We added ePHPm to the Yii3 runtime benchmark. It runs the same Yii3 API app on a bunch of PHP runtimes and compares them. Our fork with the ePHPm runner is ephpm/app-api.

The pitch for ePHPm is one binary in place of php-fpm, nginx and Redis. There was always a hole in it though. To deploy a PHP app you still need to run composer install. That drags PHP and composer.phar back onto the box or into the container build, just for that one step. ephpm composer install now runs a pure-Rust, Composer-compatible installer called vivacity inside the ePHPm binary. One binary serves the app and installs its dependencies. On Windows that works with no PHP installed at all.…

Every “build a lock on Redis” tutorial spends its time on acquisition: SET key value NX PX 30000, one winner, done. The release gets one line, DEL key. That line is where most of the lock bugs I’ve had in ePHPm lived. Over about three months the same mistake showed up in three places. First the native session handler, then two of the Composer wrapper packages, and finally the cluster. Each time it wore a slightly different costume.

Persistent workers are the big performance win in modern PHP. You boot Laravel or Symfony once, keep the container in memory, and serve thousands of requests out of the same process. ePHPm has had a worker mode for a while. Like most worker runtimes it had a quiet hole in it. You couldn’t step debug a request with Xdebug. I wanted that fixed without patching Xdebug and without giving up the warm pool. The answer ended up being to stop fighting the constraint and route around it. The debug…

I covered the design of ePHPm’s native WebSockets in a few paragraphs of the odds and ends post. Rust owns the socket and PHP runs once per event. An idle connection never costs you a PHP thread. That was the why. This post is the how. We’ll build a small chat app with login, per-user push notifications from ordinary HTTP requests and a browser client. Then we’ll serve it over TLS. Last come the limits, the sharp edges and how to debug it when the browser only tells you 1006.

In August, ePHPm turned PHP’s tracing JIT on by default in single-site serve mode. Three days later it went back off on every platform, and it’s still off. The reason turned out to be a use-after-free in PHP’s tracing JIT that has nothing to do with ePHPm. Stock php -S with a stock Laravel skeleton dies on it in a couple of requests. The fix is now released upstream. So this seemed like the right time to write up how we got there, and what still has to happen before the default…

Part 1 covered the plumbing. ePHPm registers ephpm_kv_* and ephpm_db_* functions that call straight into Rust. A cache read through one costs about a tenth of a microsecond instead of a loopback round trip. That’s nice and also useless on its own. Nobody is going to rewrite their WordPress object cache or their Laravel cache store around a function called ephpm_kv_set(). Applications talk to existing APIs instead:

Not every fix in ePHPm earns a full write-up. A few of the smaller ones have stuck with me because the lesson in each was bigger than the diff. Here are four from this summer.

In the stack guard post the villain was a -Wl,--wrap linker flag that turned off PHP’s C-stack overflow guard. It wasn’t the only one. Until August, max_execution_time did nothing in ePHPm on Linux, for the same reason. We had wrapped the function that arms it to a no-op. A runaway script ran until the HTTP layer’s request timeout gave up on it and sent a 504. The PHP thread kept burning CPU after that.

ePHPm is a single Rust binary that embeds PHP. It carries its own KV store and its own SQLite-backed database in the same process. For a long time PHP code could only reach that KV store the same way it reaches Redis. It opened a TCP socket to the RESP listener ePHPm runs on localhost, encoded a command and waited for the reply. That works, and every PHP Redis client in existence already speaks it. But it is a strange thing to do when the hash map you’re talking to lives a few pointers…