$attempt++ ) {
				$time   = microtime( true );
				$now    = number_format( $time, 6, '.', '' );
				$expiry = number_format( $time + self::ENQUEUED_PROCESSORS_LOCK_TTL, 6, '.', '' );

				// The unique option_name key makes this INSERT a mutex: it fails when the lock row already exists.
				// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching
				$acquired = $wpdb->insert(
					$wpdb->options,
					array(
						'option_name'  => self::ENQUEUED_PROCESSORS_LOCK_OPTION,
						'option_value' => $expiry,
						'autoload'     => 'no',
					),
					array( '%s', '%s', '%s' )
				);

				if ( ! $acquired ) {
					/*
					 * The lock row exists; take it over only if its stored release time is already in the past.
					 * $wpdb->update() cannot express the "<" comparison, so this conditional takeover uses raw SQL.
					 * The table is a trusted internal identifier and every value is bound through a placeholder.
					 */
					$takeover = $wpdb->prepare(
						"UPDATE {$wpdb->options} SET option_value = %s WHERE option_name = %s AND option_value < %s", // phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared
						$expiry,
						self::ENQUEUED_PROCESSORS_LOCK_OPTION,
						$now
					);
					if ( is_string( $takeover ) ) {
						// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching, WordPress.DB.PreparedSQL.NotPrepared
						$acquired = $wpdb->query( $takeover );
					}
				}

				if ( $acquired ) {
					return $expiry;
				}

				if ( $attempt < $attempts - 1 && $delay_micro > 0 ) {
					usleep( $delay_micro );
				}
			}

			return null;
		} finally {
			$wpdb->suppress_errors( $suppress );
		}
	}

	/**
	 * Release the enqueued-processors lock by deleting the options-table row we own.
	 *
	 * The delete is conditional on the stored release time still matching the one written when the lock was
	 * acquired, so a lock that expired and was taken over by another request is never released out from under it.
	 *
	 * @since 11.0.0
	 *
	 * @param string $expiry The release time returned by acquire_enqueued_processors_lock().
	 */
	private function release_enqueued_processors_lock( string $expiry ): void {
		global $wpdb;

		$suppress = $wpdb->suppress_errors( true );
		try {
			// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching
			$wpdb->delete(
				$wpdb->options,
				array(
					'option_name'  => self::ENQUEUED_PROCESSORS_LOCK_OPTION,
					'option_value' => $expiry,
				),
				array( '%s', '%s' )
			);
		} finally {
			$wpdb->suppress_errors( $suppress );
		}
	}

	/**
	 * Schedule the watchdog action.
	 *
	 * @param bool $with_delay Whether to delay the action execution. Should be true when rescheduling, false when enqueueing.
	 * @param bool $unique     Whether to make the action unique.
	 */
	private function schedule_watchdog_action( bool $with_delay = false, bool $unique = false ): void {
		$time = time();
		if ( $with_delay ) {
			/**
			 * Modify the delay interval for the batch processor's watchdog events.
			 *
			 * @since 8.2.0
			 *
			 * @param int $delay Time, in seconds, before the watchdog process will run. Defaults to 3600 (1 hour).
			 */
			$time += apply_filters( 'woocommerce_batch_processor_watchdog_delay_seconds', HOUR_IN_SECONDS );
		}

		if ( ! as_has_scheduled_action( self::WATCHDOG_ACTION_NAME ) ) {
			as_schedule_single_action(
				$time,
				self::WATCHDOG_ACTION_NAME,
				array(),
				self::ACTION_GROUP,
				$unique
			);
		}
	}

	/**
	 * Schedule a processing action for all the processors that are enqueued but not scheduled
	 * (because they have just been enqueued, or because the processing for a batch failed).
	 */
	private function handle_watchdog_action(): void {
		$pending_processes = $this->sanitize_processor_list( $this->get_enqueued_processors() );
		if ( empty( $pending_processes ) ) {
			return;
		}
		foreach ( $pending_processes as $process_name ) {
			if ( ! $this->is_scheduled( $process_name ) ) {
				$this->schedule_batch_processing( $process_name );
			}
		}
		$this->schedule_watchdog_action( true );
	}

	/**
	 * Process a batch for a single processor, and handle any required rescheduling or state cleanup.
	 *
	 * @param string $processor_class_name Fully qualified class name of the processor.
	 *
	 * @throws \Exception If error occurred during batch processing.
	 */
	private function process_next_batch_for_single_processor( string $processor_class_name ): void {
		if ( ! $this->is_enqueued( $processor_class_name ) ) {
			return;
		}

		$batch_processor = $this->get_processor_instance( $processor_class_name );
		$error           = $this->process_next_batch_for_single_processor_core( $batch_processor );
		$still_pending   = count( $batch_processor->get_next_batch_to_process( 1 ) ) > 0;
		if ( ( $error instanceof \Exception ) ) {
			// The batch processing failed and no items were processed:
			// reschedule the processing with a delay, unless this is a repeatead failure.
			if ( $this->is_consistently_failing( $batch_processor ) ) {
				$this->log_consistent_failure( $batch_processor, $this->get_process_details( $batch_processor ) );
				$this->remove_processor( $processor_class_name );
			} else {
				$this->schedule_batch_processing( $processor_class_name, true );
			}

			throw $error;
		}
		if ( $still_pending ) {
			$this->schedule_batch_processing( $processor_class_name );
		} else {
			$this->dequeue_processor( $processor_class_name );
		}
	}

