boost asio例子中的coroutine库，有点意思

Cpp/Platform/Thread/Coroutine.h

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+//
+// coroutine.hpp
+// ~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2011 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef THREAD_COROUTINE_H
+#define THREAD_COROUTINE_H
+
+class Coroutine
+{
+public:
+	Coroutine() : value(0)
+	{
+	}
+	bool isChild() const
+	{
+		return value < 0;
+	}
+	bool isParent() const
+	{
+		return !isChild();
+	}
+	bool isComplete() const
+	{
+		return value == -1;
+	}
+private:
+	friend class CoroutineRef;
+	int value;
+};
+
+class CoroutineRef
+{
+private:
+	void operator=(const CoroutineRef&);
+	int& value;
+	bool modified;
+
+public:
+	CoroutineRef(Coroutine& c) : value(c.value), modified(false)
+	{
+	}
+	CoroutineRef(Coroutine* c) : value(c->value), modified(false)
+	{
+	}
+	~CoroutineRef()
+	{
+		if (!modified)
+		{
+			value = -1;
+		}
+	}
+	operator int() const
+	{
+		return value;
+	}
+	int& operator=(int v)
+	{
+		modified = true;
+		return value = v;
+	}
+};
+
+#define CORO_REENTER(c) \
+	switch (CoroutineRef coroValue = c) \
+		case -1: if (coroValue) \
+		{ \
+			goto terminateCoroutine; \
+			terminateCoroutine: \
+			coroValue = -1; \
+			goto bailOutOfCoroutine; \
+			bailOutOfCoroutine: \
+			break; \
+		} \
+		else case 0:
+
+#define CORO_YIELD_IMPL(n) \
+	for (coroValue = (n);;) \
+		if (coroValue == 0) \
+		{ \
+			case (n): ; \
+			break; \
+		} \
+		else \
+			switch (coroValue ? 0 : 1) \
+				for (;;) \
+					case -1: if (coroValue) \
+						goto terminateCoroutine; \
+					else for (;;) \
+						case 1: if (coroValue) \
+							goto bailOutOfCoroutine; \
+						else case 0:
+
+#define CORO_FORK_IMPL(n) \
+	for (coroValue = -(n);; coroValue = (n)) \
+		if (coroValue == (n)) \
+		{ \
+			case -(n): ; \
+			break; \
+		} \
+		else
+
+#if defined(_MSC_VER)
+# define CORO_YIELD CORO_YIELD_IMPL(__COUNTER__ + 1)
+# define CORO_FORK CORO_FORK_IMPL(__COUNTER__ + 1)
+#else // defined(_MSC_VER)
+# define CORO_YIELD CORO_YIELD_IMPL(__LINE__)
+# define CORO_FORK CORO_FORK_IMPL(__LINE__)
+#endif // defined(_MSC_VER)
+#endif // THREAD_COROUTINE_H

Cpp/Platform/Thread/Yield.h

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+//
+// yield.hpp
+// ~~~~~~~~~
+//
+// Copyright (c) 2003-2011 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include "Thread/Coroutine.h"
+
+#ifndef reenter
+# define reenter(c) CORO_REENTER(c)
+#endif
+
+#ifndef yield
+# define yield CORO_YIELD
+#endif
+
+#ifndef fork
+# define fork CORO_FORK
+#endif