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minix/kernel/proc.c
Jorrit Herder 852008d669 Kinfo counts lock_notify() and lock_send() calls.
2005-05-27 14:54:40 +00:00

684 lines
24 KiB
C
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#define NEW_SCHED_Q 1
#define OLD_SEND 0
#define OLD_RECV 0
/* This file contains essentially all of the process and message handling.
* It has one main entry point from the outside:
*
* sys_call: a system call, i.e., the kernel is trapped with an INT
*
* It also has several minor entry points to be used from the task level:
*
* lock_notify: send a notification to inform a process of a system event
* lock_send: send a message to a process
* lock_ready: put a process on one of the ready queues so it can be run
* lock_unready: remove a process from the ready queues
* lock_sched: a process has run too long; schedule another one
* lock_pick_proc: pick a process to run (used by system initialization)
*
* Changes:
* May 26, 2005 optimized message passing functions (Jorrit N. Herder)
* May 24, 2005 new, queued NOTIFY system call (Jorrit N. Herder)
* Oct 28, 2004 non-blocking SEND and RECEIVE (Jorrit N. Herder)
* Oct 28, 2004 rewrite of sys_call() (Jorrit N. Herder)
* Oct 10, 2004 require SENDREC for kernel sys_call() (Jorrit N. Herder)
* (to protect kernel tasks from being blocked)
* Aug 19, 2004 generalized ready()/unready() (Jorrit N. Herder)
*/
#include "kernel.h"
#include <minix/callnr.h>
#include <minix/com.h>
#include "proc.h"
#include "ipc.h"
#include "sendmask.h"
/* Scheduling and message passing functions. The functions are available to
* other parts of the kernel through lock_...(). The lock temporarily disables
* interrupts to prevent race conditions.
*/
FORWARD _PROTOTYPE( int mini_send, (struct proc *caller_ptr, int dst,
message *m_ptr, unsigned flags) );
FORWARD _PROTOTYPE( int mini_rec, (struct proc *caller_ptr, int src,
message *m_ptr, unsigned flags) );
FORWARD _PROTOTYPE( int mini_notify, (struct proc *caller_ptr, int dst,
message *m_ptr ) );
FORWARD _PROTOTYPE( void ready, (struct proc *rp) );
FORWARD _PROTOTYPE( void sched, (int queue) );
FORWARD _PROTOTYPE( void unready, (struct proc *rp) );
FORWARD _PROTOTYPE( void pick_proc, (void) );
#define BuildMess(m,n) \
(m).NOTIFY_SOURCE = (n)->n_source, \
(m).NOTIFY_TYPE = (n)->n_type, \
(m).NOTIFY_FLAGS = (n)->n_flags, \
(m).NOTIFY_ARG = (n)->n_arg;
#if (CHIP == INTEL)
#define CopyMess(s,sp,sm,dp,dm) \
cp_mess(s, (sp)->p_memmap[D].mem_phys, (vir_bytes)sm, (dp)->p_memmap[D].mem_phys, (vir_bytes)dm)
#endif /* (CHIP == INTEL) */
#if (CHIP == M68000)
/* M68000 does not have cp_mess() in assembly like INTEL. Declare prototype
* for cp_mess() here and define the function below. Also define CopyMess.
*/
#endif /* (CHIP == M68000) */
/* Declare buffer space and a bit map for notification messages. */
PRIVATE struct notification notify_buffer[NR_NOTIFY_BUFS];
PRIVATE bitchunk_t notify_bitmap[BITMAP_CHUNKS(NR_NOTIFY_BUFS)];
/*===========================================================================*
* sys_call *
*===========================================================================*/
PUBLIC int sys_call(call_nr, src_dst, m_ptr)
int call_nr; /* (NB_)SEND, (NB_)RECEIVE, SENDREC */
int src_dst; /* src to receive from or dst to send to */
message *m_ptr; /* pointer to message in the caller's space */
{
/* System calls are done by trapping to the kernel with an INT instruction.
* The trap is caught and sys_call() is called to send or receive a message
* (or both). The caller is always given by 'proc_ptr'.
