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Explicit sync: forward progress requirements for never-signaled acquire fences

If a client

commits a buffer with an acquire fence
never signals the acquire fence
commits a different buffer

can the client expect forward progress or does it have to assume that the second buffer will never be displayed?

Example 1:

Consider an xdg_toplevel (no subsurfaces)
Client attaches buffer A with acquire fence N
Client commits
Client attaches buffer B with acquire fence M
Client commits

If the client signals M but never signals N, can he expect that buffer B will eventually be shown?

Example 2:

Consider an xdg_toplevel X with a SYNC sub-surface Y
Client attaches buffer A to X (no explicit sync)
Client attaches buffer B to Y with acquire fence N
Client commits both
Client destroys the sub-surface

If the client never signals N, can he expect that the commit will eventually be shown?

Example 3:

Consider two independent xdg_toplevel X and Y
Client attaches buffer A to X with acquire fence N
Client commits X
Client attaches buffer B to Y (no explicit sync)
Client commits Y

If the client never signals N, can he expect that buffer B will eventually be shown?

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