	/**
	 * Process a batch for a single processor, updating state and logging any error.
	 *
	 * @param BatchProcessorInterface $batch_processor Batch processor instance.
	 *
	 * @return null|\Exception Exception if error occurred, null otherwise.
	 */
	private function process_next_batch_for_single_processor_core( BatchProcessorInterface $batch_processor ): ?\Exception {
		$details    = $this->get_process_details( $batch_processor );
		$time_start = microtime( true );
		$batch      = $batch_processor->get_next_batch_to_process( $details['current_batch_size'] );
		if ( empty( $batch ) ) {
			return null;
		}
		try {
			$batch_processor->process_batch( $batch );
			$time_taken = microtime( true ) - $time_start;
			$this->update_processor_state( $batch_processor, $time_taken );
		} catch ( \Exception $exception ) {
			$time_taken = microtime( true ) - $time_start;
			$this->log_error( $exception, $batch_processor, $batch );
			$this->update_processor_state( $batch_processor, $time_taken, $exception );
			return $exception;
		}
		return null;
	}

	/**
	 * Get the current state for a given enqueued processor.
	 *
	 * @param BatchProcessorInterface $batch_processor Batch processor instance.
	 *
	 * @return array Current state for the processor, or a "blank" state if none exists yet.
	 */
	private function get_process_details( BatchProcessorInterface $batch_processor ): array {
		$defaults = array(
			'total_time_spent'    => 0,
			'current_batch_size'  => $batch_processor->get_default_batch_size(),
			'last_error'          => null,
			'recent_failures'     => 0,
			'batch_first_failure' => null,
			'batch_last_failure'  => null,
		);

		$process_details = get_option( $this->get_processor_state_option_name( $batch_processor ) );
		$process_details = wp_parse_args( is_array( $process_details ) ? $process_details : array(), $defaults );

		return $process_details;
	}

	/**
	 * Get the name of the option where we will be saving state for a given processor.
	 *
	 * @param BatchProcessorInterface|string $batch_processor Batch processor instance or class name.
	 *
	 * @return string Option name.
	 */
	private function get_processor_state_option_name( $batch_processor ): string {
		$class_name = is_a( $batch_processor, BatchProcessorInterface::class ) ? get_class( $batch_processor ) : $batch_processor;
		$class_md5  = md5( $class_name );
		// truncate the class name so we know that it will fit in the option name column along with md5 hash and prefix.
		$class_name = substr( $class_name, 0, 140 );
		return 'wc_batch_' . $class_name . '_' . $class_md5;
	}

	/**
	 * Update the state for a processor after a batch has completed processing.
	 *
	 * @param BatchProcessorInterface $batch_processor Batch processor instance.
	 * @param float                   $time_taken Time take by the batch to complete processing.
	 * @param \Exception|null         $last_error Exception object in processing the batch, if there was one.
	 */
	private function update_processor_state( BatchProcessorInterface $batch_processor, float $time_taken, ?\Exception $last_error = null ): void {
		$current_status                      = $this->get_process_details( $batch_processor );
		$current_status['total_time_spent'] += $time_taken;
		$current_status['last_error']        = null !== $last_error ? $last_error->getMessage() : null;

		if ( null !== $last_error ) {
			$current_status['recent_failures']    = ( $current_status['recent_failures'] ?? 0 ) + 1;
			$current_status['batch_last_failure'] = current_time( 'mysql' );

			if ( is_null( $current_status['batch_first_failure'] ) ) {
				$current_status['batch_first_failure'] = $current_status['batch_last_failure'];
			}
		} else {
			$current_status['recent_failures']     = 0;
			$current_status['batch_first_failure'] = null;
			$current_status['batch_last_failure']  = null;
		}

		update_option( $this->get_processor_state_option_name( $batch_processor ), $current_status, false );
	}

	/**
	 * Removes the option where we store state for a given processor.
	 *
	 * @since 9.1.0
	 *
	 * @param string $processor_class_name Fully qualified class name of the processor.
	 */
	private function clear_processor_state( string $processor_class_name ): void {
		delete_option( $this->get_processor_state_option_name( $processor_class_name ) );
	}

	/**
	 * Schedule a processing action for a single processor.
	 *
	 * @param string $processor_class_name Fully qualified class name of the processor.
	 * @param bool   $with_delay   Whether to schedule the action for immediate execution or for later.
	 */
	private function schedule_batch_processing( string $processor_class_name, bool $with_delay = false ): void {
		$time = $with_delay ? time() + MINUTE_IN_SECONDS : time();
		as_schedule_single_action( $time, self::PROCESS_SINGLE_BATCH_ACTION_NAME, array( $processor_class_name ) );
	}

	/**
	 * Check if a batch processing action is already scheduled for a given processor.
	 * Differs from `as_has_scheduled_action` in that this excludes actions in progress.
	 *
	 * @param string $processor_class_name Fully qualified class name of the batch processor.
	 *
	 * @return bool True if a batch processing action is already scheduled for the processor.
	 */
	public function is_scheduled( string $processor_class_name ): bool {
		return as_has_scheduled_action( self::PROCESS_SINGLE_BATCH_ACTION_NAME, array( $processor_class_name ) );
	}

	/**
	 * Get an instance of a processor given its class name.
	 *
	 * @param string $processor_class_name Full class name of the batch processor.
	 *
	 * @return BatchProcessorInterface Instance of batch processor for the given class.
	 * @throws \Exception If it's not possible to get an instance of the class.
	 */
	private function get_processor_instance( string $processor_class_name ): BatchProcessorInterface {

		$container = wc_get_container();
		$processor = $container->has( $processor_class_name ) ? $container->get( $processor_class_name ) : null;

		/**
		 * Filters the instance of a processor for a given class name.
		 *
		 * @param object|null $processor The processor instance given by the dependency injection container, or null if none was obtained.
		 * @param string $processor_class_name The full class name of the processor.
		 * @return BatchProcessorInterface|null The actual processor instance to use, or null if none could be retrieved.
		 *
		 * @since 6.8.0.
		 */
		$processor = apply_filters( 'woocommerce_get_batch_processor', $processor, $processor_class_name );
		if ( ! isset( $processor ) && class_exists( $processor_class_name ) ) {
			// This is a fallback for when the batch processor is not registered in the container.
			$processor = new $processor_class_name();
		}
		if ( ! is_a( $processor, BatchProcessorInterface::class ) ) {
			throw new \Exception( "Unable to initialize batch processor instance for $processor_class_name" );
		}
		return $processor;
	}