*/
register struct proc *caller_ptr = proc_ptr; /* get pointer to caller */
int function = call_nr & SYSCALL_FUNC; /* get system call function */
unsigned flags = call_nr & SYSCALL_FLAGS; /* get flags */
int mask_entry; /* bit to check in send mask */
int result; /* the system call's result */
vir_bytes vb; /* message buffer pointer as vir_bytes */
vir_clicks vlo, vhi; /* virtual clicks containing message to send */
/* Calls directed to the kernel may only be sendrec(), because tasks always
* reply and may not block if the caller doesn't do receive(). Users also
* may only use sendrec() to protect the process manager and file system.
*/
if (iskernel(src_dst) && function != SENDREC)
return(ECALLDENIED); /* SENDREC was required */
/* Verify that requested source and/ or destination is a valid process. */
if (! isoksrc_dst(src_dst) && function != ECHO)
return(EBADSRCDST);
/* Check validity of message pointer. */
vb = (vir_bytes) m_ptr;
vlo = vb >> CLICK_SHIFT; /* vir click for bottom of message */
vhi = (vb + MESS_SIZE - 1) >> CLICK_SHIFT; /* vir click for top of msg */
#if ALLOW_GAP_MESSAGES
/* This check allows a message to be anywhere in data or stack or gap.
* It will have to be made more elaborate later for machines which
* don't have the gap mapped.
*/
if (vlo < caller_ptr->p_memmap[D].mem_vir || vlo > vhi ||
vhi >= caller_ptr->p_memmap[S].mem_vir + caller_ptr->p_memmap[S].mem_len)
return(EFAULT);
#else
/* Check for messages wrapping around top of memory or outside data seg. */
if (vhi < vlo ||
vhi - caller_ptr->p_memmap[D].mem_vir >= caller_ptr->p_memmap[D].mem_len)
return(EFAULT);
#endif
/* Now check if the call is known and try to perform the request. The only
* system calls that exist in MINIX are sending and receiving messages.
* Receiving is straightforward. Sending requires to check caller's send
* mask and whether the destination is alive.
*/
switch(function) {
case SENDREC:
flags |= FRESH_ANSWER; /* ignore pending notifications */
/* fall through */
case SEND:
if (! isalive(src_dst)) {
result = EDEADDST; /* cannot send to the dead */
break;
}
mask_entry = isuser(src_dst) ? USER_PROC_NR : src_dst;
if (! isallowed(caller_ptr->p_sendmask, mask_entry)) {
kprintf("WARNING: sys_call denied %d ", caller_ptr->p_nr);
kprintf("sending to %d\n", proc_addr(src_dst)->p_nr);
result = ECALLDENIED; /* call denied by send mask */
break;
}
result = mini_send(caller_ptr, src_dst, m_ptr, flags);
if (function == SEND || result != OK) {
break; /* done, or SEND failed */
} /* fall through for SENDREC */
case RECEIVE:
result = mini_rec(caller_ptr, src_dst, m_ptr, flags);
break;
case NOTIFY:
result = mini_notify(caller_ptr, src_dst, m_ptr);
break;
case ECHO:
kprintf("Echo message from process %s\n", proc_nr(caller_ptr));
CopyMess(caller_ptr->p_nr, caller_ptr, m_ptr, caller_ptr, m_ptr);
result = OK;
break;
default:
result = EBADCALL; /* illegal system call */
}
/* Now, return the result of the system call to the caller. */
return(result);
}
/*===========================================================================*
* mini_send *
*===========================================================================*/
PRIVATE int mini_send(caller_ptr, dst, m_ptr, flags)
register struct proc *caller_ptr; /* who is trying to send a message? */
int dst; /* to whom is message being sent? */
message *m_ptr; /* pointer to message buffer */
unsigned flags; /* system call flags */
{
/* Send a message from 'caller_ptr' to 'dst'. If 'dst' is blocked waiting
* for this message, copy the message to it and unblock 'dst'. If 'dst' is
* not waiting at all, or is waiting for another source, queue 'caller_ptr'.
*/
register struct proc *dst_ptr;
#if OLD_SEND
register struct proc *next_ptr;
register struct proc *xp;
#else
register struct proc **xpp;
#endif
dst_ptr = proc_addr(dst); /* pointer to destination's proc entry */
/* Check for deadlock by 'caller_ptr' and 'dst' sending to each other.
* This check is rare, so overhead is acceptable.
