thread_act.c   [plain text]

/*
 * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * The contents of this file constitute Original Code as defined in and
 * are subject to the Apple Public Source License Version 1.1 (the
 * "License").  You may not use this file except in compliance with the
 * License.  Please obtain a copy of the License at
 * http://www.apple.com/publicsource and read it before using this file.
 * 
 * This Original Code and all software distributed under the License are
 * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
 * License for the specific language governing rights and limitations
 * under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */
/*
 * @OSF_FREE_COPYRIGHT@
 */
/*
 * Copyright (c) 1993 The University of Utah and
 * the Center for Software Science (CSS).  All rights reserved.
 *
 * Permission to use, copy, modify and distribute this software and its
 * documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 *
 * THE UNIVERSITY OF UTAH AND CSS ALLOW FREE USE OF THIS SOFTWARE IN ITS "AS
 * IS" CONDITION.  THE UNIVERSITY OF UTAH AND CSS DISCLAIM ANY LIABILITY OF
 * ANY KIND FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 *
 * CSS requests users of this software to return to css-dist@cs.utah.edu any
 * improvements that they make and grant CSS redistribution rights.
 *
 *	Author:	Bryan Ford, University of Utah CSS
 *
 *	Thread_Activation management routines
 */

#include <cpus.h>
#include <task_swapper.h>
#include <mach/kern_return.h>
#include <mach/alert.h>
#include <kern/etap_macros.h>
#include <kern/mach_param.h>
#include <kern/zalloc.h>
#include <kern/thread.h>
#include <kern/thread_swap.h>
#include <kern/task.h>
#include <kern/task_swap.h>
#include <kern/thread_act.h>
#include <kern/thread_pool.h>
#include <kern/sched_prim.h>
#include <kern/misc_protos.h>
#include <kern/assert.h>
#include <kern/exception.h>
#include <kern/ipc_mig.h>
#include <kern/ipc_tt.h>
#include <kern/profile.h>
#include <kern/machine.h>
#include <kern/spl.h>
#include <kern/syscall_subr.h>
#include <kern/sync_lock.h>
#include <kern/mk_sp.h>	/*** ??? fix so this can be removed ***/
#include <kern/processor.h>
#include <mach_prof.h>
#include <mach/rpc.h>

/*
 * Debugging printf control
 */
#if	MACH_ASSERT
unsigned int	watchacts =	  0 /* WA_ALL */
				    ;	/* Do-it-yourself & patchable */
#endif

/*
 * Track the number of times we need to swapin a thread to deallocate it.
 */
int act_free_swapin = 0;

/*
 * Forward declarations for functions local to this file.
 */
kern_return_t	act_abort( thread_act_t, int);
void		special_handler(ReturnHandler *, thread_act_t);
void		nudge(thread_act_t);
kern_return_t	act_set_state_locked(thread_act_t, int,
					thread_state_t,
					mach_msg_type_number_t);
kern_return_t	act_get_state_locked(thread_act_t, int,
					thread_state_t,
					mach_msg_type_number_t *);
void		act_set_apc(thread_act_t);
void		act_clr_apc(thread_act_t);
void		act_user_to_kernel(thread_act_t);
void		act_ulock_release_all(thread_act_t thr_act);

void		install_special_handler_locked(thread_act_t);

static zone_t	thr_act_zone;

/*
 * Thread interfaces accessed via a thread_activation:
 */


/*
 * Internal routine to terminate a thread.
 * Called with task locked.
 */
kern_return_t
thread_terminate_internal(
	register thread_act_t	thr_act)
{
	thread_t	thread;
	task_t		task;
	struct ipc_port	*iplock;
	kern_return_t	ret;

#if	THREAD_SWAPPER
	thread_swap_disable(thr_act);
#endif	/* THREAD_SWAPPER */

	thread = act_lock_thread(thr_act);
	if (!thr_act->active) {
		act_unlock_thread(thr_act);
		return(KERN_TERMINATED);
	}

	act_disable_task_locked(thr_act);
	ret = act_abort(thr_act,FALSE);

#if	NCPUS > 1
	/* 
	 * Make sure this thread enters the kernel
	 */
	if (thread != current_thread()) {
		thread_hold(thr_act);
		act_unlock_thread(thr_act);

		if (thread_stop_wait(thread))
			thread_unstop(thread);
		else
			ret = KERN_ABORTED;

		(void)act_lock_thread(thr_act);
		thread_release(thr_act);
	}
#endif	/* NCPUS > 1 */

	act_unlock_thread(thr_act);
	return(ret);
}

/*
 * Terminate a thread.  Called with nothing locked.
 * Returns same way.
 */
kern_return_t
thread_terminate(
	register thread_act_t	thr_act)
{
	task_t		task;
	kern_return_t	ret;

	if (thr_act == THR_ACT_NULL)
		return KERN_INVALID_ARGUMENT;

	task = thr_act->task;
	if (((task == kernel_task) || (thr_act->kernel_loaded == TRUE))
	    && (current_act() != thr_act)) {
		return(KERN_FAILURE);
        }

	/*
	 * Take the task lock and then call the internal routine
	 * that terminates a thread (it needs the task locked).
	 */
	task_lock(task);
	ret = thread_terminate_internal(thr_act);
	task_unlock(task);

	/*
	 * If a kernel thread is terminating itself, force an AST here.
	 * Kernel threads don't normally pass through the AST checking
	 * code - and all threads finish their own termination in the
	 * special handler APC.
	 */
	if (	(	thr_act->task == kernel_task	||
				thr_act->kernel_loaded == TRUE	) 	&& 
			current_act() == thr_act					) {
		ast_taken(AST_APC, FALSE);
		panic("thread_terminate(): returning from ast_taken() for %x kernel activation\n", thr_act);
        }

	return ret;
}

/*
 *	thread_hold:
 *
 *	Suspend execution of the specified thread.
 *	This is a recursive-style suspension of the thread, a count of
 *	suspends is maintained.
 *
 *	Called with thr_act locked "appropriately" for synchrony with
 *	RPC (see act_lock_thread()).  Returns same way.
 */
void
thread_hold(
	register thread_act_t	thr_act)
{
	if (thr_act->suspend_count++ == 0) {
		install_special_handler(thr_act);
		nudge(thr_act);
	}
}

/*
 * Decrement internal suspension count for thr_act, setting thread
 * runnable when count falls to zero.
 *
 * Called with thr_act locked "appropriately" for synchrony
 * with RPC (see act_lock_thread()).
 */
void
thread_release(
	register thread_act_t	thr_act)
{
	if( thr_act->suspend_count &&
		(--thr_act->suspend_count == 0) )
		nudge( thr_act );
}

kern_return_t
thread_suspend(
	register thread_act_t	thr_act)
{
	thread_t		thread;

	if (thr_act == THR_ACT_NULL) {
		return(KERN_INVALID_ARGUMENT);
	}
	thread = act_lock_thread(thr_act);
	if (!thr_act->active) {
		act_unlock_thread(thr_act);
		return(KERN_TERMINATED);
	}
	if (thr_act->user_stop_count++ == 0 &&
		thr_act->suspend_count++ == 0 ) {
		install_special_handler(thr_act);
		if (thread &&
			thr_act == thread->top_act && thread != current_thread()) {
			nudge(thr_act);
			act_unlock_thread(thr_act);
			(void)thread_wait(thread);
		}
		else {
			/*
			 * No need to wait for target thread
			 */
			act_unlock_thread(thr_act);
		}
	}
	else {
		/*
		 * Thread is already suspended
		 */
		act_unlock_thread(thr_act);
	}
	return(KERN_SUCCESS);
}

kern_return_t
thread_resume(
	register thread_act_t	thr_act)
{
	register kern_return_t	ret;
	spl_t			s;
	thread_t		thread;

	if (thr_act == THR_ACT_NULL)
		return(KERN_INVALID_ARGUMENT);
	thread = act_lock_thread(thr_act);
	ret = KERN_SUCCESS;

	if (thr_act->active) {
		if (thr_act->user_stop_count > 0) {
		    	if( --thr_act->user_stop_count == 0 ) {
				--thr_act->suspend_count;
				nudge( thr_act );
			}
		}
		else
			ret = KERN_FAILURE;
	}
	else
		ret = KERN_TERMINATED;
	act_unlock_thread( thr_act );
	return ret;
}

