kernel: Add notification interface

This commit is part of the libbitcoinkernel project and seeks to remove
the ChainstateManager's and, more generally, the kernel library's
dependency on interface_ui with options methods in this and the following
few commits. By removing interface_ui from the kernel library, its
dependency on boost is reduced to just boost::multi_index.

Define a new kernel notification class with virtual methods for
notifying about internal kernel events. Create a new file in the node
library for defining a function creating the default set of notification
methods such that these do not need to be re-defined all over the
codebase. As a first step, add a `blockTip` method, wrapping
`uiInterface.NotifyBlockTip`.

Author: TheCharlatan

src/Makefile.am

@@ -186,6 +186,7 @@ BITCOIN_CORE_H = \
   kernel/mempool_limits.h \
   kernel/mempool_options.h \
   kernel/mempool_persist.h \
+  kernel/notifications_interface.h \
   kernel/validation_cache_sizes.h \
   key.h \
   key_io.h \
@@ -214,6 +215,7 @@ BITCOIN_CORE_H = \
   node/database_args.h \
   node/eviction.h \
   node/interface_ui.h \
+  node/kernel_notifications.h \
   node/mempool_args.h \
   node/mempool_persist_args.h \
   node/miner.h \
@@ -408,6 +410,7 @@ libbitcoin_node_a_SOURCES = \
   node/eviction.cpp \
   node/interface_ui.cpp \
   node/interfaces.cpp \
+  node/kernel_notifications.cpp \
   node/mempool_args.cpp \
   node/mempool_persist_args.cpp \
   node/miner.cpp \

src/bitcoin-chainstate.cpp

@@ -12,6 +12,7 @@
 // It is part of the libbitcoinkernel project.
 
 #include <kernel/chainparams.h>
+#include <kernel/chainstatemanager_opts.h>
 #include <kernel/checks.h>
 #include <kernel/context.h>
 #include <kernel/validation_cache_sizes.h>
@@ -34,6 +35,7 @@
 #include <filesystem>
 #include <functional>
 #include <iosfwd>
+#include <memory>
 
 int main(int argc, char* argv[])
 {
@@ -80,12 +82,22 @@ int main(int argc, char* argv[])
 
     GetMainSignals().RegisterBackgroundSignalScheduler(scheduler);
 
+    class KernelNotifications : public kernel::Notifications
+    {
+    public:
+        void blockTip(SynchronizationState, CBlockIndex&) override
+        {
+            std::cout << "Block tip changed" << std::endl;
+        }
+    };
+    auto notifications = std::make_unique<KernelNotifications>();
 
     // SETUP: Chainstate
     const ChainstateManager::Options chainman_opts{
         .chainparams = *chainparams,
         .datadir = gArgs.GetDataDirNet(),
         .adjusted_time_callback = NodeClock::now,
+        .notifications = *notifications,
     };
     const node::BlockManager::Options blockman_opts{
         .chainparams = chainman_opts.chainparams,

src/init.cpp

@@ -45,6 +45,7 @@
 #include <node/chainstatemanager_args.h>
 #include <node/context.h>
 #include <node/interface_ui.h>
+#include <node/kernel_notifications.h>
 #include <node/mempool_args.h>
 #include <node/mempool_persist_args.h>
 #include <node/miner.h>
@@ -124,6 +125,7 @@ using node::DEFAULT_PERSIST_MEMPOOL;
 using node::DEFAULT_PRINTPRIORITY;
 using node::fReindex;
 using node::g_indexes_ready_to_sync;
+using node::KernelNotifications;
 using node::LoadChainstate;
 using node::MempoolPath;
 using node::NodeContext;
@@ -1019,9 +1021,11 @@ bool AppInitParameterInteraction(const ArgsManager& args, bool use_syscall_sandb
 
     // Also report errors from parsing before daemonization
     {
+        KernelNotifications notifications{};
         ChainstateManager::Options chainman_opts_dummy{
             .chainparams = chainparams,
             .datadir = args.GetDataDirNet(),
+            .notifications = notifications,
         };
         if (const auto error{ApplyArgsManOptions(args, chainman_opts_dummy)}) {
             return InitError(*error);
@@ -1427,12 +1431,14 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
 
     // ********************************************************* Step 7: load block chain
 
+    node.notifications = std::make_unique<KernelNotifications>();
     fReindex = args.GetBoolArg("-reindex", false);
     bool fReindexChainState = args.GetBoolArg("-reindex-chainstate", false);
     ChainstateManager::Options chainman_opts{
         .chainparams = chainparams,
         .datadir = args.GetDataDirNet(),
         .adjusted_time_callback = GetAdjustedTime,
+        .notifications = *node.notifications,
     };
     Assert(!ApplyArgsManOptions(args, chainman_opts)); // no error can happen, already checked in AppInitParameterInteraction
 

src/kernel/chainstatemanager_opts.h

@@ -5,6 +5,8 @@
 #ifndef BITCOIN_KERNEL_CHAINSTATEMANAGER_OPTS_H
 #define BITCOIN_KERNEL_CHAINSTATEMANAGER_OPTS_H
 
+#include <kernel/notifications_interface.h>
+
 #include <arith_uint256.h>
 #include <dbwrapper.h>
 #include <txdb.h>
@@ -42,6 +44,7 @@ struct ChainstateManagerOpts {
     DBOptions block_tree_db{};
     DBOptions coins_db{};
     CoinsViewOptions coins_view{};
+    Notifications& notifications;
 };
 
 } // namespace kernel

src/kernel/notifications_interface.h

@@ -0,0 +1,26 @@
+// Copyright (c) 2023 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_KERNEL_NOTIFICATIONS_INTERFACE_H
+#define BITCOIN_KERNEL_NOTIFICATIONS_INTERFACE_H
+
+class CBlockIndex;
+enum class SynchronizationState;
+
+namespace kernel {
+
+/**
+ * A base class defining functions for notifying about certain kernel
+ * events.
+ */
+class Notifications
+{
+public:
+    virtual ~Notifications(){};
+
+    virtual void blockTip(SynchronizationState state, CBlockIndex& index) {}
+};
+} // namespace kernel
+
+#endif // BITCOIN_KERNEL_NOTIFICATIONS_INTERFACE_H

src/node/context.cpp

@@ -11,6 +11,7 @@
 #include <net.h>
 #include <net_processing.h>
 #include <netgroup.h>
+#include <node/kernel_notifications.h>
 #include <policy/fees.h>
 #include <scheduler.h>
 #include <txmempool.h>

src/node/context.h

@@ -30,6 +30,8 @@ class WalletLoader;
 } // namespace interfaces
 
 namespace node {
+class KernelNotifications;
+
 //! NodeContext struct containing references to chain state and connection
 //! state.
 //!
@@ -62,6 +64,7 @@ struct NodeContext {
     interfaces::WalletLoader* wallet_loader{nullptr};
     std::unique_ptr<CScheduler> scheduler;
     std::function<void()> rpc_interruption_point = [] {};
+    std::unique_ptr<KernelNotifications> notifications;
 
     //! Declare default constructor and destructor that are not inline, so code
     //! instantiating the NodeContext struct doesn't need to #include class

src/node/kernel_notifications.cpp

@@ -0,0 +1,16 @@
+// Copyright (c) 2023 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <node/kernel_notifications.h>
+
+#include <node/interface_ui.h>
+
+namespace node {
+
+void KernelNotifications::blockTip(SynchronizationState state, CBlockIndex& index)
+{
+    uiInterface.NotifyBlockTip(state, &index);
+}
+
+} // namespace node

src/node/kernel_notifications.h

@@ -0,0 +1,21 @@
+// Copyright (c) 2023 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_NODE_KERNEL_NOTIFICATIONS_H
+#define BITCOIN_NODE_KERNEL_NOTIFICATIONS_H
+
+#include <kernel/notifications_interface.h>
+
+class CBlockIndex;
+enum class SynchronizationState;
+
+namespace node {
+class KernelNotifications : public kernel::Notifications
+{
+public:
+    void blockTip(SynchronizationState state, CBlockIndex& index) override;
+};
+} // namespace node
+
+#endif // BITCOIN_NODE_KERNEL_NOTIFICATIONS_H

src/test/util/setup_common.cpp

@@ -23,6 +23,7 @@
 #include <node/blockstorage.h>
 #include <node/chainstate.h>
 #include <node/context.h>
+#include <node/kernel_notifications.h>
 #include <node/mempool_args.h>
 #include <node/miner.h>
 #include <node/validation_cache_args.h>
@@ -64,6 +65,7 @@ using node::ApplyArgsManOptions;
 using node::BlockAssembler;
 using node::BlockManager;
 using node::CalculateCacheSizes;
+using node::KernelNotifications;
 using node::LoadChainstate;
 using node::RegenerateCommitments;
 using node::VerifyLoadedChainstate;
@@ -182,11 +184,14 @@ ChainTestingSetup::ChainTestingSetup(const ChainType chainType, const std::vecto
 
     m_cache_sizes = CalculateCacheSizes(m_args);
 
+    m_node.notifications = std::make_unique<KernelNotifications>();
+
     const ChainstateManager::Options chainman_opts{
         .chainparams = chainparams,
         .datadir = m_args.GetDataDirNet(),
         .adjusted_time_callback = GetAdjustedTime,
         .check_block_index = true,
+        .notifications = *m_node.notifications,
     };
     const BlockManager::Options blockman_opts{
         .chainparams = chainman_opts.chainparams,