*/
if (dst_ptr->p_flags & SENDING) {
next_ptr = proc_addr(dst_ptr->p_sendto);
while (TRUE) {
if (next_ptr == caller_ptr) return(ELOCKED);
if (next_ptr->p_flags & SENDING)
next_ptr = proc_addr(next_ptr->p_sendto);
else
break;
}
}
/* Check if 'dst' is blocked waiting for this message. The destination's
* SENDING flag may be set when SENDREC couldn't send. Await a pure RECEIVE.
*/
if ( (dst_ptr->p_flags & (RECEIVING | SENDING)) == RECEIVING &&
(dst_ptr->p_getfrom == ANY || dst_ptr->p_getfrom == caller_ptr->p_nr)) {
/* Destination is indeed waiting for this message. */
CopyMess(caller_ptr->p_nr, caller_ptr, m_ptr, dst_ptr,
dst_ptr->p_messbuf);
if ((dst_ptr->p_flags &= ~RECEIVING) == 0)
ready(dst_ptr);
} else if ( ! (flags & NON_BLOCKING)) {
/* Destination is not waiting. Block and queue caller. */
caller_ptr->p_messbuf = m_ptr;
if (caller_ptr->p_flags == 0) unready(caller_ptr);
caller_ptr->p_flags |= SENDING;
caller_ptr->p_sendto = dst;
/* Process is now blocked. Put in on the destination's queue. */
#if OLD_SEND
if ( (next_ptr = dst_ptr->p_caller_q) == NIL_PROC)
dst_ptr->p_caller_q = caller_ptr;
else {
while (next_ptr->p_q_link != NIL_PROC)
next_ptr = next_ptr->p_q_link;
next_ptr->p_q_link = caller_ptr;
}
#else
xpp = &dst_ptr->p_caller_q;
while (*xpp != NIL_PROC) xpp = &(*xpp)->p_q_link;
*xpp = caller_ptr;
#endif
caller_ptr->p_q_link = NIL_PROC;
} else {
kprintf("Didn't block... ;-), flags: 0x%x\n", flags);
return(ENOTREADY);
}
return(OK);
}
/*===========================================================================*
* mini_rec *
*===========================================================================*/
PRIVATE int mini_rec(caller_ptr, src, m_ptr, flags)
register struct proc *caller_ptr; /* process trying to get message */
int src; /* which message source is wanted */
message *m_ptr; /* pointer to message buffer */
unsigned flags; /* system call flags */
{
/* A process or task wants to get a message. If one is already queued,
* acquire it and deblock the sender. If no message from the desired source
* is available, block the caller.
*/
#if OLD_RECV
register struct proc *sender_ptr;
register struct proc *previous_ptr;
#else
register struct proc **xpp;
#endif
register struct notification **ntf_q_pp;
message m;
int bit_nr;
/* Check to see if a message from desired source is already available.
* The caller's SENDING flag may be set if SENDREC couldn't send. If it is
* set, the process should be blocked.
*/
if (!(caller_ptr->p_flags & SENDING)) {
/* Check caller queue. Use pointer pointers to keep code simple. */
#if OLD_RECV /* to hairy, unreadable */
for (sender_ptr = caller_ptr->p_caller_q; sender_ptr != NIL_PROC;
previous_ptr = sender_ptr, sender_ptr = sender_ptr->p_q_link) {
if (src == ANY || src == proc_nr(sender_ptr)) {
/* An acceptable message has been found. */
CopyMess(sender_ptr->p_nr, sender_ptr,
sender_ptr->p_messbuf, caller_ptr, m_ptr);
if (sender_ptr == caller_ptr->p_caller_q)
caller_ptr->p_caller_q = sender_ptr->p_q_link;
else
previous_ptr->p_q_link = sender_ptr->p_q_link;
if ((sender_ptr->p_flags &= ~SENDING) == 0)
ready(sender_ptr); /* deblock sender */
return(OK);
}
}
#else
xpp = &caller_ptr->p_caller_q;
while (*xpp != NIL_PROC) {
if (src == ANY || src == proc_nr(*xpp)) {
/* An acceptable source has been found. Copy the message to the
* caller, update the sender's status, and remove the sender from
* the caller's queue.
