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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def check_available(self):
 """ Check for availability of a layer and provide run metrics. """

        success = True
        start_time = datetime.datetime.utcnow()
        message = ''
        LOGGER.debug('Checking layer id %s' % self.id)

        signals.post_save.disconnect(layer_post_save, sender=Layer)

        try:
            self.update_thumbnail()
        except ValueError, err:
            # caused by update_thumbnail()
            # self.href is empty in arcserver.ExportMap
            if str(err).startswith("unknown url type:"):
                LOGGER.debug('Thumbnail can not be updated: %s' % str(err))
        except Exception, err:
            message = str(err)
            success = False

        signals.post_save.connect(layer_post_save, sender=Layer)

        end_time = datetime.datetime.utcnow()

        delta = end_time - start_time
        response_time = '%s.%s' % (delta.seconds, delta.microseconds)

        check = Check(
            content_object=self,
            success=success,
            response_time=response_time,
            message=message
        )
        check.save()
        LOGGER.debug('Layer checked in %s seconds, status is %s' % (response_time, success))
        return success, message