[PrematureStopping] Add on_next() and on_complete() method to CMachine.

The default behaviour of these method is to set a variable called
m_cancel_computation which can be used to terminate prematurely
algorithms, by pressing CTRL+C.

The algorithm has to be registered into the signal handler
by calling connect_to_signal_handler().

Fixed also a bug inside Signal.cpp.

src/shogun/lib/Signal.cpp

@@ -60,7 +60,8 @@ void CSignal::handler(int signal)
 		    "\n[ShogunSignalHandler] Immediately return to prompt / "
 		    "Prematurely finish "
 		    "computations / Do nothing (I/P/D)? ")
-		char answer = fgetc(stdin);
+		char answer = getchar();
+		getchar();
 		switch (answer)
 		{
 		case 'I':
@@ -73,6 +74,10 @@ void CSignal::handler(int signal)
 			    "[ShogunSignalHandler] Terminating"
 			    " prematurely current algorithm...\n");
 			m_sigurg_observable.connect();
+			m_sigurg_observable =
+			    rxcpp::observable<>::create<int>([](rxcpp::subscriber<int> s) {
+				    s.on_next(1);
+				}).publish();
 			break;
 		default:
 			SG_SPRINT("[ShogunSignalHandler] Continuing...\n")

src/shogun/machine/Machine.cpp

@@ -9,6 +9,9 @@
  * Copyright (C) 1999-2009 Fraunhofer Institute FIRST and Max-Planck-Society
  */
 
+#include <rxcpp/rx.hpp>
+#include <shogun/base/init.h>
+#include <shogun/lib/Signal.h>
 #include <shogun/machine/Machine.h>
 
 using namespace shogun;
@@ -18,6 +21,7 @@ CMachine::CMachine() : CSGObject(), m_max_train_time(0), m_labels(NULL),
 {
 	m_data_locked=false;
 	m_store_model_features=false;
+	m_cancel_computation = false;
 
 	SG_ADD(&m_max_train_time, "max_train_time",
 	       "Maximum training time.", MS_NOT_AVAILABLE);
@@ -269,3 +273,12 @@ CLatentLabels* CMachine::apply_locked_latent(SGVector<index_t> indices)
 			"for %s\n", get_name());
 	return NULL;
 }
+
+void CMachine::connect_to_signal_handler()
+{
+	// Subscribe this algorithm to the signal handler
+	auto subscriber = rxcpp::make_subscriber<int>(
+	    [this](int i) { this->on_next(); }, [this]() { this->on_complete(); });
+	get_global_signal()->get_SIGINT_observable().subscribe(subscriber);
+	get_global_signal()->get_SIGURG_observable().subscribe(subscriber);
+}

src/shogun/machine/Machine.h

@@ -306,6 +306,9 @@ class CMachine : public CSGObject
 			return PT_BINARY;
 		}
 
+		/** connect the machine instance to the signal handler */
+		void connect_to_signal_handler();
+
 		virtual const char* get_name() const { return "Machine"; }
 
 	protected:
@@ -357,6 +360,23 @@ class CMachine : public CSGObject
 		/** returns whether machine require labels for training */
 		virtual bool train_require_labels() const { return true; }
 
+		/** @return whether the algorithm needs to be stopped */
+		bool cancel_computation() const
+		{
+			return m_cancel_computation;
+		}
+
+		/** */
+		virtual void on_next()
+		{
+			m_cancel_computation = true;
+		};
+
+		/** */
+		virtual void on_complete()
+		{
+		}
+
 	protected:
 		/** maximum training time */
 		float64_t m_max_train_time;
@@ -372,6 +392,9 @@ class CMachine : public CSGObject
 
 		/** whether data is locked */
 		bool m_data_locked;
+
+		/** Cancel computation */
+		bool m_cancel_computation;
 };
 }
 #endif // _MACHINE_H__