*/
CopyMess((*xpp)->p_nr, *xpp, (*xpp)->p_messbuf, caller_ptr, m_ptr);
if (((*xpp)->p_flags &= ~SENDING) == 0) ready(*xpp);
*xpp = (*xpp)->p_q_link; /* remove from queue */
return(OK);
}
xpp = &(*xpp)->p_q_link; /* proceed to next */
}
#endif
/* Check if there are pending notifications. */
if (! (flags & FRESH_ANSWER)) {
ntf_q_pp = &caller_ptr->p_ntf_q; /* get pointer pointer */
while (*ntf_q_pp != NULL) {
if (src == ANY || src == (*ntf_q_pp)->n_source) {
/* Found notification. Assemble and copy message. */
BuildMess(m, *ntf_q_pp);
CopyMess((*ntf_q_pp)->n_source, proc_addr(HARDWARE), &m,
caller_ptr, m_ptr);
/* Remove notification from queue and bit map. */
bit_nr = (int) (*ntf_q_pp - &notify_buffer[0]);
*ntf_q_pp = (*ntf_q_pp)->n_next;/* remove from queue */
free_bit(bit_nr, notify_bitmap, NR_NOTIFY_BUFS);
return(OK); /* report success */
}
ntf_q_pp = &(*ntf_q_pp)->n_next; /* proceed to next */
}
}
}
/* No suitable message is available or the caller couldn't send in SENDREC.
* Block the process trying to receive, unless the flags tell otherwise.
*/
if ( ! (flags & NON_BLOCKING)) {
caller_ptr->p_getfrom = src;
caller_ptr->p_messbuf = m_ptr;
if (caller_ptr->p_flags == 0) unready(caller_ptr);
caller_ptr->p_flags |= RECEIVING;
return(OK);
} else {
return(ENOTREADY);
}
}
/*===========================================================================*
* mini_notify *
*===========================================================================*/
PRIVATE int mini_notify(caller_ptr, dst, m_ptr)
register struct proc *caller_ptr; /* process trying to notify */
int dst; /* which process to notify */
message *m_ptr; /* pointer to message buffer */
{
register struct proc *dst_ptr = proc_addr(dst);
register struct notification *ntf_p ;
register struct notification **ntf_q_pp;
int ntf_index;
message ntf_mess;
/* Check to see if target is blocked waiting for this message. A process
* can be both sending and receiving during a SENDREC system call.
*/
if ( (dst_ptr->p_flags & (RECEIVING|SENDING)) == RECEIVING &&
(dst_ptr->p_getfrom == ANY || dst_ptr->p_getfrom == caller_ptr->p_nr)) {
/* Destination is indeed waiting for this message. */
CopyMess(proc_nr(caller_ptr), caller_ptr, m_ptr,
dst_ptr, dst_ptr->p_messbuf);
dst_ptr->p_flags &= ~RECEIVING; /* deblock destination */
if (dst_ptr->p_flags == 0) ready(dst_ptr);
return(OK);
}
/* Destination is not ready. Add the notification to the pending queue.
* Get pointer to notification message. Don't copy for the kernel.
*/
if (! iskernelp(caller_ptr)) {
CopyMess(proc_nr(caller_ptr), caller_ptr, m_ptr,
proc_addr(HARDWARE), &ntf_mess);
m_ptr = &ntf_mess;
}
/* Enqueue the message. Existing notifications with the same source
* and type are overwritten with newer ones. New notifications that
* are not yet on the list are added to the end.
*/
ntf_q_pp = &dst_ptr->p_ntf_q;
while (*ntf_q_pp != NULL) {
/* Replace notifications with same source and type. */
if ((*ntf_q_pp)->n_type == m_ptr->NOTIFY_TYPE &&
(*ntf_q_pp)->n_source == proc_nr(caller_ptr)) {
(*ntf_q_pp)->n_flags = m_ptr->NOTIFY_FLAGS;
(*ntf_q_pp)->n_arg = m_ptr->NOTIFY_ARG;
return(OK);
}
ntf_q_pp = &(*ntf_q_pp)->n_next;
}
/* Add to end of queue (found above). Get a free notification buffer. */
if ((ntf_index = alloc_bit(notify_bitmap, NR_NOTIFY_BUFS)) < 0)
return(ENOSPC);
ntf_p = &notify_buffer[ntf_index];
*ntf_q_pp = ntf_p; /* add to end of queue */
ntf_p->n_next = NULL; /* mark new end of queue */
ntf_p->n_source = proc_nr(caller_ptr);
ntf_p->n_type = m_ptr->NOTIFY_TYPE;
ntf_p->n_flags = m_ptr->NOTIFY_FLAGS;
ntf_p->n_arg = m_ptr->NOTIFY_ARG;
return(OK);
}
/*==========================================================================*
* lock_notify *
*==========================================================================*/
PUBLIC int lock_notify(dst, m_ptr)
int dst; /* to whom is message being sent? */
message *m_ptr; /* pointer to message buffer */
{
/* Safe gateway to mini_notify() for tasks and interrupt handlers. This
* function checks if it is called from an interrupt handler and makes sure
* that the correct message source is put on the notification.
