Question

Currently I am using LinkedList to add all the Command information. How can I make the below List<Command> thread safe? Is there any other option I should be using here instead of LinkedList?

private static List<Command> commands;

Command command = new Command();
command.setName(commandName);
command.setExecutionPercentage(Double.parseDouble(percentage));
command.setAttributeIDGet(attributeIDGet);
command.setAttributeIDSet(attributeIDSet);
command.setDataUsageCriteria(dataCriteria);
command.setUserLoggingCriteria(userLoggingCriteria);
command.setSleepTime(sleepTimeOfCommand);

I am adding all the above command that I am getting by reading from the text file and putting it into the LinkedList of command just like below. So suppose if I have three command then I need to add all those three command in to some LinkedList which is what I was doing.

commands.add(command);

What If I do something like below?-

Collections.synchronizedList(commands.add(command));

or I need to do something like this-

commands = Collections.synchronizedList(new LinkedList<Command>());

Update:-

As per your suggestion, If I am using –

private static Queue<Command> commands;


commands = new ConcurrentLinkedQueue<Command>(); // Using linked list to ensure iteration order



Command command = new Command();
command.setName(commandName);
command.setExecutionPercentage(Double.parseDouble(percentage));
command.setAttributeIDGet(attributeIDGet);
command.setAttributeIDSet(attributeIDSet);
command.setDataUsageCriteria(dataCriteria);
command.setUserLoggingCriteria(userLoggingCriteria);
command.setSleepTime(sleepTimeOfCommand);


commands.add(command);

And after sometime basically when all the initialization has been done, I need to get the command information from the Queue, So I was doing something like this previously with the use of LinkedList. But after chaning to ConcurrentLinkedQueue, this get call is giving me an error as there is a error line on get call

commands.get(commandWithMaxNegativeOffset);

Error I am getting-

 The method get(int) is undefined for the type Queue<Command>

Answer 1

How can I make the below List thread safe? Is there any other option I should be using here instead of LinkedList?

ConcurrentLinkedQueue is a concurrent linked queue. To quote from the javadocs:

An unbounded thread-safe queue based on linked nodes. This queue orders elements FIFO (first-in-first-out). The head of the queue is that element that has been on the queue the longest time. The tail of the queue is that element that has been on the queue the shortest time. New elements are inserted at the tail of the queue, and the queue retrieval operations obtain elements at the head of the queue. A ConcurrentLinkedQueue is an appropriate choice when many threads will share access to a common collection. This queue does not permit null elements.

So you’d do something like:

 Queue<Command> concurrentQueue = new ConcurrentLinkedQueue<Command>();
 Command command = new Command();
 ...
 concurrentQueue.add(command);

You can also wrap your current List using the Collections.synchronizedList(...). Whether to do this or use ConcurrentLinkedQueue depends on how high performance you need the collection to be.

// turn the commands list into a synchronized list by wrapping it
commands = Collections.synchronizedList(commands);

If you provide some more information about how you are using this queue, we can provide possibly more alternatives in terms of the proper JDK concurrent collection.

Collections.synchronizedList(commands.add(command));

You edited your question and asked about the above code. It won’t compile since List.add(...) returns a boolean.