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("$FreeBSD$");
   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         WITNESS_SAVE(lock, lock_witness);
  112         class = LOCK_CLASS(lock);
  113 
  114         if (cold || panicstr) {
  115                 /*
  116                  * During autoconfiguration, just give interrupts
  117                  * a chance, then just return.  Don't run any other
  118                  * thread or panic below, in case this is the idle
  119                  * process and already asleep.
  120                  */
  121                 return;
  122         }
  123 
  124         sleepq_lock(cvp);
  125 
  126         cvp->cv_waiters++;
  127         DROP_GIANT();
  128 
  129         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
  130         if (lock != &Giant.lock_object) {
  131                 if (class->lc_flags & LC_SLEEPABLE)
  132                         sleepq_release(cvp);
  133                 lock_state = class->lc_unlock(lock);
  134                 if (class->lc_flags & LC_SLEEPABLE)
  135                         sleepq_lock(cvp);
  136         }
  137         sleepq_wait(cvp);
  138 
  139 #ifdef KTRACE
  140         if (KTRPOINT(td, KTR_CSW))
  141                 ktrcsw(0, 0);
  142 #endif
  143         PICKUP_GIANT();
  144         if (lock != &Giant.lock_object) {
  145                 class->lc_lock(lock, lock_state);
  146                 WITNESS_RESTORE(lock, lock_witness);
  147         }
  148 }
  149 
  150 /*
  151  * Wait on a condition variable.  This function differs from cv_wait by
  152  * not aquiring the mutex after condition variable was signaled.
  153  */
  154 void
  155 _cv_wait_unlock(struct cv *cvp, struct lock_object *lock)
  156 {
  157         struct lock_class *class;
  158         struct thread *td;
  159 
  160         td = curthread;
  161 #ifdef KTRACE
  162         if (KTRPOINT(td, KTR_CSW))
  163                 ktrcsw(1, 0);
  164 #endif
  165         CV_ASSERT(cvp, lock, td);
  166         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  167             "Waiting on \"%s\"", cvp->cv_description);
  168         KASSERT(lock != &Giant.lock_object,
  169             ("cv_wait_unlock cannot be used with Giant"));
  170         class = LOCK_CLASS(lock);
  171 
  172         if (cold || panicstr) {
  173                 /*
  174                  * During autoconfiguration, just give interrupts
  175                  * a chance, then just return.  Don't run any other
  176                  * thread or panic below, in case this is the idle
  177                  * process and already asleep.
  178                  */
  179                 class->lc_unlock(lock);
  180                 return;
  181         }
  182 
  183         sleepq_lock(cvp);
  184 
  185         cvp->cv_waiters++;
  186         DROP_GIANT();
  187 
  188         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
  189         if (class->lc_flags & LC_SLEEPABLE)
  190                 sleepq_release(cvp);
  191         class->lc_unlock(lock);
  192         if (class->lc_flags & LC_SLEEPABLE)
  193                 sleepq_lock(cvp);
  194         sleepq_wait(cvp);
  195 
  196 #ifdef KTRACE
  197         if (KTRPOINT(td, KTR_CSW))
  198                 ktrcsw(0, 0);
  199 #endif
  200         PICKUP_GIANT();
  201 }
  202 
  203 /*
  204  * Wait on a condition variable, allowing interruption by signals.  Return 0 if
  205  * the thread was resumed with cv_signal or cv_broadcast, EINTR or ERESTART if
  206  * a signal was caught.  If ERESTART is returned the system call should be
  207  * restarted if possible.
  208  */
  209 int
  210 _cv_wait_sig(struct cv *cvp, struct lock_object *lock)
  211 {
  212         WITNESS_SAVE_DECL(lock_witness);
  213         struct lock_class *class;
  214         struct thread *td;
  215         struct proc *p;
  216         int lock_state, rval;
  217 
  218         td = curthread;
  219         p = td->td_proc;
  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         WITNESS_SAVE(lock, lock_witness);
  229         class = LOCK_CLASS(lock);
  230 
  231         if (cold || panicstr) {
  232                 /*
  233                  * After a panic, or during autoconfiguration, just give
  234                  * interrupts a chance, then just return; don't run any other
  235                  * procs or panic below, in case this is the idle process and
  236                  * already asleep.
  237                  */
  238                 return (0);
  239         }
  240 
  241         sleepq_lock(cvp);
  242 
  243         cvp->cv_waiters++;
  244         DROP_GIANT();
  245 
  246         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR |
  247             SLEEPQ_INTERRUPTIBLE, 0);
  248         if (lock != &Giant.lock_object) {
  249                 if (class->lc_flags & LC_SLEEPABLE)
  250                         sleepq_release(cvp);
  251                 lock_state = class->lc_unlock(lock);
  252                 if (class->lc_flags & LC_SLEEPABLE)
  253                         sleepq_lock(cvp);
  254         }
  255         rval = sleepq_wait_sig(cvp);
  256 
  257 #ifdef KTRACE
  258         if (KTRPOINT(td, KTR_CSW))
  259                 ktrcsw(0, 0);
  260 #endif
  261         PICKUP_GIANT();
  262         if (lock != &Giant.lock_object) {
  263                 class->lc_lock(lock, lock_state);
  264                 WITNESS_RESTORE(lock, lock_witness);
  265         }
  266 
  267         return (rval);
  268 }
  269 
  270 /*
  271  * Wait on a condition variable for at most timo/hz seconds.  Returns 0 if the
  272  * process was resumed by cv_signal or cv_broadcast, EWOULDBLOCK if the timeout
  273  * expires.
