How to Disable a Specific MDA
How to Disable a Specific MDA
As Mike Stall has noted in his
post, the
PInvokeStackImbalance MDA can be very slow, depending on the number of
pinvoke calls in an application. Recently, we have had a few customers running
into this issue, but
MSDN does not give much information regarding disabling MDAs except for
setting COMPLUS_MDA to 0 or setting the registry key to 0. The problem with
these options is that they disable all MDAs. Moreover, if you set the registry
key, it has machine-wide impact.
There is actually a more fine-grained approach to do this. You can actually
disable an MDA using an MDA configuration file. However, as mentioned on
MSDN and in Stephen Toub’s
article, the CLR will not look for the MDA configuration file unless either
the environment variable or the registry key is set 1. Doing so has no effect
if an application has no MDA configuration file.
For example, to disable the PInvokeStackImbalance MDA, you
can do this:
1)
Set the COMPLUS_MDA environment variable to 1 (or equivalently, set
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\MDA to “1”)
2)
Assuming your application is called hello.exe, create
hello.exe.mda.config in the same directory and put the following XML in it:
<?xml version="1.0"
encoding="UTF-8" ?>
<mdaConfig>
<assistants>
<pInvokeStackImbalance
enable="false"/>
</assistants>
</mdaConfig>
Note that MDA configuration files have precedence over MDAs
activated by default for the managed debugger and the unmanaged debugger. This
means that an MDA configuration file can disable an MDA which is enabled
automatically because a debugger is attached. (In fact, it is the only way.)
Due to an oversight, the PInvokeStackImbalance MDA is not
even defined on 64-bit (both X64 and IA64) platforms. So if you try to use the
MDA configuration file above on 64-bit platforms, you will get an error. But
then again, since we only have one calling convention on X64 and one on IA64,
why would you need this MDA on 64-bit platforms anyway? ;)
