Merge #10286: Call wallet notify callbacks in scheduler thread (without cs_main)

89f0312 Remove redundant pwallet nullptr check (Matt Corallo)
c4784b5 Add a dev notes document describing the new wallet RPC blocking (Matt Corallo)
3ea8b75 Give ZMQ consistent order with UpdatedBlockTip on scheduler thread (Matt Corallo)
cb06edf Fix wallet RPC race by waiting for callbacks in sendrawtransaction (Matt Corallo)
e545ded Also call other wallet notify callbacks in scheduler thread (Matt Corallo)
17220d6 Use callbacks to cache whether wallet transactions are in mempool (Matt Corallo)
5d67a78 Add calls to CWallet::BlockUntilSyncedToCurrentChain() in RPCs (Matt Corallo)
5ee3172 Add CWallet::BlockUntilSyncedToCurrentChain() (Matt Corallo)
0b2f42d Add CallFunctionInQueue to wait on validation interface queue drain (Matt Corallo)
2b4b345 Add ability to assert a lock is not held in DEBUG_LOCKORDER (Matt Corallo)
0343676 Call TransactionRemovedFromMempool in the CScheduler thread (Matt Corallo)
a7d3936 Add a CValidationInterface::TransactionRemovedFromMempool (Matt Corallo)

Pull request description:

  Based on #10179, this effectively reverts #9583, regaining most of the original speedups of #7946.

  This concludes the work of #9725, #10178, and #10179.

  See individual commit messages for more information.

Tree-SHA512: eead4809b0a75d1fb33b0765174ff52c972e45040635e38cf3686cef310859c1e6b3c00e7186cbd17374c6ae547bfbd6c1718fe36f26c76ba8a8b052d6ed7bc9

12 files changed, 354 insertions, 28 deletions

diff --git a/doc/developer-notes.md b/doc/developer-notes.md
index 1904400c55..35797da7ae 100644
--- a/doc/developer-notes.md
+++ b/doc/developer-notes.md
@@ -675,3 +675,16 @@ A few guidelines for introducing and reviewing new RPC interfaces:
 
   - *Rationale*: If a RPC response is not a JSON object then it is harder to avoid API breakage if
     new data in the response is needed.
+
+- Wallet RPCs call BlockUntilSyncedToCurrentChain to maintain consistency with
+  `getblockchaininfo`'s state immediately prior to the call's execution. Wallet
+  RPCs whose behavior does *not* depend on the current chainstate may omit this
+  call.
+
+  - *Rationale*: In previous versions of Bitcoin Core, the wallet was always
+    in-sync with the chainstate (by virtue of them all being updated in the
+    same cs_main lock). In order to maintain the behavior that wallet RPCs
+    return results as of at least the highest best-known block an RPC
+    client may be aware of prior to entering a wallet RPC call, we must block
+    until the wallet is caught up to the chainstate as of the RPC call's entry.
+    This also makes the API much easier for RPC clients to reason about.
diff --git a/src/init.cpp b/src/init.cpp
index 7ac2cf2d32..9bdde00558 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -261,6 +261,7 @@ void Shutdown()
 #endif
     UnregisterAllValidationInterfaces();
     GetMainSignals().UnregisterBackgroundSignalScheduler();
+    GetMainSignals().UnregisterWithMempoolSignals(mempool);
 #ifdef ENABLE_WALLET
     CloseWallets();
 #endif
@@ -1236,6 +1237,7 @@ bool AppInitMain(boost::thread_group& threadGroup, CScheduler& scheduler)
     threadGroup.create_thread(boost::bind(&TraceThread<CScheduler::Function>, "scheduler", serviceLoop));
 
     GetMainSignals().RegisterBackgroundSignalScheduler(scheduler);
+    GetMainSignals().RegisterWithMempoolSignals(mempool);
 
     /* Start the RPC server already.  It will be started in "warmup" mode
      * and not really process calls already (but it will signify connections
diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
index d860dbc244..8f8cdf80ed 100644
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -11,6 +11,7 @@
 #include "init.h"
 #include "keystore.h"
 #include "validation.h"
+#include "validationinterface.h"
 #include "merkleblock.h"
 #include "net.h"
 #include "policy/policy.h"
@@ -30,6 +31,7 @@
 #include "wallet/wallet.h"
 #endif
 
+#include <future>
 #include <stdint.h>
 
 #include <univalue.h>
@@ -917,7 +919,9 @@ UniValue sendrawtransaction(const JSONRPCRequest& request)
         );
 
