Question

I have an application that uses a cron like job to update a set of data. The update process happens once a minute and doesn’t last long. A servlet exposes this data set to the users. My problem is that during the update process, the servlet requests should block and wait for the process to complete.

In bottom line I have these two functions:

private void updateData() {     }  public List getData() { } 

The first function runs once a minute. The second one can be called any number of times simultaneously. When updateData runs, all calls of getData must wait for it to complete. One getData call shouldn’t block subsequent calls of the same function. The updateData function has higher priority than the getData, i.e. when updateData is to run, it has to wait for all calls of getData to complete, but new calls shouldn’t be allowed to start.

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

Answer 1

Take a look at this article: Read / Write Locks in Java

The only drawback I can see in this example is the notifyAll() waking all waiting threads. It does, however, give priority to write lock requests.