BansheeEngine/BansheeCore/Include/BsCoreThread.h

#pragma once

#include "BsCorePrerequisites.h"
#include "BsModule.h"
#include "BsCommandQueue.h"
#include "BsCoreThreadAccessor.h"
#include "BsThreadPool.h"

namespace BansheeEngine
{
	/**
	 * @brief	Manager for the core thread. Takes care of starting, running, queuing commands
	 * 			and shutting down the core thread.
	 * 			
	 * @note	How threading works:
	 * 			 - This class contains a queue which is filled by commands from other threads via queueCommand and queueReturnCommand  
	 * 			 - Commands are executed on the core thread as soon as they are queued (if core thread is not busy with previous commands)  
	 * 			 - Core thread accessors are helpers for queuing commands. They perform better than queuing each command directly using 
	 *			   queueCommand or queueReturnCommand.
	 * 			 - Accessors contain a command queue of their own, and queuing commands in them will not automatically start executing the commands  
	 * 			   like with queueCommand or queueReturnCommand. Instead you must manually call "submitAccessors" when you are ready to send their
	 * 			   commands to the core thread. Sending commands "in bulk" like this is what makes them faster than directly queuing commands.
	 * 			 - Synced accessor is a special type of accessor which may be accessed from any thread. Its commands are always executed after all other  
	 * 			   non-synced accessors. It is primarily useful when multiple threads are managing the same resource and you must ensure proper order of operations.
	 * 			   You should use normal accessors whenever possible as synced accessors involve potentially slow synchronization operations.
	 */
	class BS_CORE_EXPORT CoreThread : public Module<CoreThread>
	{
		/** Contains data about an accessor for a specific thread. */
		struct AccessorContainer
		{
			CoreAccessorPtr accessor;
			bool isMain;
		};

		/** Wrapper for the thread-local variable because MSVC can't deal with a thread-local variable marked with dllimport or dllexport,  
		 *  and we cannot use per-member dllimport/dllexport specifiers because Module's members will then not be exported and its static
		 *  members will not have external linkage. */
		struct AccessorData
		{
			static BS_THREADLOCAL AccessorContainer* current;
		};

public:
	CoreThread();
	~CoreThread();

	/**
	 * @brief	Returns the id of the core thread. 
	 */
	BS_THREAD_ID_TYPE getCoreThreadId() { return mCoreThreadId; }

	/**
	 * @brief	Creates or retrieves an accessor that you can use for executing commands on the core thread from 
	 * 			a non-core thread. The accessor will be bound to the thread you call this method on.
	 * 			
	 * @note		Accessors contain their own command queue and their commands will only start to get executed once that queue is submitted
	 * 			to the core thread via "submitAccessors" method.
	 */
	CoreAccessorPtr getAccessor();

	/**
	 * @brief	Retrieves an accessor that you can use for executing commands on the core thread from
	 * 			a non-core thread. There is only one synchronized accessor and you may access it from any thread you wish.
	 * 			Note however that it is much more efficient to retrieve a separate non-synchronized accessor using
	 * 			"getAccessor" for each thread you will be using it on.
	 * 			
	 * @note		Accessors contain their own command queue and their commands will only start to get executed once that queue is submitted
	 * 			to the core thread via "submitAccessors" method.
	 * 			
	 *			Synced accessor commands are sent after all non-synced accessor commands are sent.
	 */
	SyncedCoreAccessor& getSyncedAccessor();

	/**
	 * @brief	Queues all the accessor commands and starts executing them on the core thread.
	 */
	void submitAccessors(bool blockUntilComplete = false);

	/**
	 * @brief	Queues a new command that will be added to the global command queue. You are allowed to call this from any thread,
	 * 			however be aware that it involves possibly slow synchronization primitives, so limit your usage.
	 * 			
	 * @param	blockUntilComplete If true the thread will be blocked until the command executes. Be aware that there may be many commands queued before it
	 * 							   and they all need to be executed in order before the current command is reached, which might take a long time.
	 * 	
	 * @see		CommandQueue::queueReturn
	 */
	AsyncOp queueReturnCommand(std::function<void(AsyncOp&)> commandCallback, bool blockUntilComplete = false);

	/**
	 * @brief	Queues a new command that will be added to the global command queue.You are allowed to call this from any thread,
	 * 			however be aware that it involves possibly slow synchronization primitives, so limit your usage.
	 * 	
	 * @param	blockUntilComplete If true the thread will be blocked until the command executes. Be aware that there may be many commands queued before it
	 * 							   and they all need to be executed in order before the current command is reached, which might take a long time.
	 * @see		CommandQueue::queue
	 */
	void queueCommand(std::function<void()> commandCallback, bool blockUntilComplete = false);

