## Name

barrier — synchronize execution of multiple shader invocations

## Declaration

`void barrier(` | void`)`;

## Description

Available only in the Tessellation Control and Compute Shaders, `barrier` provides a partially defined order of execution between shader invocations. For any given static instance of `barrier`, in a tessellation control shader, all invocations for a single input patch must enter it before any will be allowed to continue beyond it. For any given static instance of `barrier` in a compute shader, all invocations within a single work group must enter it before any are allowed to continue beyond it. This ensures that values written by one invocation prior to a given static instance of `barrier` can be safely read by other invocations after their call to the same static instance of `barrier`. Because invocations may execute in undefined order between these `barrier` calls, the values of a per-vertex or per-patch output variable, or any shared variable will be undefined in a number of cases.

`barrier` may only be placed inside the function `main()` of the tessellation control shader, but may be placed anywhere in a compute shader. Calls to `barrier` may not be placed within any control flow. Barriers are also disallowed after a return statement in the function `main()`.

## Version Support

| OpenGL Shading Language Version
--- | ---
Function Name | 1.10 | 1.20 | 1.30 | 1.40 | 1.50 | 3.30 | 4.00 | 4.10 | 4.20 | 4.30 | 4.40 | 4.50
barrier | - | - | - | - | - | - | ✔ | ✔ | ✔ | ✔ | ✔ | ✔

## Copyright

Copyright © 2011-2014 Khronos Group. This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1.0, 8 June 1999. http://opencontent.org/openpub/.