How do I synchronize data requests with the data refresh process?

Question

How do I synchronize data requests with the data refresh process?

I have an application that uses a cron job to update a dataset. The update process occurs once a minute and does not last long. The servlet provides this dataset to users. My problem is that during the update process, the servlet requests must block and wait for the process to complete.

On the bottom line, I have two functions:

private void updateData() {    
}

public List getData() {
}

The first function runs once a minute. The second can be called any number of times at the same time. When updateData is executed, all getData calls must wait for completion. A single call to getData should not block subsequent calls to the same function. The updateData function has a higher priority than getData, that is, when updateData needs to be run, it needs to wait for all getData calls to complete, but no new calls can be started.

What synchronization mechanism should I use for such a case? I am using a Java server, but I would be interested to know what solutions exist for other platforms as well.

0

java synchronization

kgiannakakis Dec 16 '08 at 10:54

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4 answers

You can use ReadWriteLock instead of synchronization .

ReadWriteLock maintains a couple of related locks, one for read-only and one for writing. A read lock can be held concurrently by multiple reader threads if there are no writers. The write lock is exclusive.

public void updateData() {
    lock.writeLock().lock();
    try {
        /* do stuff. */
    } finally {
       lock.writeLock().unlock();
    }
}


public List getData() {
    lock.readLock().lock();
    try {
       /* process/return data. */
    } finally {
       lock.readLock().unlock();
    }

}

+5

ordnungswidrig Dec 16 '08 at 11:32

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You need to synchronize data access.

public void updateData() {
    synchronized (updateLock) {
        /* do stuff. */
    }
}


public List getData() {
    List data;
    synchronized (updateLock) {
        data = getRealData();
    }
    /* process/return data. */
}