Move ChainLock signing into TrySignChainTip and call it periodically

Later commits will introduce checks for "safe TXs" which might abort the
signing on first try, but succeed a few seconds later, so we periodically
retry to sign the tip.

src/llmq/quorums_chainlocks.cpp

@@ -35,12 +35,16 @@ CChainLocksHandler::~CChainLocksHandler()
 {
 }
 
-void CChainLocksHandler::RegisterAsRecoveredSigsListener()
+void CChainLocksHandler::Start()
 {
     quorumSigningManager->RegisterRecoveredSigsListener(this);
+    scheduler->scheduleEvery([&]() {
+        // regularely retry signing the current chaintip as it might have failed before due to missing ixlocks
+        TrySignChainTip();
+    }, 5000);
 }
 
-void CChainLocksHandler::UnregisterAsRecoveredSigsListener()
+void CChainLocksHandler::Stop()
 {
     quorumSigningManager->UnregisterRecoveredSigsListener(this);
 }
@@ -184,30 +188,52 @@ void CChainLocksHandler::AcceptedBlockHeader(const CBlockIndex* pindexNew)
 
 void CChainLocksHandler::UpdatedBlockTip(const CBlockIndex* pindexNew, const CBlockIndex* pindexFork)
 {
+    // don't call TrySignChainTip directly but instead let the scheduler call it. This way we ensure that cs_main is
+    // never locked and TrySignChainTip is not called twice in parallel
+    LOCK(cs);
+    if (tryLockChainTipScheduled) {
+        return;
+    }
+    tryLockChainTipScheduled = true;
+    scheduler->scheduleFromNow([&]() {
+        TrySignChainTip();
+        LOCK(cs);
+        tryLockChainTipScheduled = false;
+    }, 0);
+}
+
+void CChainLocksHandler::TrySignChainTip()
+{
+    Cleanup();
+
+    const CBlockIndex* pindex;
+    {
+        LOCK(cs_main);
+        pindex = chainActive.Tip();
+    }
+
     if (!fMasternodeMode) {
         return;
     }
-    if (!pindexNew->pprev) {
+    if (!pindex->pprev) {
         return;
     }
     if (!sporkManager.IsSporkActive(SPORK_19_CHAINLOCKS_ENABLED)) {
         return;
     }
 
-    Cleanup();
-
     // DIP8 defines a process called "Signing attempts" which should run before the CLSIG is finalized
     // To simplify the initial implementation, we skip this process and directly try to create a CLSIG
     // This will fail when multiple blocks compete, but we accept this for the initial implementation.
     // Later, we'll add the multiple attempts process.
 
-    uint256 requestId = ::SerializeHash(std::make_pair(CLSIG_REQUESTID_PREFIX, pindexNew->nHeight));
-    uint256 msgHash = pindexNew->GetBlockHash();
+    uint256 requestId = ::SerializeHash(std::make_pair(CLSIG_REQUESTID_PREFIX, pindex->nHeight));
+    uint256 msgHash = pindex->GetBlockHash();
 
     {
         LOCK(cs);
 
-        if (bestChainLockBlockIndex == pindexNew) {
+        if (bestChainLockBlockIndex == pindex) {
             // we first got the CLSIG, then the header, and then the block was connected.
             // In this case there is no need to continue here.
             // However, NotifyChainLock might not have been called yet, so call it now if needed
@@ -218,26 +244,26 @@ void CChainLocksHandler::UpdatedBlockTip(const CBlockIndex* pindexNew, const CBl
             return;
         }
 
-        if (InternalHasConflictingChainLock(pindexNew->nHeight, pindexNew->GetBlockHash())) {
+        if (InternalHasConflictingChainLock(pindex->nHeight, pindex->GetBlockHash())) {
             if (!inEnforceBestChainLock) {
                 // we accepted this block when there was no lock yet, but now a conflicting lock appeared. Invalidate it.
                 LogPrintf("CChainLocksHandler::%s -- conflicting lock after block was accepted, invalidating now\n",
                           __func__);
-                ScheduleInvalidateBlock(pindexNew);
+                ScheduleInvalidateBlock(pindex);
             }
             return;
         }
 
-        if (bestChainLock.nHeight >= pindexNew->nHeight) {
+        if (bestChainLock.nHeight >= pindex->nHeight) {
             // already got the same CLSIG or a better one
             return;
         }
 
-        if (pindexNew->nHeight == lastSignedHeight) {
+        if (pindex->nHeight == lastSignedHeight) {
             // already signed this one
             return;
         }
-        lastSignedHeight = pindexNew->nHeight;
+        lastSignedHeight = pindex->nHeight;
         lastSignedRequestId = requestId;
         lastSignedMsgHash = msgHash;
     }

src/llmq/quorums_chainlocks.h

@@ -49,6 +49,7 @@ class CChainLocksHandler : public CRecoveredSigsListener
 private:
     CScheduler* scheduler;
     CCriticalSection cs;
+    bool tryLockChainTipScheduled{false};
     std::atomic<bool> inEnforceBestChainLock{false};
 
     uint256 bestChainLockHash;
@@ -74,8 +75,8 @@ class CChainLocksHandler : public CRecoveredSigsListener
     CChainLocksHandler(CScheduler* _scheduler);
     ~CChainLocksHandler();
 
-    void RegisterAsRecoveredSigsListener();
-    void UnregisterAsRecoveredSigsListener();
+    void Start();
+    void Stop();
 
     bool AlreadyHave(const CInv& inv);
     bool GetChainLockByHash(const uint256& hash, CChainLockSig& ret);
@@ -86,6 +87,7 @@ class CChainLocksHandler : public CRecoveredSigsListener
     void UpdatedBlockTip(const CBlockIndex* pindexNew, const CBlockIndex* pindexFork);
     void NewPoWValidBlock(const CBlockIndex* pindex, const std::shared_ptr<const CBlock>& block);
     void SyncTransaction(const CTransaction &tx, const CBlockIndex *pindex, int posInBlock);
+    void TrySignChainTip();
     void EnforceBestChainLock();
     virtual void HandleNewRecoveredSig(const CRecoveredSig& recoveredSig);
 

src/llmq/quorums_init.cpp

@@ -66,7 +66,7 @@ void StartLLMQSystem()
         quorumSigSharesManager->StartWorkerThread();
     }
     if (chainLocksHandler) {
-        chainLocksHandler->RegisterAsRecoveredSigsListener();
+        chainLocksHandler->Start();
     }
     if (quorumInstantSendManager) {
         quorumInstantSendManager->RegisterAsRecoveredSigsListener();
@@ -79,7 +79,7 @@ void StopLLMQSystem()
         quorumInstantSendManager->UnregisterAsRecoveredSigsListener();
     }
     if (chainLocksHandler) {
-        chainLocksHandler->UnregisterAsRecoveredSigsListener();
+        chainLocksHandler->Stop();
     }
     if (quorumSigSharesManager) {
         quorumSigSharesManager->StopWorkerThread();