/*

  *  CoroX.c

  *  Coroutines for Mac OS X

  *

  *  Created by Jens Alfke on 4/29/08.

  *  Adapted from Steve Dekorte's libCoroutine:

  *  <http://www.dekorte.com/projects/opensource/libCoroutine/>

  *

  *  Copyright 2008 Jens Alfke. All rights reserved.

  *  Copyright (c) 2002, 2003 Steve Dekorte. All rights reserved.

  *  License is at the bottom of this file.

  *

  */

 #define _XOPEN_SOURCE   /* decl of ucontext_t in <sys/_structs.h> is wrong unless this is defined */

 #include "CoroX.h"

 #include <stddef.h>

 #include <assert.h>

 #include <pthread.h>

 #include <ucontext.h>

 // Experimentally, the coroutine bus-errors when its stack space drops below about 10k,

 // implying that the kernel unmaps the very end of it. So allow extra room:

 #define STACK_OVERHEAD (12*1024)

 // Even with that overhead, stack sizes less than this cause an immediate crash:

 const size_t kCoroX_minStackSize = 20*1024;

 struct CoroX

 {        

     size_t stackSize;

     void *stack;

     CoroEntryPoint entryPoint;

     void *userData;

     ucontext_t env;

 };

 CoroX *CoroX_new(CoroEntryPoint entryPoint, void *userData)

 {

     CoroX *self = (CoroX *)calloc(1, sizeof(CoroX));

     self->stackSize = CoroX_getDefaultStackSize();

     self->entryPoint = entryPoint;

     self->userData = userData;

     return self;

 }

 void CoroX_free(CoroX *self)

 {

     if( self ) {

         if (self->stack)

             free(self->stack);

         free(self);

     }

 }

 void*  CoroX_userData(CoroX *self)                            {return self->userData;}

 bool   CoroX_isMain(CoroX *self)                              {return self->entryPoint==NULL;}

 #pragma mark STACK:

 void*  CoroX_stack(CoroX *self)                               {return self->stack;}

 size_t CoroX_stackSize(CoroX *self)                           {return self->stackSize;}

 void   CoroX_setStackSize_(CoroX *self, size_t sizeInBytes)   

 {

     if( sizeInBytes < kCoroX_minStackSize )

         sizeInBytes = kCoroX_minStackSize;

     self->stackSize = sizeInBytes;

 }

 static size_t sDefaultStackSize;

 size_t CoroX_getDefaultStackSize(void)

 {

     if( sDefaultStackSize == 0 ) {

         pthread_attr_t pthreadAttrs;        // Find out default pthread stack size

         int err = pthread_attr_init(&pthreadAttrs);

         if( ! err )

             err = pthread_attr_getstacksize(&pthreadAttrs, &sDefaultStackSize);

         if (err)

             sDefaultStackSize = 512*1024;

     }

     return sDefaultStackSize;

 }

 void CoroX_setDefaultStackSize( size_t size )

 {

     sDefaultStackSize = size;

 }

  __attribute__ ((noinline))

 static uint8_t *CoroX_CurrentStackPointer(void)

 {

     uint8_t a;

     uint8_t *b = &a;

     return b;

 }

 size_t CoroX_bytesLeftOnStack(CoroX *self)

 {

     uint8_t dummy;

     ptrdiff_t p1 = (ptrdiff_t)(&dummy);

     ptrdiff_t p2 = (ptrdiff_t)CoroX_CurrentStackPointer();

     int stackMovesUp = p2 > p1;

     ptrdiff_t start = ((ptrdiff_t)self->stack) ;

     ptrdiff_t end = start + self->stackSize;

     if (stackMovesUp)

         return end - p1 - STACK_OVERHEAD;

     else

         return p1 - start - STACK_OVERHEAD;

 }

 int CoroX_stackSpaceAlmostGone(CoroX *self)

 {

     return CoroX_bytesLeftOnStack(self) < 2048;

 }

 #pragma mark SETUP & SWITCH:

 typedef void (*makecontext_func)(void);

 static void CoroX_setup_(CoroX *self)

 {

     size_t stackSize = self->stackSize + STACK_OVERHEAD;

     self->stack = valloc(stackSize);

     assert(self->stack);

     getcontext(&self->env);

     self->env.uc_stack.ss_sp = self->stack;

     self->env.uc_stack.ss_size = stackSize;

     self->env.uc_stack.ss_flags = 0;

     self->env.uc_link = NULL;

     makecontext(&self->env, (makecontext_func)self->entryPoint, 1, self);

 }

 void CoroX_switchTo_(CoroX *self, CoroX *next)

 {

     if( ! next->stack && next->entryPoint )

         CoroX_setup_(next);

     swapcontext(&self->env, &next->env);

 }

 /*

  (This is a BSD License)

  Copyright (c) 2002, 2003 Steve Dekorte

  Copyright (c) 2008 Jens Alfke

  All rights reserved.

  Redistribution and use in source and binary forms, with or without modification, are

  permitted provided that the following conditions are met:

  • Redistributions of source code must retain the above copyright notice, this list of

  conditions and the following disclaimer.

  • Redistributions in binary form must reproduce the above copyright notice, this list

  of conditions and the following disclaimer in the documentation and/or other materials

  provided with the distribution.

  • Neither the name of the author nor the names of other contributors may be used to

  endorse or promote products derived from this software without specific prior written

  permission.

  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY

  EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF

  MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL

  THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,

  EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF

  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

  HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR

  TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS

  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */