protected function handle() {
		$this->lock_process();

		do {
			$batch = $this->get_batch();

			if ( empty( $batch->data ) ) {
				break;
			}

			foreach ( $batch->data as $key => $value ) {
				$task = $this->task( $value );

				if ( false !== $task ) {
					$batch->data[ $key ] = $task;
				} else {
					unset( $batch->data[ $key ] );
				}

				// Update batch before sending more to prevent duplicate email possibility.
				$this->update( $batch->key, $batch->data );

				if ( $this->time_exceeded() || $this->memory_exceeded() ) {
					// Batch limits reached.
					break;
				}
			}
			if ( empty( $batch->data ) ) {
				$this->delete( $batch->key );
			}
		} while ( ! $this->time_exceeded() && ! $this->memory_exceeded() && ! $this->is_queue_empty() );

		$this->unlock_process();

		// Start next batch or complete process.
		if ( ! $this->is_queue_empty() ) {
			$this->dispatch();
		} else {
			$this->complete();
		}
	}