PHP 7-assert（string）有时非常慢

Question

I recently copied a site to a new server which is running PHP 7. The code is heavily reliant on assert() calls. In order to get assertions running on the new server, we have to set zend.assertions to 1. Assertions work now, but about half the time, certain pages will load extremely slowly (60+ seconds).

I have debugging functions which let me see how long each block of code takes. They show me that sometimes calling assert() takes less than a millisecond, but other times it costs about 60 milliseconds.

I found this out when I added the following [pseudo-code] to an area of my code where I'd observed slowdowns:

1. output the time
2. call assert(true) 100 times
3. output the time
4. call assert('true') 100 times
5. output the time

This lets me see how costly the "assert()" calls are, both with expressions as parameters [the assert(true) call] and also with string-expressions as parameters [the assert('true') call].

Sometimes when I refresh the page, both loops take less than 1 millisecond total.

Other times, however, the first few passes through those loops might be fast, but then suddenly the assert('true') loop takes more than 6 seconds, which means each assert('true') call takes about 60 milliseconds. The assert(true) calls are still fast, however.

This implies that sometimes when we call assert() with a string parameter, the evaluation of that string is extremely slow.

It's erratic, though. Like I said, half the time I refresh the page, assert('true') is fast the whole time... but other times assert('true') stats costing about 60 milliseconds for each call.

When zend.assertions is set to -1, the assert('true') calls are apparently never evaluated, and there is never any slowness.

I have never encountered this sort of slowness before, and I've used asserts on several servers in the past. Never with PHP 7, though.

A quick "solution" might be to stop using assertions, or stop passing strings as parameters to the assert() function.... But I have hundreds or thousands of functions, all of which use assert() with string parameters! I got in the habit of using assert() with strings long ago, when it was considered best practice (so that you could log or email the failed expressions when they occur in a production environment).

So, what I need is to find a way to prevent PHP 7 from sporadically causing assert(string) to cost 60 milliseconds.

Any idea how to fix this?

Thanks!

Answer 1

A system admin/PHP export was able to find the problem. It's a compatibility bug between the opcache module and assertions.

Basically, in PHP 7.0 (at least our version), if opcache is enabled (as it is by default in PHP) and zend.assertions=1 then over time the opcache logic and the zend assertion logic start interfering with each other, resulting in very slow execution of assert(string) calls.

So, it's a very weird bug, and the only people who would encounter it are those of us who are using PHP 7.0 with lots of assert(string) calls (and opcache left in its enabled state).

The quick fix is to disable opcache, either via php.ini or by calling opcache_reset() at the start of the PHP.

I have test both fixes and they work. I prefer the php.ini fix because the opcache_reset() does not work on all installations of PHP; I got an undefined function error when I tried calling that function on another server.

Of course, the best long-term solution is for someone to fix the opcache and/or assertion libraries so that they don't conflict.