void addIdleExpiryTask() {
    synchronized (regionExpiryLock) {
      RegionIdleExpiryTask task = regionIdleExpiryTask;
      if (task != null) {
        task.cancel();
      }

      if (regionIdleTimeout > 0) {
        regionIdleExpiryTask = (RegionIdleExpiryTask) cache.getExpirationScheduler()
            .addExpiryTask(new RegionIdleExpiryTask(this));
        if (regionIdleExpiryTask != null) {
          if (logger.isDebugEnabled()) {
            logger.debug("Initialized Region Idle Expiry Task {}", regionIdleExpiryTask);
          }
        }

      } else {
        regionIdleExpiryTask = null;
      }
    }
  }
Add the Region Idle expiry task to the scheduler
geode-core/src/main/java/org/apache/geode/internal/cache/LocalRegion.java