Merge bitcoin#18452: qt: Fix shutdown when waitfor* cmds are called from RPC console

da73f15 qt: Fix shutdown when waitfor* cmds are called from RPC console (Hennadii Stepanov)

Pull request description:

  On master (7eed413), if the GUI has been started with`-server=1`, `bitcoin-qt` hangs on shutdown during calling any of the `waitfor*` commands in the GUI RPC console.

  This PR suggests minimal changes to fix this bug.

  Fix bitcoin#17495

ACKs for top commit:
  jonasschnelli:
    utACK da73f15

Tree-SHA512: 469f5332945a5f2c57d19336cda5df79b123ccc494aea6d58a85eb1293be52708b2b9c5bb6bc2c402a90b7b4e9e8d7ab8fe84cf201cf7ce612c9290c57e43681

Author: jonasschnelli

src/node/interfaces.cpp

@@ -254,7 +254,15 @@ class NodeImpl : public Node
         StartRestart();
         PrepareShutdown(*m_context);
     }
-    void startShutdown() override { StartShutdown(); }
+    void startShutdown() override
+    {
+        StartShutdown();
+        // Stop RPC for clean shutdown if any of waitfor* commands is executed.
+        if (gArgs.GetBoolArg("-server", false)) {
+            InterruptRPC();
+            StopRPC();
+        }
+    }
     bool shutdownRequested() override { return ShutdownRequested(); }
     void mapPort(bool use_upnp, bool use_natpmp) override { StartMapPort(use_upnp, use_natpmp); }
     bool getProxy(Network net, proxyType& proxy_info) override { return GetProxy(net, proxy_info); }

src/rpc/server.cpp

@@ -18,11 +18,15 @@
 
 #include <algorithm>
 #include <atomic>
+#include <cassert>
 #include <memory> // for unique_ptr
+#include <mutex>
 #include <unordered_map>
 
 static Mutex g_rpc_warmup_mutex;
 static std::atomic<bool> g_rpc_running{false};
+static std::once_flag g_rpc_interrupt_flag;
+static std::once_flag g_rpc_stop_flag;
 static bool fRPCInWarmup GUARDED_BY(g_rpc_warmup_mutex) = true;
 static std::string rpcWarmupStatus GUARDED_BY(g_rpc_warmup_mutex) = "RPC server started";
 /* Timer-creating functions */
@@ -325,17 +329,24 @@ void StartRPC()
 
 void InterruptRPC()
 {
-    LogPrint(BCLog::RPC, "Interrupting RPC\n");
-    // Interrupt e.g. running longpolls
-    g_rpc_running = false;
+    // This function could be called twice if the GUI has been started with -server=1.
+    std::call_once(g_rpc_interrupt_flag, []() {
+        LogPrint(BCLog::RPC, "Interrupting RPC\n");
+        // Interrupt e.g. running longpolls
+        g_rpc_running = false;
+    });
 }
 
 void StopRPC()
 {
-    LogPrint(BCLog::RPC, "Stopping RPC\n");
-    WITH_LOCK(g_deadline_timers_mutex, deadlineTimers.clear());
-    DeleteAuthCookie();
-    g_rpcSignals.Stopped();
+    // This function could be called twice if the GUI has been started with -server=1.
+    assert(!g_rpc_running);
+    std::call_once(g_rpc_stop_flag, []() {
+        LogPrint(BCLog::RPC, "Stopping RPC\n");
+        WITH_LOCK(g_deadline_timers_mutex, deadlineTimers.clear());
+        DeleteAuthCookie();
+        g_rpcSignals.Stopped();
+    });
 }
 
 bool IsRPCRunning()