/*  PCSX2 - PS2 Emulator for PCs
 *  Copyright (C) 2002-2014  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 <cstdio>
#include <cassert>             // assert

#include <pthread.h>           // pthread_setcancelstate()

#include <sys/time.h>          // gettimeofday()

#include <mach/mach.h>
#include <mach/task.h>         // semaphore_create() and semaphore_destroy()
#include <mach/semaphore.h>    // semaphore_*()
#include <mach/mach_error.h>   // mach_error_string()
#include <mach/mach_time.h>    // mach_absolute_time()

#include "PrecompiledHeader.h"

#include "Threading.h"
#include "ThreadingInternal.h"

#include "wxBaseTools.h"
#include "wxGuiTools.h"

// --------------------------------------------------------------------------------------
//  Semaphore Implementation for Darwin/OSX
//
//  Sadly, Darwin/OSX needs its own implementation of Semaphores instead of
//  relying on phtreads, because OSX unnamed semaphore (the best kind)
//  support is very poor.
//
//  This implementation makes use of Mach primitives instead. These are also
//  what Grand Central Dispatch (GCD) is based on, as far as I understand:
//  http://newosxbook.com/articles/GCD.html.
//
// --------------------------------------------------------------------------------------

#define MACH_CHECK(mach_retval) \
	do { \
		kern_return_t _kr = (mach_retval); \
		if (_kr != KERN_SUCCESS) { \
			fprintf(stderr, "mach error: %s", mach_error_string(_kr)); \
			assert(_kr == KERN_SUCCESS); \
		} \
	} while (0)

Threading::Semaphore::Semaphore()
{
	// other platforms explicitly make a thread-private (unshared) semaphore
	// here. But it seems Mach doesn't support that.
	MACH_CHECK(semaphore_create(mach_task_self(), (semaphore_t *)&m_sema, SYNC_POLICY_FIFO, 0));
	__atomic_store_n(&m_counter, 0, __ATOMIC_SEQ_CST);
}

Threading::Semaphore::~Semaphore() throw()
{
	MACH_CHECK(semaphore_destroy(mach_task_self(), (semaphore_t) m_sema));
	__atomic_store_n(&m_counter, 0, __ATOMIC_SEQ_CST);
}

void Threading::Semaphore::Reset()
{
	MACH_CHECK(semaphore_destroy(mach_task_self(), (semaphore_t) m_sema));
	MACH_CHECK(semaphore_create(mach_task_self(), (semaphore_t *) &m_sema, SYNC_POLICY_FIFO, 0));
	__atomic_store_n(&m_counter, 0, __ATOMIC_SEQ_CST);
}

void Threading::Semaphore::Post()
{
	MACH_CHECK(semaphore_signal(m_sema));
	__atomic_add_fetch(&m_counter, 1, __ATOMIC_SEQ_CST);
}

void Threading::Semaphore::Post(int multiple)
{
	for (int i = 0; i < multiple; ++i) {
		MACH_CHECK(semaphore_signal(m_sema));
	}
	__atomic_add_fetch(&m_counter, multiple, __ATOMIC_SEQ_CST);
}

void Threading::Semaphore::WaitWithoutYield()
{
	pxAssertMsg(!wxThread::IsMain(), "Unyielding semaphore wait issued from the main/gui thread.  Please use Wait() instead.");
	MACH_CHECK(semaphore_wait(m_sema));
	__atomic_sub_fetch(&m_counter, 1, __ATOMIC_SEQ_CST);
}

bool Threading::Semaphore::WaitWithoutYield(const wxTimeSpan& timeout)
{
	// This method is the reason why there has to be a special Darwin
	// implementation of Semaphore. Note that semaphore_timedwait() is prone
	// to returning with KERN_ABORTED, which basically signifies that some
	// signal has worken it up. The best official "documentation" for
	// semaphore_timedwait() is the way it's used in Grand Central Dispatch,
	// which is open-source.

	// on x86 platforms, mach_absolute_time() returns nanoseconds
	// TODO(aktau): on iOS a scale value from mach_timebase_info will be necessary
	u64 const kOneThousand = 1000;
	u64 const kOneBillion = kOneThousand * kOneThousand * kOneThousand;
	u64 const delta = timeout.GetMilliseconds().GetValue() * (kOneThousand * kOneThousand);
	mach_timespec_t ts;
	kern_return_t kr = KERN_ABORTED;
	for (u64 now = mach_absolute_time(), deadline = now + delta;
		kr == KERN_ABORTED; now = mach_absolute_time()) {
		if (now > deadline) {
			// timed out by definition
			return false;
		}

		u64 timeleft = deadline - now;
		ts.tv_sec = timeleft / kOneBillion;
		ts.tv_nsec = timeleft % kOneBillion;

		// possible return values of semaphore_timedwait() (from XNU sources):
		// internal kernel val -> return value
		// THREAD_INTERRUPTED  -> KERN_ABORTED
		// THREAD_TIMED_OUT    -> KERN_OPERATION_TIMED_OUT
		// THREAD_AWAKENED     -> KERN_SUCCESS
		// THREAD_RESTART      -> KERN_TERMINATED
		// default             -> KERN_FAILURE
		kr = semaphore_timedwait(m_sema, ts);
	}

	if (kr == KERN_OPERATION_TIMED_OUT) {
		return false;
	}

	// while it's entirely possible to have KERN_FAILURE here, we should
	// probably assert so we can study and correct the actual error here
	// (the thread dying while someone is wainting for it).
	MACH_CHECK(kr);

	__atomic_sub_fetch(&m_counter, 1, __ATOMIC_SEQ_CST);
	return true;
}

// 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 windows 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)) {
		WaitWithoutYield();
	}
	else if(_WaitGui_RecursionGuard( L"Semaphore::Wait" )) {
		ScopedBusyCursor hourglass( Cursor_ReallyBusy );
		WaitWithoutYield();
	}
	else {
		while (!WaitWithoutYield(def_yieldgui_interval)) {
			YieldToMain();
		}
	}
#else
	WaitWithoutYield();
#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")) {
		ScopedBusyCursor hourglass(Cursor_ReallyBusy);
		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.
//
// I'm unsure how to do this with pure Mach primitives, the docs in
// osfmk/man seem a bit out of date so perhaps there's a possibility, but
// since as far as I know Mach threads are 1-to-1 on BSD uthreads (and thus
// POSIX threads), this should work. -- aktau
void Threading::Semaphore::WaitNoCancel()
{
	int oldstate;
	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &oldstate);
	Wait();
	pthread_setcancelstate(oldstate, NULL);
}

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

int Threading::Semaphore::Count()
{
	return __atomic_load_n(&m_counter, __ATOMIC_SEQ_CST);
}