GLMAPUNSYNCHRONIZEDBIT

GL_MAP_UNSYNCHRONIZED_BIT is a bit flag used with OpenGL buffer mapping functions such as glMapBufferRange and glMapNamedBufferRange. It indicates that the mapping should proceed without the driver delaying to synchronize with existing or pending GL operations on the same buffer. This can reduce latency in scenarios where the application will manage synchronization itself or where the mapped region is known not to be accessed by GL concurrently.

The flag is defined as a specific bit in the access mask, commonly represented as the numeric value 0x0020. It is typically combined with other access flags such as GL_MAP_READ_BIT or GL_MAP_WRITE_BIT to request a reading or writing map for a given buffer range. The exact combination depends on whether the application intends to read from or write to the mapped memory.

Use and cautions: When GL_MAP_UNSYNCHRONIZED_BIT is specified, the GL driver may not wait for ongoing operations on the buffer to complete before returning the mapping. This avoids synchronization delays but introduces potential data hazards if the buffer region is also in use by the GL pipeline. Therefore, the application bears responsibility for ensuring correctness, for example by avoiding concurrent writes and reads in overlapping regions or by issuing appropriate synchronization commands such as glFlushMappedBufferRange or memory barriers when necessary.

Common use cases include streaming or ring-buffer patterns and other performance-sensitive code paths where the application guarantees proper sequencing. In modern setups with persistent mappings and coherent memory, the need for unsynchronized mappings is reduced.

See also: GL_MAP_READ_BIT, GL_MAP_WRITE_BIT, GL_MAP_INVALIDATE_RANGE_BIT, GL_MAP_INVALIDATE_BUFFER_BIT, GL_MAP_FLUSH_EXPLICIT_BIT, glFlushMappedBufferRange, glMapBufferRange.