CODEWITHSUNDEEP
javamultithreadinghashtable
raindrop_boy
raindrop_boy

Reputation: 63

Multiple threads HashTable in java

MainThread has a HashTable, which save a mapping from customId to SubThread Object, and put task to map. SubThread remove task from map. how to avoiding this problem?

thread 1:

public void start()
{
        subThreadMap = new Hashtable<Integer, SubThread>();
        while(true)
        {
            List<CloudPusherTaskInfo> taskInfos = TestDao.getTasks();

        for (CloudPusherTaskInfo task : taskInfos)
        {
            distribute(task);
        }
    }
}

private void distribute(CloudPusherTaskInfo task)
{
    SubThread subThread = null;

    if(subThreadMap.containsKey(task.getCustomerId()))
    {
        /*
         * if subThread exist, add a task to it
         */
        subThread = subThreadMap.get(task.getCustomerId());

/* -----at this point, the other subThread maybe end, and return null--------*/

        subThread.add(task);
    }
    else
    {
        /*
         * if subThread is not exist, create a new subthread, then add a task and run it 
         */
        SubThread newThread = createNewSubThread(task.getCustomerId());
        subThread = subThreadMap.put(task.getCustomerId(), newThread);
        newThread.add(task);
        new Thread(newThread).start();
    }
}

Upvotes: 0

Views: 210

Answers (2)

clinton
clinton

Reputation: 612

The HashTable Hashtable<Integer, SubThread>(); is not needed if its primary reason is to get Thread objects and start them. Make the CloudPusherTaskInfo implement the Runnable interface and then use the Executor.execute(new CloudPusherTaskInfo()). Or you could hold the CloudPusherTaskInfo tasks in a List and execute them one after another.

Upvotes: 1

Jim Garrison
Jim Garrison

Reputation: 86774

If I understand you correctly, it is possible for the subThread to have finished its tasks and ended between the call to subThreadMap.containsKey() and subThreadMap.get().

Don't reinvent the wheel. You should look at the classes in package java.util.concurrent, which provides all the functionality you need to accomplish thread pooling and task execution.

Upvotes: 2

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