Synchronous Resource Sharing: Blocking Queue based approach

Recently I had to code an application which allows to send commands to a security device which only allows one connection at the time. Furthermore, there was several devices which want to send those commands concurrently, so there was a problem because N devices had to share one resource which works synchronously.

The solution what came to my mind was implementing a scheduler using a CommandQueue managed by a Thread. So as everytime an incoming request from a device arrives to my server, it defines which kind of request is, and push it into the CommandQueue if needed, then the command is sent by the manager Thread and retrieves the result to the requester Thread.

From now I will write my posts in english and I'm using GitHub to share my code and projects so here is the current example repository.

https://github.com/ivillalba/synchronous-resource-sharing.git

BlockingQueueManager Class

This class acts as a PriorityBlockingQueue wrapper. Its responsability is to handle every incoming task queued. It basically does two things:

1. Waits for a queued task. If there is no tasks in the queue it remains blocked waiting for one.
2. Processes a task in a synchronized block, when the task process is completed, the BlockingQueueManager wakes up the Producer thread by calling task.notify() which is waiting at the task.wait() sentence.

Producer Class

This class simulates a task producer. It just builds a random task using the task factory class and pushes it into the PriorityQueue by calling the this.taskQueue.add() method. Then waits for the task to be processed by calling newTask.wait() into a synchronized block.

Task Class

Tasks will have 3 properties.

1. Priority: Sets the priority of the task.
2. Name: Is the task name.
3. Result: This property will be set by the manager with the task processing result.

Task implements Comparable interface since its needed by PriorityBlockingQueue to have a way to compare different instances of its queue collection items.

TaskFactory Class

This class allows us to easily create random Tasks. Its used by Producer to build tasks.

SynchronizedResourceSharing (Main Class)

Is the application entry point. It creates the BlockingQueueManager manager thread and starts five Producer objects. Then waits for them to finish and kills the manager thread.

Output

The result of the application execution is a non deterministic output since the tasks are randomly generated hence their priorities and names.

Task taken.

I'm cooking...

Task done.

Task taken.

Producer[3]: My task has been completed with result 1

I'm programming in JAVA...

Task done.

Producer[1]: My task has been completed with result 2

Task taken.

I'm programming in JAVA...

Task done.

Producer[0]: My task has been completed with result 3

Task taken.

I'm cooking...

Task done.

Producer[2]: My task has been completed with result 4

Task taken.

I'm programming in JAVA...

Task done.

Producer[4]: My task has been completed with result 5

Interrupt signal received. Finishing...