	/**
	 * @brief	Called once every frame.
	 * 			
	 * @note	Must be called before sim thread schedules any core thread operations for the frame. 
	 */
	void update();

	/**
	 * @brief	Returns a frame allocator that should be used for allocating temporary data being passed to the
	 * 			core thread. As the name implies the data only lasts one frame, so you need to be careful not
	 * 			to use it for longer than that.
	 * 			
	 * @note	Sim thread only.
	 */
	FrameAlloc* getFrameAlloc() const;
private:
	static const int NUM_FRAME_ALLOCS = 2;

	/**
	 * @brief	Double buffered frame allocators. Means sim thread cannot be more than 1 frame ahead of core thread
	 *			(If that changes you should be able to easily add more).
	 */
	FrameAlloc* mFrameAllocs[NUM_FRAME_ALLOCS];
	UINT32 mActiveFrameAlloc;

	static AccessorData mAccessor;
	Vector<AccessorContainer*> mAccessors;

	volatile bool mCoreThreadShutdown;

	HThread mCoreThread;
	BS_THREAD_ID_TYPE mSimThreadId;
	BS_THREAD_ID_TYPE mCoreThreadId;
	BS_MUTEX(mCommandQueueMutex)
	BS_MUTEX(mAccessorMutex)
	BS_THREAD_SYNCHRONISER(mCommandReadyCondition)
	BS_MUTEX(mCommandNotifyMutex)
	BS_THREAD_SYNCHRONISER(mCommandCompleteCondition)
	BS_MUTEX(mThreadStartedMutex)
	BS_THREAD_SYNCHRONISER(mCoreThreadStartedCondition)

	CommandQueue<CommandQueueSync>* mCommandQueue;

	UINT32 mMaxCommandNotifyId; /**< ID that will be assigned to the next command with a notifier callback. */
	Vector<UINT32> mCommandsCompleted; /**< Completed commands that have notifier callbacks set up */

	SyncedCoreAccessor* mSyncedCoreAccessor;

	/**
		* @brief	Starts the core thread worker method. Should only be called once.
		*/
	void initCoreThread();

	/**
		* @brief	Main worker method of the core thread. Called once thread is started.
		*/
	void runCoreThread();

	/**
		* @brief	Shutdowns the core thread. It will complete all ready commands
		* 			before shutdown.
		*/
	void shutdownCoreThread();

	/**
		* @brief	Blocks the calling thread until the command with the specified ID completes.
		* 			Make sure that the specified ID actually exists, otherwise this will block forever.
		*/
	void blockUntilCommandCompleted(UINT32 commandId);

	/**
		* @brief	Callback called by the command list when a specific command finishes executing.
		* 			This is only called on commands that have a special notify on complete flag set.
		*
		* @param	commandId	Identifier for the command.
		*/
	void commandCompletedNotify(UINT32 commandId);
	};

	/**
	 * @brief	Returns the core thread manager used for dealing with the core thread from external threads.
	 * 			
	 * @see		CoreThread
	 */
	BS_CORE_EXPORT CoreThread& gCoreThread();

	/**
	 * @brief	Returns a core thread accessor for the current thread. Accessor is retrieved or created depending
	 * 			if it previously existed. Each thread has its own accessor.
	 * 	
	 * @see		CoreThread
	 */
	BS_CORE_EXPORT CoreThreadAccessor<CommandQueueNoSync>& gCoreAccessor();

	/**
	 * @brief	Returns a synchronized core accessor you may call from any thread for working with the core thread.
	 * 			Only one of these exists.
	 * 			
	 * @see		CoreThread
	 */
	BS_CORE_EXPORT CoreThreadAccessor<CommandQueueSync>& gSyncedCoreAccessor();

	/**
	  * @brief	Throws an exception if current thread isn't the core thread;
	  */
	BS_CORE_EXPORT void throwIfNotCoreThread();

	/**
	  * @brief	Throws an exception if current thread is the core thread;
	  */
	BS_CORE_EXPORT void throwIfCoreThread();

#if BS_DEBUG_MODE
#define THROW_IF_NOT_CORE_THREAD throwIfNotCoreThread();
#define THROW_IF_CORE_THREAD throwIfCoreThread();
#else
#define THROW_IF_NOT_CORE_THREAD 
#define THROW_IF_CORE_THREAD
#endif
}