WordPress at a glance
function is not described

wp_check_post_lock() WP 2.5.0

Check to see if the post is currently being edited by another user.

Hooks in function
Return

Int/false. ID of the user with lock. False if the post does not exist, post is not locked, the user with lock does not exist, or the post is locked by current user.

Usage

wp_check_post_lock( $post_id );
$post_id(int) (required)
ID of the post to check for editing.

Code of wp check post lock: wp-admin/includes/post.php VER 5.0.3

<?php
function wp_check_post_lock( $post_id ) {
	if ( ! $post = get_post( $post_id ) ) {
		return false;
	}

	if ( ! $lock = get_post_meta( $post->ID, '_edit_lock', true ) ) {
		return false;
	}

	$lock = explode( ':', $lock );
	$time = $lock[0];
	$user = isset( $lock[1] ) ? $lock[1] : get_post_meta( $post->ID, '_edit_last', true );

	if ( ! get_userdata( $user ) ) {
		return false;
	}

	/** This filter is documented in wp-admin/includes/ajax-actions.php */
	$time_window = apply_filters( 'wp_check_post_lock_window', 150 );

	if ( $time && $time > time() - $time_window && $user != get_current_user_id() ) {
		return $user;
	}

	return false;
}