Commit Graph

292 Commits

Author SHA1 Message Date
jhb
f5e3969340 Allow threads to atomically release rw and sx locks while waiting for an
event.  Locking primitives that support this (mtx, rw, and sx) now each
include their own foo_sleep() routine.
- Rename msleep() to _sleep() and change it's 'struct mtx' object to a
  'struct lock_object' pointer.  _sleep() uses the recently added
  lc_unlock() and lc_lock() function pointers for the lock class of the
  specified lock to release the lock while the thread is suspended.
- Add wrappers around _sleep() for mutexes (mtx_sleep()), rw locks
  (rw_sleep()), and sx locks (sx_sleep()).  msleep() still exists and
  is now identical to mtx_sleep(), but it is deprecated.
- Rename SLEEPQ_MSLEEP to SLEEPQ_SLEEP.
- Rewrite much of sleep.9 to not be msleep(9) centric.
- Flesh out the 'RETURN VALUES' section in sleep.9 and add an 'ERRORS'
  section.
- Add __nonnull(1) to _sleep() and msleep_spin() so that the compiler will
  warn if you try to pass a NULL wait channel.  The functions already have
  a KASSERT to that effect.
2007-03-09 22:41:01 +00:00
julian
80d6cde009 Instead of doing comparisons using the pcpu area to see if
a thread is an idle thread, just see if it has the IDLETD
flag set. That flag will probably move to the pflags word
as it's permenent and never chenges for the life of the
system so it doesn't need locking.
2007-03-08 06:44:34 +00:00
rwatson
69938bd196 Further system call comment cleanup:
- Remove also "MP SAFE" after prior "MPSAFE" pass. (suggested by bde)
- Remove extra blank lines in some cases.
- Add extra blank lines in some cases.
- Remove no-op comments consisting solely of the function name, the word
  "syscall", or the system call name.
- Add punctuation.
- Re-wrap some comments.
2007-03-05 13:10:58 +00:00
jhb
b7c2a59c51 Print tid's rather than thread pointers in KTR_PROC traces. 2007-02-27 18:46:07 +00:00
jhb
401f7aaf8a Add a new kernel sleep function pause(9). pause(9) is for places that
want an equivalent of DELAY(9) that sleeps instead of spins.  It accepts
a wmesg and a timeout and is not interrupted by signals.  It uses a private
wait channel that should never be woken up by wakeup(9) or wakeup_one(9).

Glanced at by:	phk
2007-02-23 16:22:09 +00:00
jeff
b5c5ce5407 - Fix schedgraph output with KSE threads. Call thread_switchout() after
calling CTR() so we don't confuse a new kse thread with a real preemption.
2007-01-03 02:38:41 +00:00
kmacy
7327d346fc Add second sleep queue so that sx and lockmgr can have separate sleep
queues for shared and exclusive acquisitions

Submitted by: Attilio Rao
Approved by: jhb
2006-12-16 06:54:09 +00:00
phk
b911f6e6f0 Only grab the sched_lock if we actually need to modify the thread priority.
During a buildworld only 2/3 of the calls to msleep actually changed
the priority.
2006-11-30 08:27:38 +00:00
pjd
63d82b700d Change sleepq_add(9) argument from 'struct mtx *' to 'struct lock_object *',
which allows to use it with different kinds of locks. For example it allows
to implement Solaris conditions variables which will be used in ZFS port on
top of sx(9) locks.

Reviewed by:	jhb
2006-11-16 01:02:00 +00:00
jhb
fa8eeee427 Adjust assertions to allow for magical properties of the 'lbolt' wait
channel for tsleep():
- Allow tsleep() on &lbolt without Giant with a timeout 0 since &lbolt has
  an implied timeout.
- If &lbolt is used with msleep() pass NULL to sleepq_add() for the lock
  object.  Unlike other sleepq channels, &lbolt doesn't have an associated
  owning lock.
2006-11-15 20:44:07 +00:00
jb
f82c799735 Make KSE a kernel option, turned on by default in all GENERIC
kernel configs except sun4v (which doesn't process signals properly
with KSE).

