Replace RPCNotifyBlockChange with waitTipChanged()

This refactoring commit uses the newly introduced waitTipChanged mining interface method to replace the RPCNotifyBlockChange mechanism.

src/init.cpp

@@ -429,16 +429,12 @@ static void registerSignalHandler(int signal, void(*handler)(int))
 }
 #endif
 
-static boost::signals2::connection rpc_notify_block_change_connection;
 static void OnRPCStarted()
 {
-    rpc_notify_block_change_connection = uiInterface.NotifyBlockTip_connect(std::bind(RPCNotifyBlockChange, std::placeholders::_2));
 }
 
 static void OnRPCStopped()
 {
-    rpc_notify_block_change_connection.disconnect();
-    RPCNotifyBlockChange(nullptr);
     g_best_block_cv.notify_all();
     LogDebug(BCLog::RPC, "RPC stopped.\n");
 }
@@ -2011,11 +2007,6 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     // cannot yet be called. Before we make it callable, we need to make sure
     // that the RPC's view of the best block is valid and consistent with
     // ChainstateManager's active tip.
-    //
-    // If we do not do this, RPC's view of the best block will be height=0 and
-    // hash=0x0. This will lead to erroroneous responses for things like
-    // waitforblockheight.
-    RPCNotifyBlockChange(WITH_LOCK(chainman.GetMutex(), return chainman.ActiveTip()));
     SetRPCWarmupFinished();
 
     uiInterface.InitMessage(_("Done loading").translated);

src/rpc/blockchain.cpp

@@ -22,6 +22,7 @@
 #include <hash.h>
 #include <index/blockfilterindex.h>
 #include <index/coinstatsindex.h>
+#include <interfaces/mining.h>
 #include <kernel/coinstats.h>
 #include <logging/timer.h>
 #include <net.h>
@@ -61,21 +62,12 @@
 using kernel::CCoinsStats;
 using kernel::CoinStatsHashType;
 
+using interfaces::Mining;
 using node::BlockManager;
 using node::NodeContext;
 using node::SnapshotMetadata;
 using util::MakeUnorderedList;
 
-struct CUpdatedBlock
-{
-    uint256 hash;
-    int height;
-};
-
-static GlobalMutex cs_blockchange;
-static std::condition_variable cond_blockchange;
-static CUpdatedBlock latestblock GUARDED_BY(cs_blockchange);
-
 std::tuple<std::unique_ptr<CCoinsViewCursor>, CCoinsStats, const CBlockIndex*>
 PrepareUTXOSnapshot(
     Chainstate& chainstate,
@@ -262,16 +254,6 @@ static RPCHelpMan getbestblockhash()
     };
 }
 
-void RPCNotifyBlockChange(const CBlockIndex* pindex)
-{
-    if(pindex) {
-        LOCK(cs_blockchange);
-        latestblock.hash = pindex->GetBlockHash();
-        latestblock.height = pindex->nHeight;
-    }
-    cond_blockchange.notify_all();
-}
-
 static RPCHelpMan waitfornewblock()
 {
     return RPCHelpMan{"waitfornewblock",
@@ -298,16 +280,14 @@ static RPCHelpMan waitfornewblock()
         timeout = request.params[0].getInt<int>();
     if (timeout < 0) throw JSONRPCError(RPC_MISC_ERROR, "Negative timeout");
 
-    CUpdatedBlock block;
+    NodeContext& node = EnsureAnyNodeContext(request.context);
-    {
+    Mining& miner = EnsureMining(node);
-        WAIT_LOCK(cs_blockchange, lock);
+
-        block = latestblock;
+    auto block{CHECK_NONFATAL(miner.getTip()).value()};
-        if(timeout)
+    if (IsRPCRunning()) {
-            cond_blockchange.wait_for(lock, std::chrono::milliseconds(timeout), [&block]() EXCLUSIVE_LOCKS_REQUIRED(cs_blockchange) {return latestblock.height != block.height || latestblock.hash != block.hash || !IsRPCRunning(); });
+        block = timeout ? miner.waitTipChanged(block.hash, std::chrono::milliseconds(timeout)) : miner.waitTipChanged(block.hash);
-        else
-            cond_blockchange.wait(lock, [&block]() EXCLUSIVE_LOCKS_REQUIRED(cs_blockchange) {return latestblock.height != block.height || latestblock.hash != block.hash || !IsRPCRunning(); });
-        block = latestblock;
     }
+
     UniValue ret(UniValue::VOBJ);
     ret.pushKV("hash", block.hash.GetHex());
     ret.pushKV("height", block.height);
@@ -346,14 +326,20 @@ static RPCHelpMan waitforblock()
         timeout = request.params[1].getInt<int>();
     if (timeout < 0) throw JSONRPCError(RPC_MISC_ERROR, "Negative timeout");
 
