/*  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 "common/Threading.h"
#include "common/ThreadingInternal.h"

// --------------------------------------------------------------------------------------
//  Semaphore Implementations
// --------------------------------------------------------------------------------------


void Threading::WorkSema::WaitForWork()
{
	// State change:
	// SLEEPING, SPINNING: This is the worker thread and it's clearly not asleep or spinning, so these states should be impossible
	// RUNNING_0: Change state to SLEEPING, wake up thread if WAITING_EMPTY
	// RUNNING_N: Change state to RUNNING_0 (and preserve WAITING_EMPTY flag)
	s32 value = m_state.load(std::memory_order_relaxed);
	pxAssert(!IsDead(value));
	while (!m_state.compare_exchange_weak(value, NextStateWaitForWork(value), std::memory_order_acq_rel, std::memory_order_relaxed))
		;
	if (IsReadyForSleep(value))
	{
		if (value & STATE_FLAG_WAITING_EMPTY)
			m_empty_sema.Post();
		m_sema.Wait();
		// Acknowledge any additional work added between wake up request and getting here
		m_state.fetch_and(STATE_FLAG_WAITING_EMPTY, std::memory_order_acquire);
	}
}

void Threading::WorkSema::WaitForWorkWithSpin()
{
	s32 value = m_state.load(std::memory_order_relaxed);
	pxAssert(!IsDead(value));
	while (IsReadyForSleep(value))
	{
		if (m_state.compare_exchange_weak(value, STATE_SPINNING, std::memory_order_release, std::memory_order_relaxed))
		{
			if (value & STATE_FLAG_WAITING_EMPTY)
				m_empty_sema.Post();
			value = STATE_SPINNING;
			break;
		}
	}
	u32 waited = 0;
	while (value < 0)
	{
		if (waited > SPIN_TIME_NS)
		{
			if (!m_state.compare_exchange_weak(value, STATE_SLEEPING, std::memory_order_relaxed))
				continue;
			m_sema.Wait();
			break;
		}
		waited += ShortSpin();
		value = m_state.load(std::memory_order_relaxed);
	}
	// Clear back to STATE_RUNNING_0 (but preserve waiting empty flag)
	m_state.fetch_and(STATE_FLAG_WAITING_EMPTY, std::memory_order_acquire);
}

bool Threading::WorkSema::WaitForEmpty()
{
	s32 value = m_state.load(std::memory_order_acquire);
	while (true)
	{
		if (value < 0)
			return !IsDead(value); // STATE_SLEEPING or STATE_SPINNING, queue is empty!
		// Note: We technically only need memory_order_acquire on *failure* (because that's when we could leave without sleeping), but libstdc++ still asserts on failure < success
		if (m_state.compare_exchange_weak(value, value | STATE_FLAG_WAITING_EMPTY, std::memory_order_acquire))
			break;
	}
	pxAssertDev(!(value & STATE_FLAG_WAITING_EMPTY), "Multiple threads attempted to wait for empty (not currently supported)");
	m_empty_sema.WaitWithYield();
	return !IsDead(m_state.load(std::memory_order_relaxed));
}

bool Threading::WorkSema::WaitForEmptyWithSpin()
{
	s32 value = m_state.load(std::memory_order_acquire);
	u32 waited = 0;
	while (true)
	{
		if (value < 0)
			return !IsDead(value); // STATE_SLEEPING or STATE_SPINNING, queue is empty!
		if (waited > SPIN_TIME_NS && m_state.compare_exchange_weak(value, value | STATE_FLAG_WAITING_EMPTY, std::memory_order_acquire))
			break;
		waited += ShortSpin();
		value = m_state.load(std::memory_order_acquire);
	}
	pxAssertDev(!(value & STATE_FLAG_WAITING_EMPTY), "Multiple threads attempted to wait for empty (not currently supported)");
	m_empty_sema.WaitWithYield();
	return !IsDead(m_state.load(std::memory_order_relaxed));
}

void Threading::WorkSema::Kill()
{
	s32 value = m_state.exchange(std::numeric_limits<s32>::min(), std::memory_order_release);
	if (value & STATE_FLAG_WAITING_EMPTY)
		m_empty_sema.Post();
}

void Threading::WorkSema::Reset()
{
	m_state = STATE_RUNNING_0;
}

#if !defined(__APPLE__) // macOS implementations are in DarwinSemaphore

Threading::KernelSemaphore::KernelSemaphore()
{
#ifdef _WIN32
	m_sema = CreateSemaphore(nullptr, 0, LONG_MAX, nullptr);
#else
	sem_init(&m_sema, false, 0);
#endif
}

Threading::KernelSemaphore::~KernelSemaphore()
{
#ifdef _WIN32
	CloseHandle(m_sema);
#else
	sem_destroy(&m_sema);
#endif
}

void Threading::KernelSemaphore::Post()
{
#ifdef _WIN32
	ReleaseSemaphore(m_sema, 1, nullptr);
#else
	sem_post(&m_sema);
#endif
}

void Threading::KernelSemaphore::Wait()
{
	pxAssertMsg(!wxThread::IsMain(), "Unyielding semaphore wait issued from the main/gui thread.  Use WaitWithYield.");
#ifdef _WIN32
	pthreadCancelableWait(m_sema);
#else
	sem_wait(&m_sema);
#endif
}

void Threading::KernelSemaphore::WaitWithYield()
{
#if wxUSE_GUI
	if (!wxThread::IsMain() || (wxTheApp == NULL))
	{
		Wait();
	}
	else
	{
#ifdef _WIN32
		u64 millis = def_yieldgui_interval.GetMilliseconds().GetValue();
		while (pthreadCancelableTimedWait(m_sema, millis) == ETIMEDOUT)
			YieldToMain();
#else
		while (true)
		{
			wxDateTime megafail(wxDateTime::UNow() + def_yieldgui_interval);
			const timespec fail = {megafail.GetTicks(), megafail.GetMillisecond() * 1000000};
			if (sem_timedwait(&m_sema, &fail) == 0)
				break;
			YieldToMain();
		}
#endif
	}
#else
	Wait();
#endif
}

