The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_condvar.c

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    1 /*-
    2  * Copyright (c) 2000 Jake Burkholder <jake@freebsd.org>.
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  *
   14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   24  * SUCH DAMAGE.
   25  */
   26 
   27 #include <sys/cdefs.h>
   28 __FBSDID("$FreeBSD: releng/8.3/sys/kern/kern_condvar.c 199583 2009-11-20 15:27:52Z jhb $");
   29 
   30 #include "opt_ktrace.h"
   31 
   32 #include <sys/param.h>
   33 #include <sys/systm.h>
   34 #include <sys/lock.h>
   35 #include <sys/mutex.h>
   36 #include <sys/proc.h>
   37 #include <sys/kernel.h>
   38 #include <sys/ktr.h>
   39 #include <sys/condvar.h>
   40 #include <sys/sched.h>
   41 #include <sys/signalvar.h>
   42 #include <sys/sleepqueue.h>
   43 #include <sys/resourcevar.h>
   44 #ifdef KTRACE
   45 #include <sys/uio.h>
   46 #include <sys/ktrace.h>
   47 #endif
   48 
   49 /*
   50  * Common sanity checks for cv_wait* functions.
   51  */
   52 #define CV_ASSERT(cvp, lock, td) do {                                   \
   53         KASSERT((td) != NULL, ("%s: curthread NULL", __func__));        \
   54         KASSERT(TD_IS_RUNNING(td), ("%s: not TDS_RUNNING", __func__));  \
   55         KASSERT((cvp) != NULL, ("%s: cvp NULL", __func__));             \
   56         KASSERT((lock) != NULL, ("%s: lock NULL", __func__));           \
   57 } while (0)
   58 
   59 /*
   60  * Initialize a condition variable.  Must be called before use.
   61  */
   62 void
   63 cv_init(struct cv *cvp, const char *desc)
   64 {
   65 
   66         cvp->cv_description = desc;
   67         cvp->cv_waiters = 0;
   68 }
   69 
   70 /*
   71  * Destroy a condition variable.  The condition variable must be re-initialized
   72  * in order to be re-used.
   73  */
   74 void
   75 cv_destroy(struct cv *cvp)
   76 {
   77 #ifdef INVARIANTS
   78         struct sleepqueue *sq;
   79 
   80         sleepq_lock(cvp);
   81         sq = sleepq_lookup(cvp);
   82         sleepq_release(cvp);
   83         KASSERT(sq == NULL, ("%s: associated sleep queue non-empty", __func__));
   84 #endif
   85 }
   86 
   87 /*
   88  * Wait on a condition variable.  The current thread is placed on the condition
   89  * variable's wait queue and suspended.  A cv_signal or cv_broadcast on the same
   90  * condition variable will resume the thread.  The mutex is released before
   91  * sleeping and will be held on return.  It is recommended that the mutex be
   92  * held when cv_signal or cv_broadcast are called.
   93  */
   94 void
   95 _cv_wait(struct cv *cvp, struct lock_object *lock)
   96 {
   97         WITNESS_SAVE_DECL(lock_witness);
   98         struct lock_class *class;
   99         struct thread *td;
  100         int lock_state;
  101 
  102         td = curthread;
  103         lock_state = 0;
  104 #ifdef KTRACE
  105         if (KTRPOINT(td, KTR_CSW))
  106                 ktrcsw(1, 0);
  107 #endif
  108         CV_ASSERT(cvp, lock, td);
  109         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  110             "Waiting on \"%s\"", cvp->cv_description);
  111         class = LOCK_CLASS(lock);
  112 
  113         if (cold || panicstr) {
  114                 /*
  115                  * During autoconfiguration, just give interrupts
  116                  * a chance, then just return.  Don't run any other
  117                  * thread or panic below, in case this is the idle
  118                  * process and already asleep.
