Process all display events in order

Display events in each batch received from IPC were being processed in
reverse order, and stopped after the first vsync event (latest
chronologically) was handled. This makes perfect sense for vsync
events, but is broken for hotplug events.

Now we process them all in order, handling all except vsync as we see
them. For vsync events, only the last is reported.

Bug: 7491120
Change-Id: I448d139d21dc27128d75ca1d661de666fff51bcb

1 files changed, 23 insertions, 19 deletions

diff --git a/core/jni/android_view_DisplayEventReceiver.cpp b/core/jni/android_view_DisplayEventReceiver.cpp
index 3d9d005..64fb27b 100644
--- a/core/jni/android_view_DisplayEventReceiver.cpp
+++ b/core/jni/android_view_DisplayEventReceiver.cpp
@@ -62,7 +62,7 @@ private:
     bool mWaitingForVsync;
 
     virtual int handleEvent(int receiveFd, int events, void* data);
-    bool readLastVsyncMessage(nsecs_t* outTimestamp, int32_t* id, uint32_t* outCount);
+    bool processPendingEvents(nsecs_t* outTimestamp, int32_t* id, uint32_t* outCount);
     void dispatchVsync(nsecs_t timestamp, int32_t id, uint32_t count);
     void dispatchHotplug(nsecs_t timestamp, int32_t id, bool connected);
 };
@@ -111,7 +111,7 @@ status_t NativeDisplayEventReceiver::scheduleVsync() {
         nsecs_t vsyncTimestamp;
         int32_t vsyncDisplayId;
         uint32_t vsyncCount;
-        readLastVsyncMessage(&vsyncTimestamp, &vsyncDisplayId, &vsyncCount);
+        processPendingEvents(&vsyncTimestamp, &vsyncDisplayId, &vsyncCount);
 
         status_t status = mReceiver.requestNextVsync();
         if (status) {
@@ -141,43 +141,47 @@ int NativeDisplayEventReceiver::handleEvent(int receiveFd, int events, void* dat
     nsecs_t vsyncTimestamp;
     int32_t vsyncDisplayId;
     uint32_t vsyncCount;
-    if (!readLastVsyncMessage(&vsyncTimestamp, &vsyncDisplayId, &vsyncCount)) {
-        ALOGV("receiver %p ~ Woke up but there was no vsync pulse!", this);
-        return 1; // keep the callback, did not obtain a vsync pulse
+    if (processPendingEvents(&vsyncTimestamp, &vsyncDisplayId, &vsyncCount)) {
+        ALOGV("receiver %p ~ Vsync pulse: timestamp=%lld, id=%d, count=%d",
+                this, vsyncTimestamp, vsyncDisplayId, vsyncCount);
+        mWaitingForVsync = false;
+        dispatchVsync(vsyncTimestamp, vsyncDisplayId, vsyncCount);
     }
 
-    ALOGV("receiver %p ~ Vsync pulse: timestamp=%lld, id=%d, count=%d",
-            this, vsyncTimestamp, vsyncDisplayId, vsyncCount);
-    mWaitingForVsync = false;
-
-    dispatchVsync(vsyncTimestamp, vsyncDisplayId, vsyncCount);
     return 1; // keep the callback
 }
 
-bool NativeDisplayEventReceiver::readLastVsyncMessage(
+bool NativeDisplayEventReceiver::processPendingEvents(
         nsecs_t* outTimestamp, int32_t* outId, uint32_t* outCount) {
+    bool gotVsync = false;
     DisplayEventReceiver::Event buf[EVENT_BUFFER_SIZE];
     ssize_t n;
     while ((n = mReceiver.getEvents(buf, EVENT_BUFFER_SIZE)) > 0) {
         ALOGV("receiver %p ~ Read %d events.", this, int(n));
-        while (n-- > 0) {
-            const DisplayEventReceiver::Event& ev = buf[n];
-            if (ev.header.type == DisplayEventReceiver::DISPLAY_EVENT_VSYNC) {
+        for (ssize_t i = 0; i < n; i++) {
+            const DisplayEventReceiver::Event& ev = buf[i];
+            switch (ev.header.type) {
+            case DisplayEventReceiver::DISPLAY_EVENT_VSYNC:
+                // Later vsync events will just overwrite the info from earlier
+                // ones. That's fine, we only care about the most recent.
+                gotVsync = true;
                 *outTimestamp = ev.header.timestamp;
                 *outId = ev.header.id;
                 *outCount = ev.vsync.count;
-                return true; // stop at last vsync in the buffer
-            }
-
-            if (ev.header.type == DisplayEventReceiver::DISPLAY_EVENT_HOTPLUG) {
+                break;
+            case DisplayEventReceiver::DISPLAY_EVENT_HOTPLUG:
                 dispatchHotplug(ev.header.timestamp, ev.header.id, ev.hotplug.connected);
+                break;
+            default:
+                ALOGW("receiver %p ~ ignoring unknown event type %#x", this, ev.header.type);
+                break;
             }
         }
     }
     if (n < 0) {
         ALOGW("Failed to get events from display event receiver, status=%d", status_t(n));
     }
-    return false;
+    return gotVsync;
 }
 
 void NativeDisplayEventReceiver::dispatchVsync(nsecs_t timestamp, int32_t id, uint32_t count) {