From 97d2b09c124e6e5803f7fd4503348d9710d1260f Mon Sep 17 00:00:00 2001
From: Matt Corallo <git@bluematt.me>
Date: Sun, 24 Dec 2017 12:13:13 -0500
Subject: [PATCH] Add helper to wait for validation interface queue to catch up

---
 src/validation.cpp          |  6 +-----
 src/validationinterface.cpp | 12 ++++++++++++
 src/validationinterface.h   | 10 ++++++++++
 src/wallet/wallet.cpp       |  7 +------
 4 files changed, 24 insertions(+), 11 deletions(-)

diff --git a/src/validation.cpp b/src/validation.cpp
index 23ce6509d..1c024ce2a 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -2572,11 +2572,7 @@ bool CChainState::ActivateBestChain(CValidationState &state, const CChainParams&
             // 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();
+            SyncWithValidationInterfaceQueue();
         }
 
         if (ShutdownRequested())
diff --git a/src/validationinterface.cpp b/src/validationinterface.cpp
index 1ddff4b33..1e13465bf 100644
--- a/src/validationinterface.cpp
+++ b/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] {
diff --git a/src/validationinterface.h b/src/validationinterface.h
index 164059e3b..f416f6678 100644
--- a/src/validationinterface.h
+++ b/src/validationinterface.h
@@ -42,6 +42,16 @@ void UnregisterAllValidationInterfaces();
  * will result in a deadlock (that DEBUG_LOCKORDER will miss).
  */
 void CallFunctionInValidationInterfaceQueue(std::function<void ()> func);
+/**
+ * This is a synonym for the following, which asserts certain locks are not
+ * held:
+ *     std::promise<void> promise;
+ *     CallFunctionInValidationInterfaceQueue([&promise] {
+ *         promise.set_value();
+ *     });
+ *     promise.get_future().wait();
+ */
+void SyncWithValidationInterfaceQueue();
 
 class CValidationInterface {
 protected:
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index dafd708d0..cf9bb2909 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -1292,12 +1292,7 @@ void CWallet::BlockUntilSyncedToCurrentChain() {
     // ...otherwise put a callback in the validation interface queue and wait
     // for the queue to drain enough to execute it (indicating we are caught up
     // at least with the time we entered this function).
-
-    std::promise<void> promise;
-    CallFunctionInValidationInterfaceQueue([&promise] {
-        promise.set_value();
-    });
-    promise.get_future().wait();
+    SyncWithValidationInterfaceQueue();
 }