/* 
 * This routine walks toward the head of an RPC chain starting at
 * a specified thread activation. An alert bit is set and a special 
 * handler is installed for each thread it encounters.
 *
 * The target thread act and thread shuttle are already locked.
 */
kern_return_t
post_alert( 
	register thread_act_t	thr_act,
	unsigned 		alert_bits )
{
	thread_act_t	next;
	thread_t	thread;

	/* 
	 * Chase the chain, setting alert bits and installing
	 * special handlers for each thread act.
	 */
	/*** Not yet SMP safe ***/
	/*** Worse, where's the activation locking as the chain is walked? ***/
	for (next = thr_act; next != THR_ACT_NULL; next = next->higher) {
		next->alerts |= alert_bits;
		install_special_handler_locked(next);
	}

	return(KERN_SUCCESS);
}

/*
 *	thread_depress_abort:
 *
 *	Prematurely abort priority depression if there is one.
 */
kern_return_t
thread_depress_abort(
	register thread_act_t	thr_act)
{
    register thread_t		thread;
	kern_return_t			result;

    if (thr_act == THR_ACT_NULL)
		return (KERN_INVALID_ARGUMENT);

    thread = act_lock_thread(thr_act);
    /* if activation is terminating, this operation is not meaningful */
    if (!thr_act->active) {
		act_unlock_thread(thr_act);

		return (KERN_TERMINATED);
    }

    result = _mk_sp_thread_depress_abort(thread, FALSE);

    act_unlock_thread(thr_act);

	return (result);
}


/*
 * Already locked: all RPC-related locks for thr_act (see
 * act_lock_thread()).
 */
kern_return_t
act_abort( thread_act_t thr_act, int chain_break )
{
	spl_t			spl;
	thread_t		thread;
	struct ipc_port		*iplock = thr_act->pool_port;
	thread_act_t		orphan;
	kern_return_t		kr;
	etap_data_t		probe_data;

	ETAP_DATA_LOAD(probe_data[0], thr_act);
	ETAP_DATA_LOAD(probe_data[1], thr_act->thread);
	ETAP_PROBE_DATA(ETAP_P_ACT_ABORT,
			0,
			current_thread(),
			&probe_data,
			ETAP_DATA_ENTRY*2);

	/*
	 *  If the target thread activation is not the head... 
	 */
	if ( thr_act->thread->top_act != thr_act ) {
		/*
		 * mark the activation for abort,
		 * update the suspend count,
		 * always install the special handler
		 */
		install_special_handler(thr_act);

#ifdef AGRESSIVE_ABORT
		/* release state buffer for target's outstanding invocation */
		if (unwind_invoke_state(thr_act) != KERN_SUCCESS) {
			panic("unwind_invoke_state failure");
		}

		/* release state buffer for target's incoming invocation */
		if (thr_act->lower != THR_ACT_NULL) {
			if (unwind_invoke_state(thr_act->lower)
			    != KERN_SUCCESS) {
				panic("unwind_invoke_state failure");
			}
		}

		/* unlink target thread activation from shuttle chain */
		if ( thr_act->lower == THR_ACT_NULL ) {
			/*
			 * This is the root thread activation of the chain.
			 * Unlink the root thread act from the bottom of
			 * the chain.
			 */
			thr_act->higher->lower = THR_ACT_NULL;
		} else {
			/*
			 * This thread act is in the middle of the chain.
			 * Unlink the thread act from the middle of the chain.
			 */
			thr_act->higher->lower = thr_act->lower;
			thr_act->lower->higher = thr_act->higher;

			/* set the terminated bit for RPC return processing */
			thr_act->lower->alerts |= SERVER_TERMINATED;
		}

		orphan = thr_act->higher;

		/* remove the activation from its thread pool */
		/* (note: this is okay for "rooted threads," too) */
		act_locked_act_set_thread_pool(thr_act, IP_NULL);

		/* (just to be thorough) release the IP lock */
		if (iplock != IP_NULL) ip_unlock(iplock);

		/* release one more reference for a rooted thread */
		if (iplock == IP_NULL) act_locked_act_deallocate(thr_act);

		/* Presumably, the only reference to this activation is
		 * now held by the caller of this routine. */
		assert(thr_act->ref_count == 1);
#else /*AGRESSIVE_ABORT*/
		/* If there is a lower activation in the RPC chain... */
		if (thr_act->lower != THR_ACT_NULL) {
			/* ...indicate the server activation was terminated */
			thr_act->lower->alerts |= SERVER_TERMINATED;
		}
		/* Mark (and process) any orphaned activations */
		orphan = thr_act->higher;
#endif /*AGRESSIVE_ABORT*/

		/* indicate client of orphaned chain has been terminated */
		orphan->alerts |= CLIENT_TERMINATED;

		/* 
		 * Set up posting of alert to headward portion of
		 * the RPC chain.
		 */
		/*** fix me -- orphan act is not locked ***/
		post_alert(orphan, ORPHANED);

		/*
		 * Get attention of head of RPC chain.
		 */
		nudge(thr_act->thread->top_act);
		return (KERN_SUCCESS);
	}

	/*
	 * If the target thread is the end of the chain, the thread
	 * has to be marked for abort and rip it out of any wait.
	 */
	spl = splsched();
	thread_lock(thr_act->thread);
	if (thr_act->thread->top_act == thr_act) {
	    thr_act->thread->state |= TH_ABORT;
	    clear_wait_internal(thr_act->thread, THREAD_INTERRUPTED);
	    thread_unlock(thr_act->thread);
	    splx(spl);
	    install_special_handler(thr_act);
	    nudge( thr_act );
	}
	return KERN_SUCCESS;
}
	
kern_return_t
thread_abort(
	register thread_act_t	thr_act)
{
	int		ret;
	thread_t		thread;

	if (thr_act == THR_ACT_NULL || thr_act == current_act())
		return (KERN_INVALID_ARGUMENT);
	/*
	 *	Lock the target thread and the current thread now,
	 *	in case thread_halt() ends up being called below.
	 */
	thread = act_lock_thread(thr_act);
	if (!thr_act->active) {
		act_unlock_thread(thr_act);
		return(KERN_TERMINATED);
	}

	ret = act_abort( thr_act, FALSE );
	act_unlock_thread( thr_act );
	return ret;
}

kern_return_t
thread_abort_safely(
	register thread_act_t	thr_act)
{
	thread_t		thread;
	spl_t			s;

	if (thr_act == THR_ACT_NULL || thr_act == current_act())
		return(KERN_INVALID_ARGUMENT);

	thread = act_lock_thread(thr_act);
	if (!thr_act->active) {
		act_unlock_thread(thr_act);
		return(KERN_TERMINATED);
	}
	if (thread->top_act != thr_act) {
		act_unlock_thread(thr_act);
		return(KERN_FAILURE);
	}
	s = splsched();
	thread_lock(thread);

	if ( thread->at_safe_point ) {
		/*
		 * It's an abortable wait, clear it, then
		 * let the thread go and return successfully.
		 */
		clear_wait_internal(thread, THREAD_INTERRUPTED);
		thread_unlock(thread);
		act_unlock_thread(thr_act);
		splx(s);
		return KERN_SUCCESS;
	}

	/*
	 * if not stopped at a safepoint, just let it go and return failure.
	 */
	thread_unlock(thread);
	act_unlock_thread(thr_act);
	splx(s);
	return KERN_FAILURE;
}

/*** backward compatibility hacks ***/
#include <mach/thread_info.h>
#include <mach/thread_special_ports.h>
#include <ipc/ipc_port.h>
#include <mach/thread_act_server.h>

kern_return_t
thread_info(
	thread_act_t			thr_act,
	thread_flavor_t			flavor,
	thread_info_t			thread_info_out,
	mach_msg_type_number_t	*thread_info_count)
{
	register thread_t		thread;
	kern_return_t			result;

	if (thr_act == THR_ACT_NULL)
		return (KERN_INVALID_ARGUMENT);

	thread = act_lock_thread(thr_act);
	if (!thr_act->active) {
		act_unlock_thread(thr_act);

		return (KERN_TERMINATED);
	}

	result = thread_info_shuttle(thr_act, flavor,
					thread_info_out, thread_info_count);

	act_unlock_thread(thr_act);

	return (result);
}

/*
 *	Routine:	thread_get_special_port [kernel call]
 *	Purpose:
 *		Clones a send right for one of the thread's
 *		special ports.
 *	Conditions:
 *		Nothing locked.
 *	Returns:
 *		KERN_SUCCESS		Extracted a send right.
 *		KERN_INVALID_ARGUMENT	The thread is null.
 *		KERN_FAILURE		The thread is dead.
 *		KERN_INVALID_ARGUMENT	Invalid special port.
 */

kern_return_t
thread_get_special_port(
	thread_act_t	thr_act,
	int		which,
	ipc_port_t	*portp)
{
	ipc_port_t	*whichp;
	ipc_port_t	port;
	thread_t	thread;

#if	MACH_ASSERT
	if (watchacts & WA_PORT)
	    printf("thread_get_special_port(thr_act=%x, which=%x port@%x=%x\n",
		thr_act, which, portp, (portp ? *portp : 0));
#endif	/* MACH_ASSERT */

	if (!thr_act)
		return KERN_INVALID_ARGUMENT;
 	thread = act_lock_thread(thr_act);
	switch (which) {
		case THREAD_KERNEL_PORT:
			whichp = &thr_act->ith_sself;
			break;

		default:
			act_unlock_thread(thr_act);
			return KERN_INVALID_ARGUMENT;
	}

	if (!thr_act->active) {
		act_unlock_thread(thr_act);
		return KERN_FAILURE;
	}

	port = ipc_port_copy_send(*whichp);
	act_unlock_thread(thr_act);

	*portp = port;
	return KERN_SUCCESS;
}

/*
 *	Routine:	thread_set_special_port [kernel call]
 *	Purpose:
 *		Changes one of the thread's special ports,
 *		setting it to the supplied send right.
 *	Conditions:
 *		Nothing locked.  If successful, consumes
 *		the supplied send right.
 *	Returns:
 *		KERN_SUCCESS		Changed the special port.
 *		KERN_INVALID_ARGUMENT	The thread is null.
 *		KERN_FAILURE		The thread is dead.
 *		KERN_INVALID_ARGUMENT	Invalid special port.
 */

kern_return_t
thread_set_special_port(
	thread_act_t	thr_act,
	int		which,
	ipc_port_t	port)
{
	ipc_port_t	*whichp;
	ipc_port_t	old;
	thread_t	thread;

#if	MACH_ASSERT
	if (watchacts & WA_PORT)
		printf("thread_set_special_port(thr_act=%x,which=%x,port=%x\n",
			thr_act, which, port);
#endif	/* MACH_ASSERT */

	if (thr_act == 0)
		return KERN_INVALID_ARGUMENT;

	thread = act_lock_thread(thr_act);
	switch (which) {
		case THREAD_KERNEL_PORT:
			whichp = &thr_act->ith_self;
			break;

		default:
			act_unlock_thread(thr_act);
			return KERN_INVALID_ARGUMENT;
	}

	if (!thr_act->active) {
		act_unlock_thread(thr_act);
		return KERN_FAILURE;
	}

	old = *whichp;
	*whichp = port;
	act_unlock_thread(thr_act);

	if (IP_VALID(old))
		ipc_port_release_send(old);
	return KERN_SUCCESS;
}

/*
 *  thread state should always be accessible by locking the thread
 *  and copying it.  The activation messes things up so for right
 *  now if it's not the top of the chain, use a special handler to
 *  get the information when the shuttle returns to the activation.
 */
kern_return_t
thread_get_state(
	register thread_act_t	thr_act,
	int			flavor,
	thread_state_t		state,	/* pointer to OUT array */
	mach_msg_type_number_t	*state_count)	/*IN/OUT*/
{
	kern_return_t		ret;
	thread_t		thread, nthread;

	if (thr_act == THR_ACT_NULL || thr_act == current_act())
		return (KERN_INVALID_ARGUMENT);

	thread = act_lock_thread(thr_act);
	if (!thr_act->active) {
		act_unlock_thread(thr_act);
		return(KERN_TERMINATED);
	}

	thread_hold(thr_act);
	while (1) {
		if (!thread || thr_act != thread->top_act)
			break;
		act_unlock_thread(thr_act);
		(void)thread_stop_wait(thread);
		nthread = act_lock_thread(thr_act);
		if (nthread == thread)
			break;
		thread_unstop(thread);
		thread = nthread;
	}
	ret = act_machine_get_state(thr_act, flavor,
					state, state_count);
	if (thread && thr_act == thread->top_act)
	    thread_unstop(thread);
	thread_release(thr_act);
	act_unlock_thread(thr_act);

	return(ret);
}

/*
 *	Change thread's machine-dependent state.  Called with nothing
 *	locked.  Returns same way.
 */
kern_return_t
thread_set_state(
	register thread_act_t	thr_act,
	int			flavor,
	thread_state_t		state,
	mach_msg_type_number_t	state_count)
{
	kern_return_t		ret;
	thread_t		thread, nthread;

	if (thr_act == THR_ACT_NULL || thr_act == current_act())
		return (KERN_INVALID_ARGUMENT);
	/*
	 * We have no kernel activations, so Utah's MO fails for signals etc.
	 *
	 * If we're blocked in the kernel, use non-blocking method, else
	 * pass locked thr_act+thread in to "normal" act_[gs]et_state().
	 */

	thread = act_lock_thread(thr_act);
	if (!thr_act->active) {
		act_unlock_thread(thr_act);
		return(KERN_TERMINATED);
	}

	thread_hold(thr_act);
	while (1) {
		if (!thread || thr_act != thread->top_act)
			break;
		act_unlock_thread(thr_act);
		(void)thread_stop_wait(thread);
		nthread = act_lock_thread(thr_act);
		if (nthread == thread)
			break;
		thread_unstop(thread);
		thread = nthread;
	}
	ret = act_machine_set_state(thr_act, flavor,
					state, state_count);
	if (thread && thr_act == thread->top_act)
	    thread_unstop(thread);
	thread_release(thr_act);
	act_unlock_thread(thr_act);

	return(ret);
}

/*
 * Kernel-internal "thread" interfaces used outside this file:
 */

kern_return_t
thread_dup(
	thread_act_t source_thr_act, 
	thread_act_t target_thr_act)
{
	kern_return_t		ret;
	thread_t		thread, nthread;

	if (target_thr_act == THR_ACT_NULL || target_thr_act == current_act())
		return (KERN_INVALID_ARGUMENT);

	thread = act_lock_thread(target_thr_act);
	if (!target_thr_act->active) {
		act_unlock_thread(target_thr_act);
		return(KERN_TERMINATED);
	}

	thread_hold(target_thr_act);
	while (1) {
	    	if (!thread || target_thr_act != thread->top_act)
			break;
		act_unlock_thread(target_thr_act);
		(void)thread_stop_wait(thread);
		nthread = act_lock_thread(target_thr_act);
		if (nthread == thread)
			break;
		thread_unstop(thread);
		thread = nthread;
	}
	ret = act_thread_dup(source_thr_act, target_thr_act);
	if (thread && target_thr_act == thread->top_act)
	    thread_unstop(thread);
	thread_release(target_thr_act);
	act_unlock_thread(target_thr_act);

	return(ret);
}


/*
 *	thread_setstatus:
 *
 *	Set the status of the specified thread.
 *	Called with (and returns with) no locks held.
 */
kern_return_t
thread_setstatus(
	thread_act_t		thr_act,
	int			flavor,
	thread_state_t		tstate,
	mach_msg_type_number_t	count)
{
	kern_return_t		kr;
	thread_t		thread;

	thread = act_lock_thread(thr_act);
	assert(thread);
	assert(thread->top_act == thr_act);
	kr = act_machine_set_state(thr_act, flavor, tstate, count);
	act_unlock_thread(thr_act);
	return(kr);
}

/*
 *	thread_getstatus:
 *
 *	Get the status of the specified thread.
 */
kern_return_t
thread_getstatus(
	thread_act_t		thr_act,
	int			flavor,
	thread_state_t		tstate,
	mach_msg_type_number_t	*count)
{
	kern_return_t		kr;
	thread_t		thread;

	thread = act_lock_thread(thr_act);
	assert(thread);
	assert(thread->top_act == thr_act);
	kr = act_machine_get_state(thr_act, flavor, tstate, count);
	act_unlock_thread(thr_act);
	return(kr);
}