	/**
	 * Helper method to get list of all the enqueued processors.
	 *
	 * @return array List (of string) of the class names of the enqueued processors.
	 */
	public function get_enqueued_processors(): array {
		$enqueued_processors = get_option( self::ENQUEUED_PROCESSORS_OPTION_NAME, array() );

		if ( ! is_array( $enqueued_processors ) ) {
			$this->logger->error( 'Could not fetch list of processors. Clearing up queue.', array( 'source' => 'batch-processing' ) );
			delete_option( self::ENQUEUED_PROCESSORS_OPTION_NAME );
			$enqueued_processors = array();
		}

		return $enqueued_processors;
	}

	/**
	 * Dequeue a processor once it has no more items pending processing.
	 *
	 * @param string $processor_class_name Full processor class name.
	 */
	private function dequeue_processor( string $processor_class_name ): void {
		// Always resolve membership authoritatively inside the lock (no unguarded fast-path read): this runs when a
		// batch finishes, not on a per-request hot path, so correctness is preferred over skipping the lock.
		$removed = false;
		$this->mutate_enqueued_processors(
			function ( array $pending_processes ) use ( $processor_class_name, &$removed ): array {
				if ( ! in_array( $processor_class_name, $pending_processes, true ) ) {
					return $pending_processes;
				}
				$removed = true;
				return array_values( array_diff( $this->sanitize_processor_list( $pending_processes ), array( $processor_class_name ) ) );
			}
		);

		if ( $removed ) {
			$this->clear_processor_state( $processor_class_name );
		}
	}

	/**
	 * Helper method to set the enqueued processor class names.
	 *
	 * @param array $processors List of full processor class names.
	 */
	private function set_enqueued_processors( array $processors ): void {
		update_option( self::ENQUEUED_PROCESSORS_OPTION_NAME, $processors, false );
	}

	/**
	 * Check if a particular processor is enqueued.
	 *
	 * @param string $processor_class_name Fully qualified class name of the processor.
	 *
	 * @return bool True if the processor is enqueued.
	 */
	public function is_enqueued( string $processor_class_name ): bool {
		return in_array( $processor_class_name, $this->get_enqueued_processors(), true );
	}

	/**
	 * Dequeue and de-schedule a processor instance so that it won't be processed anymore.
	 *
	 * @param string $processor_class_name Fully qualified class name of the processor.
	 * @return bool True if the processor has been dequeued, false if the processor wasn't enqueued (so nothing has been done).
	 */
	public function remove_processor( string $processor_class_name ): bool {
		// Resolve membership authoritatively inside the lock (no unguarded fast-path read). remove_processor() is
		// not a per-request hot path — the continuous-sync 'shutdown' handler enqueues rather than removes — so it
		// always takes the lock and re-reads the freshest list rather than acting on a possibly-stale cached copy.
		$was_enqueued         = false;
		$remaining_processors = $this->mutate_enqueued_processors(
			function ( array $enqueued_processors ) use ( $processor_class_name, &$was_enqueued ): array {
				if ( ! in_array( $processor_class_name, $enqueued_processors, true ) ) {
					return $enqueued_processors;
				}
				$was_enqueued = true;
				return array_values( array_diff( $this->sanitize_processor_list( $enqueued_processors ), array( $processor_class_name ) ) );
			}
		);

		if ( ! $was_enqueued ) {
			return false;
		}

		/*
		 * $remaining_processors is the list exactly as persisted inside the critical section above, so the empty
		 * check is decided from the lock-guarded snapshot rather than a second, unguarded re-read (which would only
		 * ever see this request's own post-mutation value anyway). When that snapshot is empty we unschedule every
		 * single-batch action to sweep up any orphaned "ghost" actions left in Action Scheduler for processors that
		 * are no longer enqueued; otherwise only the removed processor's own scheduling needs tearing down, so we
		 * unschedule by class name.
		 *
		 * This intentionally does NOT unschedule the watchdog: handle_watchdog_action() returns without rescheduling
		 * itself once the list is empty (so a lingering watchdog fires at most once more and then stops), and leaving
		 * it in place is what makes the empty-list sweep safe. force_clear_all_processes() is deliberately avoided:
		 * its own unguarded read-modify-write would clobber a processor that a concurrent request enqueued in the gap
		 * after this mutation committed — the exact lost-update race this change exists to prevent.
		 *
		 * There is still a narrow window: a concurrent request can enqueue processor Q and have the watchdog schedule
		 * Q's single-batch action after our lock releases but before the sweep runs, in which case the sweep cancels
		 * Q's action even though Q remains enqueued. Q is never lost from the option (the source of truth), so this is
		 * a bounded scheduling delay, not a lost update: the watchdog we leave in place reschedules Q on its next run.
		 * That recovery is bounded by the watchdog delay (woocommerce_batch_processor_watchdog_delay_seconds), not the
		 * next request, because remove_or_retry_failed_processors() no-ops while any watchdog is already scheduled.
		 */
		if ( empty( $remaining_processors ) ) {
			as_unschedule_all_actions( self::PROCESS_SINGLE_BATCH_ACTION_NAME );
		} else {
			as_unschedule_all_actions( self::PROCESS_SINGLE_BATCH_ACTION_NAME, array( $processor_class_name ) );
		}
		$this->clear_processor_state( $processor_class_name );

		return true;
	}

	/**
	 * Dequeues and de-schedules all the processors.
	 */
	public function force_clear_all_processes(): void {
		as_unschedule_all_actions( self::PROCESS_SINGLE_BATCH_ACTION_NAME );
		as_unschedule_all_actions( self::WATCHDOG_ACTION_NAME );

		foreach ( $this->get_enqueued_processors() as $processor ) {
			$this->clear_processor_state( $processor );
		}

		update_option( self::ENQUEUED_PROCESSORS_OPTION_NAME, array(), false );
	}

	/**
	 * Log an error that happened while processing a batch.
	 *
	 * @param \Exception              $error Exception object to log.
	 * @param BatchProcessorInterface $batch_processor Batch processor instance.
	 * @param array                   $batch Batch that was being processed.
	 */
	protected function log_error( \Exception $error, BatchProcessorInterface $batch_processor, array $batch ): void {
		$error_message = "Error processing batch for {$batch_processor->get_name()}: {$error->getMessage()}";
		$error_context = array(
			'exception' => $error,
			'source'    => 'batch-processing',
		);

