[Mesa-dev] [PATCH 3/4] dri3: Fix dri3_wait_for_sbc to wait for completion of requested SBC

[Keith Packard]

Eric figured out that glXWaitForSbcOML wanted to block until the requested SBC
had been completed, which means to wait until the PresentCompleteNotify event
for that SBC had been received.

This replaces the simple sleep(1) loop (which was bogus) with a loop that just
checks to see if we've seen the specified SBC value come back in a
PresentCompleteNotify event yet.

The change is a bit larger than that as I've broken out a piece of common code
to wait for and process a single Present event for the target drawable.

Signed-off-by: Keith Packard <keithp at keithp.com>
---
 src/glx/dri3_glx.c | 55 ++++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 39 insertions(+), 16 deletions(-)

diff --git a/src/glx/dri3_glx.c b/src/glx/dri3_glx.c
index c0915f2..da3f08b 100644
--- a/src/glx/dri3_glx.c
+++ b/src/glx/dri3_glx.c
@@ -397,14 +397,33 @@ dri3_handle_present_event(struct dri3_drawable *priv, xcb_present_generic_event_
    free(ge);
 }
 
+static bool
+dri3_wait_for_event(__GLXDRIdrawable *pdraw)
+{
+   xcb_connection_t *c = XGetXCBConnection(pdraw->psc->dpy);
+   struct dri3_drawable *priv = (struct dri3_drawable *) pdraw;
+   xcb_generic_event_t *ev;
+   xcb_present_generic_event_t *ge;
+
+   ev = xcb_wait_for_special_event(c, priv->special_event);
+   if (!ev)
+      return false;
+   ge = (void *) ev;
+   dri3_handle_present_event(priv, ge);
+   return true;
+}
+
+/** dri3_wait_for_msc
+ *
+ * Get the X server to send an event when the target msc/divisor/remainder is
+ * reached.
+ */
 static int
 dri3_wait_for_msc(__GLXDRIdrawable *pdraw, int64_t target_msc, int64_t divisor,
                   int64_t remainder, int64_t *ust, int64_t *msc, int64_t *sbc)
 {
    xcb_connection_t *c = XGetXCBConnection(pdraw->psc->dpy);
    struct dri3_drawable *priv = (struct dri3_drawable *) pdraw;
-   xcb_generic_event_t *ev;
-   xcb_present_generic_event_t *ge;
    uint32_t msc_serial;
 
    /* Ask for the an event for the target MSC */
@@ -421,11 +440,8 @@ dri3_wait_for_msc(__GLXDRIdrawable *pdraw, int64_t target_msc, int64_t divisor,
    /* Wait for the event */
    if (priv->special_event) {
       while ((int32_t) (msc_serial - priv->recv_msc_serial) > 0) {
-         ev = xcb_wait_for_special_event(c, priv->special_event);
-         if (!ev)
-            break;
-         ge = (void *) ev;
-         dri3_handle_present_event(priv, ge);
+         if (!dri3_wait_for_event(pdraw))
+            return 0;
       }
    }
 
@@ -436,6 +452,11 @@ dri3_wait_for_msc(__GLXDRIdrawable *pdraw, int64_t target_msc, int64_t divisor,
    return 1;
 }
 
+/** dri3_drawable_get_msc
+ *
+ * Return the current UST/MSC/SBC triplet by asking the server
+ * for an event
+ */
 static int
 dri3_drawable_get_msc(struct glx_screen *psc, __GLXDRIdrawable *pdraw,
                       int64_t *ust, int64_t *msc, int64_t *sbc)
@@ -445,12 +466,9 @@ dri3_drawable_get_msc(struct glx_screen *psc, __GLXDRIdrawable *pdraw,
 
 /** dri3_wait_for_sbc
  *
- * Wait for the swap buffer count to increase. The only way this
- * can happen is if some other thread is doing swap buffers as
- * we no longer share swap buffer counts with other processes.
- *
- * I'm not sure this is actually useful as such, and so this
- * implementation is a kludge that just polls once a second
+ * Wait for the completed swap buffer count to reach the specified
+ * target. Presumably the application knows that this will be reached with
+ * outstanding complete events, or we're going to be here awhile.
  */
 static int
 dri3_wait_for_sbc(__GLXDRIdrawable *pdraw, int64_t target_sbc, int64_t *ust,
@@ -458,10 +476,15 @@ dri3_wait_for_sbc(__GLXDRIdrawable *pdraw, int64_t target_sbc, int64_t *ust,
 {
    struct dri3_drawable *priv = (struct dri3_drawable *) pdraw;
 
-   while (priv->send_sbc < target_sbc) {
-      sleep(1);
+   while (priv->recv_sbc < target_sbc) {
+      if (!dri3_wait_for_event(pdraw))
+         return 0;
    }
-   return dri3_wait_for_msc(pdraw, 0, 0, 0, ust, msc, sbc);
+
+   *ust = priv->ust;
+   *msc = priv->msc;
+   *sbc = priv->recv_sbc;
+   return 1;
 }
 
 /**
-- 
1.8.4.4