/*  PCSX2 - PS2 Emulator for PCs
 *  Copyright (C) 2002-2010  PCSX2 Dev Team
 *
 *  PCSX2 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 Found-
 *  ation, either version 3 of the License, or (at your option) any later version.
 *
 *  PCSX2 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 General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License along with PCSX2.
 *  If not, see <http://www.gnu.org/licenses/>.
 */

#include "PrecompiledHeader.h"

#include "System.h"
#include "SysThreads.h"
#include "CDVD/CDVDaccess.h"

// --------------------------------------------------------------------------------------
//  SysThreadBase *External Thread* Implementations
//    (Called form outside the context of this thread)
// --------------------------------------------------------------------------------------

SysThreadBase::SysThreadBase()
	: m_ExecMode(ExecMode_NoThreadYet)
	, m_ExecModeMutex()
{
}

void SysThreadBase::Start()
{
	_parent::Start();

	Sleep(1);

	pxAssertDev((m_ExecMode == ExecMode_Closing) || (m_ExecMode == ExecMode_Closed),
				"Unexpected thread status during SysThread startup.");

	m_sem_event.NotifyOfWork();
}


void SysThreadBase::OnStart()
{
	if (!pxAssertDev(m_ExecMode == ExecMode_NoThreadYet, "SysSustainableThread:Start(): Invalid execution mode"))
		return;

	m_sem_Resume.Reset();
	m_sem_ChangingExecMode.Reset();

	FrankenMutex(m_ExecModeMutex);
	FrankenMutex(m_RunningLock);

	_parent::OnStart();
}

// Suspends emulation and closes the emulation state at the next PS2 vsync,
// and returns control to the calling thread; or does nothing if the core is already suspended.
//
// Parameters:
//   isNonblocking - if set to true then the function will not block for emulation suspension.
//      Defaults to false if parameter is not specified.  Performing non-blocking suspension
//      is mostly useful for starting certain non-Emu related gui activities (improves gui
//      responsiveness).
//
// Returns:
//   The previous suspension state; true if the thread was running or false if it was
//   suspended.
//
// Exceptions:
//   CancelEvent  - thrown if the thread is already in a Paused or Closing state.  Because
//      actions that pause emulation typically rely on subcomponents remaining loaded/active,
//      Suspension must cancel itself forcefully or risk crashing whatever other action is
//      in progress.
//
void SysThreadBase::Suspend(bool isBlocking)
{
	if (!pxAssertDev(!IsSelf(), "Suspend/Resume are not allowed from this thread."))
		return;
	if (!IsRunning())
		return;

	// shortcut ExecMode check to avoid deadlocking on redundant calls to Suspend issued
	// from Resume or OnResumeReady code.
	if (m_ExecMode == ExecMode_Closed)
		return;

	{
		ScopedLock locker(m_ExecModeMutex);

		switch (m_ExecMode.load())
		{
			// Invalid thread state, nothing to suspend
			case ExecMode_NoThreadYet:
			// Check again -- status could have changed since above.
			case ExecMode_Closed:
				return;

			case ExecMode_Pausing:
			case ExecMode_Paused:
				if (!isBlocking)
					throw Exception::CancelEvent(L"Cannot suspend in non-blocking fashion: Another thread is pausing the VM state.");

				m_ExecMode = ExecMode_Closing;
				m_sem_Resume.Post();
				m_sem_ChangingExecMode.Wait();
				break;

			case ExecMode_Opened:
				m_ExecMode = ExecMode_Closing;
				break;

			case ExecMode_Closing:
				break;
		}

		pxAssertDev(m_ExecMode == ExecMode_Closing, "ExecMode should be nothing other than Closing...");
		m_sem_event.NotifyOfWork();
	}

	if (isBlocking)
		m_RunningLock.Wait();
}

// Returns:
//   The previous suspension state; true if the thread was running or false if it was
//   closed, not running, or paused.
//
void SysThreadBase::Pause(SystemsMask systemsToTearDown, bool debug)
{
	if (IsSelf() || !IsRunning())
		return;

	// shortcut ExecMode check to avoid deadlocking on redundant calls to Suspend issued
	// from Resume or OnResumeReady code.
	if ((m_ExecMode == ExecMode_Closed) || (m_ExecMode == ExecMode_Paused))
		return;

	{
		ScopedLock locker(m_ExecModeMutex);

		// Check again -- status could have changed since above.
		if ((m_ExecMode == ExecMode_Closed) || (m_ExecMode == ExecMode_Paused))
			return;

		m_SystemsToTearDown.store(systemsToTearDown, std::memory_order_relaxed);
		if (m_ExecMode == ExecMode_Opened)
			m_ExecMode = ExecMode_Pausing;

		pxAssertDev(m_ExecMode == ExecMode_Pausing, "ExecMode should be nothing other than Pausing...");

		if (debug)
			OnPauseDebug();
		else
			OnPause();
		m_sem_event.NotifyOfWork();
	}

	m_RunningLock.Wait();
}

void SysThreadBase::PauseSelf()
{
	if (!IsSelf() || !IsRunning())
		return;

	{
		ScopedLock locker(m_ExecModeMutex);

		if (m_ExecMode == ExecMode_Opened)
			m_ExecMode = ExecMode_Pausing;

		OnPause();
		m_sem_event.NotifyOfWork();
	}
}

void SysThreadBase::PauseSelfDebug()
{
	if (!IsSelf() || !IsRunning())
		return;

	{
		ScopedLock locker(m_ExecModeMutex);

		if (m_ExecMode == ExecMode_Opened)
			m_ExecMode = ExecMode_Pausing;

