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# Overrun Detection

Overrun detection is an experimental feature. It helps you detect corrupted memory at the time that the corruption occurs. If you think memory corruption might be caused by read or write operations outside of allocated memory, overrun detection can help you detect the problem.

Note:
Overrun detection mode is similar to the Microsoft Debugging Tools for Windows GFlags with full page heap verification . However, it can be used with the O3DE memory allocators and does not require recompiling.

## Prerequisites and Limitations

The following are the prerequisites and limitations for using the O3DE overrun detection feature:

• You must build and run your project for Windows PC in a Debug or Profile build.
• Overrun detection is available only on platforms that use the Windows API.
• Only allocations that go through the O3DE allocators benefit from overrun detection. Allocations that go through new or malloc do not use overrun detection unless you overload those functions to use the O3DE allocators.

## When to Enable Overrun Detection

The most common indicator of overwritten memory is a crash that occurs with no obvious explanation. The crash frequently occurs in a low-level system or structure, such as an AZStd:: container, or within the memory allocator. The memory overrun is not an out-of-memory error.

## Enabling Overrun Detection

Overrun detection is enabled by a setting in your project’s Game.xml file.

To enable overrun detection

1. Open your project’s Config\Game.xml file.

2. Change useOverrunDetection from the default false to true, as shown in the following example.

<Class name="bool" field="useOverrunDetection" value="true" type="{A0CA880C-AFE4-43CB-926C-59AC48496112}"/>


## Using Overrun Detection

When overrun detection is enabled, debug your game as usual. Keep the following points in mind:

• Your game runs more slowly and uses significantly more memory with overrun detection enabled.
• If a system reads or writes outside allocated memory, the game crashes with a call stack at the point of the invalid read or write. An invalid read or write includes the usual Exception thrown: invalid read/write message near the end of the output. If this message does not appear, the exception is not a memory read or write bug.
• If the game doesn’t crash, but locks up instead, you can pause the debugger to see where the game stopped.
Note:
The detector doesn’t always release memory after the memory is acquired from the operating system. Depending on the game, the detector can increase memory consumption as gameplay continues. If you run out of memory when you use the detector, a crash occurs in either WindowsPlatformAllocator::ReserveBytes or WindowsPlatformAllocator::CommitBytes.