/*************************************************************************
 *
 *  (c) 1996 California Institute of Technology
 *  Department of Computer Science
 *  Pasadena, CA 91125.
 *  All Rights Reserved
 *
 *  $Id$
 *
 *************************************************************************/
#ifndef __CONTEXTS_H__
#define __CONTEXTS_H__

#include <stdlib.h>
#include <setjmp.h>

#define DEFAULT_STACK_SIZE 0x5000

#ifdef __cplusplus
extern "C" {
#endif


/*
 * A process record. The first field of a process record must be
 * a context.
 *
 * The user must provide:
 *
 *       struct process_record {
 *             context_t c; 
 *             ...
 *       };
 *
 */
typedef struct process_record process_t;


/*
 * A context consists of the state of the process, which is the
 * value of all registers (including pc) and the execution stack.
 *
 * For implementation purposes, we need the start address of the process
 * so that we can handle termination/invocation in a clean manner.
 *
 */
typedef struct {
  jmp_buf buf;
  char *stack;
  void (*start) ();
} context_t;


/*
 * At any given instant, "current_process" points to the process record
 * for the currently executing thread of control.
 */
extern process_t *current_process;


/*
 * Under the timed scheduling option, the following user-defined routine
 * will be called when the time slice for a particular process is over.
 *
 * This routine is called with interrupts disabled, and should enable
 * interrupts on exit (usually by performing a context switch)
 */
extern void context_timeout (void);


/*
 * The following routine returns the next process to be executed.
 * The user must provide this routine.
 */
extern process_t *context_select (void);


/*
 * Disable/enable timer interrupts.
 */
extern void context_disable (void);
extern void context_enable (void);


/*
 * Perform a context switch. This routine must be called with interrupts
 * disabled. It re-enables interrupts.
 */
extern void context_switch (process_t *);


/*
 * Initialize the context field of the process record.
 */
extern void context_init (process_t *, void (*f)(), int);


/*
 * Unfair scheduling
 */
extern void context_unfair (void);


/*
 * User must provide a function that deletes the process record.
 */
extern void context_destroy (process_t *);

#ifdef __cplusplus
}
#endif

#endif /* __CONTEXTS_H__ */