     ObserveSafeMode();
-    LOCK(cs_main);
+
+    std::promise<void> promise;
+
     RPCTypeCheck(request.params, {UniValue::VSTR, UniValue::VBOOL});
 
     // parse hex string from parameter
@@ -931,6 +935,8 @@ UniValue sendrawtransaction(const JSONRPCRequest& request)
     if (!request.params[1].isNull() && request.params[1].get_bool())
         nMaxRawTxFee = 0;
 
+    { // cs_main scope
+    LOCK(cs_main);
     CCoinsViewCache &view = *pcoinsTip;
     bool fHaveChain = false;
     for (size_t o = 0; !fHaveChain && o < tx->vout.size(); o++) {
@@ -952,10 +958,24 @@ UniValue sendrawtransaction(const JSONRPCRequest& request)
                 }
                 throw JSONRPCError(RPC_TRANSACTION_ERROR, state.GetRejectReason());
             }
+        } else {
+            // If wallet is enabled, ensure that the wallet has been made aware
+            // of the new transaction prior to returning. This prevents a race
+            // where a user might call sendrawtransaction with a transaction
+            // to/from their wallet, immediately call some wallet RPC, and get
+            // a stale result because callbacks have not yet been processed.
+            CallFunctionInValidationInterfaceQueue([&promise] {
+                promise.set_value();
+            });
         }
     } else if (fHaveChain) {
         throw JSONRPCError(RPC_TRANSACTION_ALREADY_IN_CHAIN, "transaction already in block chain");
     }
+
+    } // cs_main
+
+    promise.get_future().wait();
+
     if(!g_connman)
         throw JSONRPCError(RPC_CLIENT_P2P_DISABLED, "Error: Peer-to-peer functionality missing or disabled");
 
@@ -964,6 +984,7 @@ UniValue sendrawtransaction(const JSONRPCRequest& request)
     {
         pnode->PushInventory(inv);
     });
+
     return hashTx.GetHex();
 }
 
diff --git a/src/sync.cpp b/src/sync.cpp
index 87024ccdf2..4ef419cd09 100644
--- a/src/sync.cpp
+++ b/src/sync.cpp
@@ -155,6 +155,16 @@ void AssertLockHeldInternal(const char* pszName, const char* pszFile, int nLine,
     abort();
 }
 
+void AssertLockNotHeldInternal(const char* pszName, const char* pszFile, int nLine, void* cs)
+{
+    for (const std::pair<void*, CLockLocation>& i : *lockstack) {
+        if (i.first == cs) {
+            fprintf(stderr, "Assertion failed: lock %s held in %s:%i; locks held:\n%s", pszName, pszFile, nLine, LocksHeld().c_str());
+            abort();
+        }
+    }
+}
+
 void DeleteLock(void* cs)
 {
     if (!lockdata.available) {
diff --git a/src/sync.h b/src/sync.h
index 20556af890..12160f8dc1 100644
--- a/src/sync.h
+++ b/src/sync.h
@@ -77,14 +77,17 @@ void EnterCritical(const char* pszName, const char* pszFile, int nLine, void* cs
 void LeaveCritical();
 std::string LocksHeld();
 void AssertLockHeldInternal(const char* pszName, const char* pszFile, int nLine, void* cs);
+void AssertLockNotHeldInternal(const char* pszName, const char* pszFile, int nLine, void* cs);
 void DeleteLock(void* cs);
 #else
 void static inline EnterCritical(const char* pszName, const char* pszFile, int nLine, void* cs, bool fTry = false) {}
 void static inline LeaveCritical() {}
 void static inline AssertLockHeldInternal(const char* pszName, const char* pszFile, int nLine, void* cs) {}
+void static inline AssertLockNotHeldInternal(const char* pszName, const char* pszFile, int nLine, void* cs) {}
 void static inline DeleteLock(void* cs) {}
 #endif
 #define AssertLockHeld(cs) AssertLockHeldInternal(#cs, __FILE__, __LINE__, &cs)
+#define AssertLockNotHeld(cs) AssertLockNotHeldInternal(#cs, __FILE__, __LINE__, &cs)
 