*/
int result;
struct proc *caller_ptr;
lock();
kinfo.lock_notify ++;
caller_ptr = (k_reenter >= 0) ? proc_addr(HARDWARE) : proc_ptr;
result = mini_notify(caller_ptr, dst, m_ptr);
unlock();
return(result);
}
/*===========================================================================*
* pick_proc *
*===========================================================================*/
PRIVATE void pick_proc()
{
/* Decide who to run now. A new process is selected by setting 'next_ptr'.
* When a fresh user (or idle) process is selected, record it in 'bill_ptr',
* so the clock task can tell who to bill for system time.
*/
register struct proc *rp; /* process to run */
int q; /* iterate over queues */
/* Check each of the scheduling queues for ready processes. The number of
* queues is defined in proc.h, and priorities are set in the task table.
* The lowest queue contains IDLE, which is always ready.
*/
for (q=0; q < NR_SCHED_QUEUES; q++) {
if ( (rp = rdy_head[q]) != NIL_PROC) {
next_ptr = rp; /* run process 'rp' next */
if (isuserp(rp) || isidlep(rp)) /* possible bill 'rp' */
bill_ptr = rp;
return;
}
}
}
/*===========================================================================*
* ready *
*===========================================================================*/
PRIVATE void ready(rp)
register struct proc *rp; /* this process is now runnable */
{
/* Add 'rp' to one of the queues of runnable processes. */
register int q = rp->p_priority; /* scheduling queue to use */
register struct proc **xpp; /* iterate over queue */
#if ENABLE_K_DEBUGGING
if(rp->p_ready) {
kprintf("ready() already ready process\n", NO_NUM);
}
rp->p_ready = 1;
#endif
/* Processes, in principle, are added to the end of the queue. However,
* user processes are added in front of the queue, because this is a bit
* fairer to I/O bound processes.
*/
#if NEW_SCHED_Q
if (isuserp(rp)) { /* add to front of queue */
rp->p_nextready = rdy_head[q]; /* chain current front */
rdy_head[q] = rp; /* ready process becomes front */
}
else { /* add to end of queue */
xpp = &rdy_head[q]; /* find pointer to end of queue */
while (*xpp != NIL_PROC) xpp = &(*xpp)->p_nextready;
*xpp = rp; /* replace end with ready process */
rp->p_nextready = NIL_PROC; /* mark end of queue */
}
#else
if (isuserp(rp)) { /* add to front of queue */
if (rdy_head[q] == NIL_PROC)
rdy_tail[q] = rp;
rp->p_nextready = rdy_head[q]; /* add to front of queue */
rdy_head[q] = rp;
}
else {
if (rdy_head[q] != NIL_PROC)
rdy_tail[q]->p_nextready = rp; /* add to end of queue */
else
rdy_head[q] = rp; /* add to empty queue */
rdy_tail[q] = rp;
rp->p_nextready = NIL_PROC;
}
#endif
/* Run 'rp' next if it has a higher priority than 'proc_ptr' or 'next_ptr'.
* This actually should be done via pick_proc(), but the message passing
* functions rely on this side-effect. High priorities have a lower number.
*/
if (next_ptr && next_ptr->p_priority > rp->p_priority) next_ptr = rp;
else if (proc_ptr->p_priority > rp->p_priority) next_ptr = rp;
}
/*===========================================================================*
* unready *
*===========================================================================*/
PRIVATE void unready(rp)
register struct proc *rp; /* this process is no longer runnable */
{
/* A process has blocked. See ready for a description of the queues. */
register int q = rp->p_priority; /* queue to use */
#if NEW_SCHED_Q
register struct proc **xpp; /* iterate over queue */
#else
register struct proc **qtail; /* queue's rdy_tail */
register struct proc *xp;
#endif
#if ENABLE_K_DEBUGGING
if(!rp->p_ready) {
kprintf("unready() already unready process\n", NO_NUM);
}
rp->p_ready = 0;
#endif
/* Side-effect for tasks: check if the task's stack still is ok? */
if (istaskp(rp)) {
if (*rp->p_stguard != STACK_GUARD)
panic("stack overrun by task", proc_nr(rp));
}
/* Now make sure that the process is not in its ready queue. Remove the
* process if it is found. A process can be made unready even if it is not
* running by being sent a signal that kills it.
