Add shared queue to AsynRPCQueue.

src/asyncrpcqueue.cpp

@@ -6,6 +6,15 @@
 
 static std::atomic<size_t> workerCounter(0);
 
+/**
+ * Static method to return the shared/default queue.
+ */
+shared_ptr<AsyncRPCQueue> AsyncRPCQueue::sharedInstance() {
+    // Thread-safe in C+11 and gcc 4.3
+    static shared_ptr<AsyncRPCQueue> q = std::make_shared<AsyncRPCQueue>();
+    return q;
+}
+
 AsyncRPCQueue::AsyncRPCQueue() : closed_(false), finish_(false) {
 }