Creating a Cross-Process EventWaitHandle

Question

I have two windows application, one is a windows service which create EventWaitHandle and wait for it. Second application is a windows gui which open it by calling EventWait

Answer 1

This might be caused by the service process running at an elevated privilege level, but the GUI process is not. If you put the same code into two console apps, they'll both be running at user level and won't have any trouble accessing each other's named shared objects.

Try running the GUI app with the "Run as administrator" flag from the Windows start menu. If that solves the issue, you need to read up on how to request elevation within your code. (I haven't done that)

Answer 2

You need to use the version of the EventWaitHandle constructor that takes an EventWaitHandleSecurity instance. For example, the following code should work (it's not tested, but hopefully will get you started):

// create a rule that allows anybody in the "Users" group to synchronise with us
var users = new SecurityIdentifier(WellKnownSidType.BuiltinUsersSid, null);
var rule = new EventWaitHandleAccessRule(users, EventWaitHandleRights.Synchronize | EventWaitHandleRights.Modify,
                          AccessControlType.Allow);
var security = new EventWaitHandleSecurity();
security.AddAccessRule(rule);

bool created;
var wh = new EventWaitHandle(false, EventResetMode.AutoReset, "MyEventName", out created, security);
...

Also, if you're running on Vista or later, you need to create the event in the global namespace (that is, prefix the name with "Global\"). You'd also have to do this on Windows XP if you use the "Fast User Switching" feature.