/*	Copyright (C) 1995, 1996 Free Software Foundation, Inc.
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 * 
 * This program 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 this software; see the file COPYING.  If not, write to
 * the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 * As a special exception, the Free Software Foundation gives permission
 * for additional uses of the text contained in its release of GUILE.
 *
 * The exception is that, if you link the GUILE library with other files
 * to produce an executable, this does not by itself cause the
 * resulting executable to be covered by the GNU General Public License.
 * Your use of that executable is in no way restricted on account of
 * linking the GUILE library code into it.
 *
 * This exception does not however invalidate any other reasons why
 * the executable file might be covered by the GNU General Public License.
 *
 * This exception applies only to the code released by the
 * Free Software Foundation under the name GUILE.  If you copy
 * code from other Free Software Foundation releases into a copy of
 * GUILE, as the General Public License permits, the exception does
 * not apply to the code that you add in this way.  To avoid misleading
 * anyone as to the status of such modified files, you must delete
 * this exception notice from them.
 *
 * If you write modifications of your own for GUILE, it is your choice
 * whether to permit this exception to apply to your modifications.
 * If you do not wish that, delete this exception notice.  
 */


#ifndef GSCM_COOP_THREADS_H
#define GSCM_COOP_THREADS_H

#include <qt.h>
#include <time.h>

/* This code is based on a sample thread libraru by David Keppel.
   Portions of this file fall under the following copyright: */

/*
 * QuickThreads -- Threads-building toolkit.
 * Copyright (c) 1993 by David Keppel
 *
 * Permission to use, copy, modify and distribute this software and
 * its documentation for any purpose and without fee is hereby
 * granted, provided that the above copyright notice and this notice
 * appear in all copies.  This software is provided as a
 * proof-of-concept and for demonstration purposes; there is no
 * representation about the suitability of this software for any
 * purpose.
 */

/* The notion of a thread is merged with the notion of a queue.
   Thread stuff: thread status (sp) and stuff to use during
   (re)initialization.  Queue stuff: next thread in the queue
   (next). */

typedef struct coop_t {
  qt_t *sp;              /* QuickThreads handle. */
  void *sto;             /* `malloc'-allocated stack. */

  struct coop_t *next;    /* Next thread in the queue. */

  struct coop_t *all_next;    
  struct coop_t *all_prev;    

  void *data;            /* Thread local data */
  
  void *base;            /* Base of stack */
  void *top;             /* Top of stack */

  void *joining;         /* A queue of threads waiting to join this
			    thread */

  time_t wakeup_time;    /* Time to stop sleeping */

} coop_t;

/* A queue is a circular list of threads.  The queue head is a
   designated list element.  If this is a uniprocessor-only
   implementation we can store the `main' thread in this, but in a
   multiprocessor there are several `heavy' threads but only one run
   queue.  A fancier implementation might have private run queues,
   which would lead to a simpler (trivial) implementation */

typedef struct coop_q_t {
  coop_t t;
  coop_t *tail;
} coop_q_t;

/* A Mutex variable is made up of a owner thread, and a queue of threads
   waiting on the mutex */

typedef struct coop_m {
  coop_t *owner;          /* Mutex owner */
  coop_q_t waiting;      /* Queue of waiting threads */
} coop_m;

/* A Condition variable is made up of a list of threads waiting on the
   condition. */

typedef struct coop_c {
  coop_q_t waiting;      /* Queue of waiting threads */
} coop_c;

/* Each thread starts by calling a user-supplied function of this
   type. */

typedef void (coop_userf_t)(void *p0);

/* Call this before any other primitives. */
extern void coop_init();

/* When one or more threads are created by the main thread,
   the system goes multithread when this is called.  It is done
   (no more runable threads) when this returns. */

extern void coop_start (void);

/* Create a thread and make it runable.  When the thread starts
   running it will call `f' with arguments `p0' and `p1'. */

extern coop_t *coop_create (coop_userf_t *f, void *p0);

/* The current thread stops running but stays runable.
   It is an error to call `coop_yield' before `coop_start'
   is called or after `coop_start' returns. */

extern void coop_yield (void);

/* Like `coop_yield' but the thread is discarded.  Any intermediate
   state is lost.  The thread can also terminate by simply
   returning. */

extern void coop_abort (void);

extern coop_q_t coop_global_allq;  /* A queue of all threads. */
extern coop_t *coop_global_curr;	 /* Currently-executing thread. */



extern size_t scm_switch_counter;
extern size_t scm_thread_count;



/* Cooperative threads don't need to have these defined */

#define SCM_THREAD_CRITICAL_SECTION_START 
#define SCM_THREAD_CRITICAL_SECTION_END 
#define SCM_THREAD_INITIALIZE_STORAGE gscm_threads_init_coop_threads()



#define SCM_NO_CRITICAL_SECTION_OWNER 0
#define SCM_THREAD_SWITCH_COUNT       10



#define SCM_DEFER_INTS \
{ \
  scm_ints_disabled = 1; \
}

#define SCM_ALLOW_INTS \
{ \
  scm_ints_disabled = 0; \
  SCM_CHECK_INTS; \
  scm_switch_counter--; \
  if (scm_switch_counter == 0) \
    { \
      scm_switch_counter = SCM_THREAD_SWITCH_COUNT; \
      if (scm_thread_count > 1) \
        coop_yield(); \
    } \
}

#define SCM_REDEFER_INTS \
{ \
  ++scm_ints_disabled; \
}

#define SCM_REALLOW_INTS \
{ \
  --scm_ints_disabled; \
  if (!scm_ints_disabled) \
    { \
      SCM_CHECK_INTS; \
    } \
  scm_switch_counter--; \
  if (scm_switch_counter == 0) \
    { \
      scm_switch_counter = SCM_THREAD_SWITCH_COUNT; \
      if (scm_thread_count > 1) \
        coop_yield(); \
    } \
}



/* This structure is used when creating new threads. */

struct scm_coop_create_info_type
{
  SCM thunk;
  SCM error;
};

extern struct scm_coop_create_info_type scm_coop_create_info;

#endif