Reviewed by:	davidxu@
2006-10-26 21:42:22 +00:00
davidxu
1689a257a3 Use scheduler API sched_relinquish() to implement yield() syscall. 2006-06-15 06:41:57 +00:00
jhb
dc064c4d48 In the case of reentering the debugger due to an attempt to perform a
context switch while in the debugger, reenter the debugger sooner before
performing any statistics updates.
2006-06-03 20:49:44 +00:00
jhb
d535a5cb81 Change msleep() and tsleep() to not alter the calling thread's priority
if the specified priority is zero.  This avoids a race where the calling
thread could read a snapshot of it's current priority, then a different
thread could change the first thread's priority, then the original thread
would call sched_prio() inside msleep() undoing the change made by the
second thread.  I used a priority of zero as no thread that calls msleep()
or tsleep() should be specifying a priority of zero anyway.

The various places that passed 'curthread->td_priority' or some variant
as the priority now pass 0.
2006-04-17 18:20:38 +00:00
davidxu
e29c8e080b Fix a sleep queue race for KSE thread.
Reviewed by: jhb
2006-02-23 00:13:58 +00:00
jhb
1462e3bf37 Fixup some comments. Mutexes's are locked, not entered for several years
now and msleep blocks threads rather than processes.
2006-02-22 20:46:10 +00:00
davidxu
f1ce5c8660 Fix a long standing race between sleep queue and thread
suspension code. When a thread A is going to sleep, it calls
sleepq_catch_signals() to detect any pending signals or thread
suspension request, if nothing happens, it returns without
holding process lock or scheduler lock, this opens a race
window which allows thread B to come in and do process
suspension work, however since A is still at running state,
thread B can do nothing to A, thread A continues, and puts
itself into actually sleeping state, but B has never seen it,
and it sits there forever until B is woken up by other threads
sometimes later(this can be very long delay or never
happen). Fix this bug by forcing sleepq_catch_signals to
return with scheduler lock held.
Fix sleepq_abort() by passing it an interrupted code, previously,
it worked as wakeup_one(), and the interruption can not be
identified correctly by sleep queue code when the sleeping
thread is resumed.
Let thread_suspend_check() returns EINTR or ERESTART, so sleep
queue no longer has to use SIGSTOP as a hack to build a return
value.

Reviewed by:	jhb
MFC after:	1 week
2006-02-15 23:52:01 +00:00
phk
79081baaf0 CPU time accounting speedup (step 2)
Keep accounting time (in per-cpu) cputicks and the statistics counts
in the thread and summarize into struct proc when at context switch.

Don't reach across CPUs in calcru().

Add code to calibrate the top speed of cpu_tickrate() for variable
cpu_tick hardware (like TSC on power managed machines).

Don't enforce monotonicity (at least for now) in calcru.  While the
calibrated cpu_tickrate ramps up it may not be true.

Use 27MHz counter on i386/Geode.

Use TSC on amd64 & i386 if present.

Use tick counter on sparc64
2006-02-11 09:33:07 +00:00
phk
bb2f62f536 Modify the way we account for CPU time spent (step 1)
Keep track of time spent by the cpu in various contexts in units of
"cputicks" and scale to real-world microsec^H^H^H^H^H^H^H^Hclock_t
only when somebody wants to inspect the numbers.

For now "cputicks" are still derived from the current timecounter
and therefore things should by definition remain sensible also on
SMP machines.  (The main reason for this first milestone commit is
to verify that hypothesis.)

On slower machines, the avoided multiplications to normalize timestams
at every context switch, comes out as a 5-7% better score on the
unixbench/context1 microbenchmark.  On more modern hardware no change
in performance is seen.
2006-02-07 21:22:02 +00:00
jhb
c0024de329 patch(1) and I aren't friends today. Axe a duplicate copy of
the msleep_spin() function definition.

Spotted by:	pjd
2005-12-29 21:15:32 +00:00
jhb
dc2b7b5f5d Add a new function msleep_spin() which is a slightly stripped down version
of msleep().  msleep_spin() doesn't support changing the priority of the
thread while it is asleep nor does it support interruptible sleeps (PCATCH)
or the PDROP flag.  It does support timeouts however.  It differs from
msleep() in that the passed in mutex is a spin mutex.  This means one can
use msleep_spin() and wakeup() with a spin mutex similar to msleep() and
wakeup() with a regular mutex.  Note that the spin mutex in question needs
to come before sched_lock and the sleepq locks in lock order.
2005-12-29 20:57:45 +00:00
jhb
76c1ae2002 When checking to see if a process has exceeded its time limit, flag the
process as over the limit when its time is >= to the limit rather than >
the limit.  Technically, if p->p_rux.rux_runtime.sec == p->p_pcpulimit
and p->p_rux.rux_runtime.frac == 0, the process hasn't exceeded the limit
yet.  However, having the fraction exactly equal to 0 is rather rare, and
it is not worth the overhead to handle that edge case.  With just the >
comparison, the process would have to exceed its limit by almost a second
before it was killed.

