filename of - the final destination (e.g. `$GIT_DIR/index`) and a flag - `die_on_error`. Attempt to create a lockfile for the - destination and return the file descriptor for writing - to the file. If `die_on_error` flag is true, it dies if - a lock is already taken for the file; otherwise it - returns a negative integer to the caller on failure. - -commit_lock_file:: - - Take a pointer to the `struct lock_file` initialized - with an earlier call to `hold_lock_file_for_update()`, - close the file descriptor and rename the lockfile to its - final destination. Returns 0 upon success, a negative - value on failure to close(2) or rename(2). - -rollback_lock_file:: - - Take a pointer to the `struct lock_file` initialized - with an earlier call to `hold_lock_file_for_update()`, - close the file descriptor and remove the lockfile. - -close_lock_file:: - Take a pointer to the `struct lock_file` initialized - with an earlier call to `hold_lock_file_for_update()`, - and close the file descriptor. Returns 0 upon success, - a negative value on failure to close(2). - -Because the structure is used in an `atexit(3)` handler, its -storage has to stay throughout the life of the program. It -cannot be an auto variable allocated on the stack. - -Call `commit_lock_file()` or `rollback_lock_file()` when you are -done writing to the file descriptor. If you do not call either -and simply `exit(3)` from the program, an `atexit(3)` handler -will close and remove the lockfile. - -If you need to close the file descriptor you obtained from -`hold_lock_file_for_update` function yourself, do so by calling -`close_lock_file()`. You should never call `close(2)` yourself! -Otherwise the `struct -lock_file` structure still remembers that the file descriptor -needs to be closed, and a later call to `commit_lock_file()` or -`rollback_lock_file()` will result in duplicate calls to -`close(2)`. Worse yet, if you `close(2)`, open another file -descriptor for completely different purpose, and then call -`commit_lock_file()` or `rollback_lock_file()`, they may close -that unrelated file descriptor. |