Accurately track the sequence numbers of batched events.

Instead of sending finished signals immediately when appending to
a batch, record the chain of sequence numbers that were part of
the batch and then send finished signals all at once when done.
This change helps the dispatcher keep track of the true state
of the application and can improve ANR detection slightly.

This is part of a series of changes to improve input system pipelining.

Bug: 5963420
Change-Id: I463c2221e2aa8fdf1c3d670c18e39e59ab69b0db

Author: Jeff Brown

include/ui/InputTransport.h

@@ -306,12 +306,23 @@ class InputConsumer {
 
     // Batched motion events per device and source.
     struct Batch {
-        uint32_t seq;
+        uint32_t seq; // sequence number of last input message batched in the event
         MotionEvent event;
     };
     Vector<Batch> mBatches;
 
+    // Chain of batched sequence numbers.  When multiple input messages are combined into
+    // a batch, we append a record here that associates the last sequence number in the
+    // batch with the previous one.  When the finished signal is sent, we traverse the
+    // chain to individually finish all input messages that were part of the batch.
+    struct SeqChain {
+        uint32_t seq;   // sequence number of batched input message
+        uint32_t chain; // sequence number of previous batched input message
+    };
+    Vector<SeqChain> mSeqChains;
+
     ssize_t findBatch(int32_t deviceId, int32_t source) const;
+    status_t sendUnchainedFinishedSignal(uint32_t seq, bool handled);
 
     static void initializeKeyEvent(KeyEvent* event, const InputMessage* msg);
     static void initializeMotionEvent(MotionEvent* event, const InputMessage* msg);

libs/ui/InputTransport.cpp

@@ -401,17 +401,16 @@ status_t InputConsumer::consume(InputEventFactoryInterface* factory,
             if (batchIndex >= 0) {
                 Batch& batch = mBatches.editItemAt(batchIndex);
                 if (canAppendSamples(&batch.event, &mMsg)) {
-                    // Send finished message for the earlier part of the batch.
-                    // Claim that we handled the event.  (The dispatcher doesn't care either
-                    // way at the moment.)
-                    status_t status = sendFinishedSignal(batch.seq, true);
-                    if (status) {
-                        return status;
-                    }
-
                     // Append to the batch and save the new sequence number for the tail end.
+                    uint32_t chain = batch.seq;
                     appendSamples(&batch.event, &mMsg);
                     batch.seq = mMsg.body.motion.seq;
+
+                    // Update the sequence number chain.
+                    SeqChain seqChain;
+                    seqChain.seq = batch.seq;
+                    seqChain.chain = chain;
+                    mSeqChains.push(seqChain);
 #if DEBUG_TRANSPORT_ACTIONS
                     ALOGD("channel '%s' consumer ~ appended to batch event",
                             mChannel->getName().string());
@@ -486,6 +485,41 @@ status_t InputConsumer::sendFinishedSignal(uint32_t seq, bool handled) {
         return BAD_VALUE;
     }
 
+    // Send finished signals for the batch sequence chain first.
+    size_t seqChainCount = mSeqChains.size();
+    if (seqChainCount) {
+        uint32_t currentSeq = seq;
+        uint32_t chainSeqs[seqChainCount];
+        size_t chainIndex = 0;
+        for (size_t i = seqChainCount; i-- > 0; ) {
+             const SeqChain& seqChain = mSeqChains.itemAt(i);
+             if (seqChain.seq == currentSeq) {
+                 currentSeq = seqChain.chain;
+                 chainSeqs[chainIndex++] = currentSeq;
+                 mSeqChains.removeAt(i);
+             }
+        }
+        status_t status = OK;
+        while (!status && chainIndex-- > 0) {
+            status = sendUnchainedFinishedSignal(chainSeqs[chainIndex], handled);
+        }
+        if (status) {
+            // An error occurred so at least one signal was not sent, reconstruct the chain.
+            do {
+                SeqChain seqChain;
+                seqChain.seq = chainIndex != 0 ? chainSeqs[chainIndex - 1] : seq;
+                seqChain.chain = chainSeqs[chainIndex];
+                mSeqChains.push(seqChain);
+            } while (chainIndex-- > 0);
+            return status;
+        }
+    }
+
+    // Send finished signal for the last message in the batch.
+    return sendUnchainedFinishedSignal(seq, handled);
+}
+
+status_t InputConsumer::sendUnchainedFinishedSignal(uint32_t seq, bool handled) {
     InputMessage msg;
     msg.header.type = InputMessage::TYPE_FINISHED;
     msg.body.finished.seq = seq;