FreeBSD/Linux Kernel Cross Reference
sys/contrib/ck/include/ck_swlock.h

     /*
      * Copyright 2014 Jaidev Sridhar.
      * Copyright 2014 Samy Al Bahra.
      * All rights reserved.
      *
      * 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 AUTHOR 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 AUTHOR 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.
     */
    
    #ifndef CK_SWLOCK_H
    #define CK_SWLOCK_H
    
    #include <ck_elide.h>
    #include <ck_limits.h>
    #include <ck_pr.h>
    #include <ck_stdbool.h>
    #include <ck_stddef.h>
    
    struct ck_swlock {
            uint32_t value;
    };
    typedef struct ck_swlock ck_swlock_t;
    
    #define CK_SWLOCK_INITIALIZER   {0}
    #define CK_SWLOCK_WRITER_BIT    (1UL << 31)
    #define CK_SWLOCK_LATCH_BIT     (1UL << 30)
    #define CK_SWLOCK_WRITER_MASK   (CK_SWLOCK_LATCH_BIT | CK_SWLOCK_WRITER_BIT)
    #define CK_SWLOCK_READER_MASK   (UINT32_MAX ^ CK_SWLOCK_WRITER_MASK)
    
    CK_CC_INLINE static void
    ck_swlock_init(struct ck_swlock *rw)
    {
    
            rw->value = 0;
            ck_pr_barrier();
            return;
    }
    
    CK_CC_INLINE static void
    ck_swlock_write_unlock(ck_swlock_t *rw)
    {
    
            ck_pr_fence_unlock();
            ck_pr_and_32(&rw->value, CK_SWLOCK_READER_MASK);
            return;
    }
    
    CK_CC_INLINE static bool
    ck_swlock_locked_writer(ck_swlock_t *rw)
    {
            bool r;
    
            r = ck_pr_load_32(&rw->value) & CK_SWLOCK_WRITER_BIT;
            ck_pr_fence_acquire();
            return r;
    }
    
    CK_CC_INLINE static void
    ck_swlock_write_downgrade(ck_swlock_t *rw)
    {
    
            ck_pr_inc_32(&rw->value);
            ck_swlock_write_unlock(rw);
            return;
    }
    
    CK_CC_INLINE static bool
    ck_swlock_locked(ck_swlock_t *rw)
    {
            bool r;
    
            r = ck_pr_load_32(&rw->value);
            ck_pr_fence_acquire();
            return r;
    }
    
    CK_CC_INLINE static bool
    ck_swlock_write_trylock(ck_swlock_t *rw)
    {
            bool r;
    
           r = ck_pr_cas_32(&rw->value, 0, CK_SWLOCK_WRITER_BIT);
           ck_pr_fence_lock();
           return r;
   }
   
   CK_ELIDE_TRYLOCK_PROTOTYPE(ck_swlock_write, ck_swlock_t,
       ck_swlock_locked, ck_swlock_write_trylock)
   
   CK_CC_INLINE static void
   ck_swlock_write_lock(ck_swlock_t *rw)
   {
   
           ck_pr_or_32(&rw->value, CK_SWLOCK_WRITER_BIT);
           while (ck_pr_load_32(&rw->value) & CK_SWLOCK_READER_MASK)
                   ck_pr_stall();
   
           ck_pr_fence_lock();
           return;
   }
   
   CK_CC_INLINE static void
   ck_swlock_write_latch(ck_swlock_t *rw)
   {
   
           /* Publish intent to acquire lock. */
           ck_pr_or_32(&rw->value, CK_SWLOCK_WRITER_BIT);
   
           /* Stall until readers have seen the writer and cleared. */
           while (ck_pr_cas_32(&rw->value, CK_SWLOCK_WRITER_BIT,
               CK_SWLOCK_WRITER_MASK) == false)  {
                   do {
                           ck_pr_stall();
                   } while (ck_pr_load_32(&rw->value) != CK_SWLOCK_WRITER_BIT);
           }
   
           ck_pr_fence_lock();
           return;
   }
   
   CK_CC_INLINE static void
   ck_swlock_write_unlatch(ck_swlock_t *rw)
   {
   
           ck_pr_fence_unlock();
           ck_pr_store_32(&rw->value, 0);
           return;
   }
   
   CK_ELIDE_PROTOTYPE(ck_swlock_write, ck_swlock_t,
       ck_swlock_locked, ck_swlock_write_lock,
       ck_swlock_locked_writer, ck_swlock_write_unlock)
   
   CK_ELIDE_TRYLOCK_PROTOTYPE(ck_swlock_read, ck_swlock_t,
       ck_swlock_locked_writer, ck_swlock_read_trylock)
   
   CK_CC_INLINE static bool
   ck_swlock_read_trylock(ck_swlock_t *rw)
   {
           uint32_t l = ck_pr_load_32(&rw->value);
   
           if (l & CK_SWLOCK_WRITER_BIT)
                   return false;
   
           l = ck_pr_faa_32(&rw->value, 1) & CK_SWLOCK_WRITER_MASK;
           if (l == CK_SWLOCK_WRITER_BIT)
                   ck_pr_dec_32(&rw->value);
   
           ck_pr_fence_lock();
           return l == 0;
   }
   
   CK_CC_INLINE static void
   ck_swlock_read_lock(ck_swlock_t *rw)
   {
           uint32_t l;
   
           for (;;) {
                   while (ck_pr_load_32(&rw->value) & CK_SWLOCK_WRITER_BIT)
                           ck_pr_stall();
   
                   l = ck_pr_faa_32(&rw->value, 1) & CK_SWLOCK_WRITER_MASK;
                   if (l == 0)
                           break;
   
                   /*
                    * If the latch bit has not been set, then the writer would
                    * have observed the reader and will wait to completion of
                    * read-side critical section.
                    */
                   if (l == CK_SWLOCK_WRITER_BIT)
                           ck_pr_dec_32(&rw->value);
           }
   
           ck_pr_fence_lock();
           return;
   }
   
   CK_CC_INLINE static bool
   ck_swlock_locked_reader(ck_swlock_t *rw)
   {
   
           ck_pr_fence_load();
           return ck_pr_load_32(&rw->value) & CK_SWLOCK_READER_MASK;
   }
   
   CK_CC_INLINE static void
   ck_swlock_read_unlock(ck_swlock_t *rw)
   {
   
           ck_pr_fence_unlock();
           ck_pr_dec_32(&rw->value);
           return;
   }
   
   CK_ELIDE_PROTOTYPE(ck_swlock_read, ck_swlock_t,
       ck_swlock_locked_writer, ck_swlock_read_lock,
       ck_swlock_locked_reader, ck_swlock_read_unlock)
   
   #endif /* CK_SWLOCK_H */

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