The HsResourceControlService

  Although it is possible to implement synchronized methods within the context of a single Java VM by means of the synchronized key word, it is impossible to guarantee locks outside that scope. To allow for locking, Haystack includes a resource control service, HsResourceControlService. This service allows for locking and unlocking of arbitrarily named resources. Locks are held for a preset amount of time (currently 5 minutes).

The methods currently implemented by HsResourceControlService are:

• testResource(n) which returns true if the resource n is locked, and false otherwise.
• unlockResource(n) forces an unlock of the resource n. HsResourceControlService doesn't verify that the caller has the ``right'' to do this.
• lockResource(n) tries to lock the resource n. If the lock was successful it returns true, if the attempt to lock times out, false is returned.
• nonBlockLock(n) tries to lock the resource, and immediately returns (i.e. there is no timeout).

The HsResourceControlService internally maintains an extension to the Hashtable class called ResourceControlHash. The ResourceControlHash maintains a list of current resources as well as a list of their timeouts. The ResourceControlHash manages the synchronization necessary to ensure atomic lock functionality.

• Future Improvements