Concurrent

Thread-safe shared state for PHP. Wrap any value (object, array, scalar) in a proxy that handles locking, caching, and persistence across processes. Works with Laravel out of the box; pluggable cache and lock drivers otherwise.

Why?

When multiple processes (web requests, queue workers, cron jobs) share state, you scatter cache calls across the codebase: duplicated keys, no locking, race conditions on read-modify-write, business logic tangled with cache plumbing.

Concurrent wraps the value in a thread-safe proxy. You interact with it normally; it handles locking and persistence. Writes are atomic.

Installation

composer require jessegall/concurrent

Wrapping Any Value

Wrap any value by passing it (or a factory) as the default. The wrapper looks and acts like the value itself: methods, properties, array access all proxy through. Reads hit the cache directly; writes lock, mutate, write back.

use JesseGall\Concurrent\Concurrent;

/** @var Concurrent<ShoppingCart> $cart */
$cart = new Concurrent(
    key: "cart:{$userId}",
    default: fn () => new ShoppingCart(),
    ttl: 1800,
);

$cart->addItem('T-Shirt', 2);  // method call: locks, writes back
$cart->itemCount();            // method call: locks (see Read-only methods to skip)
$cart->items;                  // property read: no lock
$cart->couponCode = 'SAVE10';  // property write: locks, writes back
$cart();                       // get the value
$cart(null);                   // forget

Every write persists to the cache automatically. No save() or flush() step. Each write is atomic on its own.

Grouping Writes Into One Atomic Update

Use a callback when you need several writes (or a read-then-write) to land as one atomic step, so nothing else can interleave.

// Two separate atomic writes. Another worker can read or write
// between them and see a half-updated cart.
$cart->discount = 10;
$cart->total = $cart->subtotal - 10;

// One atomic update. The lock is held across both lines.
$cart(function (Cart $data) {
    $data->discount = 10;
    $data->total = $data->subtotal - 10;
    return $data;
});

Three ways to express the grouped update. Pick whichever fits.

1. Methods on the wrapped class

The cleanest option when you own the source: put the mutation logic in a method on the wrapped class.

class Cart {
    public array $items = [];

    public function addItem(string $sku): void {
        $this->items[] = $sku;     
        $this->lastSku = $sku;    
    }
}

/** @var Concurrent<Cart> $cart */
$cart = new Concurrent(key: 'cart', default: fn () => new Cart);
$cart->addItem('shirt');           // atomic: Concurrent locks, runs the method, writes back

2. Callbacks

Bound Callback

Pass a zero-param closure to $concurrent(...):

$cart(function () {
    $this->items[] = $newItem;
    $this->totals['subtotal'] = 100;
    $this->status = 'pending';
});

Inside the callback, $this behaves like the Concurrent wrapper merged with the wrapped value: the wrapped value's properties and methods take precedence, anything missing falls through to the wrapper. self::, parent::, and static:: still resolve to the wrapper class, so constants and static methods on it work as you'd expect.

Arrow functions work too:

$counter(fn () => $this->count++);
$cart(fn () => $this->items[] = $newItem);

Transform Callback

Receive the value, return the new one. Best for replacing the whole value, especially scalars:

// Arrow functions return the expression's value implicitly.
$counter(fn (int $n) => $n + 1);
$concurrent(fn (array $value) => [...$value, 'new entry']);

// Non-arrow functions need an explicit return.
$cart(function (Cart $data) {
    $data->discount = 10;
    return $data;
});

By-reference Callback

Take the wrapped value as a &-marked parameter and mutate it directly. Concurrent sees the mutated value and writes it back; no return needed.

$cart(fn (Cart &$data) => $data->items[] = $newItem);

$cart(function (Cart &$data) {
    $data->items[] = $newItem;
    $data->totals['count']++;
});

Use a By-reference Callback when:

• The wrapped value is an array. $this[] doesn't work on the bound proxy; $data[] does.
• You want better static analysis. PHPStan and Psalm read a typed Cart &$data parameter directly. With bound $this they see BoundProxy.
• You want the outer $this. Any callback with a parameter keeps $this as the surrounding class, so you can still call its methods or read its properties.

Without the &, the closure falls back to a Transform Callback (above). A block with no return writes null to the cache. An arrow writes the expression value, so fn ($d) => $d->items[] = $x writes $x, not the cart. Use &, or return the value yourself.

3. A wrapper subclass that owns the domain API

When you control neither the source nor want ad-hoc callbacks all over your codebase, define your own Concurrent subclass with domain methods that internally use callbacks. See Subclassing.

Subclassing

Encapsulate the key, default, TTL, and domain methods. Add @extends Concurrent<T> so the IDE picks up the wrapped class's methods on the subclass too. If your IDE doesn't resolve the generic and apply the @mixin through it, fall back to /** @mixin T */ on the subclass:

/** @extends Concurrent<SessionData> */
class ProcessingSession extends Concurrent
{
    public function __construct(string $id)
    {
        parent::__construct(
            key: "processing:{$id}",
            default: fn () => new SessionData(),
            ttl: 3600,
            validator: fn ($v) => $v instanceof SessionData,
        );
    }

    public function start(int $total): void
    {
        $this(function () use ($total) {
            $this->total = $total;
            $this->status = 'processing';
        });
    }

    public function advance(): void
    {
        $this(fn () => $this->processed++);
    }

    public function addError(string $message): void
    {
        $this(fn () => $this->errors[] = $message);
    }
}

Auto-generated Keys

When a Concurrent is constructed inside another class's __construct and stored on a property of that class, you can omit key:. The wrapper figures out the key on first use by reflecting on the owning class and finding the property it's assigned to. The result is {FullyQualifiedClassName}:{propertyName}.

class RateLimiter
{
    /** @var Concurrent<array> */
    private Concurrent $attempts; // <-- Will receive auto-generated key "App\RateLimiter:attempts"

    public function __construct()
    {
        $this->attempts = new Concurrent(default: fn () => []);
    }
}

Two RateLimiter instances share the same auto-key, so they see the same cached state.

WithAccessors

Concurrent's public surface is deliberately small. Every method on Concurrent is one that can't appear on the wrapped value or a subclass, so wrapping a raw value or extending Concurrent with your own domain methods doesn't collide with the proxy's API.

WithAccessors is opt-in for that reason: it adds helpers (get, set, has, update, clear) on subclasses that want them, without baking them into the base class where they'd shadow methods on whatever you wrap.

/** @extends Concurrent<ActivityData> */
class UserActivity extends Concurrent
{
    use WithAccessors;

    public function __construct(int $userId) {
        parent::__construct(
            key: "activity:{$userId}",
            default: fn () => new ActivityData,
            ttl: 86400,
        );
    }

    public function recordLogin(): void
    {
        $this->update(function () {
            $this->loginCount++;
            $this->lastLoginAt = time();
        });
    }

    public function loginCount(): int   { return $this->get('loginCount', 0); }
    public function lastLoginAt(): ?int { return $this->get('lastLoginAt'); }
    public function reset(): void       { $this->clear(); }
}

Private by default. Expose any of them via PHP's trait conflict resolution:

class Settings extends Concurrent
{
    use WithAccessors {
        get as public;
        set as public;
    }
}

$settings->set('theme', 'dark');
$settings->get('theme');

WithPointer

Tracks "the current" instance of a Concurrent class. Implement fromPointerId() (constructor shapes vary), get start() / current() / release() for free.

final class CurrentImport extends Concurrent
{
    use WithPointer;

    public function __construct(public readonly string $runId) { /* ... */ }

    protected static function fromPointerId(string $id, mixed ...$args): static
    {
        return new static($id);
    }
}

CurrentImport::start();      // mint a new run, claim the pointer
CurrentImport::current();    // resolve the pointed-to instance, or null
CurrentImport::release();    // clear the pointer

Override pointerKey() for a stable key, generateId() for UUIDs/ULIDs/etc. For ad-hoc usage, ConcurrentPointer is the underlying primitive.

Read-only Methods

Mark pure accessors as read-only to skip locking. Either #[ReadonlyMethod] on the wrapped value's method, or list method names on a Concurrent subclass via DeclaresReadOnlyMethods. Mutating from a read-only method throws ReadonlyViolationException so silent write loss is caught early.

Built-in Data Structures

Thread-safe data structures built on top of Concurrent:

• ConcurrentMap: key-value map.
• ConcurrentSet: collection of unique values.
• ConcurrentCounter: atomic counter, optional min/max/wrap.
• ConcurrentQueue: FIFO queue.
• ConcurrentList: ordered list with chainable map/filter/each.

Each has its own focused API; see the source for the full method list.

Using Without Laravel

Implement CacheDriver and LockDriver against your backend (Redis, etc.) and register them globally:

Concurrent::useCache(new RedisCache());
Concurrent::useLock(new RedisLock());

Or pass them to a single instance via the constructor's cache: and lock: arguments. For tests, the package ships InMemoryCache and InMemoryLock.

With Laravel, no setup needed: the service provider auto-registers everything.

How It Works

Writes lock, reads don't. A mutating operation acquires the lock, reads from cache, runs the operation, writes back, releases. Reads ($concurrent(), property reads, isset, read-only methods) hit the cache directly and never block.

Locks are re-entrant: nested writes inside a callback (e.g. multiple $this->prop = X inside a bound closure) reuse the outer lock. The whole callback is one atomic operation, one acquire/release.

Caveats

A plain overwrite like $concurrent->value = 10 is its own atomic write, no callback needed. Two shapes look like single writes but aren't:

• $concurrent->count++ is not atomic. ++ is really three steps: read the value, add one, write it back. Each step locks, but nothing holds a lock across all three. If two workers both run count++ on a value of 5, both read 5 before either writes, both compute 6, both write 6. One increment is lost. Wrap it in a callback so the read and write share one lock.
• $concurrent->items[] = $x silently does nothing. PHP fetches items by value (a copy), appends to the copy, throws the copy away. The cache never sees the change. Wrap it in a callback to mutate the real array.

For read-modify-write or nested mutations, use a callback.

Requirements

• PHP 8.4+
• A cache backend (Redis recommended for production)
• Optional: Laravel 10–13 for zero-config integration

License

MIT