Don't Wait; Generate!

MidwestPHP 2020

Ian Littman / @iansltx

follow along at https://ian.im/gen20mw

We'll Answer

• What's a Generator?
• What's a Coroutine?
• Why async/non-blocking I/O && event loops?
• Why not?
• What a Generator + Coroutine based app looks like
  (with real code, time permitting)

This is a generator

function gRange($min, $max, $step): \Generator
{
    for ($i = $min; $i < $max; $i += $step) {
        yield $i;
    }
}

foreach (gRange(12, 82, 5) as $n) {
    echo "$n\n"; // 12, 17, 22, etc.
}

What's going on here?

• Resumable function
• Uses yield rather than (or in addition to) return
• Incremental, iterable results
• Behaves a bit like an Iterator
• Values and Exceptions can be sent/thrown in
  (more on this in a moment)

<spooky>This is a generator</spooky>

function spooky(): \Generator
{
    while (true) {
        yield random_int(0, 1) ? 'O' : 'o';
    }
}

foreach (spooky() as $chr) {
    echo $chr; usleep(100000);
}

When can I use it?

• PHP 5.5+, but 7.0+ gets you...
  • return
  • yield from
  • Throwables
• Was on HHVM and predecessors before PHP
• ES2015 (aka ES6) via function*
• C# (.NET 4.5+)
• Python 2.2+

Before we look at our next example...

If you call a function that yields, you will not execute that function. You'll get back a Generator object. To execute the function, you need to call methods on the Generator.

Also, "return" means something different for a Generator than for a normal function.

A Visual Example

Generator

Parent

$g = gen(1);

$a = $g->current();

2

$b = yield $arg1 + 1;

$c = $g->send($a + 1);

$d = yield $b + 2;

5

3

function gen($arg1)

$e = $g->send($c + 1);

6

return $d + 2;

null

echo $g->getReturn();

8

We just did a coroutine.

• Yield: stop execution until caller restarts it via send()
• Yield from: pass through execution until yielded-from object has nothing else to yield
• Return: use just like normal
• Cooperative multitasking!

Standard PHP-FPM Request Model

Client (or Load Balancer)

Web Server (nginx or Apache)

FastCGI Daemon (php-fpm) + Workers

HTTP

FastCGI

Pros

• Common
• Multicore
• Shared-nothing (safe)
• Fast for static resources
• Library support
  • Request\Response wrappers
  • Database engines
  • ...basically anything else
• Don't worry (much) about blocking the thread

Cons

• No in-request parallelism*
• Blocking I/O
• Not memory-efficient
• Startup penalty on every req
• Not 12-factor
  • Process manager (runit)
  • nginx
  • php-fpm + workers

* Ignoring curl_multi and wrappers (e.g. Guzzle)

DEMO TIME: ngx + FPM + SLIM APP

iansltx/raphple

Blocking I/O is drive-thru
Async is delivery

Event Loops!

T_PARADIGM_SHIFT

• Async I/O
• For compute-heavy operations...
  • Don't do in-process if you can avoid it
  • Don't do all at once if it must be in-process

Callbacks/Promises

• Very common (used in e.g. ReactPHP), but...
• Hard to follow execution flow
  • Error callback convention (vs. Exceptions)
  • Messages only at function borders
  • Callback Pyramid of Doom

Why Generators?

• Easier to follow
• Cleaner error handling
• Pass control inside functions
• Can still do async!

With generator-based concurrency, you're trading flexibility in defining concurrency for clarity in defining your task.

Generators in an Event Loop

1. Run until blocking I/O
2. Yield promise representing blocking I/O
3. Event loop skips coroutine until promise is resolved (can use yield from inside a coroutine when you want to call another coroutine and wait for it to complete)
4. Event loop send()s promise result to coroutine
5. Repeat from 1 until coroutine is complete (return)

Modern JS

• async () => somePromise()
• const foo = await somePromise()

PHP

• fn(): \Generator => yield somePromise();
• $foo = yield somePromise();

Event Loop Extensions

• Not required, but highly recommended
• ev
• event
• php-uv

Amphp http-server Request Model

Client (or Load Balancer)

Application Server (AMPHP)

HTTP

var_dump(is_12_factor()); // bool(true)

Pros

• No per-request bootstrap time
• Fewer moving parts (12F app)
• Async execution
• Generator based (!pyramid)
• Async database access
• Lower memory use per request
• Fast!

Cons

• A bit fragile*
• Requires port match
• Single-threaded**
• Plenty to refactor

* Throwables to the rescue!
** amphp/cluster to the rescue!

Demo Time: Amp

Benchmarks!

• System under test
  • Vultr 4GB high frequency server (2 vCPUs), Dallas
  • Ubuntu 19.10 + Docker, HTTP-only
  • Current docker-compose setups from GitHub
• Load generation system
  • Vultr 1GB high frequency server, same data center
  • Siege 4.0.4 on Ubuntu 19.10
  • Benchmarked a few times to allow for warm-up
  • Hitting raffle entrants URL w\cookie, one "blank" raffle

  • siege -c 15 -t 30S -b <url> <cookie header> 

Benchmarks! Nginx + PHP-FPM (7.4)

Transactions:                3616 hits
Availability:              100.00 %
Elapsed time:               29.19 secs
Data transferred:            0.14 MB
Response time:               0.12 secs
Transaction rate:          123.88 trans/sec
Throughput:                  0.00 MB/sec
Concurrency:                14.96
Successful transactions:     3616
Failed transactions:            0
Longest transaction:         0.25
Shortest transaction:        0.02

~28MB RAM, ~190% CPU

Benchmarks! AMPHP (7.4, 2 workers)

Transactions:                8767 hits
Availability:              100.00 %
Elapsed time:               29.24 secs
Data transferred:            0.33 MB
Response time:               0.05 secs
Transaction rate:          299.83 trans/sec
Throughput:                  0.01 MB/sec
Concurrency:                14.99
Successful transactions:     8767
Failed transactions:            0
Longest transaction:         0.16
Shortest transaction:        0.00

~30MB RAM, ~80% CPU

Benchmark Caveats

• In favor of amphp
  • Relatively low concurrency
  • Didn't turn opcache revalidation completely off on FPM
  • Failing requests didn't automatically disqualify
• In favor of nginx + fpm
  • Very little I/O (a couple very quick DB calls)
  • Tiny I/O latency (DB was on-server)

Thanks! Questions?

• ian.im/gen20mw - these slides
• github.com/iansltx/raphple - raffle code
• twitter.com/iansltx - me
• github.com/iansltx - my code
• Yield sign photo is mine
• ...and I'm available for part-time contract dev work