Added option to close a queue and wait for queued up operations to finish,

rather than just closing a queue and immediately cancelling all operations.

src/asyncrpcqueue.h

@@ -1,4 +1,4 @@
-// Copyright (c) 2014 The Zcash developers
+// Copyright (c) 2016 The Zcash developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -36,9 +36,12 @@ public:
     void addWorker();
     size_t getNumberOfWorkers() const;
     bool isClosed() const;
-    void close();
-    void closeAndWait();
-    void cancelAllOperations();
+    bool isFinishing() const;
+    void close(); // close queue and cancel all operations
+    void finish(); // close queue but finishing existing operations
+    void closeAndWait(); // block thread until all threads have terminated.
+    void finishAndWait(); // block thread until existing operations have finished, threads terminated
+    void cancelAllOperations(); // mark all operations in the queue as cancelled
     size_t getOperationCount() const;
     std::shared_ptr<AsyncRPCOperation> getOperationForId(AsyncRPCOperationId) const;
     std::shared_ptr<AsyncRPCOperation> popOperationForId(AsyncRPCOperationId);
@@ -46,13 +49,15 @@ public:
     std::vector<AsyncRPCOperationId> getAllOperationIds() const;
 
 private:
-    // addWorker() will spawn a new thread on this method
+    // addWorker() will spawn a new thread on run())
     void run(size_t workerId);
+    void wait_for_worker_threads();
 
     // Why this is not a recursive lock: http://www.zaval.org/resources/library/butenhof1.html
     mutable std::mutex lock_;
     std::condition_variable condition_;
-    bool closed_;
+    std::atomic<bool> closed_;
+    std::atomic<bool> finish_;
     AsyncRPCOperationMap operation_map_;
     std::queue <AsyncRPCOperationId> operation_id_queue_;
     std::vector<std::thread> workers_;