 /**
  * Wrapped mutex: supports recursive locking, but no waiting
diff --git a/src/txmempool.h b/src/txmempool.h
index f112ee1775..87f2297c04 100644
--- a/src/txmempool.h
+++ b/src/txmempool.h
@@ -513,6 +513,9 @@ public:
     // to track size/count of descendant transactions.  First version of
     // addUnchecked can be used to have it call CalculateMemPoolAncestors(), and
     // then invoke the second version.
+    // Note that addUnchecked is ONLY called from ATMP outside of tests
+    // and any other callers may break wallet's in-mempool tracking (due to
+    // lack of CValidationInterface::TransactionAddedToMempool callbacks).
     bool addUnchecked(const uint256& hash, const CTxMemPoolEntry &entry, bool validFeeEstimate = true);
     bool addUnchecked(const uint256& hash, const CTxMemPoolEntry &entry, setEntries &setAncestors, bool validFeeEstimate = true);
 
diff --git a/src/validation.cpp b/src/validation.cpp
index e7b6fc52a8..c5d73187b7 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -2494,7 +2494,7 @@ 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).
diff --git a/src/validationinterface.cpp b/src/validationinterface.cpp
index 281bc04b0a..d91707cf9f 100644
--- a/src/validationinterface.cpp
+++ b/src/validationinterface.cpp
@@ -9,6 +9,7 @@
 #include "primitives/block.h"
 #include "scheduler.h"
 #include "sync.h"
+#include "txmempool.h"
 #include "util.h"
 
 #include <list>
@@ -21,6 +22,7 @@ struct MainSignalsInstance {
     boost::signals2::signal<void (const CTransactionRef &)> TransactionAddedToMempool;
     boost::signals2::signal<void (const std::shared_ptr<const CBlock> &, const CBlockIndex *pindex, const std::vector<CTransactionRef>&)> BlockConnected;
     boost::signals2::signal<void (const std::shared_ptr<const CBlock> &)> BlockDisconnected;
+    boost::signals2::signal<void (const CTransactionRef &)> TransactionRemovedFromMempool;
     boost::signals2::signal<void (const CBlockLocator &)> SetBestChain;
     boost::signals2::signal<void (const uint256 &)> Inventory;
     boost::signals2::signal<void (int64_t nBestBlockTime, CConnman* connman)> Broadcast;
@@ -50,6 +52,14 @@ void CMainSignals::FlushBackgroundCallbacks() {
     m_internals->m_schedulerClient.EmptyQueue();
 }
 
+void CMainSignals::RegisterWithMempoolSignals(CTxMemPool& pool) {
+    pool.NotifyEntryRemoved.connect(boost::bind(&CMainSignals::MempoolEntryRemoved, this, _1, _2));
+}
+
+void CMainSignals::UnregisterWithMempoolSignals(CTxMemPool& pool) {
+    pool.NotifyEntryRemoved.disconnect(boost::bind(&CMainSignals::MempoolEntryRemoved, this, _1, _2));
+}
+
 CMainSignals& GetMainSignals()
 {
     return g_signals;
@@ -60,6 +70,7 @@ void RegisterValidationInterface(CValidationInterface* pwalletIn) {
     g_signals.m_internals->TransactionAddedToMempool.connect(boost::bind(&CValidationInterface::TransactionAddedToMempool, pwalletIn, _1));
     g_signals.m_internals->BlockConnected.connect(boost::bind(&CValidationInterface::BlockConnected, pwalletIn, _1, _2, _3));
     g_signals.m_internals->BlockDisconnected.connect(boost::bind(&CValidationInterface::BlockDisconnected, pwalletIn, _1));
+    g_signals.m_internals->TransactionRemovedFromMempool.connect(boost::bind(&CValidationInterface::TransactionRemovedFromMempool, pwalletIn, _1));
     g_signals.m_internals->SetBestChain.connect(boost::bind(&CValidationInterface::SetBestChain, pwalletIn, _1));
     g_signals.m_internals->Inventory.connect(boost::bind(&CValidationInterface::Inventory, pwalletIn, _1));
     g_signals.m_internals->Broadcast.connect(boost::bind(&CValidationInterface::ResendWalletTransactions, pwalletIn, _1, _2));
@@ -75,6 +86,7 @@ void UnregisterValidationInterface(CValidationInterface* pwalletIn) {
     g_signals.m_internals->TransactionAddedToMempool.disconnect(boost::bind(&CValidationInterface::TransactionAddedToMempool, pwalletIn, _1));
     g_signals.m_internals->BlockConnected.disconnect(boost::bind(&CValidationInterface::BlockConnected, pwalletIn, _1, _2, _3));
     g_signals.m_internals->BlockDisconnected.disconnect(boost::bind(&CValidationInterface::BlockDisconnected, pwalletIn, _1));
+    g_signals.m_internals->TransactionRemovedFromMempool.disconnect(boost::bind(&CValidationInterface::TransactionRemovedFromMempool, pwalletIn, _1));
     g_signals.m_internals->UpdatedBlockTip.disconnect(boost::bind(&CValidationInterface::UpdatedBlockTip, pwalletIn, _1, _2, _3));
     g_signals.m_internals->NewPoWValidBlock.disconnect(boost::bind(&CValidationInterface::NewPoWValidBlock, pwalletIn, _1, _2));
 }
@@ -87,32 +99,57 @@ void UnregisterAllValidationInterfaces() {
     g_signals.m_internals->TransactionAddedToMempool.disconnect_all_slots();
     g_signals.m_internals->BlockConnected.disconnect_all_slots();
     g_signals.m_internals->BlockDisconnected.disconnect_all_slots();
+    g_signals.m_internals->TransactionRemovedFromMempool.disconnect_all_slots();
     g_signals.m_internals->UpdatedBlockTip.disconnect_all_slots();
     g_signals.m_internals->NewPoWValidBlock.disconnect_all_slots();
 }
 
