SurfaceFlinger: Force runHandleTransaction

In the linked bug, there are traces documenting cases where
the user observes jank while deferred transactions are in play.
We can see several cases where the client gets stuck for a long
time on dequeueBuffer. Around these times we can also see cases where
latchBuffer aborts early due to the !allTransactionsSignaled condition.
We expect all the transactions to be signalled at this point, because
before handlePageFlip we expect to reach handleTransactionLocked,
which should call notifyAvailableFrames, marking the sync points
available based on the head frame number. However if we study the trace
we also see there is an onMessageInvalidate, which contains
a handlePageFlip but does NOT contain the handleTransaction before it
which we would expect. However we know if onMessageInvalidate calls
handlePageFlip (via handleMessageInvalidate) then it must have called
handleMessageTransaction, as these two lines are right next to
eachother. We can thus conclude that we see the problem because
handleMessageTransaction didn't call handleTransaction due to
runHandleTransaction evaluating to false. This makes sense in the
context of recent changes. Previously deferred transactions would set
the transaction flags continuously while they were pending, so the
server would always perform transactions when waking up, and we wouldn't
get in this condition. However, setting the transaction flags
always triggers a wake up! But we don't actually want to wake up until
the frame actually arrives, so first we tried setting the transaction
flags without triggering a wake up. But we found this could prevent
other people from triggering wakeups, so a recent CL modified it to
set mForceTraversal instead. Intending to force that we call
doTransaction from handleMessageInvalidate regardless of whether a
new transaction has arrived (because we need to check if an old
transaction is now ready). However, it didn't quite work because of this
early abort due to runHandleTransaction.

Bug: 159677043
Test: Existing tests pass
Change-Id: I84f2a9cca2ebb3f59d30924efdb39c917f47111b

1 files changed, 2 insertions, 1 deletions

diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 2e019039f8..07690cbf32 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -2023,7 +2023,8 @@ bool SurfaceFlinger::handleMessageTransaction() {
 
     bool runHandleTransaction =
             (transactionFlags && (transactionFlags != eTransactionFlushNeeded)) ||
-            flushedATransaction;
+            flushedATransaction ||
+            mForceTraversal;
 
     if (runHandleTransaction) {
         handleTransaction(eTransactionMask);