From 734d503b78f8983cf7430d707fbdf938dadf6124 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Fri, 28 Aug 2015 00:35:44 +0100
Subject: Add RuntimeContext for easy context switching

---
 libadhocutil/Jamfile.jam               |  2 ++
 libadhocutil/runtimeContext.cpp        | 38 ++++++++++++++++++++++++++++++++++
 libadhocutil/runtimeContext.h          | 28 +++++++++++++++++++++++++
 libadhocutil/unittests/Jamfile.jam     | 19 +++++++++++++++++
 libadhocutil/unittests/testContext.cpp | 34 ++++++++++++++++++++++++++++++
 5 files changed, 121 insertions(+)
 create mode 100644 libadhocutil/runtimeContext.cpp
 create mode 100644 libadhocutil/runtimeContext.h
 create mode 100644 libadhocutil/unittests/Jamfile.jam
 create mode 100644 libadhocutil/unittests/testContext.cpp

diff --git a/libadhocutil/Jamfile.jam b/libadhocutil/Jamfile.jam
index 8169ad0..b689242 100644
--- a/libadhocutil/Jamfile.jam
+++ b/libadhocutil/Jamfile.jam
@@ -26,5 +26,7 @@ lib adhocutil :
 	<include>.
 	;
 
+build-project unittests ;
+
 package.install install : <install-source-root>. : : adhocutil : [ glob *.h ] ;
 
diff --git a/libadhocutil/runtimeContext.cpp b/libadhocutil/runtimeContext.cpp
new file mode 100644
index 0000000..f4e12c2
--- /dev/null
+++ b/libadhocutil/runtimeContext.cpp
@@ -0,0 +1,38 @@
+#include "runtimeContext.h"
+#include <stdexcept>
+
+RuntimeContext::RuntimeContext(size_t stacksize) :
+	swapped(false)
+{
+	stack = malloc(stacksize);
+	if (getcontext(&callback) == -1)
+		throw std::runtime_error("Failed to getcontext");
+	callback.uc_stack.ss_sp = stack;
+	callback.uc_stack.ss_size = stacksize;
+	callback.uc_link = &initial;
+	makecontext(&callback, (void (*)())&RuntimeContext::ccallback, 1, this);
+}
+
+RuntimeContext::~RuntimeContext()
+{
+	free(stack);
+}
+
+void
+RuntimeContext::SwapContext()
+{
+	swapped = !swapped;
+	if (swapped) {
+		swapcontext(&initial, &callback);
+	}
+	else {
+		swapcontext(&callback, &initial);
+	}
+}
+
+void
+RuntimeContext::ccallback(RuntimeContext * rc)
+{
+	rc->Callback();
+}
+
diff --git a/libadhocutil/runtimeContext.h b/libadhocutil/runtimeContext.h
new file mode 100644
index 0000000..6fe26f0
--- /dev/null
+++ b/libadhocutil/runtimeContext.h
@@ -0,0 +1,28 @@
+#ifndef ADHOCUTIL_RUNTIMECONTEXT_H
+#define ADHOCUTIL_RUNTIMECONTEXT_H
+
+#include <stdlib.h>
+#include <ucontext.h>
+#include "visibility.h"
+
+class DLL_PUBLIC RuntimeContext {
+	public:
+		RuntimeContext(size_t stacksize = 16384);
+		virtual ~RuntimeContext();
+
+		void SwapContext();
+
+	protected:
+		DLL_PRIVATE virtual void Callback() = 0;
+
+	private:
+		DLL_PRIVATE static void ccallback(RuntimeContext * rc);
+
+		void * stack;
+		ucontext_t initial;
+		ucontext_t callback;
+		bool swapped;
+};
+
+#endif
+
diff --git a/libadhocutil/unittests/Jamfile.jam b/libadhocutil/unittests/Jamfile.jam
new file mode 100644
index 0000000..65d8fad
--- /dev/null
+++ b/libadhocutil/unittests/Jamfile.jam
@@ -0,0 +1,19 @@
+import testing ;
+
+path-constant me : . ;
+
+lib boost_utf : : <name>boost_unit_test_framework ;
+lib boost_filesystem ;
+lib boost_system ;
+
+run
+	testContext.cpp
+	: : :
+	<define>ROOT=\"$(me)\"
+	<define>BOOST_TEST_DYN_LINK
+	<library>..//adhocutil
+	<library>boost_utf
+	:
+	testContext
+	;
+
diff --git a/libadhocutil/unittests/testContext.cpp b/libadhocutil/unittests/testContext.cpp
new file mode 100644
index 0000000..6a291bf
--- /dev/null
+++ b/libadhocutil/unittests/testContext.cpp
@@ -0,0 +1,34 @@
+#define BOOST_TEST_MODULE Context
+#include <boost/test/unit_test.hpp>
+
+#include "runtimeContext.h"
+
+class testRuntimeContext : RuntimeContext {
+	public:
+		void Run()
+		{
+			log += "a";
+			SwapContext();
+			log += "b";
+			SwapContext();
+			log += "c";
+		}
+
+		void Callback() override
+		{
+			log += "d";
+			SwapContext();
+			log += "e";
+			SwapContext();
+		}
+
+		std::string log;
+};
+
+BOOST_AUTO_TEST_CASE ( basic )
+{
+	testRuntimeContext trc;
+	trc.Run();
+	BOOST_REQUIRE_EQUAL("adbec", trc.log);
+}
+
-- 
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