Remove dependency on marshal and many other async changes

This makes a number of changes:
  * Remove the dependency on marshal by using string.dump and loadstring.
  * Use lua_tolstring rather than having Lua functions pass string lengths to C++.
  * Move lua_api/l_async_events.* to cpp_api/s_async.*, where it belongs.
  * Make AsyncWorkerThread a child of ScriptApiBase, this removes some duplicate functionality.
  * Don't wait for async threads to shut down.  (Is this safe?  Might result in corruption if the thread is writing to a file.)
  * Pop more unused items from the stack
  * Code style fixes
  * Other misc changes

src/script/cpp_api/s_async.h

@@ -0,0 +1,171 @@
+/*
+Minetest
+Copyright (C) 2013 sapier, <sapier AT gmx DOT net>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License along
+with this program; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
+
+#ifndef L_ASYNC_EVENTS_H_
+#define L_ASYNC_EVENTS_H_
+
+#include <vector>
+#include <map>
+
+#include "jthread/jthread.h"
+#include "jthread/jmutex.h"
+#include "jthread/jsemaphore.h"
+#include "debug.h"
+#include "lua.h"
+#include "cpp_api/s_base.h"
+
+// Forward declarations
+class AsyncEngine;
+
+
+// Declarations
+
+// Data required to queue a job
+struct LuaJobInfo {
+	// Function to be called in async environment
+	std::string serializedFunction;
+	// Parameter to be passed to function
+	std::string serializedParams;
+	// Result of function call
+	std::string serializedResult;
+	// JobID used to identify a job and match it to callback
+	unsigned int JobId;
+
+	bool valid;
+};
+
+// Asynchronous working environment
+class AsyncWorkerThread : public JThread, public ScriptApiBase {
+public:
+	/**
+	 * default constructor
+	 * @param pointer to job dispatcher
+	 */
+	AsyncWorkerThread(AsyncEngine* jobDispatcher, unsigned int threadNum);
+
+	virtual ~AsyncWorkerThread();
+
+	void* Thread();
+
+private:
+	AsyncEngine* m_JobDispatcher;
+
+	// Thread number. Used for debug output
+	unsigned int m_threadnum;
+
+};
+
+// Asynchornous thread and job management
+class AsyncEngine {
+	friend class AsyncWorkerThread;
+public:
+	AsyncEngine();
+	~AsyncEngine();
+
+	/**
+	 * Register function to be used within engine
+	 * @param name Function name to be used within Lua environment
+	 * @param func C function to be called
+	 */
+	bool registerFunction(const char* name, lua_CFunction func);
+
+	/**
+	 * Create async engine tasks and lock function registration
+	 * @param numEngines Number of async threads to be started
+	 */
+	void Initialize(unsigned int numEngines);
+
+	/**
+	 * queue/run a async job
+	 * @param func Serialized lua function
+	 * @param params Serialized parameters
+	 * @return jobid The job is queued
+	 */
+	unsigned int doAsyncJob(std::string func, std::string params);
+
+	/**
+	 * Engine step to process finished jobs
+	 *   the engine step is one way to pass events back, PushFinishedJobs another
+	 * @param L The Lua stack
+	 * @param errorhandler Stack index of the Lua error handler
+	 */
+	void Step(lua_State *L, int errorhandler);
+
+	/**
+	 * Push a list of finished jobs onto the stack
+	 * @param L The Lua stack
+	 */
+	void PushFinishedJobs(lua_State *L);
+
+protected:
+	/**
+	 * Get a Job from queue to be processed
+	 *  this function blocks until a job is ready
+	 * @return a job to be processed
+	 */
+	LuaJobInfo getJob();
+
+	/**
+	 * Put a Job result back to result queue
+	 * @param result result of completed job
+	 */
+	void putJobResult(LuaJobInfo result);
+
+	/**
+	 * Initialize environment with current registred functions
+	 *  this function adds all functions registred by registerFunction to the
+	 *  passed lua stack
+	 * @param L Lua stack to initialize
+	 * @param top Stack position
+	 */
+	void PrepareEnvironment(lua_State* L, int top);
+
+private:
+
+	// Stack index of error handler
+	int m_errorhandler;
+
+	// variable locking the engine against further modification
+	bool m_initDone;
+
+	// Internal store for registred functions
+	std::map<std::string, lua_CFunction> m_FunctionList;
+
+	// Internal counter to create job IDs
+	unsigned int m_JobIdCounter;
+
+	// Mutex to protect job queue
+	JMutex m_JobQueueMutex;
+
+	// Job queue
+	std::vector<LuaJobInfo> m_JobQueue;
+
+	// Mutex to protect result queue
+	JMutex m_ResultQueueMutex;
+	// Result queue
+	std::vector<LuaJobInfo> m_ResultQueue;
+
+	// List of current worker threads
+	std::vector<AsyncWorkerThread*> m_WorkerThreads;
+
+	// Counter semaphore for job dispatching
+	JSemaphore m_JobQueueCounter;
+};
+
+#endif // L_ASYNC_EVENTS_H_