/*
 * Kernel-internal thread_activation interfaces used outside this file:
 */

/*
 * act_init()	- Initialize activation handling code
 */
void
act_init()
{
	thr_act_zone = zinit(
			sizeof(struct thread_activation),
			ACT_MAX * sizeof(struct thread_activation), /* XXX */
			ACT_CHUNK * sizeof(struct thread_activation),
			"activations");
	act_machine_init();
}


/*
 * act_create	- Create a new activation in a specific task.
 */
kern_return_t
act_create(task_t task,
           thread_act_t *new_act)
{
	thread_act_t thr_act;
	int rc;
	vm_map_t map;

	thr_act = (thread_act_t)zalloc(thr_act_zone);
	if (thr_act == 0)
		return(KERN_RESOURCE_SHORTAGE);

#if	MACH_ASSERT
	if (watchacts & WA_ACT_LNK)
		printf("act_create(task=%x,thr_act@%x=%x)\n",
			task, new_act, thr_act);
#endif	/* MACH_ASSERT */

	/* Start by zeroing everything; then init non-zero items only */
	bzero((char *)thr_act, sizeof(*thr_act));

#ifdef MACH_BSD
	{
		/*
		 * Take care of the uthread allocation
		 * do it early in order to make KERN_RESOURCE_SHORTAGE
		 * handling trivial
		 * uthread_alloc() will bzero the storage allocated.
		 */
		extern void *uthread_alloc(void);
		thr_act->uthread = uthread_alloc();
		if(thr_act->uthread == 0) {
			/* Put the thr_act back on the thr_act zone */
			zfree(thr_act_zone, (vm_offset_t)thr_act);
			return(KERN_RESOURCE_SHORTAGE);
		}
	}
#endif	/* MACH_BSD */

	/*
	 * Start with one reference for the caller and one for the
	 * act being alive.
	 */
	act_lock_init(thr_act);
	thr_act->ref_count = 2;

	/* Latch onto the task.  */
	thr_act->task = task;
	task_reference(task);

	/* Initialize sigbufp for High-Watermark buffer allocation */
        thr_act->r_sigbufp = (routine_descriptor_t) &thr_act->r_sigbuf;
        thr_act->r_sigbuf_size = sizeof(thr_act->r_sigbuf);

#if	THREAD_SWAPPER
	thr_act->swap_state = TH_SW_IN;
#if	MACH_ASSERT
	thr_act->kernel_stack_swapped_in = TRUE;
#endif	/* MACH_ASSERT */
#endif	/* THREAD_SWAPPER */

	/* special_handler will always be last on the returnhandlers list.  */
	thr_act->special_handler.next = 0;
	thr_act->special_handler.handler = special_handler;

#if	MACH_PROF
	thr_act->act_profiled = FALSE;
	thr_act->act_profiled_own = FALSE;
	thr_act->profil_buffer = NULLPROFDATA;
#endif

	/* Initialize the held_ulocks queue as empty */
	queue_init(&thr_act->held_ulocks);

	/* Inherit the profiling status of the parent task */
	act_prof_init(thr_act, task);

	ipc_thr_act_init(task, thr_act);
	act_machine_create(task, thr_act);

	/*
	 * If thr_act created in kernel-loaded task, alter its saved
	 * state to so indicate
	 */
	if (task->kernel_loaded) {
		act_user_to_kernel(thr_act);
	}

	/* Cache the task's map and take a reference to it */
	map = task->map;
	thr_act->map = map;

	/* Inline vm_map_reference cause we don't want to increment res_count */
	mutex_lock(&map->s_lock);
#if	TASK_SWAPPER
	assert(map->res_count > 0);
	assert(map->ref_count >= map->res_count);
#endif	/* TASK_SWAPPER */
	map->ref_count++;
	mutex_unlock(&map->s_lock);

	*new_act = thr_act;
	return KERN_SUCCESS;
}

/*
 * act_free	- called when an thr_act's ref_count drops to zero.
 *
 * This can only happen after the activation has been reaped, and
 * all other references to it have gone away.  We can now release
 * the last critical resources, unlink the activation from the
 * task, and release the reference on the thread shuttle itself.
 *
 * Called with activation locked.
 */
#if	MACH_ASSERT
int	dangerous_bzero = 1;	/* paranoia & safety */
#endif

void
act_free(thread_act_t thr_act)
{
	task_t		task;
	thread_t	thr;
	vm_map_t	map;
	unsigned int	ref;

#if	MACH_ASSERT
	if (watchacts & WA_EXIT)
		printf("act_free(%x(%d)) thr=%x tsk=%x(%d) pport=%x%sactive\n",
			thr_act, thr_act->ref_count, thr_act->thread,
			thr_act->task,
			thr_act->task ? thr_act->task->ref_count : 0,
			thr_act->pool_port,
			thr_act->active ? " " : " !");
#endif	/* MACH_ASSERT */


#if	THREAD_SWAPPER
	assert(thr_act->kernel_stack_swapped_in);
#endif	/* THREAD_SWAPPER */

	assert(!thr_act->active);
	assert(!thr_act->pool_port);

	task = thr_act->task;
	task_lock(task);

	if (thr = thr_act->thread) {
		time_value_t	user_time, system_time;

		thread_read_times(thr, &user_time, &system_time);
		time_value_add(&task->total_user_time, &user_time);
		time_value_add(&task->total_system_time, &system_time);
	
		/* Unlink the thr_act from the task's thr_act list,
		 * so it doesn't appear in calls to task_threads and such.
		 * The thr_act still keeps its ref on the task, however.
		 */
		queue_remove(&task->thr_acts, thr_act, thread_act_t, thr_acts);
		thr_act->thr_acts.next = NULL;
		task->thr_act_count--;

#if     THREAD_SWAPPER
		/*
		 * Thread is supposed to be unswappable by now...
		 */
		assert(thr_act->swap_state == TH_SW_UNSWAPPABLE ||
		       !thread_swap_unwire_stack);
#endif  /* THREAD_SWAPPER */

		task->res_act_count--;
		task_unlock(task);
		task_deallocate(task);
		thread_deallocate(thr);
		act_machine_destroy(thr_act);
	} else {
		/*
		 * Must have never really gotten started
		 * no unlinking from the task and no need
		 * to free the shuttle.
		 */
		task_unlock(task);
		task_deallocate(task);
	}

	sigbuf_dealloc(thr_act);
	act_prof_deallocate(thr_act);
	ipc_thr_act_terminate(thr_act);

	/*
	 * Drop the cached map reference.
	 * Inline version of vm_map_deallocate() because we
	 * don't want to decrement the map's residence count here.
	 */
	map = thr_act->map;
	mutex_lock(&map->s_lock);
#if	TASK_SWAPPER
	assert(map->res_count >= 0);
	assert(map->ref_count > map->res_count);
#endif	/* TASK_SWAPPER */
	ref = --map->ref_count;
	mutex_unlock(&map->s_lock);
	if (ref == 0)
		vm_map_destroy(map);

#ifdef MACH_BSD 
	{
		/*
		 * Free uthread BEFORE the bzero.
		 * Not doing so will result in a leak.
		 */
		extern void uthread_free(void *);
		void *ut = thr_act->uthread;
		thr_act->uthread = 0;
		uthread_free(ut);
	}
#endif  /* MACH_BSD */   

#if	MACH_ASSERT
	if (dangerous_bzero)	/* dangerous if we're still using it! */
		bzero((char *)thr_act, sizeof(*thr_act));
#endif	/* MACH_ASSERT */
	/* Put the thr_act back on the thr_act zone */
	zfree(thr_act_zone, (vm_offset_t)thr_act);
}


/*
 * act_attach	- Attach an thr_act to the top of a thread ("push the stack").
 *
 * The thread_shuttle must be either the current one or a brand-new one.
 * Assumes the thr_act is active but not in use, also, that if it is
 * attached to an thread_pool (i.e. the thread_pool pointer is nonzero),
 * the thr_act has already been taken off the thread_pool's list.
 *
 * Already locked: thr_act plus "appropriate" thread-related locks
 * (see act_lock_thread()).
 */
void 
act_attach(
	thread_act_t	thr_act,
	thread_t	thread,
	unsigned	init_alert_mask)
{
        thread_act_t    lower;

#if	MACH_ASSERT
	assert(thread == current_thread() || thread->top_act == THR_ACT_NULL);
	if (watchacts & WA_ACT_LNK)
		printf("act_attach(thr_act %x(%d) thread %x(%d) mask %d)\n",
		       thr_act, thr_act->ref_count, thread, thread->ref_count,
		       init_alert_mask);
#endif	/* MACH_ASSERT */

