Limit the number of total sign ups for a given membership level

pmpro-limit-members-per-level.php

function pmproml_pmpro_save_membership_level($level_id)
{
	if( $level_id <= 0 )
	{
		return;
	}

	$limit = $_REQUEST['pmpro_member_limit'];

	update_option('pmpro_limit_'.$level_id, $limit);
}
add_action('pmpro_save_membership_level','pmproml_pmpro_save_membership_level');

function pmproml_pmpro_membership_level_after_other_settings(){
	?>
		<h3 class="topborder"><?php _e('Membership Limits', 'pmpro');?></h3>
		<table class="form-table">
			<tbody>
				<tr>
					<th scope="row" valign="top"><label for="pmpro_member_limit"><?php _e('Maximum', 'pmpro');?>:</label></th>
					<td>
						<?php
								
							if(isset($_REQUEST['edit'])){
								
								$edit = intval($_REQUEST['edit']);
								
								$limit = get_option('pmpro_limit_'.$edit);
							}
							else{
								$limit = "";
							}
							
							?>
							
						<input type="text" name="pmpro_member_limit" id="pmpro_member_limit" value= '<?php echo $limit; ?>' >
			
						<p class="description">Set the maximum number of members for this level</p>
					</td>
				</tr>
			</tbody>
		</table>
	
	
	<?php 
}
add_action('pmpro_membership_level_after_other_settings','pmproml_pmpro_membership_level_after_other_settings');


function pmproml_pmpro_registration_checks($value)
{
	global $wpdb;
	
	$level_id = intval($_REQUEST['level']);
	$limit = get_option('pmpro_limit_'.$level_id);
	
	$sql = "SELECT COUNT(*)
            FROM {$wpdb->pmpro_memberships_users}
            WHERE `status` LIKE 'active' AND `membership_id` = ". $level_id;
		  
	$member_count = $wpdb->get_var($sql);
	
	if($member_count >= $limit)
	{
		global $pmpro_msg, $pmpro_msgt;
		$pmpro_msg = "Membership Limit has been reached for this level";
		$pmpro_msgt = "pmpro_error";
		$value = false;
	}
	
	return $value;
	
}

add_filter('pmpro_registration_checks', 'pmproml_pmpro_registration_checks');