+void CallFunctionInValidationInterfaceQueue(std::function<void ()> func) {
+    g_signals.m_internals->m_schedulerClient.AddToProcessQueue(std::move(func));
+}
+
+void CMainSignals::MempoolEntryRemoved(CTransactionRef ptx, MemPoolRemovalReason reason) {
+    if (reason != MemPoolRemovalReason::BLOCK && reason != MemPoolRemovalReason::CONFLICT) {
+        m_internals->m_schedulerClient.AddToProcessQueue([ptx, this] {
+            m_internals->TransactionRemovedFromMempool(ptx);
+        });
+    }
+}
+
 void CMainSignals::UpdatedBlockTip(const CBlockIndex *pindexNew, const CBlockIndex *pindexFork, bool fInitialDownload) {
-    m_internals->UpdatedBlockTip(pindexNew, pindexFork, fInitialDownload);
+    m_internals->m_schedulerClient.AddToProcessQueue([pindexNew, pindexFork, fInitialDownload, this] {
+        m_internals->UpdatedBlockTip(pindexNew, pindexFork, fInitialDownload);
+    });
 }
 
 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) {
diff --git a/src/validationinterface.h b/src/validationinterface.h
index d6da2bc1fd..1494c6dc21 100644
--- a/src/validationinterface.h
+++ b/src/validationinterface.h
@@ -6,10 +6,11 @@
 #ifndef BITCOIN_VALIDATIONINTERFACE_H
 #define BITCOIN_VALIDATIONINTERFACE_H
 
-#include <memory>
-
 #include "primitives/transaction.h" // CTransaction(Ref)
 
+#include <functional>
+#include <memory>
+
 class CBlock;
 class CBlockIndex;
 struct CBlockLocator;
@@ -20,6 +21,8 @@ class CValidationInterface;
 class CValidationState;
 class uint256;
 class CScheduler;
+class CTxMemPool;
+enum class MemPoolRemovalReason;
 
 // These functions dispatch to one or all registered wallets
 
@@ -29,23 +32,66 @@ void RegisterValidationInterface(CValidationInterface* pwalletIn);
 void UnregisterValidationInterface(CValidationInterface* pwalletIn);
 /** Unregister all wallets from core */
 void UnregisterAllValidationInterfaces();
+/**
+ * Pushes a function to callback onto the notification queue, guaranteeing any
+ * callbacks generated prior to now are finished when the function is called.
+ *
+ * Be very careful blocking on func to be called if any locks are held -
+ * validation interface clients may not be able to make progress as they often
+ * wait for things like cs_main, so blocking until func is called with cs_main
+ * will result in a deadlock (that DEBUG_LOCKORDER will miss).
+ */
+void CallFunctionInValidationInterfaceQueue(std::function<void ()> func);
 
 class CValidationInterface {
 protected:
-    /** Notifies listeners of updated block chain tip */
+    /**
+     * Notifies listeners of updated block chain tip
+     *
+     * Called on a background thread.
+     */
     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.
+     *
+     * This only fires for transactions which leave mempool because of expiry,
+     * size limiting, reorg (changes in lock times/coinbase maturity), or
+     * replacement. This does not include any transactions which are included
+     * in BlockConnectedDisconnected either in block->vtx or in txnConflicted.
+     *
+     * Called on a background thread.
+     */
+    virtual void TransactionRemovedFromMempool(const CTransactionRef &ptx) {}
+    /**
      * 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) {}
@@ -73,6 +119,9 @@ private:
     friend void ::RegisterValidationInterface(CValidationInterface*);
     friend void ::UnregisterValidationInterface(CValidationInterface*);
     friend void ::UnregisterAllValidationInterfaces();
+    friend void ::CallFunctionInValidationInterfaceQueue(std::function<void ()> func);
+
+    void MempoolEntryRemoved(CTransactionRef tx, MemPoolRemovalReason reason);
 
 public:
     /** Register a CScheduler to give callbacks which should run in the background (may only be called once) */
@@ -82,9 +131,14 @@ public:
     /** Call any remaining callbacks on the calling thread */
     void FlushBackgroundCallbacks();
 
+    /** Register with mempool to call TransactionRemovedFromMempool callbacks */
+    void RegisterWithMempoolSignals(CTxMemPool& pool);
+    /** Unregister with mempool */
+    void UnregisterWithMempoolSignals(CTxMemPool& pool);
+
     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 &);
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
index 8abb4c9a25..cba0538e7e 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -455,6 +455,11 @@ UniValue sendtoaddress(const JSONRPCRequest& request)
         );
 
     ObserveSafeMode();
+
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     LOCK2(cs_main, pwallet->cs_wallet);
 
     CTxDestination dest = DecodeDestination(request.params[0].get_str());
@@ -533,6 +538,11 @@ UniValue listaddressgroupings(const JSONRPCRequest& request)
         );
 
     ObserveSafeMode();
+
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     LOCK2(cs_main, pwallet->cs_wallet);
 
     UniValue jsonGroupings(UniValue::VARR);
@@ -645,6 +655,11 @@ UniValue getreceivedbyaddress(const JSONRPCRequest& request)
        );
 
     ObserveSafeMode();
+
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     LOCK2(cs_main, pwallet->cs_wallet);
 
     // Bitcoin address
@@ -707,6 +722,11 @@ UniValue getreceivedbyaccount(const JSONRPCRequest& request)
         );
 
     ObserveSafeMode();
+
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     LOCK2(cs_main, pwallet->cs_wallet);
 
     // Minimum confirmations
@@ -780,6 +800,11 @@ UniValue getbalance(const JSONRPCRequest& request)
         );
 
     ObserveSafeMode();
+
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     LOCK2(cs_main, pwallet->cs_wallet);
 
     const UniValue& account_value = request.params[0];
@@ -825,6 +850,11 @@ UniValue getunconfirmedbalance(const JSONRPCRequest &request)
                 "Returns the server's total unconfirmed balance\n");
 
     ObserveSafeMode();
+
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     LOCK2(cs_main, pwallet->cs_wallet);
 
     return ValueFromAmount(pwallet->GetUnconfirmedBalance());
@@ -919,6 +949,11 @@ UniValue sendfrom(const JSONRPCRequest& request)
         );
 
     ObserveSafeMode();
+
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     LOCK2(cs_main, pwallet->cs_wallet);
 
     std::string strAccount = AccountFromValue(request.params[0]);
@@ -1004,6 +1039,11 @@ UniValue sendmany(const JSONRPCRequest& request)
         );
 
     ObserveSafeMode();
+
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     LOCK2(cs_main, pwallet->cs_wallet);
 
     if (pwallet->GetBroadcastTransactions() && !g_connman) {
@@ -1455,6 +1495,11 @@ UniValue listreceivedbyaddress(const JSONRPCRequest& request)
         );
 
     ObserveSafeMode();
+
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     LOCK2(cs_main, pwallet->cs_wallet);
 
     return ListReceived(pwallet, request.params, false);
@@ -1495,6 +1540,11 @@ UniValue listreceivedbyaccount(const JSONRPCRequest& request)
         );
 
     ObserveSafeMode();
+
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     LOCK2(cs_main, pwallet->cs_wallet);
 
     return ListReceived(pwallet, request.params, true);
@@ -1683,6 +1733,11 @@ UniValue listtransactions(const JSONRPCRequest& request)
         );
 
     ObserveSafeMode();
+
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     LOCK2(cs_main, pwallet->cs_wallet);
 
     std::string strAccount = "*";
@@ -1777,6 +1832,11 @@ UniValue listaccounts(const JSONRPCRequest& request)
         );
 
     ObserveSafeMode();
+
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     LOCK2(cs_main, pwallet->cs_wallet);
 
     int nMinDepth = 1;
@@ -1886,6 +1946,11 @@ UniValue listsinceblock(const JSONRPCRequest& request)
         );
 
     ObserveSafeMode();
+
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     LOCK2(cs_main, pwallet->cs_wallet);
 
     const CBlockIndex* pindex = nullptr;    // Block index of the specified block or the common ancestor, if the block provided was in a deactivated chain.
@@ -2019,6 +2084,11 @@ UniValue gettransaction(const JSONRPCRequest& request)
         );
 
     ObserveSafeMode();
+
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     LOCK2(cs_main, pwallet->cs_wallet);
 
     uint256 hash;
@@ -2081,6 +2151,11 @@ UniValue abandontransaction(const JSONRPCRequest& request)
         );
 
     ObserveSafeMode();
+
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     LOCK2(cs_main, pwallet->cs_wallet);
 
     uint256 hash;
@@ -2115,6 +2190,10 @@ UniValue backupwallet(const JSONRPCRequest& request)
             + HelpExampleRpc("backupwallet", "\"backup.dat\"")
         );
 
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     LOCK2(cs_main, pwallet->cs_wallet);
 
     std::string strDest = request.params[0].get_str();
@@ -2434,6 +2513,10 @@ UniValue lockunspent(const JSONRPCRequest& request)
             + HelpExampleRpc("lockunspent", "false, \"[{\\\"txid\\\":\\\"a08e6907dbbd3d809776dbfc5d82e371b764ed838b5655e72f463568df1aadf0\\\",\\\"vout\\\":1}]\"")
         );
 
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     LOCK2(cs_main, pwallet->cs_wallet);
 
     RPCTypeCheckArgument(request.params[0], UniValue::VBOOL);
@@ -2593,6 +2676,11 @@ UniValue getwalletinfo(const JSONRPCRequest& request)
         );
 
     ObserveSafeMode();
+
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     LOCK2(cs_main, pwallet->cs_wallet);
 
     UniValue obj(UniValue::VOBJ);
@@ -2802,9 +2890,12 @@ UniValue listunspent(const JSONRPCRequest& request)
             nMaximumCount = options["maximumCount"].get_int64();
     }
 
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     UniValue results(UniValue::VARR);
     std::vector<COutput> vecOutputs;
-    assert(pwallet != nullptr);
     LOCK2(cs_main, pwallet->cs_wallet);
 
     pwallet->AvailableCoins(vecOutputs, !include_unsafe, nullptr, nMinimumAmount, nMaximumAmount, nMinimumSumAmount, nMaximumCount, nMinDepth, nMaxDepth);
@@ -2912,6 +3003,10 @@ UniValue fundrawtransaction(const JSONRPCRequest& request)
     ObserveSafeMode();
     RPCTypeCheck(request.params, {UniValue::VSTR});
 
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     CCoinControl coinControl;
     int changePosition = -1;
     bool lockUnspents = false;
@@ -3122,6 +3217,10 @@ UniValue bumpfee(const JSONRPCRequest& request)
         }
     }
 
+    // Make sure the results are valid at least up to the most recent block
+    // the user could have gotten from another RPC command prior to now
+    pwallet->BlockUntilSyncedToCurrentChain();
+
     LOCK2(cs_main, pwallet->cs_wallet);
     EnsureWalletIsUnlocked(pwallet);
 
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index dceb818b50..8eb84d397f 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -33,6 +33,7 @@
 #include "wallet/fees.h"
 
 #include <assert.h>
+#include <future>
 
 #include <boost/algorithm/string/replace.hpp>
 #include <boost/thread.hpp>
@@ -1217,6 +1218,19 @@ void CWallet::SyncTransaction(const CTransactionRef& ptx, const CBlockIndex *pin
 void CWallet::TransactionAddedToMempool(const CTransactionRef& ptx) {
     LOCK2(cs_main, cs_wallet);
     SyncTransaction(ptx);
+
+    auto it = mapWallet.find(ptx->GetHash());
+    if (it != mapWallet.end()) {
+        it->second.fInMempool = true;
+    }
+}
+
+void CWallet::TransactionRemovedFromMempool(const CTransactionRef &ptx) {
+    LOCK(cs_wallet);
+    auto it = mapWallet.find(ptx->GetHash());
+    if (it != mapWallet.end()) {
+        it->second.fInMempool = false;
+    }
 }
 
