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pthread_lock.c revision 1.1.2.3 
      1 /*	$NetBSD: pthread_lock.c,v 1.1.2.3 2001/07/13 02:42:38 nathanw Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2001 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Nathan J. Williams.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  * 3. All advertising materials mentioning features or use of this software
     19  *    must display the following acknowledgement:
     20  *        This product includes software developed by the NetBSD
     21  *        Foundation, Inc. and its contributors.
     22  * 4. Neither the name of The NetBSD Foundation nor the names of its
     23  *    contributors may be used to endorse or promote products derived
     24  *    from this software without specific prior written permission.
     25  *
     26  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     27  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     28  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     29  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     30  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     31  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     32  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     33  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     34  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     35  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     36  * POSSIBILITY OF SUCH DAMAGE.
     37  */
     38 
     39 #include <assert.h>
     40 #include <errno.h>
     41 #include <signal.h>
     42 #include <stdlib.h>
     43 #include <ucontext.h>
     44 #include <sys/queue.h>
     45 
     46 #include "pthread.h"
     47 #include "pthread_int.h"
     48 
     49 /* How many times to try before checking whether we've been continued. */
     50 #define NSPINS 20	/* XXX arbitrary */
     51 
     52 static int nspins = NSPINS;
     53 
     54 void
     55 pthread_lockinit(pt_spin_t *lock)
     56 {
     57 
     58 	__cpu_simple_lock_init(lock);
     59 }
     60 
     61 void
     62 pthread_spinlock(pthread_t thread, pt_spin_t *lock)
     63 {
     64 	int count, ret;
     65 
     66 	count = nspins;
     67 	++thread->pt_spinlocks;
     68 
     69 	do {
     70 		while (((ret = __cpu_simple_lock_try(lock)) == 0) && --count)
     71 			;
     72 
     73 		if (ret == 1)
     74 			break;
     75 
     76 		--thread->pt_spinlocks;
     77 
     78 		/* We may be preempted while spinning. If so, we will
     79 		 * be restarted here if thread->pt_spinlocks is
     80 		 * nonzero, which can happen if:
     81 		 * a) we just got the lock
     82 		 * b) we haven't yet decremented the lock count.
     83 		 * If we're at this point, (b) applies. Therefore,
     84 		 * check if we're being continued, and if so, bail.
     85 		 * (in case (a), we should let the code finish and
     86 		 * we will bail out in pthread_spinunlock()).
     87 		 */
     88 		if (thread->pt_next != NULL) {
     89 			PTHREADD_ADD(PTHREADD_SPINPREEMPT);
     90 			pthread__switch(thread, thread->pt_next, 0);
     91 		}
     92 		/* try again */
     93 		count = nspins;
     94 		++thread->pt_spinlocks;
     95 	} while (/*CONSTCOND*/1);
     96 
     97 	PTHREADD_ADD(PTHREADD_SPINLOCKS);
     98 	/* Got it! We're out of here. */
     99 }
    100 
    101 
    102 int
    103 pthread_spintrylock(pthread_t thread, pt_spin_t *lock)
    104 {
    105 	int ret;
    106 
    107 	++thread->pt_spinlocks;
    108 
    109 	ret = __cpu_simple_lock_try(lock);
    110 
    111 	if (ret == 0) {
    112 		--thread->pt_spinlocks;
    113 		/* See above. */
    114 		if (thread->pt_next != NULL) {
    115 			PTHREADD_ADD(PTHREADD_SPINPREEMPT);
    116 			pthread__switch(thread, thread->pt_next, 0);
    117 		}
    118 	}
    119 
    120 	return ret;
    121 }
    122 
    123 
    124 void
    125 pthread_spinunlock(pthread_t thread, pt_spin_t *lock)
    126 {
    127 	__cpu_simple_unlock(lock);
    128 	--thread->pt_spinlocks;
    129 
    130 	PTHREADD_ADD(PTHREADD_SPINUNLOCKS);
    131 
    132 	/* If we were preempted while holding a spinlock, the
    133 	 * scheduler will notice this and continue us. To be good
    134 	 * citzens, we must now get out of here if that was our
    135 	 * last spinlock.
    136 	 * XXX when will we ever have more than one?
    137 	 */
    138 
    139 	if ((thread->pt_spinlocks == 0) && (thread->pt_next != NULL)) {
    140 		PTHREADD_ADD(PTHREADD_SPINPREEMPT);
    141 		pthread__switch(thread, thread->pt_next, 0);
    142 	}
    143 }
    144 
    145