	/* 
	 *	Chain the thr_act onto the thread's thr_act stack.  
	 *	Set mask and auto-propagate alerts from below.
	 */
	thr_act->ref_count++;
	thr_act->thread = thread;
	thr_act->higher = THR_ACT_NULL;  /*safety*/
	thr_act->alerts = 0;
	thr_act->alert_mask = init_alert_mask;
	lower = thr_act->lower = thread->top_act;

        if (lower != THR_ACT_NULL) {
                lower->higher = thr_act;
                thr_act->alerts = (lower->alerts & init_alert_mask);
        }

	thread->top_act = thr_act;
}

/*
 * 	act_detach	
 *
 *	Remove the current thr_act from the top of the current thread, i.e.
 *	"pop the stack". Assumes already locked: thr_act plus "appropriate"
 * 	thread-related locks (see act_lock_thread).
 */
void 
act_detach(
	thread_act_t	cur_act)
{
	thread_t	cur_thread = cur_act->thread;

#if	MACH_ASSERT
	if (watchacts & (WA_EXIT|WA_ACT_LNK))
		printf("act_detach: thr_act %x(%d), thrd %x(%d) task=%x(%d)\n",
		       cur_act, cur_act->ref_count,
		       cur_thread, cur_thread->ref_count,
		       cur_act->task,
		       cur_act->task ? cur_act->task->ref_count : 0);
#endif	/* MACH_ASSERT */

	/* Unlink the thr_act from the thread's thr_act stack */
	cur_thread->top_act = cur_act->lower;
	cur_act->thread = 0;
	cur_act->ref_count--;
	assert(cur_act->ref_count > 0);

	thread_pool_put_act(cur_act);

#if	MACH_ASSERT
	cur_act->lower = cur_act->higher = THR_ACT_NULL; 
	if (cur_thread->top_act)
		cur_thread->top_act->higher = THR_ACT_NULL;
#endif	/* MACH_ASSERT */

	return;
}


/*
 * Synchronize a thread operation with RPC.  Called with nothing
 * locked.   Returns with thr_act locked, plus one of four
 * combinations of other locks held:
 *	none - for new activation not yet associated with thread_pool
 *		or shuttle
 *	rpc_lock(thr_act->thread) only - for base activation (one
 *		without pool_port)
 *	ip_lock(thr_act->pool_port) only - for empty activation (one
 *		with no associated shuttle)
 *	both locks - for "active" activation (has shuttle, lives
 *		on thread_pool)
 * If thr_act has an associated shuttle, this function returns
 * its address.  Otherwise it returns zero.
 */
thread_t
act_lock_thread(
	thread_act_t thr_act)
{
	ipc_port_t pport;

	/*
	 * Allow the shuttle cloning code (q.v., when it
	 * exists :-}) to obtain ip_lock()'s while holding
	 * an rpc_lock().
	 */
	while (1) {
		act_lock(thr_act);
		pport = thr_act->pool_port;
		if (!pport || ip_lock_try(pport)) {
			if (!thr_act->thread)
				break;
			if (rpc_lock_try(thr_act->thread))
				break;
			if (pport)
				ip_unlock(pport);
		}
		act_unlock(thr_act);
		mutex_pause();
	}
	return (thr_act->thread);
}

/*
 * Unsynchronize with RPC (i.e., undo an act_lock_thread() call).
 * Called with thr_act locked, plus thread locks held that are
 * "correct" for thr_act's state.  Returns with nothing locked.
 */
void
act_unlock_thread(thread_act_t	thr_act)
{
	if (thr_act->thread)
		rpc_unlock(thr_act->thread);
	if (thr_act->pool_port)
		ip_unlock(thr_act->pool_port);
	act_unlock(thr_act);
}

/*
 * Synchronize with RPC given a pointer to a shuttle (instead of an
 * activation).  Called with nothing locked; returns with all
 * "appropriate" thread-related locks held (see act_lock_thread()).
 */
thread_act_t
thread_lock_act(
	thread_t	thread)
{
	thread_act_t	thr_act;

	while (1) {
		rpc_lock(thread);
		thr_act = thread->top_act;
		if (!thr_act)
			break;
		if (!act_lock_try(thr_act)) {
			rpc_unlock(thread);
			mutex_pause();
			continue;
		}
		if (thr_act->pool_port &&
			!ip_lock_try(thr_act->pool_port)) {
			rpc_unlock(thread);
			act_unlock(thr_act);
			mutex_pause();
			continue;
		}
		break;
	}
	return (thr_act);
}

/*
 * Unsynchronize with RPC starting from a pointer to a shuttle.
 * Called with RPC-related locks held that are appropriate to
 * shuttle's state; any activation is also locked.
 */
void
thread_unlock_act(
	thread_t	thread)
{
	thread_act_t 	thr_act;

	if (thr_act = thread->top_act) {
		if (thr_act->pool_port)
			ip_unlock(thr_act->pool_port);
		act_unlock(thr_act);
	}
	rpc_unlock(thread);
}

/*
 * switch_act
 *
 * If a new activation is given, switch to it. If not,
 * switch to the lower activation (pop). Returns the old
 * activation. This is for RPC support.
 */
thread_act_t
switch_act( 
	thread_act_t act)
{
	thread_t	thread;
	thread_act_t	old, new;
	unsigned	cpu;
	spl_t		spl;


	disable_preemption();

	cpu = cpu_number();
	thread  = current_thread();

	/*
	 *	Find the old and new activation for switch.
	 */
	old = thread->top_act;

	if (act) {
		new = act;
                new->thread = thread;
	}
	else {
		new = old->lower;
	}

	assert(new != THR_ACT_NULL);
#if	THREAD_SWAPPER
	assert(new->swap_state != TH_SW_OUT &&
	       new->swap_state != TH_SW_COMING_IN);
#endif	/* THREAD_SWAPPER */

        assert(cpu_data[cpu].active_thread == thread);
	active_kloaded[cpu] = (new->kernel_loaded) ? new : 0;

	/* This is where all the work happens */
	machine_switch_act(thread, old, new, cpu);

	/*
	 *	Push or pop an activation on the chain.
	 */
	if (act) {
		act_attach(new, thread, 0);
	}
	else {
		act_detach(old);
	}

        enable_preemption();

	return(old);
}

/*
 * install_special_handler
 *	Install the special returnhandler that handles suspension and
 *	termination, if it hasn't been installed already.
 *
 * Already locked: RPC-related locks for thr_act, but not
 * scheduling lock (thread_lock()) of the associated thread.
 */
void
install_special_handler(
	thread_act_t	thr_act)
{
	spl_t		spl;
	thread_t	thread = thr_act->thread;

#if	MACH_ASSERT
	if (watchacts & WA_ACT_HDLR)
	    printf("act_%x: install_special_hdlr(%x)\n",current_act(),thr_act);
#endif	/* MACH_ASSERT */

	spl = splsched();
	thread_lock(thread);
	install_special_handler_locked(thr_act);
	thread_unlock(thread);
	splx(spl);
}

/*
 * install_special_handler_locked
 *	Do the work of installing the special_handler.
 *
 * Already locked: RPC-related locks for thr_act, plus the
 * scheduling lock (thread_lock()) of the associated thread.
 */
void
install_special_handler_locked(
	thread_act_t	thr_act)
{
	ReturnHandler	**rh;
	thread_t	thread = thr_act->thread;

	/* The work handler must always be the last ReturnHandler on the list,
	   because it can do tricky things like detach the thr_act.  */
	for (rh = &thr_act->handlers; *rh; rh = &(*rh)->next)
		/* */ ;
	if (rh != &thr_act->special_handler.next) {
		*rh = &thr_act->special_handler;
	}
	if (thread && thr_act == thread->top_act) {
		/*
		 * Temporarily undepress, so target has
		 * a chance to do locking required to
		 * block itself in special_handler().
		 */
		if (thread->depress_priority >= 0) {
			thread->priority = thread->depress_priority;

			/*
			 * Use special value -2 to indicate need
			 * to redepress priority in special_handler
			 * as thread blocks
			 */
			thread->depress_priority = -2;
			compute_priority(thread, FALSE);
		}	
	}
	act_set_apc(thr_act);
}

/*
 * JMM -
 * These two routines will be enhanced over time to call the general handler registration
 * mechanism used by special handlers and alerts.  They are hack in for now to avoid
 * having to export the gory details of ASTs to the BSD code right now.
 */
extern thread_apc_handler_t bsd_ast;

kern_return_t
thread_apc_set(
	thread_act_t thr_act,
	thread_apc_handler_t apc)
{
	assert(apc == bsd_ast);
	thread_ast_set(thr_act, AST_BSD);
	if (thr_act == current_act())
		ast_propagate(thr_act->ast);
	return KERN_SUCCESS;
}

kern_return_t
thread_apc_clear(
	thread_act_t thr_act,
	thread_apc_handler_t apc)
{
	assert(apc == bsd_ast);
	thread_ast_clear(thr_act, AST_BSD);
	if (thr_act == current_act())
		ast_off(AST_BSD);
	return KERN_SUCCESS;
}

/*
 * act_set_thread_pool	- Assign an activation to a specific thread_pool.
 * Fails if the activation is already assigned to another pool.
 * If thread_pool == 0, we remove the thr_act from its thread_pool.
 *
 * Called the port containing thread_pool already locked.
 * Returns the same way.
 */
kern_return_t act_set_thread_pool(
	thread_act_t	thr_act,
	ipc_port_t	pool_port)
{
	thread_pool_t	thread_pool;

#if	MACH_ASSERT
	if (watchacts & WA_ACT_LNK)
		printf("act_set_thread_pool: %x(%d) -> %x\n",
			thr_act, thr_act->ref_count, thread_pool);
#endif	/* MACH_ASSERT */

	if (pool_port == 0) {
		thread_act_t *lact;

		if (thr_act->pool_port == 0)
			return KERN_SUCCESS;
		thread_pool = &thr_act->pool_port->ip_thread_pool;

		for (lact = &thread_pool->thr_acts; *lact;
					lact = &((*lact)->thread_pool_next)) {
			if (thr_act == *lact) {
				*lact = thr_act->thread_pool_next;
				break;
			}
		}
		act_lock(thr_act);
		thr_act->pool_port = 0;
		thr_act->thread_pool_next = 0;
		act_unlock(thr_act);
		act_deallocate(thr_act);
		return KERN_SUCCESS;
	}
	if (thr_act->pool_port != pool_port) {
		thread_pool = &pool_port->ip_thread_pool;
		if (thr_act->pool_port != 0) {
#if	MACH_ASSERT
			if (watchacts & WA_ACT_LNK)
			    printf("act_set_thread_pool found %x!\n",
							thr_act->pool_port);
#endif	/* MACH_ASSERT */
			return(KERN_FAILURE);
		}
		act_lock(thr_act);
		thr_act->pool_port = pool_port;

		/* The pool gets a ref to the activation -- have
		 * to inline operation because thr_act is already
		 * locked.
		 */
		act_locked_act_reference(thr_act);

		/* If it is available,
		 * add it to the thread_pool's available-activation list.
		 */
		if ((thr_act->thread == 0) && (thr_act->suspend_count == 0)) {
			thr_act->thread_pool_next = thread_pool->thr_acts;
			pool_port->ip_thread_pool.thr_acts = thr_act;
			if (thread_pool->waiting)
				thread_pool_wakeup(thread_pool);
		}
		act_unlock(thr_act);
	}

	return KERN_SUCCESS;
}

/*
 * act_locked_act_set_thread_pool- Assign activation to a specific thread_pool.
 * Fails if the activation is already assigned to another pool.
 * If thread_pool == 0, we remove the thr_act from its thread_pool.
 *
 * Called the port containing thread_pool already locked.
 * Also called with the thread activation locked.
 * Returns the same way.
 *
 * This routine is the same as `act_set_thread_pool()' except that it does
 * not call `act_deallocate(),' which unconditionally tries to obtain the
 * thread activation lock.
 */
kern_return_t act_locked_act_set_thread_pool(
	thread_act_t	thr_act,
	ipc_port_t	pool_port)
{
	thread_pool_t	thread_pool;

#if	MACH_ASSERT
	if (watchacts & WA_ACT_LNK)
		printf("act_set_thread_pool: %x(%d) -> %x\n",
			thr_act, thr_act->ref_count, thread_pool);
#endif	/* MACH_ASSERT */

	if (pool_port == 0) {
		thread_act_t *lact;

		if (thr_act->pool_port == 0)
			return KERN_SUCCESS;
		thread_pool = &thr_act->pool_port->ip_thread_pool;

		for (lact = &thread_pool->thr_acts; *lact;
					lact = &((*lact)->thread_pool_next)) {
			if (thr_act == *lact) {
				*lact = thr_act->thread_pool_next;
				break;
			}
		}

		thr_act->pool_port = 0;
		thr_act->thread_pool_next = 0;
		act_locked_act_deallocate(thr_act);
		return KERN_SUCCESS;
	}
	if (thr_act->pool_port != pool_port) {
		thread_pool = &pool_port->ip_thread_pool;
		if (thr_act->pool_port != 0) {
#if	MACH_ASSERT
			if (watchacts & WA_ACT_LNK)
			    printf("act_set_thread_pool found %x!\n",
							thr_act->pool_port);
#endif	/* MACH_ASSERT */
			return(KERN_FAILURE);
		}
		thr_act->pool_port = pool_port;

		/* The pool gets a ref to the activation -- have
		 * to inline operation because thr_act is already
		 * locked.
		 */
		act_locked_act_reference(thr_act);

		/* If it is available,
		 * add it to the thread_pool's available-activation list.
		 */
		if ((thr_act->thread == 0) && (thr_act->suspend_count == 0)) {
			thr_act->thread_pool_next = thread_pool->thr_acts;
			pool_port->ip_thread_pool.thr_acts = thr_act;
			if (thread_pool->waiting)
				thread_pool_wakeup(thread_pool);
		}
	}

	return KERN_SUCCESS;
}

/*
 * Activation control support routines internal to this file:
 */

/*
 * act_execute_returnhandlers()	- does just what the name says
 *
 * This is called by system-dependent code when it detects that
 * thr_act->handlers is non-null while returning into user mode.
 * Activations linked onto an thread_pool always have null thr_act->handlers,
 * so RPC entry paths need not check it.
 */
void act_execute_returnhandlers(
	void)
{
	spl_t		s;
	thread_t	thread;
	thread_act_t	thr_act = current_act();

#if	MACH_ASSERT
	if (watchacts & WA_ACT_HDLR)
		printf("execute_rtn_hdlrs: thr_act=%x\n", thr_act);
#endif	/* MACH_ASSERT */

	s = splsched();
	act_clr_apc(thr_act);
	spllo();
	while (1) {
		ReturnHandler *rh;

		/* Grab the next returnhandler */
		thread = act_lock_thread(thr_act);
		(void)splsched();
		thread_lock(thread);
		rh = thr_act->handlers;
		if (!rh) {
			thread_unlock(thread);
			splx(s);
			act_unlock_thread(thr_act);
			return;
		}
		thr_act->handlers = rh->next;
		thread_unlock(thread);
		spllo();
		act_unlock_thread(thr_act);

#if	MACH_ASSERT
		if (watchacts & WA_ACT_HDLR)
		    printf( (rh == &thr_act->special_handler) ?
			"\tspecial_handler\n" : "\thandler=%x\n",
				    rh->handler);
#endif	/* MACH_ASSERT */

		/* Execute it */
		(*rh->handler)(rh, thr_act);
	}
}

/*
 * special_handler_continue
 *
 * Continuation routine for the special handler blocks.  It checks
 * to see whether there has been any new suspensions.  If so, it
 * installs the special handler again.  Otherwise, it checks to see
 * if the current depression needs to be re-instated (it may have
 * been temporarily removed in order to get to this point in a hurry).
 */
void
special_handler_continue(void)
{
	thread_act_t cur_act = current_act();
	thread_t thread = cur_act->thread;
	spl_t s;

	if (cur_act->suspend_count)
		install_special_handler(cur_act);
	else {
		s = splsched();
		thread_lock(thread);
		if (thread->depress_priority == -2) {
			/*
			 * We were temporarily undepressed by
			 * install_special_handler; restore priority
			 * depression.
			 */
			thread->depress_priority = thread->priority;
			thread->priority = thread->sched_pri = DEPRESSPRI;
		}
		thread_unlock(thread);
		splx(s);
	}
	thread_exception_return();
}

