source: libcfa/src/concurrency/coroutine.hfa

//
// 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 : Thu Feb  2 11:31:42 2023
// Update Count     : 13
//

#pragma once

#include <assert.h>
#include "invoke.h"
#include "../exception.hfa"

//-----------------------------------------------------------------------------
// Exception thrown from resume when a coroutine stack is cancelled.
forall(coroutine_t &)
exception CoroutineCancelled {
        coroutine_t * the_coroutine;
        exception_t * the_exception;
};

forall(T &)
void copy(CoroutineCancelled(T) * dst, CoroutineCancelled(T) * src);

forall(T &)
const char * msg(CoroutineCancelled(T) *);

//-----------------------------------------------------------------------------
// Coroutine trait
// Anything that implements this trait can be resumed.
// Anything that is resumed is a coroutine.
forall( T & | IS_RESUMPTION_EXCEPTION(CoroutineCancelled(T)) )
trait is_coroutine {
        void main(T & this);
        coroutine$ * get_coroutine(T & this);
};

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

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

void  ?{}( coroutine$ & this, const char name[], void * storage, size_t storageSize );
void ^?{}( coroutine$ & this );

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

//-----------------------------------------------------------------------------
// Public coroutine API
forall(T & | is_coroutine(T) | { EHM_DEFAULT_VTABLE(CoroutineCancelled(T)); })
void prime(T & cor);

static inline struct coroutine$ * active_coroutine() { return active_thread()->curr_cor; }

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

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

        forall(T &)
        void __cfactx_start(void (*main)(T &), struct coroutine$ * cor, T & this, void (*invoke)(void (*main)(void *), void *));

        extern void __cfactx_coroutine_unwind(struct _Unwind_Exception * storage, struct coroutine$ *) __attribute__ ((__noreturn__));

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

// Private wrappers for context switch and stack creation
// Wrapper for co
static inline void $ctx_switch( coroutine$ * src, coroutine$ * dst ) __attribute__((nonnull (1, 2))) {
        // set state of current coroutine to inactive
        src->state = src->state == Halted ? Halted : Blocked;

        // get the active thread once
        thread$ * athrd = active_thread();

        // Mark the coroutine
        /* paranoid */ verify( !athrd->corctx_flag );
        athrd->corctx_flag = true;

        // set new coroutine that task is executing
        athrd->curr_cor = dst;

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

        /* paranoid */ verify( athrd->corctx_flag );
        athrd->corctx_flag = false;

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

        if( unlikely(src->cancellation != 0p) ) {
                __cfactx_coroutine_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
extern "C" {
        static inline void __cfactx_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$ * src = active_coroutine();

                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 );

                $ctx_switch( src, src->last );
        }
}

forall(T & | is_coroutine(T))
void __cfaehm_cancelled_coroutine(
        T & cor, coroutine$ * desc, EHM_DEFAULT_VTABLE(CoroutineCancelled(T)) );

// Resume implementation inlined for performance
forall(T & | is_coroutine(T) | { EHM_DEFAULT_VTABLE(CoroutineCancelled(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$ * src = active_coroutine();
        coroutine$ * dst = get_coroutine(cor);

        if( unlikely(dst->context.SP == 0p) ) {
                __stack_prepare(&dst->stack, DEFAULT_STACK_SIZE);
                __cfactx_start(main, dst, cor, __cfactx_invoke_coroutine);
        }

        // 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
        $ctx_switch( src, dst );
        if ( unlikely(dst->cancellation) ) {
                __cfaehm_cancelled_coroutine( cor, dst, _default_vtable );
        }

        return cor;
}

static inline void resume( coroutine$ * dst ) __attribute__((nonnull (1))) {
        // 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$ * src = active_coroutine();

        // 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
        $ctx_switch( src, dst );
}

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