 void CWallet::BlockConnected(const std::shared_ptr<const CBlock>& pblock, const CBlockIndex *pindex, const std::vector<CTransactionRef>& vtxConflicted) {
@@ -1231,10 +1245,14 @@ void CWallet::BlockConnected(const std::shared_ptr<const CBlock>& pblock, const
 
     for (const CTransactionRef& ptx : vtxConflicted) {
         SyncTransaction(ptx);
+        TransactionRemovedFromMempool(ptx);
     }
     for (size_t i = 0; i < pblock->vtx.size(); i++) {
         SyncTransaction(pblock->vtx[i], pindex, i);
+        TransactionRemovedFromMempool(pblock->vtx[i]);
     }
+
+    m_last_block_processed = pindex;
 }
 
 void CWallet::BlockDisconnected(const std::shared_ptr<const CBlock>& pblock) {
@@ -1247,6 +1265,36 @@ void CWallet::BlockDisconnected(const std::shared_ptr<const CBlock>& pblock) {
 
 
 
+void CWallet::BlockUntilSyncedToCurrentChain() {
+    AssertLockNotHeld(cs_main);
+    AssertLockNotHeld(cs_wallet);
+
+    {
+        // Skip the queue-draining stuff if we know we're caught up with
+        // chainActive.Tip()...
+        // We could also take cs_wallet here, and call m_last_block_processed
+        // protected by cs_wallet instead of cs_main, but as long as we need
+        // cs_main here anyway, its easier to just call it cs_main-protected.
+        LOCK(cs_main);
+        const CBlockIndex* initialChainTip = chainActive.Tip();
+
+        if (m_last_block_processed->GetAncestor(initialChainTip->nHeight) == initialChainTip) {
+            return;
+        }
+    }
+
+    // ...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();
+}
+
+
 isminetype CWallet::IsMine(const CTxIn &txin) const
 {
     {
@@ -1871,8 +1919,7 @@ CAmount CWalletTx::GetChange() const
 
 bool CWalletTx::InMempool() const
 {
-    LOCK(mempool.cs);
-    return mempool.exists(GetHash());
+    return fInMempool;
 }
 
 bool CWalletTx::IsTrusted() const
@@ -2980,14 +3027,18 @@ bool CWallet::CommitTransaction(CWalletTx& wtxNew, CReserveKey& reservekey, CCon
         // Track how many getdata requests our transaction gets
         mapRequestCount[wtxNew.GetHash()] = 0;
 
+        // Get the inserted-CWalletTx from mapWallet so that the
+        // fInMempool flag is cached properly
+        CWalletTx& wtx = mapWallet[wtxNew.GetHash()];
+
         if (fBroadcastTransactions)
         {
             // Broadcast
-            if (!wtxNew.AcceptToMemoryPool(maxTxFee, state)) {
+            if (!wtx.AcceptToMemoryPool(maxTxFee, state)) {
                 LogPrintf("CommitTransaction(): Transaction cannot be broadcast immediately, %s\n", state.GetRejectReason());
                 // TODO: if we expect the failure to be long term or permanent, instead delete wtx from the wallet and return failure.
             } else {
-                wtxNew.RelayWalletTransaction(connman);
+                wtx.RelayWalletTransaction(connman);
             }
         }
     }
@@ -3903,8 +3954,6 @@ CWallet* CWallet::CreateWalletFromFile(const std::string walletFile)
 
     LogPrintf(" wallet      %15dms\n", GetTimeMillis() - nStart);
 
-    RegisterValidationInterface(walletInstance);
-
     // Try to top up keypool. No-op if the wallet is locked.
     walletInstance->TopUpKeyPool();
 
@@ -3916,6 +3965,10 @@ CWallet* CWallet::CreateWalletFromFile(const std::string walletFile)
         if (walletdb.ReadBestBlock(locator))
             pindexRescan = FindForkInGlobalIndex(chainActive, locator);
     }
+
+    walletInstance->m_last_block_processed = chainActive.Tip();
+    RegisterValidationInterface(walletInstance);
+
     if (chainActive.Tip() && chainActive.Tip() != pindexRescan)
     {
         //We can't rescan beyond non-pruned blocks, stop and throw an error
@@ -4059,8 +4112,15 @@ int CMerkleTx::GetBlocksToMaturity() const
 }
 
