/*
    (C) 1995-96 AROS - The Amiga Replacement OS
    $Id: settaskpri.c,v 1.8 1997/05/12 10:32:21 aros Exp $

    Desc: Change the priority of a task.
    Lang: english
*/
#include <exec/execbase.h>
#include <aros/libcall.h>
#include <proto/exec.h>

/*****************************************************************************

    NAME */

	AROS_LH2(BYTE, SetTaskPri,

/*  SYNOPSIS */
	AROS_LHA(struct Task *, task,      A1),
	AROS_LHA(LONG,          priority,  D0),

/*  LOCATION */
	struct ExecBase *, SysBase, 50, Exec)

/*  FUNCTION
	Change the priority of a given task. As a general rule the higher
	the priority the more CPU time a task gets. Useful values are within
	-127 to 5.

    INPUTS
	task	 - Pointer to task structure.
	priority - New priority of the task.

    RESULT
	Old task priority.

    NOTES

    EXAMPLE

    BUGS

    SEE ALSO

    INTERNALS

    HISTORY

******************************************************************************/
{
    AROS_LIBFUNC_INIT

    BYTE old;

    /* Always Disable() when doing something with task lists. */
    Disable();

    /* Get returncode */
    old=task->tc_Node.ln_Pri;

    /* Set new value. */
    task->tc_Node.ln_Pri=priority;

    /* Check if the task is willing to run. */
    if(task->tc_State!=TS_WAIT)
    {
	/* If it is in the ready list remove and reinsert it. */
	if(task->tc_State==TS_READY)
	{
	    Remove(&task->tc_Node);
	    Enqueue(&SysBase->TaskReady,&task->tc_Node);
	}

	/*
	    I could check the task priorities here to determine if
	    the following is really necessary, but OTOH priority
	    changes are rare and the hassle isn't really worth it.

	    This should be reconsidered, because of Executive [ldp].
	*/

	/* Are taskswitches allowed? */
	if(SysBase->TDNestCnt>=0||SysBase->IDNestCnt>0)
	    /* No. Store it for later. */
	    SysBase->AttnResched|=0x80;
	else
	{
	    /* Switches are allowed. Move the current task away. */
	    SysBase->ThisTask->tc_State=TS_READY;
	    Enqueue(&SysBase->TaskReady,&SysBase->ThisTask->tc_Node);

	    /* And force a reschedule. */
	    Switch();
	}
    }

    /* All done. */
    Enable();
    return old;
    AROS_LIBFUNC_EXIT
} /* SetTaskPri */