php-disposable

A tiny library that adds the disposable pattern to PHP

Requirements

PHP 7.1 or above (at least PHP 7.1.0 for now)

Install

You can easily install this library using Composer with the following command:

    $ composer require cgtag/php-disposable

Documentation

The basic instructions for using this library is implementing the IDisposable interface and declaring the dispose() method that implements all the resource cleanup logic.

The following example shows a simple implementation of the basic pattern.

use cgTag\Disposable\IDisposable;

class ResourceHolder implements IDisposable {
    
    private $file;
    
    public function __constructor(string $filename) {
        $this->file = fopen($filename, "r");
    }
    
    public function read() {
        return stream_get_contents($this->file);
    }
    
    public function dispose() {
        if($this->file) {
            fclose($this->file);
        }
        $this->file = null;
    }
}

Now you can use the global using function to dispose of the object when you're finished with it.

Here's an example of the using function:

$content = using(new ResourceHolder(), function($resource) {
    return $resource->read();
});

That might look simple but once you start following the disposable pattern memory leaks are going to be a thing of the past.

dispose()

Make sure to propagate calls to dispose() to inherited classes. You can do this by overriding the dispose() method and making sure to call parent::dispose().

Note: dispose() will only ever be called once. It will be the last method executed on a class before __destruct() is called. You don't have to worry about properties being used afterwards as dispose() is called.

The IDisposable Interface

This is the primary interface used by the library. In PHP the garbage collector automatically releases memory allocated to a managed object when that object is no longer used. However, it is not possible to predict when the garbage collection will occur. Furthermore, the garbage collector has no knowledge of unmanaged resources such as file handles, images and streams.

Use the dispose() method if this interface to explicitly release unmanaged resources in conjunction with the garbage collector. The consumer of an object can call this method when the object is no longer needed.

Global using() Function

Provides a convenience function that ensures the correct use of IDisposable objects. The following example shows how to use the global using() function.

    using(new ConfigReader("config.ini"), function(ConfigReader $reader) {
        $debug = $reader->get('debug');
    });

The using function ensures that dispose() is called even if an exception occurs while you are calling methods on the object. You can achieve the same result by putting the object inside a try block and then calling dispose() in the finally block; in fact, this is how the using function is written. The code example earlier could be written as the following example:

    $reader = new ConfigReader("config.ini");
    try {
        $debug = $reader->get('debug');
    } finally {
        $reader->dispose();
    }

You can instantiate the resource object and then pass the variable to the using function, but this is not a best practice. In this case, the object remains in scope after control leaves the using block even though it will probably no longer have access to its unmanaged resources. In other words, it will no longer be fully initialized. If you try to use the object outside the using callback, you risk causing an exception to be thrown. For this reason, it is generally better to instantiate the object as an argument passed to using and limit its scope to the using callback.

   $reader = new ConfigReader("config.ini");
   using($reader, function(ConfigReader $reader) {
       // use reader
   });
   // reader is still in scope, but calling it throws an exception
   $debug = $reader->get('debug');

Note: using should not be confused with use

The DisposableTrait

The DisposeTrait allows an object to automatically dispose of public properties. When an object implements the IDisposable interface and uses the DisposeTrait when that object is disposed then all the public properties that reference an IDisposable object are also disposed of and unset. The trait also deeply walks all public arrays disposing of any objects that are in those arrays.

Here is an example object that uses the ConfigReader from above examples:

use cgTag\Disposable\IDisposable;
use cgTag\Disposable\Traits\DisposeTrait;

class Service implements IDispose {
    use DisposeTrait;
    
    public $reader;
    
    public function __constructor() {
        $this->reader = new ConfigReader("config.ini");
    }
}

Privates And Memory Leaks

The DisposeTrait can not dispose of private properties, but will throw an exception when a private property references an object that implements the IDisposable interface. The trait does this because it found a possible memory leak. Since the object is using the trait and private properties are not supported it means that the property might not be disposed.

To resolve this conflict make the property public or implement the dispose() method on the object.

License

php-disposable is licensed under the MIT License - see the LICENSE file for details

cgTag/php-disposable