PR:		kern/83192
Submitted by:	Maciej Zawadzinski mzawadzinski at gmail dot com
Reviewed by:	bde
MFC after:	1 week
2005-11-28 19:09:08 +00:00
ups
acfce18a2a Use low level constructs borrowed from interrupt threads to wait for
work in proc0.
Remove the TDP_WAKEPROC0 workaround.
2005-05-23 23:01:53 +00:00
ups
7bac02c146 Sprinkle some volatile magic and rearrange things a bit to avoid race
conditions in critical_exit now that it no longer blocks interrupts.

Reviewed by:	jhb
2005-04-08 03:37:53 +00:00
jhb
c5e6b72803 Don't recursively panic when we call mi_switch() in a critical section,
even though calling mi_switch() after a panic is likely a bug anyway as
the recursive panic only serves to make things worse.
2005-03-31 20:36:44 +00:00
jhb
7b611b0cb2 Stop explicitly touching td_base_pri outside of the scheduler and simply
set a thread's priority via sched_prio() when that is the desired action.
The schedulers will start managing td_base_pri internally shortly.
2004-12-30 20:29:58 +00:00
jeff
c2b9649e7a - Define KTR points for KTR_SCHED. 2004-12-26 00:14:21 +00:00
davidxu
9188104a8f Unlock mutex if PDROP was set by caller. 2004-11-27 11:43:31 +00:00
scottl
e049505e4b If a process needs to be swapped in, wakeup the swapper from within
critical_exit as the process is getting scheduled to run.  This is subotimal
but for now avoid the LOR between the scheduler and the sleepq systems.
This is a 5.3 candidate.

Submitted by: davidxu
MFC After: 3 days
2004-10-16 06:38:22 +00:00
jhb
a8c1c80ef5 Refine the turnstile and sleep queue interfaces just a bit:
- Add a new _lock() call to each API that locks the associated chain lock
  for a lock_object pointer or wait channel.  The _lookup() functions now
  require that the chain lock be locked via _lock() when they are called.
- Change sleepq_add(), turnstile_wait() and turnstile_claim() to lookup
  the associated queue structure internally via _lookup() rather than
  accepting a pointer from the caller.  For turnstiles, this means that
  the actual lookup of the turnstile in the hash table is only done when
  the thread actually blocks rather than being done on each loop iteration
  in _mtx_lock_sleep().  For sleep queues, this means that sleepq_lookup()
  is no longer used outside of the sleep queue code except to implement an
  assertion in cv_destroy().
- Change sleepq_broadcast() and sleepq_signal() to require that the chain
  lock is already required.  For condition variables, this lets the
  cv_broadcast() and cv_signal() functions lock the sleep queue chain lock
  while testing the waiters count.  This means that the waiters count
  internal to condition variables is no longer protected by the interlock
  mutex and cv_broadcast() and cv_signal() now no longer require that the
  interlock be held when they are called.  This lets consumers of condition
  variables drop the lock before waking other threads which can result in
  fewer context switches.

MFC after:	1 month
2004-10-12 18:36:20 +00:00
jhb
ce2d3f89af Rework how we store process times in the kernel such that we always store
the raw values including for child process statistics and only compute the
system and user timevals on demand.

