File locking

There is an experimental file locking feature, disabled by default. To enable the feature, choose Tools > Preferences > Environment > Files > Experimental File Locking. The feature prevents two users from editing a mind map at the same time, thereby overwriting each other's changes. Available since FreeMind 0.6.5.

Algorithm

• When opening a mind map, FreeMind creates a lock file unless one already exists.
• After successful creation of the lock file, FreeMind refreshes the lock file every 4 minutes, by writing the user name and the current time into the lock file.
• Upon opening a mind map, if a fresh lock file exists, FreeMind opens a warning pop-up window stating which user edits the mind map and opens the mind map as read-only. A lock file is considered fresh if the time written into it is no older than 5 minutes, which is the 4 minutes stated above + 1 minute as a reserve. A read-only mind map can still be edited but cannot be saved and has to be saved-as if the content is to be preserved.
• Upon opening a mind map, if a stale lock file exists, FreeMind deletes the stale lock file and opens the mind map for writing.
• On Windows, the lock file is attempted to be made a hidden file.
• Detail: The lock file name is the name of the mind map prefixed with $~ and suffixed with ~.

Reliability

The feature is experimental. The #Bug reports section below contains a bug report that (a) provides a bug fix, and (b) reports that, after the bug fix, the reporting user is happy with the feature.

Implementation

• Class MindMapMapModel
  • Nested class LockManager
  • MindMapMapModel.tryToLock(): calls lockManager.tryToLock().
  • MindMapMapModel.destroy(): calls lockManager.releaseLock() and lockManager.releaseTimer().
• Class Tools, Tools.setHidden().

Bug reports

• fix for experimental file locking on windows, 2010-09-05 - contains a fix for LockManager.writeSemaphoreFile() consisting in catching an exception.

See also

• Collaboration