From e9297f8e7ee09fa39b1d4293fad6e97705ccff21 Mon Sep 17 00:00:00 2001 From: Pekka Paalanen Date: Thu, 25 Apr 2013 13:57:51 +0300 Subject: window: prevent EGL sub-surface deadlock Mesa's eglSwapBuffers() waits for the frame event from the previous swapBuffers, before it returns. Apparently eglSwapInterval(), which should be able to disable the wait, is unimplemented for now. When a sub-surface contains an EGL widget, and the commit mode is synchronized, the frame events will not be delivered to EGL until the parent surface gets committed. Therefore rendering the EGL widget twice would lead to a deadlock. When the window is being resized, we need to force a repaint of the EGL widget, too, to make the whole window consistent. For that, we need to make sure the frame event from the previous eglSwapBuffers() actually arrives. This patch adds an extra wl_surface.commit(parent), when the window is being resized, which should guarantee, that the previous eglSwapBuffers gets its event. To properly handle an EGL widget in a sub-surface, running in its own thread, the EGL widget's automatic updates should be paused before sending the extra wl_surface.commit(parent). A natural place for the pause would be in the widget's resize hook. However, wl_surface.commit cannot be called right after resize hooks, because it would commit new, incomplete surface state. Therefore this patch is not enough for threaded toytoolkit applications. Luckily those do not exist yet. When eglSwapInterval() gets implemented, this patch should be reverted. Signed-off-by: Pekka Paalanen --- clients/window.c | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) diff --git a/clients/window.c b/clients/window.c index b12c21c..ab9a36e 100644 --- a/clients/window.c +++ b/clients/window.c @@ -3362,6 +3362,36 @@ surface_resize(struct surface *surface) widget->allocation.height); } +static void +hack_prevent_EGL_sub_surface_deadlock(struct window *window) +{ + /* + * This hack should be removed, when EGL respects + * eglSwapInterval(0). + * + * If this window has sub-surfaces, especially a free-running + * EGL-widget, we need to post the parent surface once with + * all the old state to guarantee, that the EGL-widget will + * receive its frame callback soon. Otherwise, a forced call + * to eglSwapBuffers may end up blocking, waiting for a frame + * event that will never come, because we will commit the parent + * surface with all new state only after eglSwapBuffers returns. + * + * This assumes, that: + * 1. When the EGL widget's resize hook is called, it pauses. + * 2. When the EGL widget's redraw hook is called, it forces a + * repaint and a call to eglSwapBuffers(), and maybe resumes. + * In a single threaded application condition 1 is a no-op. + * + * XXX: This should actually be after the surface_resize() calls, + * but cannot, because then it would commit the incomplete state + * accumulated from the widget resize hooks. + */ + if (window->subsurface_list.next != &window->main_surface->link || + window->subsurface_list.prev != &window->main_surface->link) + wl_surface_commit(window->main_surface->surface); +} + static void idle_resize(struct window *window) { @@ -3370,6 +3400,8 @@ idle_resize(struct window *window) window->resize_needed = 0; window->redraw_needed = 1; + hack_prevent_EGL_sub_surface_deadlock(window); + widget_set_allocation(window->main_surface->widget, window->pending_allocation.x, window->pending_allocation.y, -- cgit v1.2.3