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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 );

}