Dispose pattern: Difference between revisions

Revision as of 01:06, 15 September 2009

Revision as of 22:19, 18 May 2010

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In [[computer programming]], the '''dispose pattern''' is a [[design pattern (computer science)|design pattern]] which is used to handle resource cleanup in [[runtime environment]]s that use [[automatic garbage collection]]. The fundamental problem that the dispose pattern aims to solve is that, because objects in a garbage-collected environment have [[finalizer]]s rather than [[destructor (computer science)|destructors]], there is no guarantee that an object will be destroyed at any deterministic point in time—a guarantee that is necessary for some other resource management patterns, such as [[Resource Acquisition Is Initialization]]. The dispose pattern works around this by giving an object a [[method (computer science)|method]] (usually called <code>Dispose()</code> or something similar) which frees any resources the object is holding onto. ThisUnless the language offers an alternative, this method must be manually invoked by clients that use the object once they are finished with it.

== Examples ==

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</source>

The <code>try...finally</code> construct is necessary for proper [[exception safety]]—if the code that uses the resource throws an exception, the resource will not be freed unless the <code>Dispose()</code> call is in a <code>finally</code> block. Also, the check against <code>null</code> is necessary if the object representing the resource is not directly instantiated, but rather is obtained from some other source that could return <code>null</code>.

To make this pattern less verbose, several languages have some kind of built-in support for it. For example, [[C Sharp (programming language)|C#]] features the <code>using</code> statement, which automatically and safely calls the <code>Dispose()</code> method on an object that implements the <code>IDisposable</code> [[interface (computer science)|interface]]:

<source lang="csharp">

using (Resource resource = getResourcenew Resource()) {

// Perform actions with the resource.

...