Add wait(CtrlCHandler&)

cpp/include/Ice/CtrlCHandler.h

@@ -9,58 +9,47 @@
 
 namespace Ice
 {
-    /**
-     * Invoked when a signal occurs. The callback must not raise exceptions.
-     * On Linux and macOS, the callback is NOT a signal handler and can call
-     * functions that are not async-signal safe.
-     * @param sig The signal number that occurred.
-     */
+    /// The function called by CtrlCHandler when it catches a signal. This function must not throw exceptions. On Linux
+    /// and macOS, this function is NOT a signal handler and can call functions that are not async-signal safe.
+    /// @param sig The signal number that occurred.
+    /// \headerfile Ice/Ice.h
     using CtrlCHandlerCallback = std::function<void(int sig)>;
 
-    /**
-     * Provides a portable way to handle Ctrl-C and Ctrl-C like signals.
-     * On Linux and macOS, the CtrlCHandler handles SIGHUP, SIGINT and SIGTERM.
-     * On Windows, it is essentially a wrapper for SetConsoleCtrlHandler().
-     *
-     * \headerfile Ice/Ice.h
-     */
+    /// Provides a portable way to handle Ctrl-C and Ctrl-C like signals. On Linux and macOS, the CtrlCHandler handles
+    /// SIGHUP, SIGINT and SIGTERM. On Windows, it is essentially a wrapper for SetConsoleCtrlHandler.
+    /// \headerfile Ice/Ice.h
     class ICE_API CtrlCHandler
     {
     public:
-        /**
-         * Registers a callback function that handles Ctrl-C like signals.
-         * On Linux and macOS, this constructor masks the SIGHUP, SIGINT and SIGTERM
-         * signals and then creates a thread that waits for these signals using sigwait.
-         * On Windows, this constructor calls SetConsoleCtrlCHandler to register a handler
-         * routine that calls the supplied callback function.
-         * Only a single CtrlCHandler object can exist in a process at a give time.
-         * @param cb The callback function to invoke when a signal is received.
-         */
+        /// Constructs a CtrlCHandler.
+        /// On Linux and macOS, this constructor masks the SIGHUP, SIGINT and SIGTERM signals and then creates a thread
+        /// that waits for these signals using sigwait. On Windows, this constructor calls SetConsoleCtrlCHandler to
+        /// register a handler routine that calls the supplied callback function.
+        /// Only a single CtrlCHandler object can exist in a process at a give time.
+        /// @param cb The callback function to invoke when a signal is received. The default (nullptr) means do nothing.
         explicit CtrlCHandler(CtrlCHandlerCallback cb = nullptr);
 
-        /**
-         * Unregisters the callback function.
-         * On Linux and macOS, this destructor joins and terminates the thread created
-         * by the constructor but does not "unmask" SIGHUP, SIGINT and SIGTERM. As a result,
-         * these signals are ignored after this destructor completes.
-         * On Windows, this destructor unregisters the SetConsoleCtrlHandler handler
-         * routine, and as a result a Ctrl-C or similar signal will terminate the application
-         * after this destructor completes.
-         */
+        /// Unregisters the callback function.
+        /// On Linux and macOS, this destructor joins and terminates the thread created by the constructor but does not
+        /// "unmask" SIGHUP, SIGINT and SIGTERM. As a result, these signals are ignored after this destructor completes.
+        /// On Windows, this destructor unregisters the SetConsoleCtrlHandler handler routine, and as a result a
+        /// Ctrl-C or similar signal will terminate the application after this destructor completes.
         ~CtrlCHandler();
 
-        /**
-         * Replaces the signal callback.
-         * @param cb The new callback.
-         * @return The old callback, or nil if no callback is currently set.
-         */
+        /// Replaces the signal callback.
+        /// @param cb The new callback.
+        /// @return The old callback, which may be nullptr.
         CtrlCHandlerCallback setCallback(CtrlCHandlerCallback cb);
 
-        /**
-         * Obtains the signal callback.
-         * @return The callback.
-         */
+        /// Obtains the current signal callback.
+        /// @return The callback.
         [[nodiscard]] CtrlCHandlerCallback getCallback() const;
+
+        /// Waits until this handler catches a signal.
+        /// @return The signal number that was caught.
+        /// @remark This function installs a signal callback. It must not be called when a non-null callback is already
+        /// installed.
+        int wait();
     };
 }
 

cpp/src/Ice/CtrlCHandler.cpp

@@ -8,6 +8,7 @@
 #endif
 
 #include <cassert>
+#include <future>
 #include <mutex>
 
 #ifndef _WIN32
@@ -202,3 +203,24 @@ CtrlCHandler::~CtrlCHandler()
 }
 
 #endif
+
+int
+CtrlCHandler::wait()
+{
+    promise<int> promise;
+
+    CtrlCHandlerCallback oldCallback = setCallback(
+        [&promise, this](int sig)
+        {
+            setCallback(nullptr); // ignore further signals
+            promise.set_value(sig);
+        });
+
+    if (oldCallback)
+    {
+        setCallback(oldCallback);
+        throw Ice::LocalException{__FILE__, __LINE__, "do not call wait on a CtrlCHandler with a registered callback"};
+    }
+
+    return promise.get_future().get();
+}