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/11.0/sys/kern/kern_condvar.c 298819 2016-04-29 22:15:33Z pfg $");
   29 
   30 #include "opt_ktrace.h"
   31 
   32 #include <sys/param.h>
   33 #include <sys/systm.h>
   34 #include <sys/limits.h>
   35 #include <sys/lock.h>
   36 #include <sys/mutex.h>
   37 #include <sys/proc.h>
   38 #include <sys/kernel.h>
   39 #include <sys/ktr.h>
   40 #include <sys/condvar.h>
   41 #include <sys/sched.h>
   42 #include <sys/signalvar.h>
   43 #include <sys/sleepqueue.h>
   44 #include <sys/resourcevar.h>
   45 #ifdef KTRACE
   46 #include <sys/uio.h>
   47 #include <sys/ktrace.h>
   48 #endif
   49 
   50 /*
   51  * A bound below which cv_waiters is valid.  Once cv_waiters reaches this bound,
   52  * cv_signal must manually check the wait queue for threads.
   53  */
   54 #define CV_WAITERS_BOUND        INT_MAX
   55 
   56 #define CV_WAITERS_INC(cvp) do {                                        \
   57         if ((cvp)->cv_waiters < CV_WAITERS_BOUND)                       \
   58                 (cvp)->cv_waiters++;                                    \
   59 } while (0)
   60 
   61 /*
   62  * Common sanity checks for cv_wait* functions.
   63  */
   64 #define CV_ASSERT(cvp, lock, td) do {                                   \
   65         KASSERT((td) != NULL, ("%s: td NULL", __func__));               \
   66         KASSERT(TD_IS_RUNNING(td), ("%s: not TDS_RUNNING", __func__));  \
   67         KASSERT((cvp) != NULL, ("%s: cvp NULL", __func__));             \
   68         KASSERT((lock) != NULL, ("%s: lock NULL", __func__));           \
   69 } while (0)
   70 
   71 /*
   72  * Initialize a condition variable.  Must be called before use.
   73  */
   74 void
   75 cv_init(struct cv *cvp, const char *desc)
   76 {
   77 
   78         cvp->cv_description = desc;
   79         cvp->cv_waiters = 0;
   80 }
   81 
   82 /*
   83  * Destroy a condition variable.  The condition variable must be re-initialized
   84  * in order to be re-used.
   85  */
   86 void
   87 cv_destroy(struct cv *cvp)
   88 {
   89 #ifdef INVARIANTS
   90         struct sleepqueue *sq;
   91 
   92         sleepq_lock(cvp);
   93         sq = sleepq_lookup(cvp);
   94         sleepq_release(cvp);
   95         KASSERT(sq == NULL, ("%s: associated sleep queue non-empty", __func__));
   96 #endif
   97 }
   98 
   99 /*
  100  * Wait on a condition variable.  The current thread is placed on the condition
  101  * variable's wait queue and suspended.  A cv_signal or cv_broadcast on the same
  102  * condition variable will resume the thread.  The mutex is released before
  103  * sleeping and will be held on return.  It is recommended that the mutex be
  104  * held when cv_signal or cv_broadcast are called.
