How to Fix Empty Mark Records in Java Performance Tests with Thread‑Safe Save

During performance testing the author created two virtual classes ThreadLimitTimeCount and ThreadLimitTimesCount to mark threads and record timeout requests. The original after() method used a synchronized block on this.getClass() to write the collected marks:

@Override
protected void after() {
    requestMark.addAll(marks);
    marks = new ArrayList<>();
    GCThread.stop();
    synchronized (this.getClass()) {
        if (countDownLatch.getCount() == 0 && requestMark.size() != 0) {
            Save.saveStringList(requestMark, MARK_Path.replace(LONG_Path, EMPTY) + Time.getDate().replace(SPACE_1, CONNECTOR));
            requestMark = new Vector<>();
        }
    }
}

In unit tests that use anonymous classes, the clone() method is unavailable, preventing deep copies of the objects. Consequently, multiple anonymous thread classes are created, each with its own runtime class object. Synchronizing on this.getClass() therefore locks only the specific anonymous class instance, not all of them, leading to occasional empty markrequest records.

To guarantee proper thread safety across all anonymous classes, the author replaced the class‑level lock with a dedicated synchronized save method. The new utility method synchronizes on the Save class itself:

/**
 * Synchronously save data, used by multiple anonymous test threads.
 * @param data the collection of strings to save
 * @param name the file name
 */
public static void saveStringListSync(Collection<String> data, String name) {
    synchronized (Save.class) {
        if (data.isEmpty()) return;
        saveStringList(data, name);
    }
}

The after() method is then simplified to call this thread‑safe method:

if (countDownLatch.getCount() == 0 && requestMark.size() != 0) {
    Save.saveStringListSync(requestMark, MARK_Path.replace(LONG_Path, EMPTY) + Time.getDate().replace(SPACE_1, CONNECTOR));
}

By synchronizing on a single, shared class object ( Save.class), all threads—regardless of which anonymous class created them—contend for the same lock, eliminating the race condition that produced empty mark files.