Cacher is the code snippet organizer for pro developers

/**
 * Gravity Perks // GP Limit Choices // Prevent Concurrent Submissions from Consuming the Last Choice
 * http://gravitywiz.com/documentation/gravity-forms-limit-choices/
 */
add_action( 'gform_validation', 'gplc_lock', 99 );
function gplc_lock ( $result ) {

	$is_last_page = GFFormDisplay::get_target_page( $result['form'], GFFormDisplay::get_source_page( $result['form']['id'] ), rgpost( 'gform_field_values' ) ) == '0';

	$lock = new GP_Lock( 'gplc-lock' );
	if ( $result['is_valid'] && $is_last_page && ! $lock->lock() ) {
		$result['is_valid'] = false;
		add_filter( 'gform_validation_message', function( $message ) {
			return "<div class='validation_error'>There was a problem processing your submission. Please resubmit the form.</div>";
		} );
	}

	return $result;
}

add_action( 'gform_entry_created', function() {
	$lock = new GP_Lock( 'gplc-lock' );
	$lock->unlock();
} );