- Fix the various kern_wait() syscall wrappers to only pass in a rusage
  pointer if they are going to use the result.
- Add a kern_getrusage() function for the ABI syscalls to use so that they
  don't have to play stackgap games to call getrusage().
- Fix the svr4_sys_times() syscall to just call calcru() to calculate the
  times it needs rather than calling getrusage() twice with associated
  stackgap, etc.
- Add a new rusage_ext structure to store raw time stats such as tick counts
  for user, system, and interrupt time as well as a bintime of the total
  runtime.  A new p_rux field in struct proc replaces the same inline fields
  from struct proc (i.e. p_[isu]ticks, p_[isu]u, and p_runtime).  A new p_crux
  field in struct proc contains the "raw" child time usage statistics.
  ruadd() has been changed to handle adding the associated rusage_ext
  structures as well as the values in rusage.  Effectively, the values in
  rusage_ext replace the ru_utime and ru_stime values in struct rusage.  These
  two fields in struct rusage are no longer used in the kernel.
- calcru() has been split into a static worker function calcru1() that
  calculates appropriate timevals for user and system time as well as updating
  the rux_[isu]u fields of a passed in rusage_ext structure.  calcru() uses a
  copy of the process' p_rux structure to compute the timevals after updating
  the runtime appropriately if any of the threads in that process are
  currently executing.  It also now only locks sched_lock internally while
  doing the rux_runtime fixup.  calcru() now only requires the caller to
  hold the proc lock and calcru1() only requires the proc lock internally.
  calcru() also no longer allows callers to ask for an interrupt timeval
  since none of them actually did.
- calcru() now correctly handles threads executing on other CPUs.
- A new calccru() function computes the child system and user timevals by
  calling calcru1() on p_crux.  Note that this means that any code that wants
  child times must now call this function rather than reading from p_cru
  directly.  This function also requires the proc lock.
- This finishes the locking for rusage and friends so some of the Giant locks
  in exit1() and kern_wait() are now gone.
- The locking in ttyinfo() has been tweaked so that a shared lock of the
  proctree lock is used to protect the process group rather than the process
  group lock.  By holding this lock until the end of the function we now
  ensure that the process/thread that we pick to dump info about will no
  longer vanish while we are trying to output its info to the console.

Submitted by:	bde (mostly)
MFC after:	1 month
2004-10-05 18:51:11 +00:00
julian
6461286b21 clean up thread runq accounting a bit.
MFC after:	3 days
2004-09-16 07:12:59 +00:00
julian
9993c65718 Add some code to allow threads to nominat a sibling to run if theyu are going to sleep.
MFC after:	1 week
2004-09-10 21:04:38 +00:00
julian
5813d27029 Refactor a bunch of scheduler code to give basically the same behaviour
but with slightly cleaned up interfaces.

The KSE structure has become the same as the "per thread scheduler
private data" structure. In order to not make the diffs too great
one is #defined as the other at this time.

The KSE (or td_sched) structure is  now allocated per thread and has no
allocation code of its own.

Concurrency for a KSEGRP is now kept track of via a simple pair of counters
rather than using KSE structures as tokens.

Since the KSE structure is different in each scheduler, kern_switch.c
is now included at the end of each scheduler. Nothing outside the
scheduler knows the contents of the KSE (aka td_sched) structure.

The fields in the ksegrp structure that are to do with the scheduler's
queueing mechanisms are now moved to the kg_sched structure.
(per ksegrp scheduler private data structure). In other words how the
scheduler queues and keeps track of threads is no-one's business except
the scheduler's. This should allow people to write experimental
schedulers with completely different internal structuring.

A scheduler call sched_set_concurrency(kg, N) has been added that
notifies teh scheduler that no more than N threads from that ksegrp
should be allowed to be on concurrently scheduled. This is also
used to enforce 'fainess' at this time so that a ksegrp with
10000 threads can not swamp a the run queue and force out a process
with 1 thread, since the current code will not set the concurrency above
NCPU, and both schedulers will not allow more than that many
onto the system run queue at a time. Each scheduler should eventualy develop
their own methods to do this now that they are effectively separated.

Rejig libthr's kernel interface to follow the same code paths as
linkse for scope system threads. This has slightly hurt libthr's performance
but I will work to recover as much of it as I can.

