Emulating Windows Synchronization Objects
Recently, a client called to describe a specific problem, the general aspects of which are relevant to all script and Windows Script Host (WSH) developers. The problem per se—ensuring synchronization between multiple tasks—wasn't particularly difficult, but the range of tools I needed to use to solve it made the process difficult.
Synchronizing a few tasks in a Win32 application, even in a Microsoft Visual Basic (VB) application, is a matter of calling a couple of API functions: one for creating an appropriate event object and one for putting the calling thread on standby until the OS wakes it up when the event is signaled. So, if you can use Visual C++ (VC++) or VB, the process is easy. However, if—as in this case—the surrounding environment is WSH and VBScript is the language of choice, you must resort to emulation and a bit of creativity.
The Synchronization Problem
My client described the problem thusly: One WSH script has to spawn a few other scripts that use existing executables. The main script has to stop and wait for all the spawned processes to terminate. (The stop-and-wait action is called a blocking wait.) If an error occurs in any child process, the whole operation must be considered canceled, and ideally the overall outcome is as if nothing ever happened. . . .
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