  105  */
  106 void
  107 _cv_wait(struct cv *cvp, struct lock_object *lock)
  108 {
  109         WITNESS_SAVE_DECL(lock_witness);
  110         struct lock_class *class;
  111         struct thread *td;
  112         uintptr_t lock_state;
  113 
  114         td = curthread;
  115         lock_state = 0;
  116 #ifdef KTRACE
  117         if (KTRPOINT(td, KTR_CSW))
  118                 ktrcsw(1, 0, cv_wmesg(cvp));
  119 #endif
  120         CV_ASSERT(cvp, lock, td);
  121         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  122             "Waiting on \"%s\"", cvp->cv_description);
  123         class = LOCK_CLASS(lock);
  124 
  125         if (SCHEDULER_STOPPED())
  126                 return;
  127 
  128         sleepq_lock(cvp);
  129 
  130         CV_WAITERS_INC(cvp);
  131         if (lock == &Giant.lock_object)
  132                 mtx_assert(&Giant, MA_OWNED);
  133         DROP_GIANT();
  134 
  135         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
  136         if (lock != &Giant.lock_object) {
  137                 if (class->lc_flags & LC_SLEEPABLE)
  138                         sleepq_release(cvp);
  139                 WITNESS_SAVE(lock, lock_witness);
  140                 lock_state = class->lc_unlock(lock);
  141                 if (class->lc_flags & LC_SLEEPABLE)
  142                         sleepq_lock(cvp);
  143         }
  144         sleepq_wait(cvp, 0);
  145 
  146 #ifdef KTRACE
  147         if (KTRPOINT(td, KTR_CSW))
  148                 ktrcsw(0, 0, cv_wmesg(cvp));
  149 #endif
  150         PICKUP_GIANT();
  151         if (lock != &Giant.lock_object) {
  152                 class->lc_lock(lock, lock_state);
  153                 WITNESS_RESTORE(lock, lock_witness);
  154         }
  155 }
  156 
  157 /*
  158  * Wait on a condition variable.  This function differs from cv_wait by
  159  * not acquiring the mutex after condition variable was signaled.
  160  */
  161 void
  162 _cv_wait_unlock(struct cv *cvp, struct lock_object *lock)
  163 {
  164         struct lock_class *class;
  165         struct thread *td;
  166 
  167         td = curthread;
  168 #ifdef KTRACE
  169         if (KTRPOINT(td, KTR_CSW))
  170                 ktrcsw(1, 0, cv_wmesg(cvp));
  171 #endif
  172         CV_ASSERT(cvp, lock, td);
  173         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  174             "Waiting on \"%s\"", cvp->cv_description);
  175         KASSERT(lock != &Giant.lock_object,
  176             ("cv_wait_unlock cannot be used with Giant"));
  177         class = LOCK_CLASS(lock);
  178 
  179         if (SCHEDULER_STOPPED()) {
  180                 class->lc_unlock(lock);
  181                 return;
  182         }
  183 
  184         sleepq_lock(cvp);
  185 
  186         CV_WAITERS_INC(cvp);
  187         DROP_GIANT();
  188 
  189         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
  190         if (class->lc_flags & LC_SLEEPABLE)
  191                 sleepq_release(cvp);
  192         class->lc_unlock(lock);
  193         if (class->lc_flags & LC_SLEEPABLE)
  194                 sleepq_lock(cvp);
  195         sleepq_wait(cvp, 0);
  196 
  197 #ifdef KTRACE
  198         if (KTRPOINT(td, KTR_CSW))
  199                 ktrcsw(0, 0, cv_wmesg(cvp));
  200 #endif
  201         PICKUP_GIANT();
  202 }
  203 
  204 /*
  205  * Wait on a condition variable, allowing interruption by signals.  Return 0 if
  206  * the thread was resumed with cv_signal or cv_broadcast, EINTR or ERESTART if
  207  * a signal was caught.  If ERESTART is returned the system call should be
  208  * restarted if possible.