  119                  */
  120                 return;
  121         }
  122 
  123         sleepq_lock(cvp);
  124 
  125         cvp->cv_waiters++;
  126         if (lock == &Giant.lock_object)
  127                 mtx_assert(&Giant, MA_OWNED);
  128         DROP_GIANT();
  129 
  130         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
  131         if (lock != &Giant.lock_object) {
  132                 if (class->lc_flags & LC_SLEEPABLE)
  133                         sleepq_release(cvp);
  134                 WITNESS_SAVE(lock, lock_witness);
  135                 lock_state = class->lc_unlock(lock);
  136                 if (class->lc_flags & LC_SLEEPABLE)
  137                         sleepq_lock(cvp);
  138         }
  139         sleepq_wait(cvp, 0);
  140 
  141 #ifdef KTRACE
  142         if (KTRPOINT(td, KTR_CSW))
  143                 ktrcsw(0, 0);
  144 #endif
  145         PICKUP_GIANT();
  146         if (lock != &Giant.lock_object) {
  147                 class->lc_lock(lock, lock_state);
  148                 WITNESS_RESTORE(lock, lock_witness);
  149         }
  150 }
  151 
  152 /*
  153  * Wait on a condition variable.  This function differs from cv_wait by
  154  * not aquiring the mutex after condition variable was signaled.
  155  */
  156 void
  157 _cv_wait_unlock(struct cv *cvp, struct lock_object *lock)
  158 {
  159         struct lock_class *class;
  160         struct thread *td;
  161 
  162         td = curthread;
  163 #ifdef KTRACE
  164         if (KTRPOINT(td, KTR_CSW))
  165                 ktrcsw(1, 0);
  166 #endif
  167         CV_ASSERT(cvp, lock, td);
  168         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  169             "Waiting on \"%s\"", cvp->cv_description);
  170         KASSERT(lock != &Giant.lock_object,
  171             ("cv_wait_unlock cannot be used with Giant"));
  172         class = LOCK_CLASS(lock);
  173 
  174         if (cold || panicstr) {
  175                 /*
  176                  * During autoconfiguration, just give interrupts
  177                  * a chance, then just return.  Don't run any other
  178                  * thread or panic below, in case this is the idle
  179                  * process and already asleep.
  180                  */
  181                 class->lc_unlock(lock);
  182                 return;
  183         }
  184 
  185         sleepq_lock(cvp);
  186 
  187         cvp->cv_waiters++;
  188         DROP_GIANT();
  189 
  190         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
  191         if (class->lc_flags & LC_SLEEPABLE)
  192                 sleepq_release(cvp);
  193         class->lc_unlock(lock);
  194         if (class->lc_flags & LC_SLEEPABLE)
  195                 sleepq_lock(cvp);
  196         sleepq_wait(cvp, 0);
  197 
  198 #ifdef KTRACE
  199         if (KTRPOINT(td, KTR_CSW))
  200                 ktrcsw(0, 0);
  201 #endif
  202         PICKUP_GIANT();
  203 }
  204 
  205 /*
  206  * Wait on a condition variable, allowing interruption by signals.  Return 0 if
  207  * the thread was resumed with cv_signal or cv_broadcast, EINTR or ERESTART if
  208  * a signal was caught.  If ERESTART is returned the system call should be
  209  * restarted if possible.
  210  */
  211 int
  212 _cv_wait_sig(struct cv *cvp, struct lock_object *lock)
  213 {
  214         WITNESS_SAVE_DECL(lock_witness);
  215         struct lock_class *class;
  216         struct thread *td;
  217         int lock_state, rval;
  218 
  219         td = curthread;
  220         lock_state = 0;
  221 #ifdef KTRACE
  222         if (KTRPOINT(td, KTR_CSW))
  223                 ktrcsw(1, 0);
  224 #endif
  225         CV_ASSERT(cvp, lock, td);
  226         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  227             "Waiting on \"%s\"", cvp->cv_description);
  228         class = LOCK_CLASS(lock);
  229 
  230         if (cold || panicstr) {
  231                 /*
  232                  * After a panic, or during autoconfiguration, just give
  233                  * interrupts a chance, then just return; don't run any other
  234                  * procs or panic below, in case this is the idle process and
  235                  * already asleep.