/*
 * special_handler	- handles suspension, termination.  Called
 * with nothing locked.  Returns (if it returns) the same way.
 */
void
special_handler(
	ReturnHandler	*rh,
	thread_act_t	cur_act)
{
	spl_t		s;
	thread_t	lthread;
	thread_t	thread = act_lock_thread(cur_act);
	unsigned	alert_bits;
	exception_data_type_t
			codes[EXCEPTION_CODE_MAX];
	kern_return_t	kr;
	kern_return_t	exc_kr;

	assert(thread != THREAD_NULL);
#if	MACH_ASSERT
	if (watchacts & WA_ACT_HDLR)
	    printf("\t\tspecial_handler(thr_act=%x(%d))\n", cur_act,
				(cur_act ? cur_act->ref_count : 0));
#endif	/* MACH_ASSERT */

	s = splsched();

	thread_lock(thread);
	thread->state &= ~TH_ABORT;	/* clear any aborts */
	thread_unlock(thread);
	splx(s);

	/*
	 * If someone has killed this invocation,
	 * invoke the return path with a terminated exception.
	 */
	if (!cur_act->active) {
		act_unlock_thread(cur_act);
		act_machine_return(KERN_TERMINATED);
	}

#ifdef CALLOUT_RPC_MODEL
	/*
	 * JMM - We don't intend to support this RPC model in Darwin.
	 * We will support inheritance through chains of activations
	 * on shuttles, but it will be universal and not just for RPC.
	 * As such, each activation will always have a base shuttle.
	 * Our RPC model will probably even support the notion of
	 * alerts (thrown up the chain of activations to affect the
	 * work done on our behalf), but the unlinking of the shuttles
	 * will be completely difference because we will never have
	 * to clone them.
	 */

	/* strip server terminated bit */
	alert_bits = cur_act->alerts & (~SERVER_TERMINATED);

	/* clear server terminated bit */
	cur_act->alerts &= ~SERVER_TERMINATED;

	if ( alert_bits ) {
		/*
		 * currently necessary to coordinate with the exception 
		 * code -fdr
		 */
		act_unlock_thread(cur_act);

		/* upcall exception/alert port */
		codes[0] = alert_bits;

		/*
		 * Exception makes a lot of assumptions. If there is no
		 * exception handler or the exception reply is broken, the 
		 * thread will be terminated and exception will not return. If
		 * we decide we don't like that behavior, we need to check
		 * for the existence of an exception port before we call 
		 * exception.
		 */
		exc_kr = exception( EXC_RPC_ALERT, codes, 1 );

		/* clear the orphaned and time constraint indications */
		cur_act->alerts &= ~(ORPHANED | TIME_CONSTRAINT_UNSATISFIED);

		/* if this orphaned activation should be terminated... */
		if (exc_kr == KERN_RPC_TERMINATE_ORPHAN) {
			/*
			 * ... terminate the activation
			 *
			 * This is done in two steps.  First, the activation is
			 * disabled (prepared for termination); second, the
			 * `special_handler()' is executed again -- this time
			 * to terminate the activation.
			 * (`act_disable_task_locked()' arranges for the
			 * additional execution of the `special_handler().')
			 */

#if	THREAD_SWAPPER
			thread_swap_disable(cur_act);
#endif	/* THREAD_SWAPPER */

			/* acquire appropriate locks */
			task_lock(cur_act->task);
			act_lock_thread(cur_act);

			/* detach the activation from its task */
			kr = act_disable_task_locked(cur_act);
			assert( kr == KERN_SUCCESS );

			/* release locks */
			task_unlock(cur_act->task);
		}
		else {
			/* acquire activation lock again (released below) */
			act_lock_thread(cur_act);
			s = splsched();
			thread_lock(thread);
			if (thread->depress_priority == -2) {
				/*
				 * We were temporarily undepressed by
				 * install_special_handler; restore priority
				 * depression.
				 */
				thread->depress_priority = thread->priority;
				thread->priority = thread->sched_pri = DEPRESSPRI;
			}
			thread_unlock(thread);
			splx(s);
		}
	}
#endif /* CALLOUT_RPC_MODEL */

	/*
	 * If we're suspended, go to sleep and wait for someone to wake us up.
	 */
	if (cur_act->suspend_count) {
		if( cur_act->handlers == NULL ) {
			assert_wait((event_t)&cur_act->suspend_count,
				    THREAD_ABORTSAFE);
			act_unlock_thread(cur_act);
			thread_block(special_handler_continue);
			/* NOTREACHED */
		}
		special_handler_continue();
	}

	act_unlock_thread(cur_act);
}

/*
 * Try to nudge a thr_act into executing its returnhandler chain.
 * Ensures that the activation will execute its returnhandlers
 * before it next executes any of its user-level code.
 *
 * Called with thr_act's act_lock() and "appropriate" thread-related
 * locks held.  (See act_lock_thread().)  Returns same way.
 */
void
nudge(thread_act_t	thr_act)
{
#if	MACH_ASSERT
	if (watchacts & WA_ACT_HDLR)
	    printf("\tact_%x: nudge(%x)\n", current_act(), thr_act);
#endif	/* MACH_ASSERT */

	/*
	 * Don't need to do anything at all if this thr_act isn't the topmost.
	 */
	if (thr_act->thread && thr_act->thread->top_act == thr_act) {
		/*
		 * If it's suspended, wake it up. 
		 * This should nudge it even on another CPU.
		 */
		thread_wakeup((event_t)&thr_act->suspend_count);
	}
}

/*
 * Update activation that belongs to a task created via kernel_task_create().
 */
void
act_user_to_kernel(
	thread_act_t	thr_act)
{
	pcb_user_to_kernel(thr_act);
	thr_act->kernel_loading = TRUE;
}

/*
 * Already locked: thr_act->task, RPC-related locks for thr_act
 *
 * Detach an activation from its task, and prepare it to terminate
 * itself.
 */
kern_return_t
act_disable_task_locked(
	thread_act_t	thr_act)
{
	thread_t	thread = thr_act->thread;
	task_t		task = thr_act->task;

#if	MACH_ASSERT
	if (watchacts & WA_EXIT) {
		printf("act_%x: act_disable_tl(thr_act=%x(%d))%sactive task=%x(%d)",
			       current_act(), thr_act, thr_act->ref_count,
			       (thr_act->active ? " " : " !"),
			       thr_act->task, thr_act->task? thr_act->task->ref_count : 0);
		if (thr_act->pool_port)
			printf(", pool_port %x", thr_act->pool_port);
		printf("\n");
		(void) dump_act(thr_act);
	}
#endif	/* MACH_ASSERT */

	/* This will allow no more control ops on this thr_act. */
	thr_act->active = 0;
	ipc_thr_act_disable(thr_act);

	/* Clean-up any ulocks that are still owned by the thread
	 * activation (acquired but not released or handed-off).
	 */
	act_ulock_release_all(thr_act);

	/* When the special_handler gets executed,
	 * it will see the terminated condition and exit
	 * immediately.
	 */
	install_special_handler(thr_act);


	/* If the target happens to be suspended,
	 * give it a nudge so it can exit.
	 */
	if (thr_act->suspend_count)
		nudge(thr_act);

	/* Drop the thr_act reference taken for being active.
	 * (There is still at least one reference left:
	 * the one we were passed.)
	 * Inline the deallocate because thr_act is locked.
	 */
	act_locked_act_deallocate(thr_act);

	return(KERN_SUCCESS);
}

/*
 * act_alert	- Register an alert from this activation.
 *
 * Each set bit is propagated upward from (but not including) this activation,
 * until the top of the chain is reached or the bit is masked.
 */
kern_return_t
act_alert(thread_act_t thr_act, unsigned alerts)
{
	thread_t thread = act_lock_thread(thr_act);

#if	MACH_ASSERT
	if (watchacts & WA_ACT_LNK)
		printf("act_alert %x: %x\n", thr_act, alerts);
#endif	/* MACH_ASSERT */

	if (thread) {
		thread_act_t act_up = thr_act;
		while ((alerts) && (act_up != thread->top_act)) {
			act_up = act_up->higher;
			alerts &= act_up->alert_mask;
			act_up->alerts |= alerts;
		}
		/*
		 * XXXX If we reach the top, and it is blocked in glue
		 * code, do something to kick it.  XXXX
		 */
	}
	act_unlock_thread(thr_act);

	return KERN_SUCCESS;
}

kern_return_t act_alert_mask(thread_act_t thr_act, unsigned alert_mask)
{
	panic("act_alert_mask NOT YET IMPLEMENTED\n");
	return KERN_SUCCESS;
}

typedef struct GetSetState {
	struct ReturnHandler rh;
	int flavor;
	void *state;
	int *pcount;
	int result;
} GetSetState;

