Also call other wallet notify callbacks in scheduler thread

This runs Block{Connected,Disconnected}, SetBestChain, Inventory,
and TransactionAddedToMempool on the background scheduler thread.

Of those, only BlockConnected is used outside of Wallet/ZMQ, and
is used only for orphan transaction removal in net_processing,
something which does not need to be synchronous with anything
else.

This partially reverts #9583, re-enabling some of the gains from
 #7946. This does not, however, re-enable the gains achieved by
repeatedly releasing cs_main between each transaction processed.

src/validation.cpp

@@ -2469,7 +2469,7 @@ bool ActivateBestChain(CValidationState &state, const CChainParams& chainparams,
 
             for (const PerBlockConnectTrace& trace : connectTrace.GetBlocksConnected()) {
                 assert(trace.pblock && trace.pindex);
-                GetMainSignals().BlockConnected(trace.pblock, trace.pindex, *trace.conflictedTxs);
+                GetMainSignals().BlockConnected(trace.pblock, trace.pindex, trace.conflictedTxs);
             }
         }
         // When we reach this point, we switched to a new tip (stored in pindexNewTip).

src/validationinterface.cpp

@@ -121,23 +121,33 @@ void CMainSignals::UpdatedBlockTip(const CBlockIndex *pindexNew, const CBlockInd
 }
 
 void CMainSignals::TransactionAddedToMempool(const CTransactionRef &ptx) {
-    m_internals->TransactionAddedToMempool(ptx);
+    m_internals->m_schedulerClient.AddToProcessQueue([ptx, this] {
+        m_internals->TransactionAddedToMempool(ptx);
+    });
 }
 
-void CMainSignals::BlockConnected(const std::shared_ptr<const CBlock> &pblock, const CBlockIndex *pindex, const std::vector<CTransactionRef>& vtxConflicted) {
-    m_internals->BlockConnected(pblock, pindex, vtxConflicted);
+void CMainSignals::BlockConnected(const std::shared_ptr<const CBlock> &pblock, const CBlockIndex *pindex, const std::shared_ptr<const std::vector<CTransactionRef>>& pvtxConflicted) {
+    m_internals->m_schedulerClient.AddToProcessQueue([pblock, pindex, pvtxConflicted, this] {
+        m_internals->BlockConnected(pblock, pindex, *pvtxConflicted);
+    });
 }
 
 void CMainSignals::BlockDisconnected(const std::shared_ptr<const CBlock> &pblock) {
-    m_internals->BlockDisconnected(pblock);
+    m_internals->m_schedulerClient.AddToProcessQueue([pblock, this] {
+        m_internals->BlockDisconnected(pblock);
+    });
 }
 
 void CMainSignals::SetBestChain(const CBlockLocator &locator) {
-    m_internals->SetBestChain(locator);
+    m_internals->m_schedulerClient.AddToProcessQueue([locator, this] {
+        m_internals->SetBestChain(locator);
+    });
 }
 
 void CMainSignals::Inventory(const uint256 &hash) {
-    m_internals->Inventory(hash);
+    m_internals->m_schedulerClient.AddToProcessQueue([hash, this] {
+        m_internals->Inventory(hash);
+    });
 }
 
 void CMainSignals::Broadcast(int64_t nBestBlockTime, CConnman* connman) {

src/validationinterface.h

@@ -47,7 +47,11 @@ class CValidationInterface {
 protected:
     /** Notifies listeners of updated block chain tip */
     virtual void UpdatedBlockTip(const CBlockIndex *pindexNew, const CBlockIndex *pindexFork, bool fInitialDownload) {}
-    /** Notifies listeners of a transaction having been added to mempool. */
+    /**
+     * Notifies listeners of a transaction having been added to mempool.
+     *
+     * Called on a background thread.
+     */
     virtual void TransactionAddedToMempool(const CTransactionRef &ptxn) {}
     /**
      * Notifies listeners of a transaction leaving mempool.
@@ -63,13 +67,27 @@ protected:
     /**
      * Notifies listeners of a block being connected.
      * Provides a vector of transactions evicted from the mempool as a result.
+     *
+     * Called on a background thread.
      */
     virtual void BlockConnected(const std::shared_ptr<const CBlock> &block, const CBlockIndex *pindex, const std::vector<CTransactionRef> &txnConflicted) {}
-    /** Notifies listeners of a block being disconnected */
+    /**
+     * Notifies listeners of a block being disconnected
+     *
+     * Called on a background thread.
+     */
     virtual void BlockDisconnected(const std::shared_ptr<const CBlock> &block) {}
-    /** Notifies listeners of the new active block chain on-disk. */
+    /**
+     * Notifies listeners of the new active block chain on-disk.
+     *
+     * Called on a background thread.
+     */
     virtual void SetBestChain(const CBlockLocator &locator) {}
-    /** Notifies listeners about an inventory item being seen on the network. */
+    /**
+     * Notifies listeners about an inventory item being seen on the network.
+     *
+     * Called on a background thread.
+     */
     virtual void Inventory(const uint256 &hash) {}
     /** Tells listeners to broadcast their data. */
     virtual void ResendWalletTransactions(int64_t nBestBlockTime, CConnman* connman) {}
@@ -116,7 +134,7 @@ public:
 
     void UpdatedBlockTip(const CBlockIndex *, const CBlockIndex *, bool fInitialDownload);
     void TransactionAddedToMempool(const CTransactionRef &);
-    void BlockConnected(const std::shared_ptr<const CBlock> &, const CBlockIndex *pindex, const std::vector<CTransactionRef> &);
+    void BlockConnected(const std::shared_ptr<const CBlock> &, const CBlockIndex *pindex, const std::shared_ptr<const std::vector<CTransactionRef>> &);
     void BlockDisconnected(const std::shared_ptr<const CBlock> &);
     void SetBestChain(const CBlockLocator &);
     void Inventory(const uint256 &);