logd: in nonblocking read, sched_yield() synchronization

- sched_yield and lock synchronization in reader thread
  startup to give writer thread a chance to catch up

(cherry picked from commit f669acb018)

Bug: 17512203
Change-Id: I43cf0b4e2829b22b3ab4e537fa95ce13c76a869c

logd/LogReader.cpp

@@ -92,6 +92,11 @@ bool LogReader::onDataAvailable(SocketClient *cli) {
 
     bool nonBlock = false;
     if (strncmp(buffer, "dumpAndClose", 12) == 0) {
+        // Allow writer to get some cycles, and wait for pending notifications
+        sched_yield();
+        LogTimeEntry::lock();
+        LogTimeEntry::unlock();
+        sched_yield();
         nonBlock = true;
     }