The methods in this class influence when garbage collection is performed on an object and when resources allocated by an object are released. Properties in this class provide information about the total amount of memory available in the system and the age category, or generation, of memory allocated to an object.

The garbage collector tracks and reclaims objects allocated in managed memory. Periodically, the garbage collector performs garbage collection to reclaim memory allocated to objects for which there are no valid references. Garbage collection happens automatically when a request for memory cannot be satisfied using available free memory. Alternatively, an application can force garbage collection using the GC.Collect(int) method.

Garbage collection consists of the following steps:

[The 'ordered' type of list has not been implemented in the ECMA stylesheet.]

During a collection, the garbage collector will not free an object if it finds one or more references to the object in managed code. However, the garbage collector does not recognize references to an object from unmanaged code, and might free objects that are being used exclusively in unmanaged code unless explicitly prevented from doing so. The GC.KeepAlive(object) method provides a mechanism that prevents the garbage collector from collecting objects that are still in use in unmanaged code.

Aside from managed memory allocations, implementations of the garbage collector do not maintain information about resources held by an object, such as file handles or database connections. When a type uses unmanaged resources that must be released before instances of the type are reclaimed, the type can implement a finalizer.

In most cases, finalizers are implemented by overriding the object.Finalize method; however, types written in C# or C++ implement destructors, which compilers turn into an override of object.Finalize. In most cases, if an object has a finalizer, the garbage collector calls it prior to freeing the object. However, the garbage collector is not required to call finalizers in all situations; for example, the GC.SuppressFinalize(object) method explicitly prevents a finalizer from being called. Also, the garbage collector is not required to use a specific thread to finalize objects, or guarantee the order in which finalizers are called for objects that reference each other but are otherwise available for garbage collection.

In scenarios where resources must be released at a specific time, classes can implement the IDisposable interface, which contains the IDisposable.Dispose method that performs resource management and cleanup tasks. Classes that implement IDisposable.Dispose must specify, as part of their class contract, if and when class consumers call the method to clean up the object. The garbage collector does not, by default, call the IDisposable.Dispose method; however, implementations of the IDisposable.Dispose method can call methods in the GC class to customize the finalization behavior of the garbage collector.

It is recommended, but not required, that garbage collectors support object aging using generations. A generation is a unit of measure of the relative age of objects in memory. The generation number, or age, of an object indicates the generation to which an object belongs. Objects created more recently are part of newer generations, and have lower generation numbers than objects created earlier in the application life cycle. Objects in the most recent generation are in generation 0.

All public static members of this type are safe for multithreaded operations. No instance members are guaranteed to be thread safe.

Namespace: System
Assembly: mscorlib (in mscorlib.dll)
Assembly Versions: 1.0.5000.0, 2.0.0.0, 4.0.0.0