  274  */
  275 int
  276 _cv_timedwait(struct cv *cvp, struct lock_object *lock, int timo)
  277 {
  278         WITNESS_SAVE_DECL(lock_witness);
  279         struct lock_class *class;
  280         struct thread *td;
  281         int lock_state, rval;
  282 
  283         td = curthread;
  284         rval = 0;
  285         lock_state = 0;
  286 #ifdef KTRACE
  287         if (KTRPOINT(td, KTR_CSW))
  288                 ktrcsw(1, 0);
  289 #endif
  290         CV_ASSERT(cvp, lock, td);
  291         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  292             "Waiting on \"%s\"", cvp->cv_description);
  293         WITNESS_SAVE(lock, lock_witness);
  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         DROP_GIANT();
  310 
  311         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
  312         sleepq_set_timeout(cvp, timo);
  313         if (lock != &Giant.lock_object) {
  314                 if (class->lc_flags & LC_SLEEPABLE)
  315                         sleepq_release(cvp);
  316                 lock_state = class->lc_unlock(lock);
  317                 if (class->lc_flags & LC_SLEEPABLE)
  318                         sleepq_lock(cvp);
  319         }
  320         rval = sleepq_timedwait(cvp);
  321 
  322 #ifdef KTRACE
  323         if (KTRPOINT(td, KTR_CSW))
  324                 ktrcsw(0, 0);
  325 #endif
  326         PICKUP_GIANT();
  327         if (lock != &Giant.lock_object) {
  328                 class->lc_lock(lock, lock_state);
  329                 WITNESS_RESTORE(lock, lock_witness);
  330         }
  331 
  332         return (rval);
  333 }
  334 
  335 /*
  336  * Wait on a condition variable for at most timo/hz seconds, allowing
  337  * interruption by signals.  Returns 0 if the thread was resumed by cv_signal
  338  * or cv_broadcast, EWOULDBLOCK if the timeout expires, and EINTR or ERESTART if
  339  * a signal was caught.
  340  */
  341 int
  342 _cv_timedwait_sig(struct cv *cvp, struct lock_object *lock, int timo)
  343 {
  344         WITNESS_SAVE_DECL(lock_witness);
  345         struct lock_class *class;
  346         struct thread *td;
  347         struct proc *p;
  348         int lock_state, rval;
  349 
  350         td = curthread;
  351         p = td->td_proc;
  352         rval = 0;
  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         WITNESS_SAVE(lock, lock_witness);
  362         class = LOCK_CLASS(lock);
  363 
  364         if (cold || panicstr) {
  365                 /*
  366                  * After a panic, or during autoconfiguration, just give
  367                  * interrupts a chance, then just return; don't run any other
  368                  * thread or panic below, in case this is the idle process and
  369                  * already asleep.
  370                  */
  371                 return 0;
  372         }
  373 
  374         sleepq_lock(cvp);
  375 
  376         cvp->cv_waiters++;
  377         DROP_GIANT();
  378 
  379         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR |
  380             SLEEPQ_INTERRUPTIBLE, 0);
  381         sleepq_set_timeout(cvp, timo);
  382         if (lock != &Giant.lock_object) {
  383                 if (class->lc_flags & LC_SLEEPABLE)
  384                         sleepq_release(cvp);
  385                 lock_state = class->lc_unlock(lock);
  386                 if (class->lc_flags & LC_SLEEPABLE)
  387                         sleepq_lock(cvp);
  388         }
  389         rval = sleepq_timedwait_sig(cvp);
  390 
  391 #ifdef KTRACE
  392         if (KTRPOINT(td, KTR_CSW))
  393                 ktrcsw(0, 0);
  394 #endif
  395         PICKUP_GIANT();
  396         if (lock != &Giant.lock_object) {
  397                 class->lc_lock(lock, lock_state);
  398                 WITNESS_RESTORE(lock, lock_witness);
  399         }
  400 
  401         return (rval);
  402 }
  403 
  404 /*
  405  * Signal a condition variable, wakes up one waiting thread.  Will also wakeup
  406  * the swapper if the process is not in memory, so that it can bring the
  407  * sleeping process in.  Note that this may also result in additional threads
  408  * being made runnable.  Should be called with the same mutex as was passed to
  409  * cv_wait held.
  410  */
  411 void
  412 cv_signal(struct cv *cvp)
  413 {
  414         int wakeup_swapper;
  415 
  416         wakeup_swapper = 0;
  417         sleepq_lock(cvp);
  418         if (cvp->cv_waiters > 0) {
  419                 cvp->cv_waiters--;
  420                 wakeup_swapper = sleepq_signal(cvp, SLEEPQ_CONDVAR, -1, 0);
  421         }
  422         sleepq_release(cvp);
  423         if (wakeup_swapper)
  424                 kick_proc0();
  425 }
  426 
  427 /*
  428  * Broadcast a signal to a condition variable.  Wakes up all waiting threads.
  429  * Should be called with the same mutex as was passed to cv_wait held.
  430  */
  431 void
  432 cv_broadcastpri(struct cv *cvp, int pri)
  433 {
  434         int wakeup_swapper;
  435 
  436         wakeup_swapper = 0;
  437         sleepq_lock(cvp);
  438         if (cvp->cv_waiters > 0) {
  439                 cvp->cv_waiters = 0;
  440                 wakeup_swapper = sleepq_broadcast(cvp, SLEEPQ_CONDVAR, pri, 0);
  441         } else
  442                 sleepq_release(cvp);
  443         if (wakeup_swapper)
  444                 kick_proc0();
  445 }

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