From 0fd2a33648ccde4b989f1d69529daea4d88b14a2 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Fri, 22 Jul 2016 15:57:25 +0200
Subject: [PATCH] Use a signal to continue init after genesis activation

---
 src/init.cpp              | 40 +++++++++++++++++++++++++++++----------
 src/main.cpp              |  2 --
 src/test/test_bitcoin.cpp |  5 +++++
 3 files changed, 35 insertions(+), 12 deletions(-)

diff --git a/src/init.cpp b/src/init.cpp
index 8d4a2cafb..4458c8331 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -510,6 +510,21 @@ static void BlockNotifyCallback(bool initialSync, const CBlockIndex *pBlockIndex
     boost::thread t(runCommand, strCmd); // thread runs free
 }
 
+static bool fHaveGenesis = false;
+static boost::mutex cs_GenesisWait;
+static CConditionVariable condvar_GenesisWait;
+
+static void BlockNotifyGenesisWait(bool, const CBlockIndex *pBlockIndex)
+{
+    if (pBlockIndex != NULL) {
+        {
+            boost::unique_lock<boost::mutex> lock_GenesisWait(cs_GenesisWait);
+            fHaveGenesis = true;
+        }
+        condvar_GenesisWait.notify_all();
+    }
+}
+
 struct CImportingNow
 {
     CImportingNow() {
@@ -1286,7 +1301,7 @@ bool AppInit2(boost::thread_group& threadGroup, CScheduler& scheduler)
                     break;
                 }
 
-                if (!fReindex) {
+                if (!fReindex && chainActive.Tip() != NULL) {
                     uiInterface.InitMessage(_("Rewinding blocks..."));
                     if (!RewindBlockIndex(chainparams)) {
                         strLoadError = _("Unable to rewind the database to a pre-fork state. You will need to redownload the blockchain");
@@ -1403,6 +1418,14 @@ bool AppInit2(boost::thread_group& threadGroup, CScheduler& scheduler)
 
     // ********************************************************* Step 10: import blocks
 
+    // Either install a handler to notify us when genesis activates, or set fHaveGenesis directly.
+    // No locking, as this happens before any background thread is started.
+    if (chainActive.Tip() == NULL) {
+        uiInterface.NotifyBlockTip.connect(BlockNotifyGenesisWait);
+    } else {
+        fHaveGenesis = true;
+    }
+
     if (mapArgs.count("-blocknotify"))
         uiInterface.NotifyBlockTip.connect(BlockNotifyCallback);
 
@@ -1412,19 +1435,16 @@ bool AppInit2(boost::thread_group& threadGroup, CScheduler& scheduler)
         BOOST_FOREACH(const std::string& strFile, mapMultiArgs["-loadblock"])
             vImportFiles.push_back(strFile);
     }
+
     threadGroup.create_thread(boost::bind(&ThreadImport, vImportFiles));
 
     // Wait for genesis block to be processed
-    bool fHaveGenesis = false;
-    while (!fHaveGenesis && !fRequestShutdown) {
-        {
-            LOCK(cs_main);
-            fHaveGenesis = (chainActive.Tip() != NULL);
-        }
-
-        if (!fHaveGenesis) {
-            MilliSleep(10);
+    {
+        boost::unique_lock<boost::mutex> lock(cs_GenesisWait);
+        while (!fHaveGenesis) {
+            condvar_GenesisWait.wait(lock);
         }
+        uiInterface.NotifyBlockTip.disconnect(BlockNotifyGenesisWait);
     }
 
     // ********************************************************* Step 11: start node
diff --git a/src/main.cpp b/src/main.cpp
index 622ec5142..f8eab7eb3 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -4331,8 +4331,6 @@ bool InitBlockIndex(const CChainParams& chainparams)
             CBlockIndex *pindex = AddToBlockIndex(block);
             if (!ReceivedBlockTransactions(block, state, pindex, blockPos))
                 return error("LoadBlockIndex(): genesis block not accepted");
-            if (!ActivateBestChain(state, chainparams, &block))
-                return error("LoadBlockIndex(): genesis block cannot be activated");
             // Force a chainstate write so that when we VerifyDB in a moment, it doesn't check stale data
             return FlushStateToDisk(state, FLUSH_STATE_ALWAYS);
         } catch (const std::runtime_error& e) {
diff --git a/src/test/test_bitcoin.cpp b/src/test/test_bitcoin.cpp
index 856f9b842..056f2982c 100644
--- a/src/test/test_bitcoin.cpp
+++ b/src/test/test_bitcoin.cpp
@@ -60,6 +60,11 @@ TestingSetup::TestingSetup(const std::string& chainName) : BasicTestingSetup(cha
         pcoinsdbview = new CCoinsViewDB(1 << 23, true);
         pcoinsTip = new CCoinsViewCache(pcoinsdbview);
         InitBlockIndex(chainparams);
+        {
+            CValidationState state;
+            bool ok = ActivateBestChain(state, chainparams);
+            BOOST_CHECK(ok);
+        }
         nScriptCheckThreads = 3;
         for (int i=0; i < nScriptCheckThreads-1; i++)
             threadGroup.create_thread(&ThreadScriptCheck);