		// Log only first and last, as the entire batch may be too big.
		if ( count( $batch ) > 0 ) {
			$error_context = array_merge(
				$error_context,
				array(
					'batch_start' => $batch[0],
					'batch_end'   => end( $batch ),
				)
			);
		}

		/**
		 * Filters the error message for a batch processing.
		 *
		 * @param string $error_message The error message that will be logged.
		 * @param \Exception $error The exception that was thrown by the processor.
		 * @param BatchProcessorInterface $batch_processor The processor that threw the exception.
		 * @param array $batch The batch that was being processed.
		 * @param array $error_context Context to be passed to the logging function.
		 * @return string The actual error message that will be logged.
		 *
		 * @since 6.8.0
		 */
		$error_message = apply_filters( 'wc_batch_processing_log_message', $error_message, $error, $batch_processor, $batch, $error_context );

		$this->logger->error( $error_message, $error_context );
	}

	/**
	 * Determines whether a given processor is consistently failing based on how many recent consecutive failures it has had.
	 *
	 * @since 9.1.0
	 *
	 * @param BatchProcessorInterface $batch_processor The processor that we want to check.
	 * @return boolean TRUE if processor is consistently failing. FALSE otherwise.
	 */
	private function is_consistently_failing( BatchProcessorInterface $batch_processor ): bool {
		$process_details = $this->get_process_details( $batch_processor );
		$max_attempts    = absint(
			/**
			 * Controls the failure threshold for batch processors. That is, the number of times we'll attempt to
			 * process a batch that has resulted in a failure. Once above this threshold, the processor won't be
			 * re-scheduled and will be removed from the queue.
			 *
			 * @since 9.1.0
			 *
			 * @param int $failure_threshold Maximum number of times for the processor to try processing a given batch.
			 * @param BatchProcessorInterface $batch_processor The processor instance.
			 * @param array $process_details Array with batch processor state.
			 */
			apply_filters(
				'wc_batch_processing_max_attempts',
				self::FAILING_PROCESS_MAX_ATTEMPTS_DEFAULT,
				$batch_processor,
				$process_details
			)
		);

		return absint( $process_details['recent_failures'] ?? 0 ) >= max( $max_attempts, 1 );
	}

	/**
	 * Creates log entry with details about a batch processor that is consistently failing.
	 *
	 * @since 9.1.0
	 *
	 * @param BatchProcessorInterface $batch_processor The batch processor instance.
	 * @param array                   $process_details Failing process details.
	 */
	private function log_consistent_failure( BatchProcessorInterface $batch_processor, array $process_details ): void {
		$this->logger->error(
			"Batch processor {$batch_processor->get_name()} appears to be failing consistently: {$process_details['recent_failures']} unsuccessful attempt(s). No further attempts will be made.",
			array(
				'source'        => 'batch-processing',
				'failures'      => $process_details['recent_failures'],
				'first_failure' => $process_details['batch_first_failure'],
				'last_failure'  => $process_details['batch_last_failure'],
			)
		);
	}

	/**
	 * Hooked onto 'shutdown'. This cleanup routine checks enqueued processors and whether they are scheduled or not to
	 * either re-eschedule them or remove them from the queue.
	 * This prevents stale states where Action Scheduler won't schedule any more attempts but we still report the
	 * processor as enqueued.
	 *
	 * @since 9.1.0
	 */
	private function remove_or_retry_failed_processors(): void {
		if ( ! did_action( 'wp_loaded' ) ) {
			return;
		}

		$last_error = error_get_last();
		if ( ! is_null( $last_error ) && in_array( $last_error['type'], array( E_ERROR, E_PARSE, E_CORE_ERROR, E_COMPILE_ERROR, E_USER_ERROR, E_RECOVERABLE_ERROR ), true ) ) {
			return;
		}

		// The most efficient way to check for an existing action is to use `as_has_scheduled_action`, but in unusual
		// cases where another plugin has loaded a very old version of Action Scheduler, it may not be available to us.
		$has_scheduled_action = function_exists( 'as_has_scheduled_action') ? 'as_has_scheduled_action' : 'as_next_scheduled_action';

		if ( call_user_func( $has_scheduled_action, self::WATCHDOG_ACTION_NAME ) ) {
			return;
		}

		/*
		 * Sanitize before array_diff()/array_filter(): array_diff() string-casts its operands (fatal on an object
		 * entry in PHP 8) and is_scheduled() is typed string, so a corrupted option must be reduced to class-name
		 * strings first.
		 */
		$enqueued_processors    = $this->sanitize_processor_list( $this->get_enqueued_processors() );
		$unscheduled_processors = array_diff( $enqueued_processors, array_filter( $enqueued_processors, array( $this, 'is_scheduled' ) ) );

		foreach ( $unscheduled_processors as $processor ) {
			try {
				$instance = $this->get_processor_instance( $processor );
			} catch ( \Exception $e ) {
				continue;
			}

			$exception = new \Exception( 'Processor is enqueued but not scheduled. Background job was probably killed or marked as failed. Reattempting execution.' );
			$this->update_processor_state( $instance, 0, $exception );
			$this->log_error( $exception, $instance, array() );

			if ( $this->is_consistently_failing( $instance ) ) {
				$this->log_consistent_failure( $instance, $this->get_process_details( $instance ) );
				$this->remove_processor( $processor );
			} else {
				$this->schedule_batch_processing( $processor, true );
			}
		}
	}
}
 $attempt++ ) {
				$time   = microtime( true );
				$now    = number_format( $time, 6, '.', '' );
				$expiry = number_format( $time + self::ENQUEUED_PROCESSORS_LOCK_TTL, 6, '.', '' );