  209  */
  210 int
  211 _cv_wait_sig(struct cv *cvp, struct lock_object *lock)
  212 {
  213         WITNESS_SAVE_DECL(lock_witness);
  214         struct lock_class *class;
  215         struct thread *td;
  216         uintptr_t lock_state;
  217         int rval;
  218 
  219         td = curthread;
  220         lock_state = 0;
  221 #ifdef KTRACE
  222         if (KTRPOINT(td, KTR_CSW))
  223                 ktrcsw(1, 0, cv_wmesg(cvp));
  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 (SCHEDULER_STOPPED())
  231                 return (0);
  232 
  233         sleepq_lock(cvp);
  234 
  235         CV_WAITERS_INC(cvp);
  236         if (lock == &Giant.lock_object)
  237                 mtx_assert(&Giant, MA_OWNED);
  238         DROP_GIANT();
  239 
  240         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR |
  241             SLEEPQ_INTERRUPTIBLE, 0);
  242         if (lock != &Giant.lock_object) {
  243                 if (class->lc_flags & LC_SLEEPABLE)
  244                         sleepq_release(cvp);
  245                 WITNESS_SAVE(lock, lock_witness);
  246                 lock_state = class->lc_unlock(lock);
  247                 if (class->lc_flags & LC_SLEEPABLE)
  248                         sleepq_lock(cvp);
  249         }
  250         rval = sleepq_wait_sig(cvp, 0);
  251 
  252 #ifdef KTRACE
  253         if (KTRPOINT(td, KTR_CSW))
  254                 ktrcsw(0, 0, cv_wmesg(cvp));
  255 #endif
  256         PICKUP_GIANT();
  257         if (lock != &Giant.lock_object) {
  258                 class->lc_lock(lock, lock_state);
  259                 WITNESS_RESTORE(lock, lock_witness);
  260         }
  261 
  262         return (rval);
  263 }
  264 
  265 /*
  266  * Wait on a condition variable for (at most) the value specified in sbt
  267  * argument. Returns 0 if the process was resumed by cv_signal or cv_broadcast,
  268  * EWOULDBLOCK if the timeout expires.
  269  */
  270 int
  271 _cv_timedwait_sbt(struct cv *cvp, struct lock_object *lock, sbintime_t sbt,
  272     sbintime_t pr, int flags)
  273 {
  274         WITNESS_SAVE_DECL(lock_witness);
  275         struct lock_class *class;
  276         struct thread *td;
  277         int lock_state, rval;
  278 
  279         td = curthread;
  280         lock_state = 0;
  281 #ifdef KTRACE
  282         if (KTRPOINT(td, KTR_CSW))
  283                 ktrcsw(1, 0, cv_wmesg(cvp));
  284 #endif
  285         CV_ASSERT(cvp, lock, td);
  286         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  287             "Waiting on \"%s\"", cvp->cv_description);
  288         class = LOCK_CLASS(lock);
  289 
  290         if (SCHEDULER_STOPPED())
  291                 return (0);
  292 
  293         sleepq_lock(cvp);
  294 
  295         CV_WAITERS_INC(cvp);
  296         if (lock == &Giant.lock_object)
  297                 mtx_assert(&Giant, MA_OWNED);
  298         DROP_GIANT();
  299 
  300         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
  301         sleepq_set_timeout_sbt(cvp, sbt, pr, flags);
  302         if (lock != &Giant.lock_object) {
  303                 if (class->lc_flags & LC_SLEEPABLE)
  304                         sleepq_release(cvp);
  305                 WITNESS_SAVE(lock, lock_witness);
  306                 lock_state = class->lc_unlock(lock);
  307                 if (class->lc_flags & LC_SLEEPABLE)
  308                         sleepq_lock(cvp);
  309         }
  310         rval = sleepq_timedwait(cvp, 0);
  311 
  312 #ifdef KTRACE
  313         if (KTRPOINT(td, KTR_CSW))
  314                 ktrcsw(0, 0, cv_wmesg(cvp));
  315 #endif
  316         PICKUP_GIANT();
  317         if (lock != &Giant.lock_object) {
  318                 class->lc_lock(lock, lock_state);
  319                 WITNESS_RESTORE(lock, lock_witness);
  320         }
  321 
  322         return (rval);
  323 }
  324 
  325 /*
  326  * Wait on a condition variable for (at most) the value specified in sbt 
  327  * argument, allowing interruption by signals.
  328  * Returns 0 if the thread was resumed by cv_signal or cv_broadcast,
  329  * EWOULDBLOCK if the timeout expires, and EINTR or ERESTART if a signal
  330  * was caught.
