File handle count

There are two limits related to the number of handles a process can create: the maximum number of handles the system sets for a process and the amount of memory available to store the handles and the objects the application is referencing with its handles. In most cases the limits on handles are far beyond what typical applications or a system ever use.

A more common class of problems arise because the lifetime of these resources must be managed by applications and, just like for virtual memory, resource lifetime management is challenging even for the best developers. An application that fails to release unneeded resources causes a leak of the resource that can ultimately cause a limit to be hit, resulting in bizarre and difficult to diagnose behaviors for the application, other applications or the system in general.

As always, I recommend you read the previous posts because they explain some of the concepts this post references, like paged pool. Each of these subsystems defines one or more types with the Object Manager to represent the resources they expose to applications.

Every release of Windows introduces new object types with Windows 7 defining a total of You can see the objects defined by running the Sysinternals Winobj utility with administrative rights and navigating to the ObjectTypes directory in the Object Manager namespace:.

When an application wants to manage one of these resources it first must call the appropriate API to create or open the resource. For instance, the CreateFile function opens or creates a file, the RegOpenKeyEx function opens a registry key, and the CreateSemaphoreEx function opens or creates a semaphore.

The system can look up the object the handle refers to by indexing into the handle table to locate the corresponding handle entry, which contains a pointer to the object. For example, if the process successfully opened a file for read access, the handle entry would look like this:. To test the number of handles a process can create, Testlimit implements the —h switch that directs it to create as many handles as possible. It does so by creating an event object with CreateEvent and then repeatedly duplicating the handle the system returns using DuplicateHandle.

By duplicating the handle, Testlimit avoids creating new events and the only resources it consumes are those for the handle table entries. The total shown for Testlimit in this case is 16,, When you run Testlimit on a bit system, the number of handles it can create is slightly different:.

The handle count you see in Task Manager is "the number of object handles in the process's object table". In effect, this is the sum of all handles that this process has open. What are Windows handles? What are threads and handles? What are system handles? What are Handles Task Manager? What is a user object? What do you mean by memory leak? How do I setup my performance monitor? Setting up Windows Performance Monitor. How do I monitor a process using Perfmon?

How can I monitor memory usage? Check Computer Memory Usage Easily. What is private bytes and working set? How do I analyze memory usage in Windows?

Monitoring Memory Usage on Windows. Once the Task Manager window has opened, click the Performance tab. How do I monitor memory leaks in Windows? What is working set memory? How do you use Umdh? How to use UMDH to find native memory leaks. Start Collecting Data. How do I check my CPU time? What is the ideal CPU usage percentage? When issue had been resolved or no longer needing the service broken out into its own svchost process, place it back into the shared svchost process by running following command from command prompt:.

Change command focus to system32 folder and run following command: copy svchost. Restart wmi service with net stop winmgmt and net start winmgmt commands again. Verify you now see wmisvchost.

You would now substitute wmisvchost. Using debugger to attach to the process in windbg. If high handle count is with wmiprvse, download the latest version of the Windows Sysinternals tool Process Explorer.

Find the instance of wmiprvse. Click on the WMI Providers tab and document the listed providers. If it is wmiprvse. Open a command prompt with elevated or administrative rights and change to the directory were you saved Procdump. Note : Replace with actual PID you documented for instances of wmiprvse. At this point with data in hand you will want to open a Support Incident with Microsoft to get the data analyzed to help determine cause of high handle count.

Please reference this blog and the following TAG when you open the Support Incident Case with Microsoft, as it will help the engineer understand what actions have been taken or followed and well help us track the effectiveness of the blog. You must be a registered user to add a comment.

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