Add helper to wait for validation interface queue to catch up

src/validationinterface.cpp

@@ -11,9 +11,11 @@
 #include <sync.h>
 #include <txmempool.h>
 #include <util.h>
+#include <validation.h>
 
 #include <list>
 #include <atomic>
+#include <future>
 
 #include <boost/signals2/signal.hpp>
 
@@ -118,6 +120,16 @@ void CallFunctionInValidationInterfaceQueue(std::function<void ()> func) {
     g_signals.m_internals->m_schedulerClient.AddToProcessQueue(std::move(func));
 }
 
+void SyncWithValidationInterfaceQueue() {
+    AssertLockNotHeld(cs_main);
+    // Block until the validation queue drains
+    std::promise<void> promise;
+    CallFunctionInValidationInterfaceQueue([&promise] {
+        promise.set_value();
+    });
+    promise.get_future().wait();
+}
+
 void CMainSignals::MempoolEntryRemoved(CTransactionRef ptx, MemPoolRemovalReason reason) {
     if (reason != MemPoolRemovalReason::BLOCK && reason != MemPoolRemovalReason::CONFLICT) {
         m_internals->m_schedulerClient.AddToProcessQueue([ptx, this] {