X-Git-Url: http://nitlanguage.org

diff --git a/lib/signals.nit b/lib/signals.nit
index 91015da..f9709da 100644
--- a/lib/signals.nit
+++ b/lib/signals.nit
@@ -15,6 +15,48 @@
 # limitations under the License.
 
 # Module to manage standard C signals
+#
+# Common usage imply 5 steps:
+#
+# 1. Implement the `SignalHandler` interface
+# 2. `redef receive_signal_unsafe` to handle `sigsegv`
+# 3. `redef receive_signal` to handle other signals safely
+# 4, Notify what signals to handle with `handle_signal`
+# 5. If using the safe handler method, routinely call `check_signals`
+#
+# Usage example:
+#
+# ~~~~
+# class MyReceiver
+#	super SignalHandler
+#
+#	redef fun receive_signal(signal)
+#	do
+#		print "received safely {signal}"
+#		if signal == sigalarm then print "Alarm!"
+#	end
+#	redef fun receive_signal_unsafe( signal ) do print "received unsafely {signal}"
+# end
+#
+# var r = new MyReceiver
+#
+# # Handle `sigsegv` signal unsafely (the only way for this one)
+# r.handle_signal(sigsegv, false)
+#
+# # Handle `sigint` and `sigalarm` safely
+# r.handle_signal(sigint, true)
+# r.handle_signal(sigalarm, true)
+#
+# # Ask system to receive a `sigalarm` signal in 1 second
+# set_alarm(1)
+#
+# loop
+#	# Check signals and callback `receive_signal`
+#	var hit = check_signals
+#
+#	if hit then break
+# end
+# ~~~~
 module signals
 
 `{
@@ -24,6 +66,21 @@ module signals
 	#include <stdio.h>
 
 	/*
+		This guard prevents errors by the C compiler when the Nit code imports this
+		module but do not use handle_signal. When it is _not_ used, the C type
+		SignalHandler and C function SignalHandler_receive_signal are not generated.
+		Which does not please the C compiler. This guard ensure that we compile this
+		code only if the type SignalHandler has been defined.
+
+		This is a HACK, FIXME by:
+		* Adding the macro to the FFI spec, or
+		* Attach the callbacks to this code block (or the module itself)
+		* Avoid using Nit types and callbacks or use them only in the C implementation
+		  of Nit method.
+	*/
+	#ifdef NIT_TYPE_SignalHandler
+
+	/*
 		Structure to manage each possible signals
 		are used in an array of 32 maximum signals.
 		This array is global to the software.
@@ -49,6 +106,8 @@ module signals
 			}
 		}
 	}
+
+	#endif
 `}
 
 # Receives the callback from system when a given signal arise
@@ -69,8 +128,7 @@ interface SignalHandler
 	#     r.handle_signal(sigint, true) # will call back when "check_signals" is called
 	#     # ...
 	#     check_signals # if a signal was received, it will invoke `r.receive_signal`
-	fun receive_signal(signal: Int) `{
-	`}
+	fun receive_signal(signal: Int) do end
 
 	# Called immediatly on receiving an unsafe signal (should be redefed by subclasses)
 	#
@@ -88,8 +146,7 @@ interface SignalHandler
 	#     
 	#     var r = new MyReceiver
 	#     r.handle_signal(sigsegv, false) # `r.receive_signal_unsafe` will be invoked on sigsegv
-	fun receive_signal_unsafe(signal: Int) `{
-	`}
+	fun receive_signal_unsafe(signal: Int) do end
 
 	# Set the receiver as the handler of the signal
 	#