		OnPauseDebug();
		m_sem_event.NotifyOfWork();
	}
}

// Resumes the core execution state, or does nothing is the core is already running.  If
// settings were changed, resets will be performed as needed and emulation state resumed from
// memory savestates.
//
// Note that this is considered a non-blocking action.  Most times the state is safely resumed
// on return, but in the case of re-entrant or nested message handling the function may return
// before the thread has resumed.  If you need explicit behavior tied to the completion of the
// Resume, you'll need to bind callbacks to either OnResumeReady or OnResumeInThread.
//
// Exceptions:
//   ThreadCreationError - Insufficient system resources to create thread.
//
void SysThreadBase::Resume()
{
	if (IsSelf())
		return;
	if (m_ExecMode == ExecMode_Opened)
		return;

	ScopedLock locker(m_ExecModeMutex);

	// Implementation Note:
	// The entire state coming out of a Wait is indeterminate because of user input
	// and pending messages being handled.  So after each call we do some seemingly redundant
	// sanity checks against m_ExecMode/m_Running status, and if something doesn't feel
	// right, we should abort; the user may have canceled the action before it even finished.

	switch (m_ExecMode.load())
	{
		case ExecMode_Opened:
			return;

		case ExecMode_NoThreadYet:
		{
			Start();
			if (!m_running || (m_ExecMode == ExecMode_NoThreadYet))
				throw Exception::ThreadCreationError(this);
			if (m_ExecMode == ExecMode_Opened)
				return;
		}
			[[fallthrough]];

		case ExecMode_Closing:
		case ExecMode_Pausing:
			// we need to make sure and wait for the emuThread to enter a fully suspended
			// state before continuing...

			m_RunningLock.Wait();
			if (!m_running)
				return;
			if ((m_ExecMode != ExecMode_Closed) && (m_ExecMode != ExecMode_Paused))
				return;
			break;

		case ExecMode_Paused:
		case ExecMode_Closed:
			break;
	}

	pxAssertDev((m_ExecMode == ExecMode_Closed) || (m_ExecMode == ExecMode_Paused),
				"SysThreadBase is not in a closed/paused state?  wtf!");

	OnResumeReady();
	m_ExecMode = ExecMode_Opened;
	m_sem_Resume.Post();
}


// --------------------------------------------------------------------------------------
//  SysThreadBase *Worker* Implementations
//    (Called from the context of this thread only)
// --------------------------------------------------------------------------------------

void SysThreadBase::OnStartInThread()
{
	m_RunningLock.Acquire();
	_parent::OnStartInThread();
	m_ExecMode = ExecMode_Closing;
}

void SysThreadBase::OnCleanupInThread()
{
	m_ExecMode = ExecMode_NoThreadYet;
	_parent::OnCleanupInThread();
	m_RunningLock.Release();
}

void SysThreadBase::OnSuspendInThread() {}
void SysThreadBase::OnResumeInThread(SystemsMask systemsToReinstate) {}

// Tests for Pause and Suspend/Close requests.  If the thread is trying to be paused or
// closed, it will enter a wait/holding pattern here in this method until the managing
// thread releases it.  Use the return value to detect if changes to the thread's state
// may have been changed (based on the rule that other threads are not allowed to modify
// this thread's state without pausing or closing it first, to prevent race conditions).
//
// Return value:
//   TRUE if the thread was paused or closed; FALSE if the thread
//   continued execution unimpeded.
bool SysThreadBase::StateCheckInThread()
{
	SystemsMask systemsToTearDown {}; // Used for Pausing/Paused

	switch (m_ExecMode.load())
	{

#ifdef PCSX2_DEVBUILD // optimize out handlers for these cases in release builds.
		case ExecMode_NoThreadYet:
			// threads should never have this state set while the thread is in any way
			// active or alive. (for obvious reasons!!)
			pxFailDev("Invalid execution state detected.");
			return false;
#endif

		case ExecMode_Opened:
			// Other cases don't need TestCancel() because its built into the various
			// threading wait/signal actions.
			TestCancel();
			return false;

		// -------------------------------------
		case ExecMode_Pausing:
		{
			systemsToTearDown = m_SystemsToTearDown.exchange({}, std::memory_order_relaxed);

			OnPauseInThread(systemsToTearDown);
			m_ExecMode = ExecMode_Paused;
			m_RunningLock.Release();
		}
			[[fallthrough]];

		case ExecMode_Paused:
			while (m_ExecMode == ExecMode_Paused)
				m_sem_Resume.WaitWithoutYield();

			m_RunningLock.Acquire();
			if (m_ExecMode != ExecMode_Closing)
			{
				// AppCoreThread deals with Reseting CDVD
				OnResumeInThread(g_CDVDReset ? static_cast<SystemsMask>(systemsToTearDown & ~(System_CDVD)) : systemsToTearDown);
				g_CDVDReset = false;
				break;
			}
			m_sem_ChangingExecMode.Post();

			[[fallthrough]];

		// fallthrough if we're switching to closing state...
		// -------------------------------------
		case ExecMode_Closing:
		{
			OnSuspendInThread();
			m_ExecMode = ExecMode_Closed;
			m_RunningLock.Release();
		}
			[[fallthrough]];

		case ExecMode_Closed:
			while (m_ExecMode == ExecMode_Closed)
				m_sem_Resume.WaitWithoutYield();

			m_RunningLock.Acquire();
			OnResumeInThread(static_cast<SystemsMask>(-1)); // All systems
			g_CDVDReset = false;
			break;

			jNO_DEFAULT;
	}

	return true;
}