restore_current_blog() vs switch_to_blog()

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After every instance of switch_to_blog() you should call restore_current_blog() to restore the current (actually, previous) blog.

But if you’re looping through two or more blogs and calling switch_to_blog() on each, is there any reason not to use an additional switch_to_blog() at the end of the loop to switch to the original blog rather than calling restore_current_blog() at each pass.

E.g.

Why not:

 $original_blog_id = get_current_blog_id();
 foreach( $blog_ids as $blog_id ){
    switch_to_blog( $blog_id );
    //Do stuff
 }
 switch_to_blog( $original_blog_id );

instead of:

 foreach( $blog_ids as $blog_id ){
    switch_to_blog( $blog_id );
    //Do stuff
    restore_current_blog_id();
 }

3

After every instance of switch_to_blog() you need to call restore_current_blog() otherwise WP will think it is in a “switched” mode and can potentially return incorrect data.

If you view the source code for both functions you will see those functions push/pop data into a global called $GLOBALS['_wp_switched_stack']. If you do not call restore_current_blog() after every switch_to_blog(), $GLOBALS['_wp_switched_stack'] will be non-empty. If $GLOBALS['_wp_switched_stack'] is non-empty WP thinks it is in a switched mode, even if you switched back to the original blog using switch_to_blog(). The switched mode function is ms_is_switched() and it affects wp_upload_dir(). If wp_upload_dir() thinks it is in a switched mode, it can return data that is incorrect. wp_upload_dir() builds URLs for the site, so it is a very critical function.

This is the correct use:

 foreach( $blog_ids as $blog_id ){
    switch_to_blog( $blog_id );
    //Do stuff
    restore_current_blog();
 }

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