Context switching

Per-request state: Scope and WeakMap

Key state by the request's Scope in a WeakMap: each request sees its own value, and the entry goes when the request ends.

Swerve runs each request in a Scope of its own (the class of the Composer package fiber-interop/scope, which phasync requires). Every coroutine the request starts runs in that scope too, also after it waits. Scope::getCurrent() returns it: use it as the key of a WeakMap.

final class CurrentUser
{
    /** @var WeakMap<Scope, string> */
    private static WeakMap $names;

    public static function set(string $name): void
    {
        self::$names ??= new WeakMap();
        self::$names[Scope::getCurrent()] = $name;
    }

    public static function name(): ?string
    {
        self::$names ??= new WeakMap();

        return self::$names[Scope::getCurrent()] ?? null;
    }
}

With handle() from the previous page calling CurrentUser::set($name) and CurrentUser::name(), the two requests answer as themselves:

hello ann
hello bob

Outside any request, Scope::getCurrent() is Scope::getRootScope(): the worker's own code has a key as well.

The entry goes with the request#

phasync keeps no reference to a scope once the request's coroutines have finished. A WeakMap does not keep its keys alive either, so the entry is freed with the request:

$map = new WeakMap();
(new Scope())->run(function () use ($map) {
    $map[Scope::getCurrent()] = 'ann';
    echo count($map), "\n";   // 1
});
echo count($map), "\n";       // 0

An array keyed by spl_object_id() does not do this: it keeps the data after the request, and PHP may give a later object the same id.

State PHP keeps for the process#

Some state is not yours to key: setlocale(), date_default_timezone_set(), a static of a library you cannot change. phasync::onScopeChange swaps it. The hook runs before a coroutine of another scope than the last one runs, never between coroutines of one request, so each request keeps using the plain functions:

$zones = new WeakMap();   // per Scope
phasync::onScopeChange(function (Scope $new, ?Scope $old) use ($zones) {
    if (null !== $old) {
        $zones[$old] = date_default_timezone_get();
    }
    date_default_timezone_set($zones[$new] ?? 'UTC');
});

Register it once, at boot. It runs in the event loop and must not wait. Prefer the WeakMap for state of your own: a hook runs at every switch between requests.

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See also#