Block ActivateBestChain to empty validationinterface queue

Author: TheBlueMatt

src/validation.cpp

@@ -53,6 +53,8 @@
 #include "zpiv/zerocoin.h"
 #include "zpiv/zpivmodule.h"
 
+#include <future>
+
 #include <boost/algorithm/string/replace.hpp>
 #include <boost/thread.hpp>
 #include <atomic>
@@ -2258,6 +2260,17 @@ bool ActivateBestChain(CValidationState& state, std::shared_ptr<const CBlock> pb
     do {
         boost::this_thread::interruption_point();
 
+        if (GetMainSignals().CallbacksPending() > 10) {
+            // Block until the validation queue drains. This should largely
+            // never happen in normal operation, however may happen during
+            // reindex, causing memory blowup  if we run too far ahead.
+            std::promise<void> promise;
+            CallFunctionInValidationInterfaceQueue([&promise] {
+                promise.set_value();
+            });
+            promise.get_future().wait();
+        }
+
         const CBlockIndex *pindexFork;
         bool fInitialDownload;
         while (true) {