*/
#if NEW_SCHED_Q
xpp = &rdy_head[q];
while (*xpp != NIL_PROC) { /* check entire queue */
if (*xpp == rp) { /* lookup unready process */
*xpp = (*xpp)->p_nextready; /* replace it with next */
if (rp == proc_ptr || rp == next_ptr) /* current process removed */
pick_proc(); /* pick new process to run */
break;
}
xpp = &(*xpp)->p_nextready; /* proceed to next */
}
#else
if ( (xp = rdy_head[q]) != NIL_PROC) { /* ready queue is empty */
if (xp == rp) { /* check head of queue */
rdy_head[q] = xp->p_nextready; /* new head of queue */
if (rp == proc_ptr || rp == next_ptr) /* current process removed */
pick_proc(); /* pick new process to run */
if(rp == rdy_tail[q])
rdy_tail[q] = NIL_PROC;
}
else { /* check body of queue */
while (xp->p_nextready != rp) /* stop if process is next */
if ( (xp = xp->p_nextready) == NIL_PROC)
return;
xp->p_nextready = xp->p_nextready->p_nextready;
if (rdy_tail[q] == rp) /* possibly update tail */
rdy_tail[q] = xp;
}
}
#endif
}
/*===========================================================================*
* sched *
*===========================================================================*/
PRIVATE void sched(queue)
int queue;
{
/* The current process has run too long. If another low priority (user)
* process is runnable, put the current process on the end of the user queue,
* possibly promoting another user to head of the queue.
*/
register struct proc **xpp;
register struct proc *xp;
if (rdy_head[queue] == NIL_PROC) return;
/* One or more user processes queued. */
#if NEW_SCHED_Q
xp = rdy_head[queue]; /* save expired process */
rdy_head[queue] = xp->p_nextready; /* advance to next process */
xpp = &rdy_head[queue]; /* find end of queue */
while (*xpp != NIL_PROC) xpp = &(*xpp)->p_nextready;
*xpp = xp; /* add expired to end */
xp->p_nextready = NIL_PROC; /* mark end of queue */
#else
rdy_tail[queue]->p_nextready = rdy_head[queue];
rdy_tail[queue] = rdy_head[queue];
rdy_head[queue] = rdy_head[queue]->p_nextready;
rdy_tail[queue]->p_nextready = NIL_PROC;
#endif
pick_proc();
}
/*==========================================================================*
* lock_pick_proc *
*==========================================================================*/
PUBLIC void lock_pick_proc()
{
/* Safe gateway to pick_proc() for tasks. */
lock();
pick_proc();
unlock();
}
/*==========================================================================*
* lock_send *
*==========================================================================*/
PUBLIC int lock_send(dst, m_ptr)
int dst; /* to whom is message being sent? */
message *m_ptr; /* pointer to message buffer */
{
/* Safe gateway to mini_send() for tasks. */
int result;
lock();
kinfo.lock_send ++;
result = mini_send(proc_ptr, dst, m_ptr, NON_BLOCKING);
unlock();
return(result);
}
/*==========================================================================*
* lock_ready *
*==========================================================================*/
PUBLIC void lock_ready(rp)
struct proc *rp; /* this process is now runnable */
{
/* Safe gateway to ready() for tasks. */
lock();
ready(rp);
unlock();
}
/*==========================================================================*
* lock_unready *
*==========================================================================*/
PUBLIC void lock_unready(rp)
struct proc *rp; /* this process is no longer runnable */
{
/* Safe gateway to unready() for tasks. */
lock();
unready(rp);
unlock();
}
/*==========================================================================*
* lock_sched *
*==========================================================================*/
PUBLIC void lock_sched(queue)
int queue;
{
/* Safe gateway to sched() for tasks. */
lock();
sched(queue);
unlock();
}
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