util: Add SignalInterrupt class and use in shutdown.cpp

This change helps generalize shutdown code so an interrupt can be
provided to libbitcoinkernel callers. This may also be useful to
eventually de-globalize all of the shutdown code.

Co-authored-by: Russell Yanofsky <russ@yanofsky.org>
Co-authored-by: TheCharlatan <seb.kung@gmail.com>

src/util/signalinterrupt.h

@@ -0,0 +1,52 @@
+// 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_UTIL_SIGNALINTERRUPT_H
+#define BITCOIN_UTIL_SIGNALINTERRUPT_H
+
+#ifdef WIN32
+#include <condition_variable>
+#include <mutex>
+#else
+#include <util/tokenpipe.h>
+#endif
+
+#include <atomic>
+#include <cstdlib>
+
+namespace util {
+/**
+ * Helper class that manages an interrupt flag, and allows a thread or
+ * signal to interrupt another thread.
+ *
+ * This class is safe to be used in a signal handler. If sending an interrupt
+ * from a signal handler is not necessary, the more lightweight \ref
+ * CThreadInterrupt class can be used instead.
+ */
+
+class SignalInterrupt
+{
+public:
+    SignalInterrupt();
+    explicit operator bool() const;
+    void operator()();
+    void reset();
+    void wait();
+
+private:
+    std::atomic<bool> m_flag;
+
+#ifndef WIN32
+    // On UNIX-like operating systems use the self-pipe trick.
+    TokenPipeEnd m_pipe_r;
+    TokenPipeEnd m_pipe_w;
+#else
+    // On windows use a condition variable, since we don't have any signals there
+    std::mutex m_mutex;
+    std::condition_variable m_cv;
+#endif
+};
+} // namespace util
+
+#endif // BITCOIN_UTIL_SIGNALINTERRUPT_H