Upgrade Guide

Learn how to migrate your existing application from generator-based coroutines to fiber-based coroutines.

We’ve brought fibers into PHP 8.1, and it’s time to make use of them. AMPHP has always been focused on synchronous feeling APIs, and fibers allow leveling-up that approach, removing all the boilerplate.

Fibers are independent call stacks that can be cooperatively scheduled by the event loop. While generator-based coroutines need promises at every function boundary, fiber-based coroutines don’t have any need like that. They also work fine with built-in functions like array_map.

You can read the full Fiber RFC on wiki.php.net if you’re interested in the low-level details.

We’re currently in the process of releasing stable versions based on Revolt. This guide is a work-in-progress.

Event Loop

AMPHP no longer ships its own event loop. It’s now based on Revolt. Revolt\EventLoop is quite similar to Amp’s previous Amp\Loop. A very important difference is using float $seconds instead of int $milliseconds for timers though!

Suspension is a new low-level API in Revolt to automatically suspend a fiber and run the event loop if needed. There’s mostly no need to call Amp\Loop::run() or rather the new equivalent Revolt\EventLoop::run() anymore. The event loop will just automatically run when there’s an await() / suspend() call, which might also be nested deeply somewhere.

You have to replace Amp\Loop with Revolt\EventLoop.


Most migration work will be removing the Amp\call boilerplate and removing all yield expressions.

function fetchIssues(string $url): Promise
    return call(function () use ($url) {
        $response = yield fetch($url);
        $body = yield $response->getBody()->buffer();
        return json_decode($body, true);
function fetchIssues(string $url): array
    $response = fetch($url);
    $body = $response->getBody()->buffer();
    return json_decode($body, true);


Future is a replacement for the previous Promise. There’s no need for callbacks or yield anymore! Its await() method is based on fibers and replaces generator based coroutines / Amp\Promise\wait().

  • Renamed Amp\Deferred to Amp\DeferredFuture.
  • Removed Amp\Promise\wait(): Use Amp\Future::await() instead, which can be called in any (nested) context unlike before.
  • Removed Amp\call(): Remove the passed closure boilerplate and all yield keywords, interruption is handled via fibers now instead of generator coroutines.
  • Removed Amp\asyncCall(): Replace invocations with Amp\async(), which starts a new fiber instead of using generators.
  • Removed Amp\coroutine(): There’s no direct replacement.
  • Removed Amp\asyncCoroutine(): There’s no direct replacement.
  • Removed Amp\Promise\timeout(): Future::await() accepts an optional Cancellation, which can be used as a replacement.
  • Removed Amp\Promise\rethrow(): Unhandled errors are now automatically thrown into the event loop, so there’s no need for that function anymore.
  • Unhandled errors can be ignored using Future::ignore() if needed, but should usually be handled in some way.
  • Removed Amp\Promise\wrap(): Use Future::finally() instead.
  • Renamed Amp\getCurrentTime() to Amp\now() returning the time in seconds instead of milliseconds.
  • Changed Amp\delay() to accept the delay in seconds now instead of milliseconds.
  • Added Amp\weakClosure() to allow a class to hold a self-referencing Closure without creating a circular reference that prevents automatic garbage collection.
  • Added Amp\trapSignal() to await one or multiple signals.

Promise Combinators

Promise combinators have been renamed:

  • Amp\Promise\race() has been renamed to Amp\Future\awaitFirst()
  • Amp\Promise\first() has been renamed to Amp\Future\awaitAny()
  • Amp\Promise\some() has been renamed to Amp\Future\awaitAnyN()
  • Amp\Promise\any() has been renamed to Amp\Future\awaitAll()
  • Amp\Promise\all() has been renamed to Amp\Future\await()


  • CancellationToken has been renamed to Cancellation.
  • CancellationTokenSource has been renamed to DeferredCancellation.
  • NullCancellationToken has been renamed to NullCancellation.
  • TimeoutCancellationToken has been renamed to TimeoutCancellation.
  • CombinedCancellationToken has been renamed to CompositeCancellation.
  • SignalCancellation has been added.


Iterators have been removed from amphp/amp as normal PHP iterators can be used with fibers now and there’s no need for a separate API. However, there’s still some need for concurrent iterators, which is covered by the new amphp/pipeline library now.


Amp\Closable has been added as a new basic interface for closable resources such as streams or sockets.

Strict Types

Strict types now declared in all library files. This will affect callbacks invoked within this library’s code which use scalar types as parameters. Functions used with Amp\async() are the most likely to be affected by this change — these functions will now be invoked within a strict-types context.

Other Packages

Please have a look at the release notes on GitHub for packages other than amphp/amp when upgrading.