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

     /*      $NetBSD: kern_rwlock_obj.c,v 1.8 2022/10/26 23:22:22 riastradh Exp $    */
     
     /*-
      * Copyright (c) 2008, 2009, 2019 The NetBSD Foundation, Inc.
      * All rights reserved.
      *
      * This code is derived from software contributed to The NetBSD Foundation
      * by Andrew Doran.
      *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     * POSSIBILITY OF SUCH DAMAGE.
     */
    
    #include <sys/cdefs.h>
    __KERNEL_RCSID(0, "$NetBSD: kern_rwlock_obj.c,v 1.8 2022/10/26 23:22:22 riastradh Exp $");
    
    #include <sys/param.h>
    #include <sys/atomic.h>
    #include <sys/pool.h>
    #include <sys/rwlock.h>
    
    /* Mutex cache */
    #define RW_OBJ_MAGIC    0x85d3c85d
    struct krwobj {
            krwlock_t       ro_lock;
            u_int           ro_magic;
            u_int           ro_refcnt;
    };
    
    static int      rw_obj_ctor(void *, void *, int);
    
    static pool_cache_t     rw_obj_cache    __read_mostly;
    
    /*
     * rw_obj_init:
     *
     *      Initialize the rw object store.
     */
    void
    rw_obj_init(void)
    {
    
            rw_obj_cache = pool_cache_init(sizeof(struct krwobj),
                coherency_unit, 0, 0, "rwlock", NULL, IPL_NONE, rw_obj_ctor,
                NULL, NULL);
    }
    
    /*
     * rw_obj_ctor:
     *
     *      Initialize a new lock for the cache.
     */
    static int
    rw_obj_ctor(void *arg, void *obj, int flags)
    {
            struct krwobj * ro = obj;
    
            ro->ro_magic = RW_OBJ_MAGIC;
    
            return 0;
    }
    
    /*
     * rw_obj_alloc:
     *
     *      Allocate a single lock object, waiting for memory if needed.
     */
    krwlock_t *
    rw_obj_alloc(void)
    {
            struct krwobj *ro;
    
            ro = pool_cache_get(rw_obj_cache, PR_WAITOK);
            _rw_init(&ro->ro_lock, (uintptr_t)__builtin_return_address(0));
            ro->ro_refcnt = 1;
    
            return (krwlock_t *)ro;
    }
    
    /*
     * rw_obj_tryalloc:
    *
    *      Allocate a single lock object, but fail if no memory is available.
    */
   krwlock_t *
   rw_obj_tryalloc(void)
   {
           struct krwobj *ro;
   
           ro = pool_cache_get(rw_obj_cache, PR_NOWAIT);
           if (__predict_true(ro != NULL)) {
                   _rw_init(&ro->ro_lock, (uintptr_t)__builtin_return_address(0));
                   ro->ro_refcnt = 1;
           }
   
           return (krwlock_t *)ro;
   }
   
   /*
    * rw_obj_hold:
    *
    *      Add a single reference to a lock object.  A reference to the object
    *      must already be held, and must be held across this call.
    */
   void
   rw_obj_hold(krwlock_t *lock)
   {
           struct krwobj *ro = (struct krwobj *)lock;
   
           KASSERT(ro->ro_magic == RW_OBJ_MAGIC);
           KASSERT(ro->ro_refcnt > 0);
   
           atomic_inc_uint(&ro->ro_refcnt);
   }
   
   /*
    * rw_obj_free:
    *
    *      Drop a reference from a lock object.  If the last reference is being
    *      dropped, free the object and return true.  Otherwise, return false.
    */
   bool
   rw_obj_free(krwlock_t *lock)
   {
           struct krwobj *ro = (struct krwobj *)lock;
   
           KASSERT(ro->ro_magic == RW_OBJ_MAGIC);
           KASSERT(ro->ro_refcnt > 0);
   
   #ifndef __HAVE_ATOMIC_AS_MEMBAR
           membar_release();
   #endif
           if (atomic_dec_uint_nv(&ro->ro_refcnt) > 0) {
                   return false;
           }
   #ifndef __HAVE_ATOMIC_AS_MEMBAR
           membar_acquire();
   #endif
           rw_destroy(&ro->ro_lock);
           pool_cache_put(rw_obj_cache, ro);
           return true;
   }
   
   /*
    * rw_obj_refcnt:
    *
    *      Return the reference count for a lock object.
    */
   u_int
   rw_obj_refcnt(krwlock_t *lock)
   {
           struct krwobj *ro = (struct krwobj *)lock;
   
           return ro->ro_refcnt;
   }

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