-    CUpdatedBlock block;
+    NodeContext& node = EnsureAnyNodeContext(request.context);
-    {
+    Mining& miner = EnsureMining(node);
-        WAIT_LOCK(cs_blockchange, lock);
+
-        if(timeout)
+    auto block{CHECK_NONFATAL(miner.getTip()).value()};
-            cond_blockchange.wait_for(lock, std::chrono::milliseconds(timeout), [&hash]() EXCLUSIVE_LOCKS_REQUIRED(cs_blockchange) {return latestblock.hash == hash || !IsRPCRunning();});
+    const auto deadline{std::chrono::steady_clock::now() + 1ms * timeout};
-        else
+    while (IsRPCRunning() && block.hash != hash) {
-            cond_blockchange.wait(lock, [&hash]() EXCLUSIVE_LOCKS_REQUIRED(cs_blockchange) {return latestblock.hash == hash || !IsRPCRunning(); });
+        if (timeout) {
-        block = latestblock;
+            auto now{std::chrono::steady_clock::now()};
+            if (now >= deadline) break;
+            const MillisecondsDouble remaining{deadline - now};
+            block = miner.waitTipChanged(block.hash, remaining);
+        } else {
+            block = miner.waitTipChanged(block.hash);
+        }
     }
 
     UniValue ret(UniValue::VOBJ);
@@ -395,15 +381,23 @@ static RPCHelpMan waitforblockheight()
         timeout = request.params[1].getInt<int>();
     if (timeout < 0) throw JSONRPCError(RPC_MISC_ERROR, "Negative timeout");
 
-    CUpdatedBlock block;
+    NodeContext& node = EnsureAnyNodeContext(request.context);
-    {
+    Mining& miner = EnsureMining(node);
-        WAIT_LOCK(cs_blockchange, lock);
+
-        if(timeout)
+    auto block{CHECK_NONFATAL(miner.getTip()).value()};
-            cond_blockchange.wait_for(lock, std::chrono::milliseconds(timeout), [&height]() EXCLUSIVE_LOCKS_REQUIRED(cs_blockchange) {return latestblock.height >= height || !IsRPCRunning();});
+    const auto deadline{std::chrono::steady_clock::now() + 1ms * timeout};
-        else
+
-            cond_blockchange.wait(lock, [&height]() EXCLUSIVE_LOCKS_REQUIRED(cs_blockchange) {return latestblock.height >= height || !IsRPCRunning(); });
+    while (IsRPCRunning() && block.height < height) {
-        block = latestblock;
+        if (timeout) {
+            auto now{std::chrono::steady_clock::now()};
+            if (now >= deadline) break;
+            const MillisecondsDouble remaining{deadline - now};
+            block = miner.waitTipChanged(block.hash, remaining);
+        } else {
+            block = miner.waitTipChanged(block.hash);
+        }
     }
+
     UniValue ret(UniValue::VOBJ);
     ret.pushKV("hash", block.hash.GetHex());
     ret.pushKV("height", block.height);

src/rpc/blockchain.h

@@ -35,9 +35,6 @@ static constexpr int NUM_GETBLOCKSTATS_PERCENTILES = 5;
  */
 double GetDifficulty(const CBlockIndex& blockindex);
 
-/** Callback for when block tip changed. */
-void RPCNotifyBlockChange(const CBlockIndex*);
-
 /** Block description to JSON */
 UniValue blockToJSON(node::BlockManager& blockman, const CBlock& block, const CBlockIndex& tip, const CBlockIndex& blockindex, TxVerbosity verbosity) LOCKS_EXCLUDED(cs_main);