				// The unique option_name key makes this INSERT a mutex: it fails when the lock row already exists.
				// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching
				$acquired = $wpdb->insert(
					$wpdb->options,
					array(
						'option_name'  => self::ENQUEUED_PROCESSORS_LOCK_OPTION,
						'option_value' => $expiry,
						'autoload'     => 'no',
					),
					array( '%s', '%s', '%s' )
				);

				if ( ! $acquired ) {
					/*
					 * The lock row exists; take it over only if its stored release time is already in the past.
					 * $wpdb->update() cannot express the "<" comparison, so this conditional takeover uses raw SQL.
					 * The table is a trusted internal identifier and every value is bound through a placeholder.
					 */
					$takeover = $wpdb->prepare(
						"UPDATE {$wpdb->options} SET option_value = %s WHERE option_name = %s AND option_value < %s", // phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared
						$expiry,
						self::ENQUEUED_PROCESSORS_LOCK_OPTION,
						$now
					);
					if ( is_string( $takeover ) ) {
						// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching, WordPress.DB.PreparedSQL.NotPrepared
						$acquired = $wpdb->query( $takeover );
					}
				}

				if ( $acquired ) {
					return $expiry;
				}

				if ( $attempt < $attempts - 1 && $delay_micro > 0 ) {
					usleep( $delay_micro );
				}
			}

			return null;
		} finally {
			$wpdb->suppress_errors( $suppress );
		}
	}

	/**
	 * Release the enqueued-processors lock by deleting the options-table row we own.
	 *
	 * The delete is conditional on the stored release time still matching the one written when the lock was
	 * acquired, so a lock that expired and was taken over by another request is never released out from under it.
	 *
	 * @since 11.0.0
	 *
	 * @param string $expiry The release time returned by acquire_enqueued_processors_lock().
	 */
	private function release_enqueued_processors_lock( string $expiry ): void {
		global $wpdb;

		$suppress = $wpdb->suppress_errors( true );
		try {
			// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching
			$wpdb->delete(
				$wpdb->options,
				array(
					'option_name'  => self::ENQUEUED_PROCESSORS_LOCK_OPTION,
					'option_value' => $expiry,
				),
				array( '%s', '%s' )
			);
		} finally {
			$wpdb->suppress_errors( $suppress );
		}
	}

	/**
	 * Schedule the watchdog action.
	 *
	 * @param bool $with_delay Whether to delay the action execution. Should be true when rescheduling, false when enqueueing.
	 * @param bool $unique     Whether to make the action unique.
	 */
	private function schedule_watchdog_action( bool $with_delay = false, bool $unique = false ): void {
		$time = time();
		if ( $with_delay ) {
			/**
			 * Modify the delay interval for the batch processor's watchdog events.
			 *
			 * @since 8.2.0
			 *
			 * @param int $delay Time, in seconds, before the watchdog process will run. Defaults to 3600 (1 hour).
			 */
			$time += apply_filters( 'woocommerce_batch_processor_watchdog_delay_seconds', HOUR_IN_SECONDS );
		}

		if ( ! as_has_scheduled_action( self::WATCHDOG_ACTION_NAME ) ) {
			as_schedule_single_action(
				$time,
				self::WATCHDOG_ACTION_NAME,
				array(),
				self::ACTION_GROUP,
				$unique
			);
		}
	}

	/**
	 * Schedule a processing action for all the processors that are enqueued but not scheduled
	 * (because they have just been enqueued, or because the processing for a batch failed).
	 */
	private function handle_watchdog_action(): void {
		$pending_processes = $this->sanitize_processor_list( $this->get_enqueued_processors() );
		if ( empty( $pending_processes ) ) {
			return;
		}
		foreach ( $pending_processes as $process_name ) {
			if ( ! $this->is_scheduled( $process_name ) ) {
				$this->schedule_batch_processing( $process_name );
			}
		}
		$this->schedule_watchdog_action( true );
	}

	/**
	 * Process a batch for a single processor, and handle any required rescheduling or state cleanup.
	 *
	 * @param string $processor_class_name Fully qualified class name of the processor.
	 *
	 * @throws \Exception If error occurred during batch processing.
	 */
	private function process_next_batch_for_single_processor( string $processor_class_name ): void {
		if ( ! $this->is_enqueued( $processor_class_name ) ) {
			return;
		}

		$batch_processor = $this->get_processor_instance( $processor_class_name );
		$error           = $this->process_next_batch_for_single_processor_core( $batch_processor );
		$still_pending   = count( $batch_processor->get_next_batch_to_process( 1 ) ) > 0;
		if ( ( $error instanceof \Exception ) ) {
			// The batch processing failed and no items were processed:
			// reschedule the processing with a delay, unless this is a repeatead failure.
			if ( $this->is_consistently_failing( $batch_processor ) ) {
				$this->log_consistent_failure( $batch_processor, $this->get_process_details( $batch_processor ) );
				$this->remove_processor( $processor_class_name );
			} else {
				$this->schedule_batch_processing( $processor_class_name, true );
			}

			throw $error;
		}
		if ( $still_pending ) {
			$this->schedule_batch_processing( $processor_class_name );
		} else {
			$this->dequeue_processor( $processor_class_name );
		}
	}

