Concurrent non-blocking refresh

Question

In my application there is a "config" object that is accessbile by multiple threads concurrently. It is a single object (singleton) injected by the DI in the "dependents". Until now, this (the "config") object was immutable which makes it inherently thread-safe. However, there is a new requirement that the "config" should be periodically "refreshed/updated". I wrote a wrapper (decorator) that refreshes itself (from a configProvider), and the refresh happens on the fly, when a method gets called (if the certian amount of time has passed) The wrapper should be thread safe and non-blocking.

Any (concurrency) issues with the following code?

package xyz;

import java.util.concurrent.atomic.AtomicBoolean;

/**
 * Implementation of {@link IMyModuleConfig} that periodically refreshes itself from the provided
 * {@link IConfiguration}.
 * The refresh is done on-the-fly when some method is called, it is thread safe.
 *
 * @Threadsafe
 */
public class MyModuleRefreshableConfig implements IMyModuleConfig {

    private IMyModuleConfig configBean; // Decorated object, Immutable, non-final should be properly fenced 
    private long lastRefreshTime;  // time when we refreshed the configuration last, non-final should be properly fenced 

    private final IConfiguration configProvider; // refresh source
    private final long refreshInterval; // how often we refresh


    private final AtomicBoolean refreshConfigMutex; // if true, a thread is refreshing configuration right now

    public MyModuleRefreshableConfig(IConfiguration configProvider, long refreshInterval) {
        refreshConfigMutex = new AtomicBoolean(false);

        this.configBean = refreshConfig();
        this.lastRefreshTime = System.currentTimeMillis();

        // Do not re-arrange, the assignment to final field latter in the constructor serves as a "store fence"

        this.configProvider = configProvider;
        this.refreshInterval = refreshInterval;
    }

    @Override
    public boolean getMyBoolean() {
        refreshConfigIfNeeded(); // full fence
        return this.configBean.getMyBoolean();
    }

    @Override
    public int getTimeout() {
        refreshConfigIfNeeded(); // full fence
        return this.configBean.getTimeout();
    }

    private void refreshConfigIfNeeded() {
        boolean aquired = refreshConfigMutex.compareAndSet(false, true); // full fence
        if (aquired) { // critical section starts, if some thread is in just continue, no need to wait
            long cTime = System.currentTimeMillis();
            boolean shouldRefresh = (cTime - lastRefreshTime) > refreshInterval;
            if (shouldRefresh) {
                lastRefreshTime = cTime;
                configBean = refreshConfig();
            }
            refreshConfigMutex.set(false); // critical section ends, write fence
        }
    }

    private IMyModuleConfig refreshConfig() {
        // creates new immutable IMyModuleConfig with values provided by configProvider
    }
}

Answer 1

As long as you are 100% certain that all threads will use the same instance of MyModuleRefreshableConfig, this code should work. Just to be certain I would make the refreshConfigMutexstatic:

private static final AtomicBoolean refreshConfigMutex;

public MyModuleRefreshableConfig(IConfiguration configProvider, long refreshInterval) {
    synchronized {
         if (refreshConfigMutex == null) {
             refreshConfigMutex = new AtomicBoolean(false);
         }
    }
    ....
}