  236                  */
  237                 return (0);
  238         }
  239 
  240         sleepq_lock(cvp);
  241 
  242         cvp->cv_waiters++;
  243         if (lock == &Giant.lock_object)
  244                 mtx_assert(&Giant, MA_OWNED);
  245         DROP_GIANT();
  246 
  247         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR |
  248             SLEEPQ_INTERRUPTIBLE, 0);
  249         if (lock != &Giant.lock_object) {
  250                 if (class->lc_flags & LC_SLEEPABLE)
  251                         sleepq_release(cvp);
  252                 WITNESS_SAVE(lock, lock_witness);
  253                 lock_state = class->lc_unlock(lock);
  254                 if (class->lc_flags & LC_SLEEPABLE)
  255                         sleepq_lock(cvp);
  256         }
  257         rval = sleepq_wait_sig(cvp, 0);
  258 
  259 #ifdef KTRACE
  260         if (KTRPOINT(td, KTR_CSW))
  261                 ktrcsw(0, 0);
  262 #endif
  263         PICKUP_GIANT();
  264         if (lock != &Giant.lock_object) {
  265                 class->lc_lock(lock, lock_state);
  266                 WITNESS_RESTORE(lock, lock_witness);
  267         }
  268 
  269         return (rval);
  270 }
  271 
  272 /*
  273  * Wait on a condition variable for at most timo/hz seconds.  Returns 0 if the
  274  * process was resumed by cv_signal or cv_broadcast, EWOULDBLOCK if the timeout
  275  * expires.
  276  */
  277 int
  278 _cv_timedwait(struct cv *cvp, struct lock_object *lock, int timo)
  279 {
  280         WITNESS_SAVE_DECL(lock_witness);
  281         struct lock_class *class;
  282         struct thread *td;
  283         int lock_state, rval;
  284 
  285         td = curthread;
  286         lock_state = 0;
  287 #ifdef KTRACE
  288         if (KTRPOINT(td, KTR_CSW))
  289                 ktrcsw(1, 0);
  290 #endif
  291         CV_ASSERT(cvp, lock, td);
  292         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  293             "Waiting on \"%s\"", cvp->cv_description);
  294         class = LOCK_CLASS(lock);
  295 
  296         if (cold || panicstr) {
  297                 /*
  298                  * After a panic, or during autoconfiguration, just give
  299                  * interrupts a chance, then just return; don't run any other
  300                  * thread or panic below, in case this is the idle process and
  301                  * already asleep.
  302                  */
  303                 return 0;
  304         }
  305 
  306         sleepq_lock(cvp);
  307 
  308         cvp->cv_waiters++;
  309         if (lock == &Giant.lock_object)
  310                 mtx_assert(&Giant, MA_OWNED);
  311         DROP_GIANT();
  312 
  313         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
  314         sleepq_set_timeout(cvp, timo);
  315         if (lock != &Giant.lock_object) {
  316                 if (class->lc_flags & LC_SLEEPABLE)
  317                         sleepq_release(cvp);
  318                 WITNESS_SAVE(lock, lock_witness);
  319                 lock_state = class->lc_unlock(lock);
  320                 if (class->lc_flags & LC_SLEEPABLE)
  321                         sleepq_lock(cvp);
  322         }
  323         rval = sleepq_timedwait(cvp, 0);
  324 
  325 #ifdef KTRACE
  326         if (KTRPOINT(td, KTR_CSW))
  327                 ktrcsw(0, 0);
  328 #endif
  329         PICKUP_GIANT();
  330         if (lock != &Giant.lock_object) {
  331                 class->lc_lock(lock, lock_state);
  332                 WITNESS_RESTORE(lock, lock_witness);
  333         }
  334 
  335         return (rval);
  336 }
  337 
  338 /*
  339  * Wait on a condition variable for at most timo/hz seconds, allowing
  340  * interruption by signals.  Returns 0 if the thread was resumed by cv_signal
  341  * or cv_broadcast, EWOULDBLOCK if the timeout expires, and EINTR or ERESTART if
  342  * a signal was caught.
