C# Avoid file lock when Assembly.Load

Question

My situation is;

I am designing a plugin application, based on dynamically loading plugin assemblies more than one user may run the application that's hosted on a server machine. Application is auto-updating plugin assemblies from my live update server on its startup. So plugin files (and its satellite dlls should not be locked on file system.

 byte[] assemblyBytes = File.ReadAllBytes("asm-path");
 var assembly = Assembly.Load(assemblyBytes);

as expected not locking the dll file. but what if the dll I am loading has static reference dlls itself? they are locked on file system now.

to name files, lets say;

APP.Exe is my base application;
PL1.dll is my first plugin, APP.exe loads it in a new Appdomain
PL2.dll is my second plugin, APP.exe loads it in a new Appdomain
PL1_S.dll is a static reference dll for PL1.dll plugin, loaded in PL1 AppDomain
PL_COMMON is a static reference dll for both PL1 and PL2 plugins, loaded by PL1 and PL2 AppDomains

PL1_S and PL_COMMON also should not be locked in file like PL1 and PL2 assemblies

Any idea on how to solve that?

If you are looking for the concept of "plugin", have you already looked to Managed Add-in framework (MAF)? Check http://channel9.msdn.com/Blogs/DanielMoth/Managed-AddIn-Framework — Paulo Correia, Jan 29 '14 at 15:42
The rule is exceedingly simple: the assembly file will be locked if the assembly is loaded in *any* AppDomain. Having to de-tune your requirements because you cannot come up with a way to get the AppDomains destroyed is the expected outcome. — Hans Passant, Jan 29 '14 at 16:03

score 5 · Accepted Answer · answered Jan 29 '14 at 15:31

There is functionality already built in to do this, as used by e.g. ASP.Net. See Shadow Copying Assemblies:

Shadow copying enables assemblies that are used in an application domain to be updated without unloading the application domain. This is particularly useful for applications that must be available continuously, such as ASP.NET sites.

So just turn that on via the AppDomainSetup.ShadowCopyFiles when creating your AppDomains

C# Avoid file lock when Assembly.Load

1 Answers1