Garbage collection and unmanaged resource

Question

Hi there,

I have a C# application which loads a C++ dll.

Is it possible that the garbage collection collect a memory block which is used by C++?

Thanks in advance.

Answer 1

Yes, if the C++ keeps a copy of a pointer passed to it, and uses that AFTER the function to which it was passed has returned.

The .Net marshalling code may pass a pointer to managed data directly to an unmanaged function, or it may make a copy of the data first and pass a copy of the data. Either way, the data passed will be "pinned" until the unmanaged function returns. However, once it has returned the managed data could be freed or moved in memory. So it is not safe for the unmanaged code to keep a copy of the pointer somewhere and use it later.

If you want to be able to do that, you will need to manually allocate the memory and mess around with the .Net marshalling methods to copy managed data into a manually-managed memory block. You then have control over when the memory block is freed, making it safe to pass to unmanaged code.

See this for more info:

http://msdn.microsoft.com/en-us/magazine/cc164193.aspx

Also google for Marshal.AllocHGlobal and GCHandle.Alloc

Answer 2

Hi,

It is possible to free the memory forcefully by calling GC.Collect, but it should be avoided because it may create performance issues.

If you are in the method/class where the object is still in scope, nothing can free up the memory. You then have to call Dispose() method on that object or make it go out of scope and after that, you can call the collect method.

For more description, check out :

GC.Collect Method

I hope this was helpful to you!

Thanks

Answer 3

Please use Finalize and Dispose to Clean Up Unmanaged Resources

or

IDisposable.Dispose Method

Please check the following URLs for your reference

http://msdn.microsoft.com/en-us/library/b1yfkh5e(v=vs.71).aspx

http://msdn.microsoft.com/en-us/library/system.idisposable.dispose(v=vs.90).aspx

---

With Thanks and Regards
Sambath Raj.C
click "Proposed As Answer by" if this post solves your problem or "Vote As Helpful" if a post has been useful to you
Happy Programming!

Answer 4

i guess memory management by the clr uses same method to clear all the garbage collection. So when you call it, it will automatically clear the memory unused.

regards

joon

Answer 5

Hi,

In addition to other response it's a bit hard to give a general response. For example some win32 api have a function to clear the previously allocated memory buffer.

---

Please always mark whatever response solved your issue so that the thread is properly marked as "Answered".