SVN Directory Lock

From Noah.org
Jump to: navigation, search


Often it is useful to lock an entire directory tree to be sure that it remains consistent during testing or build deployment. SVN does not allow directories to be locked. You can lock individual files, but not an entire directory tree. Fortunately, it's easy to add this feature using a simple pre-commit hook script on the server.

The following pre-commit hook script will allow advisory locks. That is, a lock will prevent a commit, but any user may set or clear any lock. A user must deliberately clear and commit lock before further commits to the tree are allowed. This is intended to prevent accidental commits, and to track who modified a lock and why.

Someone familiar with other version control systems might ask why we don't simply tag or branch the trunk in order to test or build a release. The answer is because Subversion makes this very expensive in terms of time and storage space. A branch or tag doubles the amount of storage required for the entire directory tree. It doubles this every single time you branch or tag. So a directory lock is a cheap alternative to ensure that a source tree remains consistent during a given period of time. Nobody said Subversion was a very good version control system.

This script requires that pexpect be installed. Pexpect is a standard Debian/Ubuntu/RedHat package. This script does not use the pysvn library. The reason for this is because I got frustrated that the stupid library would not install on Red Hat Enterprise 4. I could get neither the RPM nor the source to install. It was far easier to use just Pexpect to script the command-line svn tools, which is after all what scripts are for.

How to Use

To create a lock you just create and commit a lock property on a directory. After you commit the lock property no further commits will be allowed to the locked directory tree. The only exception is for any commit that deletes the lock itself. This is necessary to allow a directory to be unlocked.

Create a lock

To set a lock on a directory tree simply create a property on a directory called lock. Then you must commit the property to make it take effect.

svn propset lock TRUE trunk/project_a
svn commit trunk/project_a

The lock script does not care what value the lock property is set to. The script only checks if the lock property exists or not. The example above set the lock property value to TRUE, but the value could have been a descriptive text message giving the reason for the lock. For example,

svn propset lock 'Locked for bug hunting. Ask the build engineer if you have questions.' trunk/project_a
svn commit trunk/project_a

Others can then see the value of the lock for a description of why the lock was set.

$ svn propget lock trunk/project_a
Locked for bug hunting. Ask the build engineer if you have questions.

Of course, you can and should also describe the reason for the lock when you commit the lock property when you set the lock.

Delete a lock

To remove a lock simply delete the lock property and then commit:

svn propdel lock trunk/project_a
svn commit trunk/project_a

Repository Installation

  1. To install put the svn_dir_lock.py script in your server hooks directory. In this example, I use /home/svn/repository/hooks/.
  2. Add the following code to the pre-commit shell script. Note that you must update the LOCK_SCRIPT_PATH to point to the script your server hooks directory.
LOCK_SCRIPT_PATH="/home/svn/repository/hooks/svn_dir_lock.py"
SVNLOOK=/usr/bin/svnlook
REPOS="$1"
TXN="$2"
if ! python ${LOCK_SCRIPT_PATH} -v "$TXN" "$REPOS" >&2; then
    echo "ERROR: Commit failed. Delete locks before you commit." >&2
    exit 1
fi

svn_dir_lock.py Source

<include src="/home/noahspurrier/noah.org/engineering/src/python/svn_dir_lock.py" highlight="python" />