Preventing two instances of a program to run simultaneously


You can use this code to prevent a program from being started again when it already runs:

class facts
    okToRunMutex : mutex := erroneous.
class predicates
    okToRun : () determ.
    okToRun() :-
        okToRunMutex := mutex::createNamed("SomeStrangeName", false()),
        not(multiThread_native::wait_timeout = okToRunMutex:wait(0)).
        if okToRun() then
            TaskWindow = taskWindow::new(),
        end if.

You are supposed to use some strange name instead of "SomeStrangeName". Microsoft has this to say about the subject:

If you are using a named mutex to limit your application to a single instance, a malicious user can create this mutex before you do and prevent your application from starting. To prevent this situation, create a randomly named mutex and store the name so that it can only be obtained by an authorized user. Alternatively, you can use a file for this purpose. To limit your application to one instance per user, create a locked file in the user's profile directory.