kernel: Remove shutdown from kernel library

This decouples the libbitcoinkernel library from the shutdown routines.
As a library, it should not directly rely on code that manages the
termination of processes.

While touching the lines around StartShutdown, it became apparent that
there was no logging indicating the reason for a call to StartShutdown.
Add ShutdownReason enum to the startShutdown notification to communicate
this.

src/Makefile.am

@@ -396,6 +396,7 @@ libbitcoin_node_a_SOURCES = \
   kernel/context.cpp \
   kernel/cs_main.cpp \
   kernel/mempool_persist.cpp \
+  kernel/notifications_interface.cpp \
   mapport.cpp \
   net.cpp \
   net_processing.cpp \
@@ -935,6 +936,7 @@ libbitcoinkernel_la_SOURCES = \
   kernel/context.cpp \
   kernel/cs_main.cpp \
   kernel/mempool_persist.cpp \
+  kernel/notifications_interface.cpp \
   key.cpp \
   logging.cpp \
   node/blockstorage.cpp \
@@ -958,7 +960,6 @@ libbitcoinkernel_la_SOURCES = \
   script/script_error.cpp \
   script/sigcache.cpp \
   script/standard.cpp \
-  shutdown.cpp \
   signet.cpp \
   support/cleanse.cpp \
   support/lockedpool.cpp \

src/bitcoin-chainstate.cpp

@@ -117,6 +117,11 @@ int main(int argc, char* argv[])
             std::cerr << "Error: " << debug_message << std::endl;
             std::cerr << (user_message.empty() ? "A fatal internal error occurred." : user_message.original) << std::endl;
         }
+        void startShutdown(const kernel::ShutdownReason reason) override
+        {
+            m_shutdown_requested = true;
+            std::cout << "Received start shutdown notification: " << ShutdownReasonToString(reason);
+        }
     };
     auto notifications = std::make_unique<KernelNotifications>(shutdown_requested);
 

src/kernel/notifications_interface.cpp

@@ -0,0 +1,24 @@
+// 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 <kernel/notifications_interface.h>
+
+#include <string>
+
+namespace kernel {
+
+std::string ShutdownReasonToString(ShutdownReason reason)
+{
+    switch (reason) {
+    case kernel::ShutdownReason::FailedConnectingBestBlock:
+        return "Failed connecting best block.";
+    case kernel::ShutdownReason::StopAfterBlockImport:
+        return "Stopping after block import.";
+    case kernel::ShutdownReason::StopAtHeight:
+        return "Reached block height specified by stop at height.";
+    } // no default case, so the compiler can warn about missing cases
+    assert(false);
+}
+
+} // namespace kernel

src/kernel/notifications_interface.h

@@ -15,6 +15,14 @@ enum class SynchronizationState;
 
 namespace kernel {
 
+enum class ShutdownReason {
+    StopAtHeight,
+    StopAfterBlockImport,
+    FailedConnectingBestBlock,
+};
+
+std::string ShutdownReasonToString(ShutdownReason reason);
+
 /**
  * A base class defining functions for notifying about certain kernel
  * events.
@@ -34,6 +42,7 @@ class Notifications
     //! from. After this notification is sent, whatever function triggered the
     //! error should also return an error code or raise an exception.
     virtual void fatalError(const std::string& debug_message, const bilingual_str& user_message = {}) {}
+    virtual void startShutdown(const ShutdownReason reason) {}
 };
 } // namespace kernel
 

src/node/blockstorage.cpp

@@ -10,10 +10,10 @@
 #include <flatfile.h>
 #include <hash.h>
 #include <kernel/chainparams.h>
+#include <kernel/notifications_interface.h>
 #include <logging.h>
 #include <pow.h>
 #include <reverse_iterator.h>
-#include <shutdown.h>
 #include <signet.h>
 #include <streams.h>
 #include <undo.h>
@@ -25,6 +25,8 @@
 #include <map>
 #include <unordered_map>
 
+using kernel::ShutdownReason;
+
 namespace node {
 std::atomic_bool fReindex(false);
 std::atomic_bool g_indexes_ready_to_sync{false};
@@ -931,14 +933,14 @@ void ThreadImport(ChainstateManager& chainman, std::vector<fs::path> vImportFile
             BlockValidationState state;
             if (!chainstate->ActivateBestChain(state, nullptr)) {
                 LogPrintf("Failed to connect best block (%s)\n", state.ToString());
-                StartShutdown();
+                chainman.GetNotifications().startShutdown(ShutdownReason::FailedConnectingBestBlock);
                 return;
             }
         }
 
         if (chainman.m_blockman.StopAfterBlockImport()) {
             LogPrintf("Stopping after block import\n");
-            StartShutdown();
+            chainman.GetNotifications().startShutdown(ShutdownReason::StopAfterBlockImport);
             return;
         }
     } // End scope of ImportingNow

src/node/kernel_notifications.cpp

@@ -82,4 +82,12 @@ void KernelNotifications::fatalError(const std::string& debug_message, const bil
     if (m_shutdown_on_fatal_error) StartShutdown();
 }
 
+void KernelNotifications::startShutdown(const kernel::ShutdownReason reason)
+{
+    if (!ShutdownRequested()) {
+        LogPrintf("Starting shutdown: %s\n", ShutdownReasonToString(reason));
+    }
+    StartShutdown();
+}
+
 } // namespace node

src/node/kernel_notifications.h

@@ -28,6 +28,8 @@ class KernelNotifications : public kernel::Notifications
 
     void fatalError(const std::string& debug_message, const bilingual_str& user_message = {}) override;
 
+    void startShutdown(const kernel::ShutdownReason reason) override;
+
     //! Useful for tests, can be set to false to avoid shutdown on fatal error.
     bool m_shutdown_on_fatal_error{true};
 };

src/validation.cpp

@@ -38,7 +38,6 @@
 #include <reverse_iterator.h>
 #include <script/script.h>
 #include <script/sigcache.h>
-#include <shutdown.h>
 #include <signet.h>
 #include <tinyformat.h>
 #include <txdb.h>
@@ -72,6 +71,7 @@ using kernel::CoinStatsHashType;
 using kernel::ComputeUTXOStats;
 using kernel::LoadMempool;
 using kernel::Notifications;
+using kernel::ShutdownReason;
 
 using fsbridge::FopenFn;
 using node::BlockManager;
@@ -3179,7 +3179,7 @@ bool Chainstate::ActivateBestChain(BlockValidationState& state, std::shared_ptr<
         }
         // When we reach this point, we switched to a new tip (stored in pindexNewTip).
 
-        if (nStopAtHeight && pindexNewTip && pindexNewTip->nHeight >= nStopAtHeight) StartShutdown();
+        if (nStopAtHeight && pindexNewTip && pindexNewTip->nHeight >= nStopAtHeight) m_chainman.GetNotifications().startShutdown(ShutdownReason::StopAtHeight);
 
         if (WITH_LOCK(::cs_main, return m_disabled)) {
             // Background chainstate has reached the snapshot base block, so exit.

src/validation.h

@@ -23,7 +23,6 @@
 #include <policy/packages.h>
 #include <policy/policy.h>
 #include <script/script_error.h>
-#include <shutdown.h>
 #include <sync.h>
 #include <txdb.h>
 #include <txmempool.h> // For CTxMemPool::cs