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/*
 *  Thread Handler
 *
 *
 *  COPYRIGHT (c) 1989-1999.
 *  On-Line Applications Research Corporation (OAR).
 *
 *  The license and distribution terms for this file may be
 *  found in found in the file LICENSE in this distribution or at
 *  http://www.OARcorp.com/rtems/license.html.
 *
 *  threadyieldprocessor.c,v 1.2 1999/11/17 17:50:42 joel Exp
 */
 
#include <rtems/system.h>
#include <rtems/score/apiext.h>
#include <rtems/score/context.h>
#include <rtems/score/interr.h>
#include <rtems/score/isr.h>
#include <rtems/score/object.h>
#include <rtems/score/priority.h>
#include <rtems/score/states.h>
#include <rtems/score/sysstate.h>
#include <rtems/score/thread.h>
#include <rtems/score/threadq.h>
#include <rtems/score/userext.h>
#include <rtems/score/wkspace.h>
 
/*PAGE
 *
 *  _Thread_Yield_processor
 *
 *  This kernel routine will remove the running THREAD from the ready chain
 *  and place it immediatly at the rear of this chain.  Reset timeslice
 *  and yield the processor functions both use this routine, therefore if
 *  reset is TRUE and this is the only thread on the chain then the
 *  timeslice counter is reset.  The heir THREAD will be updated if the
 *  running is also the currently the heir.
 *
 *  Input parameters:   NONE
 *
 *  Output parameters:  NONE
 *
 *  INTERRUPT LATENCY:
 *    ready chain
 *    select heir
 */
 
void _Thread_Yield_processor( void )
{
  ISR_Level       level;
  Thread_Control *executing;
  Chain_Control  *ready;
 
  executing = _Thread_Executing;
  ready     = executing->ready;
  _ISR_Disable( level );
    if ( !_Chain_Has_only_one_node( ready ) ) {
      _Chain_Extract_unprotected( &executing->Object.Node );
      _Chain_Append_unprotected( ready, &executing->Object.Node );
 
      _ISR_Flash( level );
 
      if ( _Thread_Is_heir( executing ) )
        _Thread_Heir = (Thread_Control *) ready->first;
      _Context_Switch_necessary = TRUE;
    }
    else if ( !_Thread_Is_heir( executing ) )
      _Context_Switch_necessary = TRUE;
 
  _ISR_Enable( level );
}