	/**
	 * Process a batch for a single processor, updating state and logging any error.
	 *
	 * @param BatchProcessorInterface $batch_processor Batch processor instance.
	 *
	 * @return null|\Exception Exception if error occurred, null otherwise.
	 */
	private function process_next_batch_for_single_processor_core( BatchProcessorInterface $batch_processor ): ?\Exception {
		$details    = $this->get_process_details( $batch_processor );
		$time_start = microtime( true );
		$batch      = $batch_processor->get_next_batch_to_process( $details['current_batch_size'] );
		if ( empty( $batch ) ) {
			return null;
		}
		try {
			$batch_processor->process_batch( $batch );
			$time_taken = microtime( true ) - $time_start;
			$this->update_processor_state( $batch_processor, $time_taken );
		} catch ( \Exception $exception ) {
			$time_taken = microtime( true ) - $time_start;
			$this->log_error( $exception, $batch_processor, $batch );
			$this->update_processor_state( $batch_processor, $time_taken, $exception );
			return $exception;
		}
		return null;
	}

	/**
	 * Get the current state for a given enqueued processor.
	 *
	 * @param BatchProcessorInterface $batch_processor Batch processor instance.
	 *
	 * @return array Current state for the processor, or a "blank" state if none exists yet.
	 */
	private function get_process_details( BatchProcessorInterface $batch_processor ): array {
		$defaults = array(
			'total_time_spent'    => 0,
			'current_batch_size'  => $batch_processor->get_default_batch_size(),
			'last_error'          => null,
			'recent_failures'     => 0,
			'batch_first_failure' => null,
			'batch_last_failure'  => null,
		);

		$process_details = get_option( $this->get_processor_state_option_name( $batch_processor ) );
		$process_details = wp_parse_args( is_array( $process_details ) ? $process_details : array(), $defaults );

		return $process_details;
	}

	/**
	 * Get the name of the option where we will be saving state for a given processor.
	 *
	 * @param BatchProcessorInterface|string $batch_processor Batch processor instance or class name.
	 *
	 * @return string Option name.
	 */
	private function get_processor_state_option_name( $batch_processor ): string {
		$class_name = is_a( $batch_processor, BatchProcessorInterface::class ) ? get_class( $batch_processor ) : $batch_processor;
		$class_md5  = md5( $class_name );
		// truncate the class name so we know that it will fit in the option name column along with md5 hash and prefix.
		$class_name = substr( $class_name, 0, 140 );
		return 'wc_batch_' . $class_name . '_' . $class_md5;
	}

	/**
	 * Update the state for a processor after a batch has completed processing.
	 *
	 * @param BatchProcessorInterface $batch_processor Batch processor instance.
	 * @param float                   $time_taken Time take by the batch to complete processing.
	 * @param \Exception|null         $last_error Exception object in processing the batch, if there was one.
	 */
	private function update_processor_state( BatchProcessorInterface $batch_processor, float $time_taken, ?\Exception $last_error = null ): void {
		$current_status                      = $this->get_process_details( $batch_processor );
		$current_status['total_time_spent'] += $time_taken;
		$current_status['last_error']        = null !== $last_error ? $last_error->getMessage() : null;

		if ( null !== $last_error ) {
			$current_status['recent_failures']    = ( $current_status['recent_failures'] ?? 0 ) + 1;
			$current_status['batch_last_failure'] = current_time( 'mysql' );

			if ( is_null( $current_status['batch_first_failure'] ) ) {
				$current_status['batch_first_failure'] = $current_status['batch_last_failure'];
			}
		} else {
			$current_status['recent_failures']     = 0;
			$current_status['batch_first_failure'] = null;
			$current_status['batch_last_failure']  = null;
		}

		update_option( $this->get_processor_state_option_name( $batch_processor ), $current_status, false );
	}

	/**
	 * Removes the option where we store state for a given processor.
	 *
	 * @since 9.1.0
	 *
	 * @param string $processor_class_name Fully qualified class name of the processor.
	 */
	private function clear_processor_state( string $processor_class_name ): void {
		delete_option( $this->get_processor_state_option_name( $processor_class_name ) );
	}

	/**
	 * Schedule a processing action for a single processor.
	 *
	 * @param string $processor_class_name Fully qualified class name of the processor.
	 * @param bool   $with_delay   Whether to schedule the action for immediate execution or for later.
	 */
	private function schedule_batch_processing( string $processor_class_name, bool $with_delay = false ): void {
		$time = $with_delay ? time() + MINUTE_IN_SECONDS : time();
		as_schedule_single_action( $time, self::PROCESS_SINGLE_BATCH_ACTION_NAME, array( $processor_class_name ) );
	}

	/**
	 * Check if a batch processing action is already scheduled for a given processor.
	 * Differs from `as_has_scheduled_action` in that this excludes actions in progress.
	 *
	 * @param string $processor_class_name Fully qualified class name of the batch processor.
	 *
	 * @return bool True if a batch processing action is already scheduled for the processor.
	 */
	public function is_scheduled( string $processor_class_name ): bool {
		return as_has_scheduled_action( self::PROCESS_SINGLE_BATCH_ACTION_NAME, array( $processor_class_name ) );
	}

	/**
	 * Get an instance of a processor given its class name.
	 *
	 * @param string $processor_class_name Full class name of the batch processor.
	 *
	 * @return BatchProcessorInterface Instance of batch processor for the given class.
	 * @throws \Exception If it's not possible to get an instance of the class.
	 */
	private function get_processor_instance( string $processor_class_name ): BatchProcessorInterface {

		$container = wc_get_container();
		$processor = $container->has( $processor_class_name ) ? $container->get( $processor_class_name ) : null;

		/**
		 * Filters the instance of a processor for a given class name.
		 *
		 * @param object|null $processor The processor instance given by the dependency injection container, or null if none was obtained.
		 * @param string $processor_class_name The full class name of the processor.
		 * @return BatchProcessorInterface|null The actual processor instance to use, or null if none could be retrieved.
		 *
		 * @since 6.8.0.
		 */
		$processor = apply_filters( 'woocommerce_get_batch_processor', $processor, $processor_class_name );
		if ( ! isset( $processor ) && class_exists( $processor_class_name ) ) {
			// This is a fallback for when the batch processor is not registered in the container.
			$processor = new $processor_class_name();
		}
		if ( ! is_a( $processor, BatchProcessorInterface::class ) ) {
			throw new \Exception( "Unable to initialize batch processor instance for $processor_class_name" );
		}
		return $processor;
	}

	/**
	 * Helper method to get list of all the enqueued processors.
	 *
	 * @return array List (of string) of the class names of the enqueued processors.
	 */
	public function get_enqueued_processors(): array {
		$enqueued_processors = get_option( self::ENQUEUED_PROCESSORS_OPTION_NAME, array() );

		if ( ! is_array( $enqueued_processors ) ) {
			$this->logger->error( 'Could not fetch list of processors. Clearing up queue.', array( 'source' => 'batch-processing' ) );
			delete_option( self::ENQUEUED_PROCESSORS_OPTION_NAME );
			$enqueued_processors = array();
		}

		return $enqueued_processors;
	}

	/**
	 * Dequeue a processor once it has no more items pending processing.
	 *
	 * @param string $processor_class_name Full processor class name.
	 */
	private function dequeue_processor( string $processor_class_name ): void {
		// Always resolve membership authoritatively inside the lock (no unguarded fast-path read): this runs when a
		// batch finishes, not on a per-request hot path, so correctness is preferred over skipping the lock.
		$removed = false;
		$this->mutate_enqueued_processors(
			function ( array $pending_processes ) use ( $processor_class_name, &$removed ): array {
				if ( ! in_array( $processor_class_name, $pending_processes, true ) ) {
					return $pending_processes;
				}
				$removed = true;
				return array_values( array_diff( $this->sanitize_processor_list( $pending_processes ), array( $processor_class_name ) ) );
			}
		);

		if ( $removed ) {
			$this->clear_processor_state( $processor_class_name );
		}
	}

	/**
	 * Helper method to set the enqueued processor class names.
	 *
	 * @param array $processors List of full processor class names.
	 */
	private function set_enqueued_processors( array $processors ): void {
		update_option( self::ENQUEUED_PROCESSORS_OPTION_NAME, $processors, false );
	}

	/**
	 * Check if a particular processor is enqueued.
	 *
	 * @param string $processor_class_name Fully qualified class name of the processor.
	 *
	 * @return bool True if the processor is enqueued.
	 */
	public function is_enqueued( string $processor_class_name ): bool {
		return in_array( $processor_class_name, $this->get_enqueued_processors(), true );
	}

	/**
	 * Dequeue and de-schedule a processor instance so that it won't be processed anymore.
	 *
	 * @param string $processor_class_name Fully qualified class name of the processor.
	 * @return bool True if the processor has been dequeued, false if the processor wasn't enqueued (so nothing has been done).
	 */
	public function remove_processor( string $processor_class_name ): bool {
		// Resolve membership authoritatively inside the lock (no unguarded fast-path read). remove_processor() is
		// not a per-request hot path — the continuous-sync 'shutdown' handler enqueues rather than removes — so it
		// always takes the lock and re-reads the freshest list rather than acting on a possibly-stale cached copy.
		$was_enqueued         = false;
		$remaining_processors = $this->mutate_enqueued_processors(
			function ( array $enqueued_processors ) use ( $processor_class_name, &$was_enqueued ): array {
				if ( ! in_array( $processor_class_name, $enqueued_processors, true ) ) {
					return $enqueued_processors;
				}
				$was_enqueued = true;
				return array_values( array_diff( $this->sanitize_processor_list( $enqueued_processors ), array( $processor_class_name ) ) );
			}
		);

		if ( ! $was_enqueued ) {
			return false;
		}

		/*
		 * $remaining_processors is the list exactly as persisted inside the critical section above, so the empty
		 * check is decided from the lock-guarded snapshot rather than a second, unguarded re-read (which would only
		 * ever see this request's own post-mutation value anyway). When that snapshot is empty we unschedule every
		 * single-batch action to sweep up any orphaned "ghost" actions left in Action Scheduler for processors that
		 * are no longer enqueued; otherwise only the removed processor's own scheduling needs tearing down, so we
		 * unschedule by class name.
		 *
		 * This intentionally does NOT unschedule the watchdog: handle_watchdog_action() returns without rescheduling
		 * itself once the list is empty (so a lingering watchdog fires at most once more and then stops), and leaving
		 * it in place is what makes the empty-list sweep safe. force_clear_all_processes() is deliberately avoided:
		 * its own unguarded read-modify-write would clobber a processor that a concurrent request enqueued in the gap
		 * after this mutation committed — the exact lost-update race this change exists to prevent.
		 *
		 * There is still a narrow window: a concurrent request can enqueue processor Q and have the watchdog schedule
		 * Q's single-batch action after our lock releases but before the sweep runs, in which case the sweep cancels
		 * Q's action even though Q remains enqueued. Q is never lost from the option (the source of truth), so this is
		 * a bounded scheduling delay, not a lost update: the watchdog we leave in place reschedules Q on its next run.
		 * That recovery is bounded by the watchdog delay (woocommerce_batch_processor_watchdog_delay_seconds), not the
		 * next request, because remove_or_retry_failed_processors() no-ops while any watchdog is already scheduled.
		 */
		if ( empty( $remaining_processors ) ) {
			as_unschedule_all_actions( self::PROCESS_SINGLE_BATCH_ACTION_NAME );
		} else {
			as_unschedule_all_actions( self::PROCESS_SINGLE_BATCH_ACTION_NAME, array( $processor_class_name ) );
		}
		$this->clear_processor_state( $processor_class_name );

		return true;
	}

	/**
	 * Dequeues and de-schedules all the processors.
	 */
	public function force_clear_all_processes(): void {
		as_unschedule_all_actions( self::PROCESS_SINGLE_BATCH_ACTION_NAME );
		as_unschedule_all_actions( self::WATCHDOG_ACTION_NAME );

		foreach ( $this->get_enqueued_processors() as $processor ) {
			$this->clear_processor_state( $processor );
		}

		update_option( self::ENQUEUED_PROCESSORS_OPTION_NAME, array(), false );
	}

	/**
	 * Log an error that happened while processing a batch.
	 *
	 * @param \Exception              $error Exception object to log.
	 * @param BatchProcessorInterface $batch_processor Batch processor instance.
	 * @param array                   $batch Batch that was being processed.
	 */
	protected function log_error( \Exception $error, BatchProcessorInterface $batch_processor, array $batch ): void {
		$error_message = "Error processing batch for {$batch_processor->get_name()}: {$error->getMessage()}";
		$error_context = array(
			'exception' => $error,
			'source'    => 'batch-processing',
		);

