- Global Assembly Cache
The Global Assembly Cache or GAC is a machine-wide
.NET assemblies cachefor Microsoft's CLR platform. The approach of having a specially controlled central repository addresses the shared libraryconcept and helps to avoid pitfalls of other solutions that lead to drawbacks like DLL hell.
There are several reasons to install an assembly into the GAC:
Assemblies that should be used by all applications can be put in the global assembly cache. For example, if all applications should use an assembly located in the global assembly cache, a version policy statement can be added to the Machine.config file that redirects references to the assembly.
Assemblies residing in the GAC must adhere to a specific versioning scheme which allows for side-by-side execution of different code versions. Specifically, such assemblies must be
gacutil.exe is the .NET utility used to work with the GAC.
One can check the availability of a shared assembly in GAC by using the command:gacutil.exe /l
One can register a shared assembly in the GAC by using the command:gacutil.exe /i
Other options for this utility will be briefly described if you use the /? flag, i.e.:gacutil.exe /?
Example of use
A computer has two
.NET assembliesboth named AssemblyA, but one is version 1.0 and the other is version 2.0. Since it is required that both be compiled to a file named AssemblyA, they cannot exist in the same directory within the FAT32 file system. Instead, the virtual file system of the GAC can be used by programs that need to use each version of the assembly specifically.
The GAC as a construct does not actually exist within the Windows OS. It is implemented and managed by the .NET Framework. The folder within %systemroot% named assembly contains all globally-available assemblies with managed filenames so that the version and public key tokens can be included. Each version can therefore exist within the same location and be called without requiring subsequent versions to preserve code entry point locations as usual. Explorer allows the drag-and-drop installation of assemblies into this folder only if they would otherwise be permitted to be installed from the command line.
A calling application may specify specific versions of an assembly when referencing them, so the
Common Language Runtimecan simply refer to the filename to use the correct one.
The Global Assembly Cache mechanism helps to avoid older
DLL hell, but it still has some drawbacks, as for example [cite web
title=Ten Managed Application Pitfalls that Kill Version Compatibility
* By default, applications will only run with the version of the
.NET Frameworkused to compile it, which can cause the application to fail on machines with newer versions of the .NET Framework installed — even when the application would normally run properly with the newer version.
* It is sometimes necessary to use Conditional compilation if some of the core .NET calls (used in the application) are only supported for some versions of the framework.
* .NET applications that rely on native code risk incompatibilities, even with the GAC mechanism.
* [http://msdn2.microsoft.com/en-us/library/yf1d93sz.aspx .NET Framework Developer's Guide]
* [http://msdn2.microsoft.com/en-us/library/ex0ss12c.aspx Global Assembly Cache Tool (gacutil.exe)]
* [http://www.codeproject.com/dotnet/demystifygac.asp Demystifying the .NET Global Assembly Cache]
Wikimedia Foundation. 2010.
Look at other dictionaries:
Global Assembly Cache — Chaque ordinateur sous Windows sur lequel le Common Language Runtime est installé possède un cache de code à l échelle de l ordinateur appelé Global Assembly Cache. Le Global Assembly Cache stocke les assembly spécialement destinés à être… … Wikipédia en Français
Global Assembly Cache — Der Global Assembly Cache (GAC) ist ein Verfahren des .NET Frameworks, um Versionskonflikte zwischen Programmbibliotheken zu vermeiden. Inhaltsverzeichnis 1 Identität und Installation im GAC 2 Implementierung des GAC unter Windows 2.1 Dateisystem … Deutsch Wikipedia
Download Cache — Not to be confused with web cache. The Download Cache, or downloaded files cache, is a component of Microsoft s .NET Framework that is similar to the Global Assembly Cache except that it caches assemblies that have been downloaded from the… … Wikipedia
.NET assembly — In the Microsoft .NET framework, an assembly is a partially compiled code library for use in deployment, versioning and security. In the Microsoft Windows implementation of .NET, an assembly is a PE (portable executable) file. There are two types … Wikipedia
.NET-Framework — Basisdaten Entwickler: Microsoft Aktuelle Version … Deutsch Wikipedia
.NET-Klassenbibliothek — NET Framework Basisdaten Entwickler: Microsoft Aktuelle Version … Deutsch Wikipedia
.NET 3.0 — NET Framework Basisdaten Entwickler: Microsoft Aktuelle Version … Deutsch Wikipedia
.NET Framework — Basisdaten Entwickler: Microsoft Aktuelle Version … Deutsch Wikipedia
.NET Framework 3.0 — NET Framework Basisdaten Entwickler: Microsoft Aktuelle Version … Deutsch Wikipedia
.Net — Framework Basisdaten Entwickler: Microsoft Aktuelle Version … Deutsch Wikipedia