Thread exit code has been cleaned up greatly.
exit and exec code now transitions a process back to
'standard non-threaded mode' before taking the next step.
Reviewed by:	scottl, peter
MFC after:	1 week
2004-09-05 02:09:54 +00:00
jhb
9e08178eb7 Now that the return value semantics of cv's for multithreaded processes
have been unified with that of msleep(9), further refine the sleepq
interface and consolidate some duplicated code:
- Move the pre-sleep checks for theaded processes into a
  thread_sleep_check() function in kern_thread.c.
- Move all handling of TDF_SINTR to be internal to subr_sleepqueue.c.
  Specifically, if a thread is awakened by something other than a signal
  while checking for signals before going to sleep, clear TDF_SINTR in
  sleepq_catch_signals().  This removes a sched_lock lock/unlock combo in
  that edge case during an interruptible sleep.  Also, fix
  sleepq_check_signals() to properly handle the condition if TDF_SINTR is
  clear rather than requiring the callers of the sleepq API to notice
  this edge case and call a non-_sig variant of sleepq_wait().
- Clarify the flags arguments to sleepq_add(), sleepq_signal() and
  sleepq_broadcast() by creating an explicit submask for sleepq types.
  Also, add an explicit SLEEPQ_MSLEEP type rather than a magic number of
  0.  Also, add a SLEEPQ_INTERRUPTIBLE flag for use with sleepq_add() and
  move the setting of TDF_SINTR to sleepq_add() if this flag is set rather
  than sleepq_catch_signals().  Note that it is the caller's responsibility
  to ensure that sleepq_catch_signals() is called if and only if this flag
  is passed to the preceeding sleepq_add().  Note that this also removes a
  sched_lock lock/unlock pair from sleepq_catch_signals().  It also ensures
  that for an interruptible sleep, TDF_SINTR is always set when
  TD_ON_SLEEPQ() is true.
2004-08-19 11:31:42 +00:00
julian
61fada7840 Increase the amount of data exported by KTR in the KTR_RUNQ setting.
This extra data is needed to really follow what is going on in the
threaded case.
2004-08-09 18:21:12 +00:00
jhb
f513ad537c Workaround a possible deadlock on SMP due to a spin lock LOR by disabling
the immediate awakening of proc0 (scheduler kproc, controls swapping
processes in and out).  The scheduler process periodically awakens already,
so this will not result in processes not being swapped in, there will just
be more latency in between a thread being made runnable and the scheduler
waking up to swap the affected process back in.
2004-08-04 20:24:40 +00:00
davidxu
5610a7e068 Use P_SINGLE_EXIT to check single-threading case, P_WEXIT is not for that
purpose.
2004-07-28 06:30:52 +00:00
jhb
0cb3276d57 - Move TDF_OWEPREEMPT, TDF_OWEUPC, and TDF_USTATCLOCK over to td_pflags
since they are only accessed by curthread and thus do not need any
  locking.
- Move pr_addr and pr_ticks out of struct uprof (which is per-process)
  and directly into struct thread as td_profil_addr and td_profil_ticks
  as these variables are really per-thread.  (They are used to defer an
  addupc_intr() that was too "hard" until ast()).
2004-07-16 21:04:55 +00:00
marcel
a9ad69d5af Update for the KDB framework:
o  Make debugging code conditional upon KDB instead of DDB.
o  Call kdb_enter() instead of Debugger().
o  Call kdb_backtrace() instead of db_print_backtrace() or backtrace().

kern_mutex.c:
o  Replace checks for db_active with checks for kdb_active and make
   them unconditional.

kern_shutdown.c:
o  s/DDB_UNATTENDED/KDB_UNATTENDED/g
o  s/DDB_TRACE/KDB_TRACE/g
o  Save the TID of the thread doing the kernel dump so the debugger
   knows which thread to select as the current when debugging the
   kernel core file.
o  Clear kdb_active instead of db_active and do so unconditionally.
o  Remove backtrace() implementation.

kern_synch.c:
o  Call kdb_reenter() instead of db_error().
2004-07-10 21:36:01 +00:00
jhb
696704716d Implement preemption of kernel threads natively in the scheduler rather
than as one-off hacks in various other parts of the kernel:
- Add a function maybe_preempt() that is called from sched_add() to
  determine if a thread about to be added to a run queue should be
  preempted to directly.  If it is not safe to preempt or if the new
  thread does not have a high enough priority, then the function returns
  false and sched_add() adds the thread to the run queue.  If the thread
  should be preempted to but the current thread is in a nested critical
  section, then the flag TDF_OWEPREEMPT is set and the thread is added
  to the run queue.  Otherwise, mi_switch() is called immediately and the
  thread is never added to the run queue since it is switch to directly.
  When exiting an outermost critical section, if TDF_OWEPREEMPT is set,
  then clear it and call mi_switch() to perform the deferred preemption.
- Remove explicit preemption from ithread_schedule() as calling
  setrunqueue() now does all the correct work.  This also removes the
  do_switch argument from ithread_schedule().
- Do not use the manual preemption code in mtx_unlock if the architecture
  supports native preemption.
- Don't call mi_switch() in a loop during shutdown to give ithreads a
  chance to run if the architecture supports native preemption since
  the ithreads will just preempt DELAY().
- Don't call mi_switch() from the page zeroing idle thread for
  architectures that support native preemption as it is unnecessary.
- Native preemption is enabled on the same archs that supported ithread
  preemption, namely alpha, i386, and amd64.

