UNMAP

Unmap is a computing term for removing a previously established mapping between a memory object or resource and a process’s address space or other consuming entity. Unmapping releases the resources tied to the mapping and invalidates the pointers or references to the mapped region. It is typically performed when the mapped resource is no longer needed, when a different mapping is required, or when the mapping must be synchronized with other operations.

In memory management, unmapping commonly refers to releasing memory regions created by mapping operations. In POSIX-compliant systems, a region mapped with mmap is released with munmap, which takes a base address and a length. A successful munmap makes the region inaccessible; subsequent accesses trigger a fault unless a new mapping is created. munmap may fail with errors such as EINVAL if the address range is not a valid mapped region or the length is invalid.

Windows uses a related concept with UnmapViewOfFile, which removes a view of a file that was previously established by MapViewOfFile or similar APIs. A successful call returns a nonzero value; failure returns zero and extended error information can be retrieved.

In graphics and accelerated I/O, unmapping occurs when a mapped buffer or memory region used by a device is released. For example, in OpenGL a buffer mapped with glMapBuffer or glMapBufferRange must be unmapped with glUnmapBuffer (or the corresponding unmap call) before the data can be used by the GPU or CPU again. Vulkan and Direct3D provide analogous unmapping operations for device memory or mapped resources.

Proper unmapping is important for resource safety, data consistency, and avoiding memory leaks. It may involve synchronization to ensure that pending writes are completed before the mapping is invalidated.