Threading::Semaphore::Semaphore()
{
	sem_init(&m_sema, false, 0);
}

Threading::Semaphore::~Semaphore()
{
	sem_destroy(&m_sema);
}

void Threading::Semaphore::Reset()
{
	sem_destroy(&m_sema);
	sem_init(&m_sema, false, 0);
}

void Threading::Semaphore::Post()
{
	sem_post(&m_sema);
}

void Threading::Semaphore::Post(int multiple)
{
#if defined(_MSC_VER)
	sem_post_multiple(&m_sema, multiple);
#else
	// Only w32pthreads has the post_multiple, but it's easy enough to fake:
	while (multiple > 0)
	{
		multiple--;
		sem_post(&m_sema);
	}
#endif
}

void Threading::Semaphore::WaitWithoutYield()
{
	pxAssertMsg(!wxThread::IsMain(), "Unyielding semaphore wait issued from the main/gui thread.  Please use Wait() instead.");
	sem_wait(&m_sema);
}

bool Threading::Semaphore::WaitWithoutYield(const wxTimeSpan& timeout)
{
	wxDateTime megafail(wxDateTime::UNow() + timeout);
	const timespec fail = {megafail.GetTicks(), megafail.GetMillisecond() * 1000000};
	return sem_timedwait(&m_sema, &fail) == 0;
}


// This is a wxApp-safe implementation of Wait, which makes sure and executes the App's
// pending messages *if* the Wait is performed on the Main/GUI thread.  This ensures that
// user input continues to be handled and that windoes continue to repaint.  If the Wait is
// called from another thread, no message pumping is performed.
//
void Threading::Semaphore::Wait()
{
#if wxUSE_GUI
	if (!wxThread::IsMain() || (wxTheApp == NULL))
	{
		sem_wait(&m_sema);
	}
	else if (_WaitGui_RecursionGuard(L"Semaphore::Wait"))
	{
		sem_wait(&m_sema);
	}
	else
	{
		//ScopedBusyCursor hourglass( Cursor_KindaBusy );
		while (!WaitWithoutYield(def_yieldgui_interval))
			YieldToMain();
	}
#else
	sem_wait(&m_sema);
#endif
}

// This is a wxApp-safe implementation of WaitWithoutYield, which makes sure and executes the App's
// pending messages *if* the Wait is performed on the Main/GUI thread.  This ensures that
// user input continues to be handled and that windows continue to repaint.  If the Wait is
// called from another thread, no message pumping is performed.
//
// Returns:
//   false if the wait timed out before the semaphore was signaled, or true if the signal was
//   reached prior to timeout.
//
bool Threading::Semaphore::Wait(const wxTimeSpan& timeout)
{
#if wxUSE_GUI
	if (!wxThread::IsMain() || (wxTheApp == NULL))
	{
		return WaitWithoutYield(timeout);
	}
	else if (_WaitGui_RecursionGuard(L"Semaphore::TimedWait"))
	{
		return WaitWithoutYield(timeout);
	}
	else
	{
		//ScopedBusyCursor hourglass( Cursor_KindaBusy );
		wxTimeSpan countdown((timeout));

		do
		{
			if (WaitWithoutYield(def_yieldgui_interval))
				break;
			YieldToMain();
			countdown -= def_yieldgui_interval;
		} while (countdown.GetMilliseconds() > 0);

		return countdown.GetMilliseconds() > 0;
	}
#else
	return WaitWithoutYield(timeout);
#endif
}

// Performs an uncancellable wait on a semaphore; restoring the thread's previous cancel state
// after the wait has completed.  Useful for situations where the semaphore itself is stored on
// the stack and passed to another thread via GUI message or such, avoiding complications where
// the thread might be canceled and the stack value becomes invalid.
//
// Performance note: this function has quite a bit more overhead compared to Semaphore::WaitWithoutYield(), so
// consider manually specifying the thread as uncancellable and using WaitWithoutYield() instead if you need
// to do a lot of no-cancel waits in a tight loop worker thread, for example.
void Threading::Semaphore::WaitNoCancel()
{
	int oldstate;
	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &oldstate);
	//WaitWithoutYield();
	Wait();
	pthread_setcancelstate(oldstate, NULL);
}

void Threading::Semaphore::WaitNoCancel(const wxTimeSpan& timeout)
{
	int oldstate;
	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &oldstate);
	//WaitWithoutYield( timeout );
	Wait(timeout);
	pthread_setcancelstate(oldstate, NULL);
}

bool Threading::Semaphore::TryWait()
{
	return sem_trywait(&m_sema) == 0;
}

int Threading::Semaphore::Count()
{
	int retval;
	sem_getvalue(&m_sema, &retval);
	return retval;
}
#endif