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In function wait_for_buffer_release_fence simple-dmabuf-egl.c

if (d->egl.wait_sync)

		ret = d->egl.wait_sync(d->egl.display, sync, 0);

else

		ret = d->egl.client_wait_sync(d->egl.display, sync, 0,
					      EGL_FOREVER_KHR);

assert(ret == EGL_TRUE);

in case EGL_KHR_wait_sync is not supported else clause is executed and call eglClientWaitSyncKHR and this returns one of three status values from specification EGL_KHR_fence_sync

eglClientWaitSyncKHR returns one of three status values describing
the reason for returning. A return value of EGL_TIMEOUT_EXPIRED_KHR
indicates that the specified timeout period expired before <sync>
was signaled, or if <timeout> is zero, indicates that <sync> is
not signaled. A return value of EGL_CONDITION_SATISFIED_KHR
indicates that <sync> was signaled before the timeout expired, which
includes the case when <sync> was already signaled when
eglClientWaitSyncKHR was called. If an error occurs then an error is
generated and EGL_FALSE is returned.

EGL_TIMEOUT_EXPIRED_KHR - when timeout is set and time expires

EGL_CONDITION_SATISFIED_KHR - when sync is signaled

EGL_FALSE - during error

It can never return EGL_TRUE but we have assert(ret == EGL_TRUE) after it even if the sync is signaled this may cause application to abort. we should add separate assertion for client_wait_sync with assert(ret == EGL_CONDITION_SATISFIED_KHR) this is because we will never get EGL_TIMEOUT_EXPIRED_KHR since we pass EGL_FOREVER_KHR.