[Mono-devel-list] GAC (design) issues

[Karl Waclawek]

----- Original Message ----- 
From: "Jaroslaw Kowalski" <jaak at zd.com.pl>
To: "Andy Satori" <dru at druware.com>; "Todd Berman" <tberman at sevenl.net>
Cc: <mono-devel-list at lists.ximian.com>; "Gert Driesen" <gert.driesen at pandora.be>; "Ian MacLean"
<ianm at ActiveState.com>; "Miguel de Icaza" <miguel at novell.com>; "Jackson Harper" <jackson at ximian.com>
Sent: Sunday, May 02, 2004 9:39 AM


> No. In MS you don't have to specify a path in 2 cases:
>
> 1. For assemblies located in the same directory as csc.exe (that is for
> example \WINDOWS\Microsoft.NET\Framework\v1.1.4322)
> 2. For assemblies located in the current directory
>
> GAC is not on the list. See for yourself by GAC-ing your own assembly (not
> the system one, as they are also found by the first rule) and compiling
> something referencing that assembly.

Not quite true, depends on how you lod it. When using LoadWithPartialName()
then the GAC is where the runtime checks first.

In reality it is more complicated. From the SDK docs under the heading
"How the Runtime Locates Assemblies":

<quote>
To successfully deploy your .NET Framework application, you must understand how the common language
runtime locates and binds to the assemblies that make up your application. By default, the runtime
attempts to bind with the exact version of an assembly that the application was built with. This
default behavior can be overridden by configuration file settings.

The common language runtime performs a number of steps when attempting to locate an assembly and
resolve an assembly reference. Each step is explained in the following sections. The term probing is
often used when describing how the runtime locates assemblies; it refers to the set of heuristics
used to locate the assembly based on its name and culture.

  Note   You can view binding information in the log file using the Assembly Binding Log Viewer
(Fuslogvw.exe), which is included in the .NET Framework SDK.
Initiating the Bind
The process of locating and binding to an assembly begins when the runtime attempts to resolve a
reference to another assembly. This reference can be either static or dynamic. The compiler records
static references in the assembly manifest's metadata at build time. Dynamic references are
constructed on the fly as a result of calling various methods, such as
System.Reflection.Assembly.Load.

The preferred way to reference an assembly is to use a full reference, including the assembly name,
version, culture, and public key token (if one exists). The runtime uses this information to locate
the assembly, following the steps described later in this section. The runtime uses the same
resolution process regardless of whether the reference is for a static or dynamic assembly.

You can also make a dynamic reference to an assembly by providing the calling method with only
partial information about the assembly, such as specifying only the assembly name. In this case,
only the application directory is searched for the assembly, and no other checking occurs. You make
a partial reference using any of the various methods for loading assemblies such as
System.Reflection.Assembly.Load or AppDomain.Load. If you want the runtime to check the global
assembly cache as well as the application directory for a referenced assembly, you can specify a
partial reference using the System.Reflection.Assembly.LoadWithPartialName method. For more
information about partial binding, see Partial Assembly References.

Finally, you can make a dynamic reference using a method such as System.Reflection.Assembly.Load and
provide only partial information; you then qualify the reference using the <qualifyAssembly> element
in the application configuration file. This element allows you to provide the full reference
information (name, version, culture and, if applicable, the public key token) in your application
configuration file instead of in your code. You would use this technique if you wanted to fully
qualify a reference to an assembly outside the application directory, or if you wanted to reference
an assembly in the global assembly cache but you wanted the convenience of specifying the full
reference in the configuration file instead of in your code.

  Note   This type of partial reference should not be used with assemblies that are shared among
several applications. Because configuration settings are applied per application and not per
assembly, a shared assembly using this type of partial reference would require each application
using the shared assembly to have the qualifying information in its configuration file.
The runtime uses the following steps to resolve an assembly reference:

  1.. Determines the correct assembly version by examining applicable configuration files, including
the application configuration file, publisher policy file, and machine configuration file. If the
configuration file is located on a remote machine, the runtime must locate and download the
application configuration file first.
  2.. Checks whether the assembly name has been bound to before and, if so, uses the previously
loaded assembly.
  3.. Checks the global assembly cache. If the assembly is found there, the runtime uses this
assembly.
  4.. Probes for the assembly using the following steps:
    1.. If configuration and publisher policy do not affect the original reference and if the bind
request was created using the Assembly.LoadFrom method, the runtime checks for location hints.
    2.. If a codebase is found in the configuration files, the runtime checks only this location. If
this probe fails, the runtime determines that the binding request failed and no other probing
occurs.
    3.. Probes for the assembly using the heuristics described in the probing section. If the
assembly is not found after probing, the runtime requests the Windows Installer to provide the
assembly. This acts as an install-on-demand feature.
      Note   There is no version checking for assemblies without strong names, nor does the runtime
check in the global assembly cache for assemblies without strong names.
</quote>

Karl