I am queuing some WMI event watchers (using
System.Management.ManagementEventWatcher) on the ThreadPool. I cannot
start two ManagementEventWatchers that vary only by their queries on the
same thread. If I try, I get an AccessDenied error - only on the first
one.
<snip1>
using System;
using System.Management;
public class EventWatcherAsync {
public static int Main(string[] args) {
// Set up the event consumer 1
WqlEventQuery query =
new WqlEventQuery("SELECT * FROM
__InstanceOperationEvent WITHIN 5 WHERE TargetInstance ISA
\"Win32_NTLogEvent\"");
// Initialize an event watcher and subscribe to
// events that match this query
ManagementEventWatcher watcher = new
ManagementEventWatcher(query);
// Set up a listener for events
watcher.EventArrived +=
new EventArrivedEventHandler((new
EventHandler()).HandleEvent);
watcher.Scope.Options.EnablePrivileges = true;
watcher.Scope.Options.Impersonation =
ImpersonationLevel.Impersonate;
// Start listening
watcher.Start();
// The following code results in AccessDenied
// Set up the event consumer 2
WqlEventQuery query2 =
new WqlEventQuery("SELECT * FROM
__InstanceOperationEvent WITHIN 5 WHERE TargetInstance ISA
\"Win32_NTLogEvent\"");
// Initialize an event watcher and subscribe to
// events that match this query
ManagementEventWatcher watcher2 = new
ManagementEventWatcher(query2);
// Set up a listener for events
watcher2.EventArrived +=
new EventArrivedEventHandler((new
EventHandler2()).HandleEvent);
watcher.Scope.Options.EnablePrivileges = true;
watcher.Scope.Options.Impersonation =
ImpersonationLevel.Impersonate;
// Start listening
watcher2.Start();
Console.Read();
watcher.Stop();
return 0;
}
}
public class EventHandler {
public void HandleEvent(object sender, EventArrivedEventArgs e)
{
Console.WriteLine("Event Handler 1 get an event from " +
sender);
}
}
public class EventHandler2 {
public void HandleEvent(object sender, EventArrivedEventArgs e)
{
Console.WriteLine("Event Handler 2 get an event from " +
sender);
}
}
</snip1>
I thought that putting the watchers on different threads may help, but
the code sample below still results in AccessDenied. Note that for
demonstration purposes the queries are the same, but I have tried
various queries with the same result when watching the same object (in
this case the NTEventLogEvent). I need to be able to perform multiple
event queries. Any advice?
<snip2>
using System;
using System.Management;
using System.Threading;
public class EventWatcherAsync {
public static int Main(string[] args) {
WqlEventQuery query = new WqlEventQuery("SELECT * FROM
__InstanceOperationEvent WITHIN 5 WHERE TargetInstance ISA
\"Win32_NTLogEvent\"");
object oQry = (object)query;
WaitCallback callback1 = new
WaitCallback(EventWatcherAsyncWorker.Callback1);
AutoResetEvent ev = new AutoResetEvent(false);
ThreadPool.QueueUserWorkItem(callback1, oQry);
// The following results in an AccessDenied error
WqlEventQuery query2 = new WqlEventQuery("SELECT * FROM
__InstanceOperationEvent WITHIN 5 WHERE TargetInstance ISA
\"Win32_NTLogEvent\"");
object oQry2 = (object)query;
WaitCallback callback2 = new
WaitCallback(EventWatcherAsyncWorker.Callback2);
ThreadPool.QueueUserWorkItem(callback2, oQry2);
Console.Read();
return 0;
}
}
public class EventWatcherAsyncWorker {
private EventWatcherAsyncWorker() {}
public static void Callback1(object oQuery) {
WqlEventQuery query = (WqlEventQuery)oQuery;
ManagementEventWatcher watcher = new
ManagementEventWatcher(query);
watcher.EventArrived += new
EventArrivedEventHandler(EventHandler2.HandleEvent);
watcher.Scope.Options.EnablePrivileges = true;
watcher.Scope.Options.Impersonation =
ImpersonationLevel.Impersonate;
watcher.Start();
do {} while (!EventHandler2.eventArrived);
watcher.Stop();
}
public static void Callback2(object oQuery) {
WqlEventQuery query = (WqlEventQuery)oQuery;
ManagementEventWatcher watcher = new
ManagementEventWatcher(query);
watcher.EventArrived += new
EventArrivedEventHandler(EventHandler3.HandleEvent);
watcher.Scope.Options.EnablePrivileges = true;
watcher.Scope.Options.Impersonation =
ImpersonationLevel.Impersonate;
watcher.Start();
// AccessDenied!
do {} while (!EventHandler3.eventArrived);
watcher.Stop();
}
}
public class EventHandler2 {
public static bool eventArrived;
public static void HandleEvent(object sender,
EventArrivedEventArgs e) {
eventArrived = true;
Console.WriteLine("Event Handler 1 get an event from " +
sender);
}
}
public class EventHandler3 {
public static bool eventArrived;
public static void HandleEvent(object sender,
EventArrivedEventArgs e) {
eventArrived = true;
Console.WriteLine("Event Handler 2 get an event from " +
sender);
}
}
</snip2>
Richard A. Hein
Software Developer
Level Platforms Inc.
36 Antares Drive, Suite 200, Ottawa, Ontario
* 613-232-0098
* [EMAIL PROTECTED]
Please visit us at http://www.levelplatforms.com
You can read messages from the Advanced DOTNET archive, unsubscribe from Advanced
DOTNET, or
subscribe to other DevelopMentor lists at http://discuss.develop.com.
