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SimonFisher
SimonFisher

Reputation: 410

Should I free the handle returned from GCHandle::FromIntPtr?

I am using GCHandle::FromIntPtr to convert unmanaged structure pointer to managed object reference follow an example in msdn. Below is my code snippet:

GCHandle gch = GCHandle::FromIntPtr(IntPtr(someNativePtr));
MyManagedClass^ obj = static_cast<MyManagedClass^>(gch.Target);

My question is should I free gch?

UPDATE: There's a huge problem in this question just as Medinoc mentioned in his comment: GCHandle::FromIntPtr can not accept an IntPtr which points to an unmanaged object!!! So the question is completely pointless.

Upvotes: 4

Views: 1815

Answers (3)

Falk
Falk

Reputation: 111

I couldn't understand it from the answer provided… As of my understanding: Using GCHandler.Alloc it prevents the gc from collecting that allocated object, so it can be passed around to unmanaged code etc. if you dont save the address somewhere to that now unmanaged object the object will stay in memory indefinitely.

GCHandle is just an 'interface' for an unmanaged object in memory. You can call as many FromIntPtr as you wish. This wont overflow your memory as there still is only that one object you deal with. It doesnt create another one out of thin air. Doing GCHandle.Free doesnt delete the handle it passes the object to the gc.

Correct me if I am wrong

Upvotes: 0

Rami
Rami

Reputation: 7290

FromIntPtr method returns a new GCHandle (value-type) struct created from a handle to a managed object, while Alloc method Allocates a handle for the specified object.

So you need to call Free() on the GCHandle struct only if you got it by a call to Alloc() not FromIntPtr()

Reference:

http://msdn.microsoft.com/en-us/library/system.runtime.interopservices.gchandle.alloc%28v=vs.110%29.aspx

Upvotes: 4

Medinoc
Medinoc

Reputation: 6608

The MSDN doc doesn't say you can create a GCHandle out of thin air from a random IntPtr that doesn't even point to a managed object. It says you can convert a GCHandle into an IntPtr and back into a GCHandle for the purpose of passing it as context through unmanaged functions (that by definition only accept pointers or intptr_t-like types)

As a consequence, the only kind of IntPtr you're supposed to pass to GCHandle::FromIntPtr() is one that was returned by GCHandle::ToIntPtr().

Upvotes: 4

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