refactor: Split up NodeContext shutdown_signal and shutdown_request

Instead of having a single NodeContext::shutdown member that is used both to
request shutdowns and check if they have been requested, use separate members
for each. Benefits of this change:

1. Should make code a little clearer and easier to search because it is easier
   to see which parts of code are triggering shutdowns and which parts are just
   checking to see if they were triggered.

2. Makes it possible for init.cpp to specify additional code to run when a
   shutdown is requested, like signalling the m_tip_block_cv condition variable.

Motivation for this change was to remove hacky NodeContext argument and
m_tip_block_cv access from the StopRPC function, so StopRPC can just be
concerned with RPC functionality, not other node functionality.

src/node/abort.cpp

@@ -15,12 +15,12 @@
 
 namespace node {
 
-void AbortNode(util::SignalInterrupt* shutdown, std::atomic<int>& exit_status, const bilingual_str& message, node::Warnings* warnings)
+void AbortNode(const std::function<bool()>& shutdown_request, std::atomic<int>& exit_status, const bilingual_str& message, node::Warnings* warnings)
 {
     if (warnings) warnings->Set(Warning::FATAL_INTERNAL_ERROR, message);
     InitError(_("A fatal internal error occurred, see debug.log for details: ") + message);
     exit_status.store(EXIT_FAILURE);
-    if (shutdown && !(*shutdown)()) {
+    if (shutdown_request && !shutdown_request()) {
         LogError("Failed to send shutdown signal\n");
     };
 }

src/node/abort.h

@@ -6,16 +6,13 @@
 #define BITCOIN_NODE_ABORT_H
 
 #include <atomic>
+#include <functional>
 
 struct bilingual_str;
 
-namespace util {
-class SignalInterrupt;
-} // namespace util
-
 namespace node {
 class Warnings;
-void AbortNode(util::SignalInterrupt* shutdown, std::atomic<int>& exit_status, const bilingual_str& message, node::Warnings* warnings);
+void AbortNode(const std::function<bool()>& shutdown_request, std::atomic<int>& exit_status, const bilingual_str& message, node::Warnings* warnings);
 } // namespace node
 
 #endif // BITCOIN_NODE_ABORT_H

src/node/context.h

@@ -59,8 +59,10 @@ struct NodeContext {
     std::unique_ptr<ECC_Context> ecc_context;
     //! Init interface for initializing current process and connecting to other processes.
     interfaces::Init* init{nullptr};
+    //! Function to request a shutdown.
+    std::function<bool()> shutdown_request;
     //! Interrupt object used to track whether node shutdown was requested.
-    util::SignalInterrupt* shutdown{nullptr};
+    util::SignalInterrupt* shutdown_signal{nullptr};
     std::unique_ptr<AddrMan> addrman;
     std::unique_ptr<CConnman> connman;
     std::unique_ptr<CTxMemPool> mempool;

src/node/interfaces.cpp

@@ -134,13 +134,15 @@ public:
     }
     void startShutdown() override
     {
-        if (!(*Assert(Assert(m_context)->shutdown))()) {
+        NodeContext& ctx{*Assert(m_context)};
+        if (!(Assert(ctx.shutdown_request))()) {
             LogError("Failed to send shutdown signal\n");
         }
+
         // Stop RPC for clean shutdown if any of waitfor* commands is executed.
         if (args().GetBoolArg("-server", false)) {
             InterruptRPC();
-            StopRPC(m_context);
+            StopRPC();
         }
     }
     bool shutdownRequested() override { return ShutdownRequested(*Assert(m_context)); };

src/node/kernel_notifications.cpp

@@ -58,7 +58,7 @@ kernel::InterruptResult KernelNotifications::blockTip(SynchronizationState state
 
     uiInterface.NotifyBlockTip(state, &index);
     if (m_stop_at_height && index.nHeight >= m_stop_at_height) {
-        if (!m_shutdown()) {
+        if (!m_shutdown_request()) {
             LogError("Failed to send shutdown signal after reaching stop height\n");
         }
         return kernel::Interrupted{};
@@ -90,12 +90,12 @@ void KernelNotifications::warningUnset(kernel::Warning id)
 
 void KernelNotifications::flushError(const bilingual_str& message)
 {
-    AbortNode(&m_shutdown, m_exit_status, message, &m_warnings);
+    AbortNode(m_shutdown_request, m_exit_status, message, &m_warnings);
 }
 
 void KernelNotifications::fatalError(const bilingual_str& message)
 {
-    node::AbortNode(m_shutdown_on_fatal_error ? &m_shutdown : nullptr,
+    node::AbortNode(m_shutdown_on_fatal_error ? m_shutdown_request : nullptr,
                     m_exit_status, message, &m_warnings);
 }
 

src/node/kernel_notifications.h

@@ -13,6 +13,7 @@
 
 #include <atomic>
 #include <cstdint>
+#include <functional>
 
 class ArgsManager;
 class CBlockIndex;
@@ -23,10 +24,6 @@ namespace kernel {
 enum class Warning;
 } // namespace kernel
 
-namespace util {
-class SignalInterrupt;
-} // namespace util
-
 namespace node {
 
 class Warnings;
@@ -35,8 +32,8 @@ static constexpr int DEFAULT_STOPATHEIGHT{0};
 class KernelNotifications : public kernel::Notifications
 {
 public:
-    KernelNotifications(util::SignalInterrupt& shutdown, std::atomic<int>& exit_status, node::Warnings& warnings)
-        : m_shutdown(shutdown), m_exit_status{exit_status}, m_warnings{warnings} {}
+    KernelNotifications(const std::function<bool()>& shutdown_request, std::atomic<int>& exit_status, node::Warnings& warnings)
+        : m_shutdown_request(shutdown_request), m_exit_status{exit_status}, m_warnings{warnings} {}
 
     [[nodiscard]] kernel::InterruptResult blockTip(SynchronizationState state, CBlockIndex& index) override EXCLUSIVE_LOCKS_REQUIRED(!m_tip_block_mutex);
 
@@ -63,7 +60,7 @@ public:
     uint256 m_tip_block GUARDED_BY(m_tip_block_mutex);
 
 private:
-    util::SignalInterrupt& m_shutdown;
+    const std::function<bool()>& m_shutdown_request;
     std::atomic<int>& m_exit_status;
     node::Warnings& m_warnings;
 };