我正在使用workmanager为后台任务实现一个类。任务是周期性的，所以我使用PeriodicWorkRequest，但任务不执行或执行一次。上课了，怎么了？

public class PollingWorker extends Worker {
    private final static String DELAY_KEY = "initialDelayDuration";
    private final static String TAG_POLLING_WORK_KEY = "background_polling_tag";
    private final static int DEFAULT_DELAY = 20000;
    public PollingWorker(
            @Nonnull Context ctx,
            @Nonnull WorkerParameters params) {
        super(ctx, params);
    }
    @NonNull
    @Override
    public Result doWork() {
        try{
            Log.d("TEST","sending work");
            return Result.success();
        }catch (Throwable throwable) {
            Log.e("TEST", "Error applying blur", throwable);
            return Result.failure();
        }
    }
    public static void startPollingWorker(
            @Nonnull Context context,
            final long interval,
            final String pollingWorkerTag
    ) {
        Log.d("TEST","interval:"+interval);
        Log.d("TEST","pollingWorkerTag:"+pollingWorkerTag);
        PeriodicWorkRequest pollingWorkerRequest =
                new PeriodicWorkRequest.Builder(PollingWorker.class,interval,TimeUnit.SECONDS)
                        .addTag(pollingWorkerTag)
                        .build();
        Operation operationResult=WorkManager.getInstance(context).enqueueUniquePeriodicWork(pollingWorkerTag,ExistingPeriodicWorkPolicy.KEEP,pollingWorkerRequest);
        Log.d("TEST","operation result:"+operationResult.getResult().isDone());
        Log.d("TEST","operation result:"+operationResult.getResult().isCancelled());
    }
}

此日志包括：