PRB: Cannot Call ActiveX Scripting Engine Methods from Non-base Threads

• Microsoft Visual C++, 32-bit Editions, version 6.0

SYMPTOMS

When an ActiveX Scripting host calls a method on an ActiveX Scripting engine, such as Visual Basic Script or Java Script, from a thread other than the one that created the engine, the call might fail with HRESULT E_FAIL or E_UNEXPECTED.

CAUSE

After an ActiveX Scripting engine has received a reference to its host by calling the IActiveScript::SetScriptSite method, the scripting engine can no longer accept calls from non-base threads. This happens because the scripting engine checks the thread that makes each call and rejects any calls from non-base threads. NOTE: The base thread is the one that called IActiveScript::SetScriptSite.

RESOLUTION

After the IActiveScript::SetScriptSite method has been called, you cannot call scripting engine methods on non-base thread, however, there are two notable exceptions to this rule:

• You can call the IActiveScript::InterruptScriptThread method from any thread, thus giving the host a chance to stop a script that has become stuck.
• You can call the IActiveScript::Clone method from any thread, thus giving the host the ability to set up a standard scripting engine and then replicate it for multiple job runs.

STATUS

This behavior is by design.

ActiveX Scripting engines were designed to behave this way because a truly free-threaded scripting engine would require that every single method in the engine be shielded with critical sections, mutexes, or some other synchronization method. This would result in massive overhead and slow downs.

REFERENCES

For additional information about ActiveX Scripting Hosts, please see the following articles in the Microsoft Knowledge Base:

Q182946 InterruptScriptThread causes Invalid Page Fault in OLEAUT32
Q183648 Sample: AXSH.EXE Demonstrates Implementing ActiveX Script Hosts
Q168214 Sample: MFCAxs Implements an ActiveX Script Host Using MFC

Additional query words:

Keywords          : kbAXScript kbVC kbVC500 kbVC600 kbGrpDSO 
Version           : winnt:6.0
Platform          : winnt 
Issue type        : kbprb 

Last Reviewed: April 1, 1999