1.2GB memory exception

Question

I read about memory limit

• Is There Really A 1.2GB Limit For .NET?
• Is there a memory limit for a single .NET process
• Memory usage of DotNET app

I have an application which works with huge images which needs to be streamed. Like in a video processing with single frames. The application has about 40 plugins, each of them can contain database, image processing and WPF GUI.

The application also has 2 plugins which uses older DotNet Winforms.

All works well except the application goes over about 1.2GB in RAM. Then on unusual locations in the plugins where new memory is allocated I receive the "Out of Memory exception".

I am working on a 64Bit system compiled as 32Bit. I have no more idea what to do and how to search for any fault.

Is there a limit or can I catch them?

Answer 1

It is very difficult to write a 32-bit program that consumes all of the available virtual memory space. You'll hit the wall well below 2 gigabytes, what you run out of first is a chunk of virtual memory that's large enough to fit the requested size. You can only get up to the 2GB limit by making small allocations, small enough to fit in the holes.

That wall hits early in a program that manipulates bitmaps. They can consume a big chunk of VM to store the bitmap pixels and it needs to be a contiguous allocation. They are stored in an array, not a tree. It's an unmanaged memory allocation, typical .NET memory profilers tend to be a bit helpless to show you the problem.

There isn't anything reasonable you can do about address space fragmentation, the notion that consuming all available VM should be possible is just wrong. You can get more breathing space on a 64-bit operating system by running editbin.exe in a post build event and use its /LARGEADDRESSAWARE command line option. That allows the process to use the available 4 gigabytes of VM, an option that's specific to the 64-bit version of Windows and possible because Windows doesn't need the upper 2GB. And of course, changing the platform target to AnyCPU is a quick and easy way to get gobs of virtual memory.