/* Local Forward decls */
kern_return_t get_set_state(
			thread_act_t thr_act, int flavor,
			thread_state_t state, int *pcount,
			void (*handler)(ReturnHandler *rh, thread_act_t thr_act));
void get_state_handler(ReturnHandler *rh, thread_act_t thr_act);
void set_state_handler(ReturnHandler *rh, thread_act_t thr_act);

/*
 * get_set_state(thr_act ...)
 *
 * General code to install g/set_state handler.
 * Called with thr_act's act_lock() and "appropriate"
 * thread-related locks held.  (See act_lock_thread().)
 */
kern_return_t
get_set_state(thread_act_t thr_act, int flavor, thread_state_t state, int *pcount,
			void (*handler)(ReturnHandler *rh, thread_act_t thr_act))
{
	GetSetState gss;
	spl_t s;

	/* Initialize a small parameter structure */
	gss.rh.handler = handler;
	gss.flavor = flavor;
	gss.state = state;
	gss.pcount = pcount;
	gss.result = KERN_ABORTED;	/* iff wait below is interrupted */

	/* Add it to the thr_act's return handler list */
	gss.rh.next = thr_act->handlers;
	thr_act->handlers = &gss.rh;

	s = splsched();
	act_set_apc(thr_act);
	splx(s);

#if	MACH_ASSERT
	if (watchacts & WA_ACT_HDLR) {
	    printf("act_%x: get_set_state(thr_act=%x flv=%x state=%x ptr@%x=%x)",
		    current_act(), thr_act, flavor, state,
		    pcount, (pcount ? *pcount : 0));
	    printf((handler == get_state_handler ? "get_state_hdlr\n" :
		    (handler == set_state_handler ? "set_state_hdlr\n" :
			"hndler=%x\n")), handler); 
	}
#endif	/* MACH_ASSERT */

	assert(thr_act->thread);	/* Callers must ensure these */
	assert(thr_act != current_act());
	for (;;) {
		nudge(thr_act);
		/*
		 * Wait must be interruptible to avoid deadlock (e.g.) with
		 * task_suspend() when caller and target of get_set_state()
		 * are in same task.
		 */
		assert_wait((event_t)&gss, THREAD_ABORTSAFE);
		act_unlock_thread(thr_act);
		thread_block((void (*)(void))0);
		if (gss.result != KERN_ABORTED)
			break;
		if (current_act()->handlers)
			act_execute_returnhandlers();
		act_lock_thread(thr_act);
	}

#if	MACH_ASSERT
	if (watchacts & WA_ACT_HDLR)
	    printf("act_%x: get_set_state returns %x\n",
			    current_act(), gss.result);
#endif	/* MACH_ASSERT */

	return gss.result;
}

void
set_state_handler(ReturnHandler *rh, thread_act_t thr_act)
{
	GetSetState *gss = (GetSetState*)rh;

#if	MACH_ASSERT
	if (watchacts & WA_ACT_HDLR)
		printf("act_%x: set_state_handler(rh=%x,thr_act=%x)\n",
			current_act(), rh, thr_act);
#endif	/* MACH_ASSERT */

	gss->result = act_machine_set_state(thr_act, gss->flavor,
						gss->state, *gss->pcount);
	thread_wakeup((event_t)gss);
}

void
get_state_handler(ReturnHandler *rh, thread_act_t thr_act)
{
	GetSetState *gss = (GetSetState*)rh;

#if	MACH_ASSERT
	if (watchacts & WA_ACT_HDLR)
		printf("act_%x: get_state_handler(rh=%x,thr_act=%x)\n",
			current_act(), rh, thr_act);
#endif	/* MACH_ASSERT */

	gss->result = act_machine_get_state(thr_act, gss->flavor,
			gss->state, 
			(mach_msg_type_number_t *) gss->pcount);
	thread_wakeup((event_t)gss);
}

kern_return_t
act_get_state_locked(thread_act_t thr_act, int flavor, thread_state_t state,
					mach_msg_type_number_t *pcount)
{
#if	MACH_ASSERT
    if (watchacts & WA_ACT_HDLR)
	printf("act_%x: act_get_state_L(thr_act=%x,flav=%x,st=%x,pcnt@%x=%x)\n",
		current_act(), thr_act, flavor, state, pcount,
		(pcount? *pcount : 0));
#endif	/* MACH_ASSERT */

    return(get_set_state(thr_act, flavor, state, (int*)pcount, get_state_handler));
}

kern_return_t
act_set_state_locked(thread_act_t thr_act, int flavor, thread_state_t state,
					mach_msg_type_number_t count)
{
#if	MACH_ASSERT
    if (watchacts & WA_ACT_HDLR)
	printf("act_%x: act_set_state_L(thr_act=%x,flav=%x,st=%x,pcnt@%x=%x)\n",
		current_act(), thr_act, flavor, state, count, count);
#endif	/* MACH_ASSERT */

    return(get_set_state(thr_act, flavor, state, (int*)&count, set_state_handler));
}

kern_return_t
act_set_state(thread_act_t thr_act, int flavor, thread_state_t state,
					mach_msg_type_number_t count)
{
    if (thr_act == THR_ACT_NULL || thr_act == current_act())
	    return(KERN_INVALID_ARGUMENT);

    act_lock_thread(thr_act);
    return(act_set_state_locked(thr_act, flavor, state, count));
    
}

kern_return_t
act_get_state(thread_act_t thr_act, int flavor, thread_state_t state,
					mach_msg_type_number_t *pcount)
{
    if (thr_act == THR_ACT_NULL || thr_act == current_act())
	    return(KERN_INVALID_ARGUMENT);

    act_lock_thread(thr_act);
    return(act_get_state_locked(thr_act, flavor, state, pcount));
}

/*
 * These two should be called at splsched()
 * Set/clear indicator to run APC (layered on ASTs)
 */
void
act_set_apc(thread_act_t thr_act)
{

	processor_t prssr;
	thread_t thread;
	
	mp_disable_preemption();
	
	thread_ast_set(thr_act, AST_APC);
	if (thr_act == current_act()) {
		ast_propagate(thr_act->ast);
		mp_enable_preemption();
		return;							/* If we are current act, we can't be on the other processor so leave now */
	}

/*
 *	Here we want to make sure that the apc is taken quickly.  Therefore, we check
 *	if, and where, the activation is running.  If it is not running, we don't need to do 
 *	anything.  If it is, we need to signal the other processor to trigger it to 
 *	check the asts.  Note that there is a race here and we may end up sending a signal
 *	after the thread has been switched off.  Hopefully this is no big deal.
 */

	thread = thr_act->thread;			/* Get the thread for the signaled activation */
	prssr = thread->last_processor;		/* get the processor it was last on */
	if(prssr && (cpu_data[prssr->slot_num].active_thread == thread)) {	/* Is the thread active on its processor? */
		cause_ast_check(prssr);			/* Yes, kick it */
	}
	
	mp_enable_preemption();
}

void
act_clr_apc(thread_act_t thr_act)
{
	thread_ast_clear(thr_act, AST_APC);
}

void
act_ulock_release_all(thread_act_t thr_act)
{
	ulock_t	ulock;

	while (!queue_empty(&thr_act->held_ulocks)) {
		ulock = (ulock_t) queue_first(&thr_act->held_ulocks);
		(void) lock_make_unstable(ulock, thr_act);
		(void) lock_release_internal(ulock, thr_act);
	}
}

/*
 * Provide routines (for export to other components) of things that
 * are implemented as macros insternally.
 */
#undef current_act
thread_act_t
current_act(void)
{
	return(current_act_fast());
}

thread_act_t
thread_self(void)
{
	thread_act_t self = current_act_fast();

	act_reference(self);
	return self;
}

thread_act_t
mach_thread_self(void)
{
	thread_act_t self = current_act_fast();

	act_reference(self);
	return self;
}

#undef act_reference
void
act_reference(
	thread_act_t thr_act)
{
	act_reference_fast(thr_act);
}

#undef act_deallocate
void
act_deallocate(
	thread_act_t thr_act) 
{
	act_deallocate_fast(thr_act);
}