  343  */
  344 int
  345 _cv_timedwait_sig(struct cv *cvp, struct lock_object *lock, int timo)
  346 {
  347         WITNESS_SAVE_DECL(lock_witness);
  348         struct lock_class *class;
  349         struct thread *td;
  350         int lock_state, rval;
  351 
  352         td = curthread;
  353         lock_state = 0;
  354 #ifdef KTRACE
  355         if (KTRPOINT(td, KTR_CSW))
  356                 ktrcsw(1, 0);
  357 #endif
  358         CV_ASSERT(cvp, lock, td);
  359         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  360             "Waiting on \"%s\"", cvp->cv_description);
  361         class = LOCK_CLASS(lock);
  362 
  363         if (cold || panicstr) {
  364                 /*
  365                  * After a panic, or during autoconfiguration, just give
  366                  * interrupts a chance, then just return; don't run any other
  367                  * thread or panic below, in case this is the idle process and
  368                  * already asleep.
  369                  */
  370                 return 0;
  371         }
  372 
  373         sleepq_lock(cvp);
  374 
  375         cvp->cv_waiters++;
  376         if (lock == &Giant.lock_object)
  377                 mtx_assert(&Giant, MA_OWNED);
  378         DROP_GIANT();
  379 
  380         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR |
  381             SLEEPQ_INTERRUPTIBLE, 0);
  382         sleepq_set_timeout(cvp, timo);
  383         if (lock != &Giant.lock_object) {
  384                 if (class->lc_flags & LC_SLEEPABLE)
  385                         sleepq_release(cvp);
  386                 WITNESS_SAVE(lock, lock_witness);
  387                 lock_state = class->lc_unlock(lock);
  388                 if (class->lc_flags & LC_SLEEPABLE)
  389                         sleepq_lock(cvp);
  390         }
  391         rval = sleepq_timedwait_sig(cvp, 0);
  392 
  393 #ifdef KTRACE
  394         if (KTRPOINT(td, KTR_CSW))
  395                 ktrcsw(0, 0);
  396 #endif
  397         PICKUP_GIANT();
  398         if (lock != &Giant.lock_object) {
  399                 class->lc_lock(lock, lock_state);
  400                 WITNESS_RESTORE(lock, lock_witness);
  401         }
  402 
  403         return (rval);
  404 }
  405 
  406 /*
  407  * Signal a condition variable, wakes up one waiting thread.  Will also wakeup
  408  * the swapper if the process is not in memory, so that it can bring the
  409  * sleeping process in.  Note that this may also result in additional threads
  410  * being made runnable.  Should be called with the same mutex as was passed to
  411  * cv_wait held.
  412  */
  413 void
  414 cv_signal(struct cv *cvp)
  415 {
  416         int wakeup_swapper;
  417 
  418         wakeup_swapper = 0;
  419         sleepq_lock(cvp);
  420         if (cvp->cv_waiters > 0) {
  421                 cvp->cv_waiters--;
  422                 wakeup_swapper = sleepq_signal(cvp, SLEEPQ_CONDVAR, 0, 0);
  423         }
  424         sleepq_release(cvp);
  425         if (wakeup_swapper)
  426                 kick_proc0();
  427 }
  428 
  429 /*
  430  * Broadcast a signal to a condition variable.  Wakes up all waiting threads.
  431  * Should be called with the same mutex as was passed to cv_wait held.
  432  */
  433 void
  434 cv_broadcastpri(struct cv *cvp, int pri)
  435 {
  436         int wakeup_swapper;
  437 
  438         /*
  439          * XXX sleepq_broadcast pri argument changed from -1 meaning
  440          * no pri to 0 meaning no pri.
  441          */
  442         wakeup_swapper = 0;
  443         if (pri == -1)
  444                 pri = 0;
  445         sleepq_lock(cvp);
  446         if (cvp->cv_waiters > 0) {
  447                 cvp->cv_waiters = 0;
  448                 wakeup_swapper = sleepq_broadcast(cvp, SLEEPQ_CONDVAR, pri, 0);
  449         }
  450         sleepq_release(cvp);
  451         if (wakeup_swapper)
  452                 kick_proc0();
  453 }

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