https://bugs.freedesktop.org/show_bug.cgi?id=106302
--- Comment #2 from seb@vestigecounty.com --- Pierre-Eric, in my interpretation of OpenGL(R) ES Version 3.0.5 (November 3, 2016) Specification, Appendix 4: Shared Objects and Multiple Contexts, D.3. Propagating Changes to Objects, Rule 4:...
---- If the contents of an object T are changed in a context other than the current context, T must be attached or re-attached to at least one binding point in the current context, or at least one attachment point of a currently bound container object C, in order to guarantee that the new contents of T are visible in the current context.
Example: If a texture image is bound to multiple texture bind points and the texture is changed in another context, re-binding the texture at any one of the texture bind points is sufficient to cause the changes to be visible at all texture bind points. ----
...Finish or Fence are not required, since I am re-binding the texture on the secondary thread where I expect changes to be seen.