Dispatch multiple touch events in parallel.

This change enables the input dispatcher to send multiple touch
events to an application without waiting for them to be acknowledged.
Essentially this is a variation on the old streaming optimization
but it is much more comprehensive.  Event dispatch will stall as
soon as 0.5sec of unacknowledged events are accumulated or a
focused event (such as a key event) needs to be delivered.

Streaming input events makes a tremendous difference in application
performance.  The next step will be to enable batching of input
events on the client side once again.

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

Bug: 5963420
Change-Id: I025df90c06165d719fcca7f63eed322a5cce4a78

Author: Jeff Brown

libs/ui/InputTransport.cpp

@@ -28,6 +28,13 @@
 
 namespace android {
 
+// Socket buffer size.  The default is typically about 128KB, which is much larger than
+// we really need.  So we make it smaller.  It just needs to be big enough to hold
+// a few dozen large multi-finger motion events in the case where an application gets
+// behind processing touches.
+static const size_t SOCKET_BUFFER_SIZE = 32 * 1024;
+
+
 // --- InputMessage ---
 
 bool InputMessage::isValid(size_t actualSize) const {
@@ -93,6 +100,12 @@ status_t InputChannel::openInputChannelPair(const String8& name,
         return result;
     }
 
+    int bufferSize = SOCKET_BUFFER_SIZE;
+    setsockopt(sockets[0], SOL_SOCKET, SO_SNDBUF, &bufferSize, sizeof(bufferSize));
+    setsockopt(sockets[0], SOL_SOCKET, SO_RCVBUF, &bufferSize, sizeof(bufferSize));
+    setsockopt(sockets[1], SOL_SOCKET, SO_SNDBUF, &bufferSize, sizeof(bufferSize));
+    setsockopt(sockets[1], SOL_SOCKET, SO_RCVBUF, &bufferSize, sizeof(bufferSize));
+
     String8 serverChannelName = name;
     serverChannelName.append(" (server)");
     outServerChannel = new InputChannel(serverChannelName, sockets[0]);