* rate limit itself.
 *
 * {@snippet :
 * class CrawlingService extends AbstractScheduledService {
 *   private Set<Uri> visited;
 *   private Queue<Uri> toCrawl;
 *   protected void startUp() throws Exception {
 *     toCrawl = readStartingUris();
 *   }
 *
 *   protected void runOneIteration() throws Exception {
 *     Uri uri = toCrawl.remove();

  //   so that it looks like we timed out even though we didn't. For comparison FutureTask respects
  //   completion preferably and AQS is non-deterministic (depends on where in the queue the waiter
  //   is). If we wanted to be strict about it, we could store the unpark() time in the Waiter node
  //   and we could use that to make a decision about whether or not we timed out prior to being
  //   unparked.

 * rate limit itself.
 *
 * {@snippet :
 * class CrawlingService extends AbstractScheduledService {
 *   private Set<Uri> visited;
 *   private Queue<Uri> toCrawl;
 *   protected void startUp() throws Exception {
 *     toCrawl = readStartingUris();
 *   }
 *
 *   protected void runOneIteration() throws Exception {
 *     Uri uri = toCrawl.remove();

  //   so that it looks like we timed out even though we didn't. For comparison FutureTask respects
  //   completion preferably and AQS is non-deterministic (depends on where in the queue the waiter
  //   is). If we wanted to be strict about it, we could store the unpark() time in the Waiter node
  //   and we could use that to make a decision about whether or not we timed out prior to being
  //   unparked.

    }
}
```

## 9. Performance and Optimization

### 9.1 Witness Event Batching
```java
public class WitnessEventBatcher {
    private final Queue<WitnessNotification> pendingNotifications;
    private final ScheduledExecutorService scheduler;
    private final int batchSize = 10;
    private final long batchTimeout = 100;  // 100ms
    

    }
    connection.writeSynReset(id, rstStatusCode)
  }

  override fun cancel() {
    closeLater(ErrorCode.CANCEL)
  }

  /**
   * Abnormally terminate this stream. This enqueues a `RST_STREAM` frame and returns immediately.
   */
  fun closeLater(errorCode: ErrorCode) {
    if (!closeInternal(errorCode, null)) {
      return // Already closed.
    }

 *
 * <h2>Build Step States:</h2>
 * <ul>
 *   <li>CREATED: Initial state of a build step</li>
 *   <li>PLANNING: Step is being planned</li>
 *   <li>SCHEDULED: Step is queued for execution</li>
 *   <li>EXECUTED: Step has completed successfully</li>
 *   <li>FAILED: Step execution failed</li>
 * </ul>
 *

    mostRecentRebuildFailed = false
  }

  /**
   * Returns a snapshot of the entry named [key], or null if it doesn't exist is not currently
   * readable. If a value is returned, it is moved to the head of the LRU queue.
   */
  @Synchronized
  @Throws(IOException::class)
  operator fun get(key: String): Snapshot? {
    initialize()

    checkNotClosed()
    validateKey(key)

Fixed a situation when, sometimes, the scheduler incorrectly placed a pod in the `unschedulable` queue instead of the `backoff` queue. This happened when some plugin previously declared the pod as `unschedulable` and then in a later attempt encounters some other error. Scheduling of that pod then got delayed by up to five minutes, after which periodic flushing moved the pod back into the `active` queue. ([#120334](https://github.com/kubernetes/kubernetes/pull/120334), [@pohly](https://github.com/pohly))...

  Now, when unschedulable Pods are updated, the scheduling queue checks with QueueingHint(s) whether the update may make the pods schedulable, and requeues them to activeQ/backoffQ **only when** at least one QueueingHint(s) return Queue. 
  
  Action required for custom scheduler plugin developers: