util: Get rid of uncaught exceptions thrown by SignalInterrupt class

Replace exceptions thrown by signal and wait methods with [[nodiscard]] return
values.

This is mostly a refactoring, but there is a slight change of behavior if
AbortShutdown function fails. The original behavior which was unintentionally
changed in #27861 is restored, so it now triggers an assert failure again
instead of throwing an exception. (The AbortShutdown function is only ever
called in the the GUI version of Bitcoin Core when corruption is detected on
loading and the user tries to reindex.)

Problems with using exceptions were pointed out by MarcoFalke in
https://github.com/bitcoin/bitcoin/pull/27861#discussion_r1255496707.

src/shutdown.cpp

@@ -15,9 +15,7 @@
 
 void StartShutdown()
 {
-    try {
-        Assert(kernel::g_context)->interrupt();
-    } catch (const std::system_error&) {
+    if (!Assert(kernel::g_context)->interrupt()) {
         LogPrintf("Sending shutdown token failed\n");
         assert(0);
     }
@@ -25,7 +23,10 @@ void StartShutdown()
 
 void AbortShutdown()
 {
-    Assert(kernel::g_context)->interrupt.reset();
+    if (!Assert(kernel::g_context)->interrupt.reset()) {
+        LogPrintf("Reading shutdown token failed\n");
+        assert(0);
+    }
 }
 
 bool ShutdownRequested()
@@ -35,9 +36,7 @@ bool ShutdownRequested()
 
 void WaitForShutdown()
 {
-    try {
-        Assert(kernel::g_context)->interrupt.wait();
-    } catch (const std::system_error&) {
+    if (!Assert(kernel::g_context)->interrupt.wait()) {
         LogPrintf("Reading shutdown token failed\n");
         assert(0);
     }

src/util/signalinterrupt.cpp

@@ -30,15 +30,16 @@ SignalInterrupt::operator bool() const
     return m_flag;
 }
 
-void SignalInterrupt::reset()
+bool SignalInterrupt::reset()
 {
     // Cancel existing interrupt by waiting for it, this will reset condition flags and remove
     // the token from the pipe.
-    if (*this) wait();
+    if (*this && !wait()) return false;
     m_flag = false;
+    return true;
 }
 
-void SignalInterrupt::operator()()
+bool SignalInterrupt::operator()()
 {
 #ifdef WIN32
     std::unique_lock<std::mutex> lk(m_mutex);
@@ -52,13 +53,14 @@ void SignalInterrupt::operator()()
         // Write an arbitrary byte to the write end of the pipe.
         int res = m_pipe_w.TokenWrite('x');
         if (res != 0) {
-            throw std::ios_base::failure("Could not write interrupt token");
+            return false;
         }
     }
 #endif
+    return true;
 }
 
-void SignalInterrupt::wait()
+bool SignalInterrupt::wait()
 {
 #ifdef WIN32
     std::unique_lock<std::mutex> lk(m_mutex);
@@ -66,9 +68,10 @@ void SignalInterrupt::wait()
 #else
     int res = m_pipe_r.TokenRead();
     if (res != 'x') {
-        throw std::ios_base::failure("Did not read expected interrupt token");
+        return false;
     }
 #endif
+    return true;
 }
 
 } // namespace util

src/util/signalinterrupt.h

@@ -30,9 +30,9 @@ class SignalInterrupt
 public:
     SignalInterrupt();
     explicit operator bool() const;
-    void operator()();
-    void reset();
-    void wait();
+    [[nodiscard]] bool operator()();
+    [[nodiscard]] bool reset();
+    [[nodiscard]] bool wait();
 
 private:
     std::atomic<bool> m_flag;