This change should largely be a NOP for the default case as committed
except that we will do fewer context switches in a few cases and will
avoid the run queues completely when preempting.

Approved by:	scottl (with his re@ hat)
2004-07-02 20:21:44 +00:00
jhb
1b16b181d1 - Change mi_switch() and sched_switch() to accept an optional thread to
switch to.  If a non-NULL thread pointer is passed in, then the CPU will
  switch to that thread directly rather than calling choosethread() to pick
  a thread to choose to.
- Make sched_switch() aware of idle threads and know to do
  TD_SET_CAN_RUN() instead of sticking them on the run queue rather than
  requiring all callers of mi_switch() to know to do this if they can be
  called from an idlethread.
- Move constants for arguments to mi_switch() and thread_single() out of
  the middle of the function prototypes and up above into their own
  section.
2004-07-02 19:09:50 +00:00
jhb
4dab07ef95 Remove the signal_caught argument from sleepq_timedwait() as it was
effectively always zero.
2004-06-28 18:57:06 +00:00
tjr
24fcba21fb Remove a stale and misleading comment. 2004-06-07 09:35:00 +00:00
bde
802b835b3d Fixed some common printf format errors. Don't assume that "struct foo *"
is "void *" (it isn't) or that the default promotion of pid_t is int.
Instead, assume that casting "struct foo *" to "void *" and printing the
result with %p is useful, and that all pid_t's are representable as longs.

Fixed some minor style bugs (mainly spelling errors in comments).
2004-05-14 20:51:42 +00:00
imp
74cf37bd00 Remove advertising clause from University of California Regent's license,
per letter dated July 22, 1999.

Approved by: core
2004-04-05 21:03:37 +00:00
jhb
c754b5af47 - Remove old sleep queues.
- Remove sleepqueue argument from sleepq_set_timeout() since it is not
  used.
2004-03-12 19:06:18 +00:00
rwatson
8ff4e76430 Mark loadaverage callout as CALLOUT_MPSAFE.
Reviewed by:	jhb
2004-03-08 22:01:19 +00:00
jhb
93c4123deb Correct handling of PDROP in msleep() to just skip the mtx_lock() rather
than clear the lock pointer so that sleepq_add() still gets the correct
lock pointer and doesn't bogusly trip an assertion.
2004-03-02 14:58:33 +00:00
jhb
d25301c858 Switch the sleep/wakeup and condition variable implementations to use the
sleep queue interface:
- Sleep queues attempt to merge some of the benefits of both sleep queues
  and condition variables.  Having sleep qeueus in a hash table avoids
  having to allocate a queue head for each wait channel.  Thus, struct cv
  has shrunk down to just a single char * pointer now.  However, the
  hash table does not hold threads directly, but queue heads.  This means
  that once you have located a queue in the hash bucket, you no longer have
  to walk the rest of the hash chain looking for threads.  Instead, you have
  a list of all the threads sleeping on that wait channel.
- Outside of the sleepq code and the sleep/cv code the kernel no longer
  differentiates between cv's and sleep/wakeup.  For example, calls to
  abortsleep() and cv_abort() are replaced with a call to sleepq_abort().
  Thus, the TDF_CVWAITQ flag is removed.  Also, calls to unsleep() and
  cv_waitq_remove() have been replaced with calls to sleepq_remove().
- The sched_sleep() function no longer accepts a priority argument as
  sleep's no longer inherently bump the priority.  Instead, this is soley
  a propery of msleep() which explicitly calls sched_prio() before
  blocking.
- The TDF_ONSLEEPQ flag has been dropped as it was never used.  The
  associated TDF_SET_ONSLEEPQ and TDF_CLR_ON_SLEEPQ macros have also been
  dropped and replaced with a single explicit clearing of td_wchan.
  TD_SET_ONSLEEPQ() would really have only made sense if it had taken
  the wait channel and message as arguments anyway.  Now that that only
  happens in one place, a macro would be overkill.
2004-02-27 18:52:44 +00:00