  331  */
  332 int
  333 _cv_timedwait_sig_sbt(struct cv *cvp, struct lock_object *lock,
  334     sbintime_t sbt, sbintime_t pr, int flags)
  335 {
  336         WITNESS_SAVE_DECL(lock_witness);
  337         struct lock_class *class;
  338         struct thread *td;
  339         int lock_state, rval;
  340 
  341         td = curthread;
  342         lock_state = 0;
  343 #ifdef KTRACE
  344         if (KTRPOINT(td, KTR_CSW))
  345                 ktrcsw(1, 0, cv_wmesg(cvp));
  346 #endif
  347         CV_ASSERT(cvp, lock, td);
  348         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  349             "Waiting on \"%s\"", cvp->cv_description);
  350         class = LOCK_CLASS(lock);
  351 
  352         if (SCHEDULER_STOPPED())
  353                 return (0);
  354 
  355         sleepq_lock(cvp);
  356 
  357         CV_WAITERS_INC(cvp);
  358         if (lock == &Giant.lock_object)
  359                 mtx_assert(&Giant, MA_OWNED);
  360         DROP_GIANT();
  361 
  362         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR |
  363             SLEEPQ_INTERRUPTIBLE, 0);
  364         sleepq_set_timeout_sbt(cvp, sbt, pr, flags);
  365         if (lock != &Giant.lock_object) {
  366                 if (class->lc_flags & LC_SLEEPABLE)
  367                         sleepq_release(cvp);
  368                 WITNESS_SAVE(lock, lock_witness);
  369                 lock_state = class->lc_unlock(lock);
  370                 if (class->lc_flags & LC_SLEEPABLE)
  371                         sleepq_lock(cvp);
  372         }
  373         rval = sleepq_timedwait_sig(cvp, 0);
  374 
  375 #ifdef KTRACE
  376         if (KTRPOINT(td, KTR_CSW))
  377                 ktrcsw(0, 0, cv_wmesg(cvp));
  378 #endif
  379         PICKUP_GIANT();
  380         if (lock != &Giant.lock_object) {
  381                 class->lc_lock(lock, lock_state);
  382                 WITNESS_RESTORE(lock, lock_witness);
  383         }
  384 
  385         return (rval);
  386 }
  387 
  388 /*
  389  * Signal a condition variable, wakes up one waiting thread.  Will also wakeup
  390  * the swapper if the process is not in memory, so that it can bring the
  391  * sleeping process in.  Note that this may also result in additional threads
  392  * being made runnable.  Should be called with the same mutex as was passed to
  393  * cv_wait held.
  394  */
  395 void
  396 cv_signal(struct cv *cvp)
  397 {
  398         int wakeup_swapper;
  399 
  400         wakeup_swapper = 0;
  401         sleepq_lock(cvp);
  402         if (cvp->cv_waiters > 0) {
  403                 if (cvp->cv_waiters == CV_WAITERS_BOUND &&
  404                     sleepq_lookup(cvp) == NULL) {
  405                         cvp->cv_waiters = 0;
  406                 } else {
  407                         if (cvp->cv_waiters < CV_WAITERS_BOUND)
  408                                 cvp->cv_waiters--;
  409                         wakeup_swapper = sleepq_signal(cvp, SLEEPQ_CONDVAR, 0,
  410                             0);
  411                 }
  412         }
  413         sleepq_release(cvp);
  414         if (wakeup_swapper)
  415                 kick_proc0();
  416 }
  417 
  418 /*
  419  * Broadcast a signal to a condition variable.  Wakes up all waiting threads.
  420  * Should be called with the same mutex as was passed to cv_wait held.
  421  */
  422 void
  423 cv_broadcastpri(struct cv *cvp, int pri)
  424 {
  425         int wakeup_swapper;
  426 
  427         /*
  428          * XXX sleepq_broadcast pri argument changed from -1 meaning
  429          * no pri to 0 meaning no pri.
  430          */
  431         wakeup_swapper = 0;
  432         if (pri == -1)
  433                 pri = 0;
  434         sleepq_lock(cvp);
  435         if (cvp->cv_waiters > 0) {
  436                 cvp->cv_waiters = 0;
  437                 wakeup_swapper = sleepq_broadcast(cvp, SLEEPQ_CONDVAR, pri, 0);
  438         }
  439         sleepq_release(cvp);
  440         if (wakeup_swapper)
  441                 kick_proc0();
  442 }

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