		// Log only first and last, as the entire batch may be too big.
		if ( count( $batch ) > 0 ) {
			$error_context = array_merge(
				$error_context,
				array(
					'batch_start' => $batch[0],
					'batch_end'   => end( $batch ),
				)
			);
		}

		/**
		 * Filters the error message for a batch processing.
		 *
		 * @param string $error_message The error message that will be logged.
		 * @param \Exception $error The exception that was thrown by the processor.
		 * @param BatchProcessorInterface $batch_processor The processor that threw the exception.
		 * @param array $batch The batch that was being processed.
		 * @param array $error_context Context to be passed to the logging function.
		 * @return string The actual error message that will be logged.
		 *
		 * @since 6.8.0
		 */
		$error_message = apply_filters( 'wc_batch_processing_log_message', $error_message, $error, $batch_processor, $batch, $error_context );

		$this->logger->error( $error_message, $error_context );
	}

	/**
	 * Determines whether a given processor is consistently failing based on how many recent consecutive failures it has had.
	 *
	 * @since 9.1.0
	 *
	 * @param BatchProcessorInterface $batch_processor The processor that we want to check.
	 * @return boolean TRUE if processor is consistently failing. FALSE otherwise.
	 */
	private function is_consistently_failing( BatchProcessorInterface $batch_processor ): bool {
		$process_details = $this->get_process_details( $batch_processor );
		$max_attempts    = absint(
			/**
			 * Controls the failure threshold for batch processors. That is, the number of times we'll attempt to
			 * process a batch that has resulted in a failure. Once above this threshold, the processor won't be
			 * re-scheduled and will be removed from the queue.
			 *
			 * @since 9.1.0
			 *
			 * @param int $failure_threshold Maximum number of times for the processor to try processing a given batch.
			 * @param BatchProcessorInterface $batch_processor The processor instance.
			 * @param array $process_details Array with batch processor state.
			 */
			apply_filters(
				'wc_batch_processing_max_attempts',
				self::FAILING_PROCESS_MAX_ATTEMPTS_DEFAULT,
				$batch_processor,
				$process_details
			)
		);

		return absint( $process_details['recent_failures'] ?? 0 ) >= max( $max_attempts, 1 );
	}

	/**
	 * Creates log entry with details about a batch processor that is consistently failing.
	 *
	 * @since 9.1.0
	 *
	 * @param BatchProcessorInterface $batch_processor The batch processor instance.
	 * @param array                   $process_details Failing process details.
	 */
	private function log_consistent_failure( BatchProcessorInterface $batch_processor, array $process_details ): void {
		$this->logger->error(
			"Batch processor {$batch_processor->get_name()} appears to be failing consistently: {$process_details['recent_failures']} unsuccessful attempt(s). No further attempts will be made.",
			array(
				'source'        => 'batch-processing',
				'failures'      => $process_details['recent_failures'],
				'first_failure' => $process_details['batch_first_failure'],
				'last_failure'  => $process_details['batch_last_failure'],
			)
		);
	}

	/**
	 * Hooked onto 'shutdown'. This cleanup routine checks enqueued processors and whether they are scheduled or not to
	 * either re-eschedule them or remove them from the queue.
	 * This prevents stale states where Action Scheduler won't schedule any more attempts but we still report the
	 * processor as enqueued.
	 *
	 * @since 9.1.0
	 */
	private function remove_or_retry_failed_processors(): void {
		if ( ! did_action( 'wp_loaded' ) ) {
			return;
		}

		$last_error = error_get_last();
		if ( ! is_null( $last_error ) && in_array( $last_error['type'], array( E_ERROR, E_PARSE, E_CORE_ERROR, E_COMPILE_ERROR, E_USER_ERROR, E_RECOVERABLE_ERROR ), true ) ) {
			return;
		}

		// The most efficient way to check for an existing action is to use `as_has_scheduled_action`, but in unusual
		// cases where another plugin has loaded a very old version of Action Scheduler, it may not be available to us.
		$has_scheduled_action = function_exists( 'as_has_scheduled_action') ? 'as_has_scheduled_action' : 'as_next_scheduled_action';

		if ( call_user_func( $has_scheduled_action, self::WATCHDOG_ACTION_NAME ) ) {
			return;
		}

		/*
		 * Sanitize before array_diff()/array_filter(): array_diff() string-casts its operands (fatal on an object
		 * entry in PHP 8) and is_scheduled() is typed string, so a corrupted option must be reduced to class-name
		 * strings first.
		 */
		$enqueued_processors    = $this->sanitize_processor_list( $this->get_enqueued_processors() );
		$unscheduled_processors = array_diff( $enqueued_processors, array_filter( $enqueued_processors, array( $this, 'is_scheduled' ) ) );

		foreach ( $unscheduled_processors as $processor ) {
			try {
				$instance = $this->get_processor_instance( $processor );
			} catch ( \Exception $e ) {
				continue;
			}

			$exception = new \Exception( 'Processor is enqueued but not scheduled. Background job was probably killed or marked as failed. Reattempting execution.' );
			$this->update_processor_state( $instance, 0, $exception );
			$this->log_error( $exception, $instance, array() );

			if ( $this->is_consistently_failing( $instance ) ) {
				$this->log_consistent_failure( $instance, $this->get_process_details( $instance ) );
				$this->remove_processor( $processor );
			} else {
				$this->schedule_batch_processing( $processor, true );
			}
		}
	}
}