isolock

isolock is a locking manager for isolate, available as part of the MOE contest environment. isolate allows you to sandbox programs/processes into a chroot jail, with a unique user id (and group id), thereby limiting what programs can do. It is installed with a limited number of boxes, based on the user ids allocated for isolate to use. isolock is an advisory locking manager, to allocate the desired number of box_ids that are unused.

Installation

First install isolate, then download this git repository, and run make. Copy bin/isolock to a desired location, and make sure it is on your path. It is designed to run setuid and setgid with a separate user, so chown and chmod it.

git clone git://github.com/ronalchn/isolock.git
cd isolock
make
sudo chown root bin/isolock
sudo chmod +s bin/isolock

Usage

Run the help command for all the options:

isolock --help

Essentially, you can request locks for N boxes. isolock will either print the box_ids for boxes to stdout, or if there are not enough free boxes, and the timeout runs out, return an error. When you are finished, just pass those box_ids back into isolock with the --free option to release the locks. You can set a timeout using the --timeout option, which is normally set to 0, which means wait indefinitely.

The -n option, which allows you to request N boxes at once is designed to prevent deadlocks. If the required number of boxes could not be locked initially, and the waiting time has not run out, isolock will release those locks, then acquire a "master" waiting lock, before again locking any free locks as they become available. Thus, for requests which are not immediately successful, all free resources will be used to fulfill the request with the "master" lock first.

isolock locks are owned by a calling process. The lock is valid until freed, or until the calling process terminates (ie. while the PID remains valid). If you wish to transfer the lock from one process to another, you can overwrite the new PID and start_time (in jiffies since boot) in the format "%d:%llu\n" to the lock directory, which by default is printf("/var/lock/isolate/lock/%d.pidlock", box_id).

License

Copyright © 2013 Ronald Ping Man Chan

This source code is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/. All source code, unless otherwise specified, is released under the MPL v2.