[wp-trac] [WordPress Trac] #41358: Shutdown hooks can significantly slow down REST API responses

[WordPress Trac]

#41358: Shutdown hooks can significantly slow down REST API responses
-------------------------------------------------+-------------------------
 Reporter:  mikejolley                           |       Owner:
     Type:  defect (bug)                         |      Status:  new
 Priority:  normal                               |   Milestone:  Awaiting
Component:  REST API                             |  Review
 Severity:  normal                               |     Version:
 Keywords:  has-patch dev-feedback needs-        |  Resolution:
  testing                                        |     Focuses:  rest-api,
                                                 |  performance
-------------------------------------------------+-------------------------

Comment (by jnylen0):

 I tested a few things locally:

 - On nginx, `fastcgi_finish_request` is called; error logging during a
 long `shutdown` hook seems to work fine, contrary to some of the above
 reports (may depend on PHP version?)
 - On apache, the logic to send `Connection: close` and other headers is
 called, and works fine.

 As noted at https://stackoverflow.com/a/27847878/106302, on both nginx and
 apache, outputting after `finish_request` does nothing, '''unless'''
 output is flushed (using `flush()` for example), in which case the script
 will abort.  This would be pretty terrible to debug, because the abort
 doesn't appear to happen immediately.

 Fortunately, as noted at https://bugs.php.net/bug.php?id=68772, this is
 fixed for both webservers by calling `ignore_user_abort( true );` during
 `finish_request`.

 I also think we should change the Apache logic a bit:  how do we know that
 `ob_get_length()` is the correct content length?  Maybe we can have
 `serve_request` always send a `Content-Length` header based on the data it
 echoes, and `finish_request` do the rest.

--
Ticket URL: <https://core.trac.wordpress.org/ticket/41358#comment:4>
WordPress Trac <https://core.trac.wordpress.org/>
WordPress publishing platform