 
-bool CMerkleTx::AcceptToMemoryPool(const CAmount& nAbsurdFee, CValidationState& state)
+bool CWalletTx::AcceptToMemoryPool(const CAmount& nAbsurdFee, CValidationState& state)
 {
-    return ::AcceptToMemoryPool(mempool, state, tx, nullptr /* pfMissingInputs */,
+    // We must set fInMempool here - while it will be re-set to true by the
+    // entered-mempool callback, if we did not there would be a race where a
+    // user could call sendmoney in a loop and hit spurious out of funds errors
+    // because we think that the transaction they just generated's change is
+    // unavailable as we're not yet aware its in mempool.
+    bool ret = ::AcceptToMemoryPool(mempool, state, tx, nullptr /* pfMissingInputs */,
                                 nullptr /* plTxnReplaced */, false /* bypass_limits */, nAbsurdFee);
+    fInMempool = ret;
+    return ret;
 }
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index db2861c043..c372f3ba19 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -248,8 +248,6 @@ public:
     int GetDepthInMainChain() const { const CBlockIndex *pindexRet; return GetDepthInMainChain(pindexRet); }
     bool IsInMainChain() const { const CBlockIndex *pindexRet; return GetDepthInMainChain(pindexRet) > 0; }
     int GetBlocksToMaturity() const;
-    /** Pass this transaction to the mempool. Fails if absolute fee exceeds absurd fee. */
-    bool AcceptToMemoryPool(const CAmount& nAbsurdFee, CValidationState& state);
     bool hashUnset() const { return (hashBlock.IsNull() || hashBlock == ABANDON_HASH); }
     bool isAbandoned() const { return (hashBlock == ABANDON_HASH); }
     void setAbandoned() { hashBlock = ABANDON_HASH; }
@@ -326,6 +324,7 @@ public:
     mutable bool fImmatureWatchCreditCached;
     mutable bool fAvailableWatchCreditCached;
     mutable bool fChangeCached;
+    mutable bool fInMempool;
     mutable CAmount nDebitCached;
     mutable CAmount nCreditCached;
     mutable CAmount nImmatureCreditCached;
@@ -365,6 +364,7 @@ public:
         fImmatureWatchCreditCached = false;
         fAvailableWatchCreditCached = false;
         fChangeCached = false;
+        fInMempool = false;
         nDebitCached = 0;
         nCreditCached = 0;
         nImmatureCreditCached = 0;
@@ -469,6 +469,9 @@ public:
     // RelayWalletTransaction may only be called if fBroadcastTransactions!
     bool RelayWalletTransaction(CConnman* connman);
 
+    /** Pass this transaction to the mempool. Fails if absolute fee exceeds absurd fee. */
+    bool AcceptToMemoryPool(const CAmount& nAbsurdFee, CValidationState& state);
+
     std::set<uint256> GetConflicts() const;
 };
 
@@ -718,6 +721,18 @@ private:
 
     std::unique_ptr<CWalletDBWrapper> dbw;
 
+    /**
+     * The following is used to keep track of how far behind the wallet is
+     * from the chain sync, and to allow clients to block on us being caught up.
+     *
+     * Note that this is *not* how far we've processed, we may need some rescan
+     * to have seen all transactions in the chain, but is only used to track
+     * live BlockConnected callbacks.
+     *
+     * Protected by cs_main (see BlockUntilSyncedToCurrentChain)
+     */
+    const CBlockIndex* m_last_block_processed;
+
 public:
     /*
      * Main wallet lock.
@@ -916,6 +931,7 @@ public:
     bool AddToWalletIfInvolvingMe(const CTransactionRef& tx, const CBlockIndex* pIndex, int posInBlock, bool fUpdate);
     int64_t RescanFromTime(int64_t startTime, bool update);
     CBlockIndex* ScanForWalletTransactions(CBlockIndex* pindexStart, CBlockIndex* pindexStop, bool fUpdate = false);
+    void TransactionRemovedFromMempool(const CTransactionRef &ptx) override;
     void ReacceptWalletTransactions();
     void ResendWalletTransactions(int64_t nBestBlockTime, CConnman* connman) override;
     // ResendWalletTransactionsBefore may only be called if fBroadcastTransactions!
@@ -1102,6 +1118,14 @@ public:
        caller must ensure the current wallet version is correct before calling
        this function). */
     bool SetHDMasterKey(const CPubKey& key);
+
+    /**
+     * Blocks until the wallet state is up-to-date to /at least/ the current
+     * chain at the time this function is entered
+     * Obviously holding cs_main/cs_wallet when going into this call may cause
+     * deadlock
+     */
+    void BlockUntilSyncedToCurrentChain();
 };
 
 /** A key allocated from the key pool. */