//
// Cforall Version 1.0.0 Copyright (C) 2016 University of Waterloo
//
// The contents of this file are covered under the licence agreement in the
// file "LICENCE" distributed with Cforall.
//
// coroutine --
//
// Author           : Thierry Delisle
// Created On       : Mon Nov 28 12:27:26 2016
// Last Modified By : Peter A. Buhr
// Last Modified On : Tue Dec  3 22:47:58 2019
// Update Count     : 10
//

#pragma once

#include <assert.h>
#include "invoke.h"

//-----------------------------------------------------------------------------
// Coroutine trait
// Anything that implements this trait can be resumed.
// Anything that is resumed is a coroutine.
trait is_coroutine(dtype T) {
      void main(T & this);
      coroutine_desc * get_coroutine(T & this);
};

#define DECL_COROUTINE(X) static inline coroutine_desc* get_coroutine(X& this) { return &this.__cor; } void main(X& this)

//-----------------------------------------------------------------------------
// Ctors and dtors
// void ?{}( coStack_t & this );
// void ^?{}( coStack_t & this );

void ?{}( coroutine_desc & this, const char * name, void * storage, size_t storageSize );
void ^?{}( coroutine_desc & this );

static inline void ?{}( coroutine_desc & this)                                       { this{ "Anonymous Coroutine", 0p, 0 }; }
static inline void ?{}( coroutine_desc & this, size_t stackSize)                     { this{ "Anonymous Coroutine", 0p, stackSize }; }
static inline void ?{}( coroutine_desc & this, void * storage, size_t storageSize )  { this{ "Anonymous Coroutine", storage, storageSize }; }
static inline void ?{}( coroutine_desc & this, const char * name)                    { this{ name, 0p, 0 }; }
static inline void ?{}( coroutine_desc & this, const char * name, size_t stackSize ) { this{ name, 0p, stackSize }; }

//-----------------------------------------------------------------------------
// Public coroutine API
static inline void suspend(void);

forall(dtype T | is_coroutine(T))
static inline T & resume(T & cor);

forall(dtype T | is_coroutine(T))
void prime(T & cor);

static inline struct coroutine_desc * active_coroutine() { return TL_GET( this_thread )->curr_cor; }

//-----------------------------------------------------------------------------
// PRIVATE exposed because of inline

// Start coroutine routines
extern "C" {
	void CtxInvokeCoroutine(void (*main)(void *), void * this);

	forall(dtype T)
	void CtxStart(void (*main)(T &), struct coroutine_desc * cor, T & this, void (*invoke)(void (*main)(void *), void *));

	extern void _CtxCoroutine_Unwind(struct _Unwind_Exception * storage, struct coroutine_desc *) __attribute__ ((__noreturn__));

	extern void CtxSwitch( struct __stack_context_t * from, struct __stack_context_t * to ) asm ("CtxSwitch");
}

// Private wrappers for context switch and stack creation
// Wrapper for co
static inline void CoroutineCtxSwitch(coroutine_desc* src, coroutine_desc* dst) {
	// set state of current coroutine to inactive
	src->state = src->state == Halted ? Halted : Inactive;

	// set new coroutine that task is executing
	TL_GET( this_thread )->curr_cor = dst;

	// context switch to specified coroutine
	verify( dst->context.SP );
	CtxSwitch( &src->context, &dst->context );
	// when CtxSwitch returns we are back in the src coroutine

	// set state of new coroutine to active
	src->state = Active;

	if( unlikely(src->cancellation != 0p) ) {
		_CtxCoroutine_Unwind(src->cancellation, src);
	}
}

extern void __stack_prepare   ( __stack_info_t * this, size_t size /* ignored if storage already allocated */);

// Suspend implementation inlined for performance
static inline void suspend(void) {
	// optimization : read TLS once and reuse it
	// Safety note: this is preemption safe since if
	// preemption occurs after this line, the pointer
	// will also migrate which means this value will
	// stay in syn with the TLS
	coroutine_desc * src = TL_GET( this_thread )->curr_cor;

	assertf( src->last != 0,
		"Attempt to suspend coroutine \"%.256s\" (%p) that has never been resumed.\n"
		"Possible cause is a suspend executed in a member called by a coroutine user rather than by the coroutine main.",
		src->name, src );
	assertf( src->last->state != Halted,
		"Attempt by coroutine \"%.256s\" (%p) to suspend back to terminated coroutine \"%.256s\" (%p).\n"
		"Possible cause is terminated coroutine's main routine has already returned.",
		src->name, src, src->last->name, src->last );

	CoroutineCtxSwitch( src, src->last );
}

// Resume implementation inlined for performance
forall(dtype T | is_coroutine(T))
static inline T & resume(T & cor) {
	// optimization : read TLS once and reuse it
	// Safety note: this is preemption safe since if
	// preemption occurs after this line, the pointer
	// will also migrate which means this value will
	// stay in syn with the TLS
	coroutine_desc * src = TL_GET( this_thread )->curr_cor;
	coroutine_desc * dst = get_coroutine(cor);

	if( unlikely(dst->context.SP == 0p) ) {
		TL_GET( this_thread )->curr_cor = dst;
		__stack_prepare(&dst->stack, 65000);
		CtxStart(main, dst, cor, CtxInvokeCoroutine);
		TL_GET( this_thread )->curr_cor = src;
	}

	// not resuming self ?
	if ( src != dst ) {
		assertf( dst->state != Halted ,
			"Attempt by coroutine %.256s (%p) to resume terminated coroutine %.256s (%p).\n"
			"Possible cause is terminated coroutine's main routine has already returned.",
			src->name, src, dst->name, dst );

		// set last resumer
		dst->last = src;
		dst->starter = dst->starter ? dst->starter : src;
	}

	// always done for performance testing
	CoroutineCtxSwitch( src, dst );

	return cor;
}

static inline void resume(coroutine_desc * dst) {
	// optimization : read TLS once and reuse it
	// Safety note: this is preemption safe since if
	// preemption occurs after this line, the pointer
	// will also migrate which means this value will
	// stay in syn with the TLS
	coroutine_desc * src = TL_GET( this_thread )->curr_cor;

	// not resuming self ?
	if ( src != dst ) {
		assertf( dst->state != Halted ,
			"Attempt by coroutine %.256s (%p) to resume terminated coroutine %.256s (%p).\n"
			"Possible cause is terminated coroutine's main routine has already returned.",
			src->name, src, dst->name, dst );

		// set last resumer
		dst->last = src;
	}

	// always done for performance testing
	CoroutineCtxSwitch( src, dst );
}

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