FreeBSD/Linux Kernel Cross Reference
sys/sys/sx.h

     /*-
      * Copyright (c) 2007 Attilio Rao <attilio@freebsd.org>
      * Copyright (c) 2001 Jason Evans <jasone@freebsd.org>
      * 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(s), this list of conditions and the following disclaimer as
     *    the first lines of this file unmodified other than the possible 
     *    addition of one or more copyright notices.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice(s), 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 COPYRIGHT HOLDER(S) ``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 COPYRIGHT HOLDER(S) 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.
     *
     * $FreeBSD$
     */
    
    #ifndef _SYS_SX_H_
    #define _SYS_SX_H_
    
    #include <sys/_lock.h>
    #include <sys/_sx.h>
    
    #ifdef  _KERNEL
    #include <sys/pcpu.h>
    #include <sys/lock_profile.h>
    #include <machine/atomic.h>
    #endif
    
    /*
     * In general, the sx locks and rwlocks use very similar algorithms.
     * The main difference in the implementations is how threads are
     * blocked when a lock is unavailable.  For this, sx locks use sleep
     * queues which do not support priority propagation, and rwlocks use
     * turnstiles which do.
     *
     * The sx_lock field consists of several fields.  The low bit
     * indicates if the lock is locked with a shared or exclusive lock.  A
     * value of 0 indicates an exclusive lock, and a value of 1 indicates
     * a shared lock.  Bit 1 is a boolean indicating if there are any
     * threads waiting for a shared lock.  Bit 2 is a boolean indicating
     * if there are any threads waiting for an exclusive lock.  Bit 3 is a
     * boolean indicating if an exclusive lock is recursively held.  The
     * rest of the variable's definition is dependent on the value of the
     * first bit.  For an exclusive lock, it is a pointer to the thread
     * holding the lock, similar to the mtx_lock field of mutexes.  For
     * shared locks, it is a count of read locks that are held.
     *
     * When the lock is not locked by any thread, it is encoded as a
     * shared lock with zero waiters.
     *
     * A note about memory barriers.  Exclusive locks need to use the same
     * memory barriers as mutexes: _acq when acquiring an exclusive lock
     * and _rel when releasing an exclusive lock.  On the other side,
     * shared lock needs to use an _acq barrier when acquiring the lock
     * but, since they don't update any locked data, no memory barrier is
     * needed when releasing a shared lock.
     */
    
    #define SX_LOCK_SHARED                  0x01
    #define SX_LOCK_SHARED_WAITERS          0x02
    #define SX_LOCK_EXCLUSIVE_WAITERS       0x04
    #define SX_LOCK_RECURSED                0x08
    #define SX_LOCK_FLAGMASK                                                \
            (SX_LOCK_SHARED | SX_LOCK_SHARED_WAITERS |                      \
            SX_LOCK_EXCLUSIVE_WAITERS | SX_LOCK_RECURSED)
    
    #define SX_OWNER(x)                     ((x) & ~SX_LOCK_FLAGMASK)
    #define SX_SHARERS_SHIFT                4
    #define SX_SHARERS(x)                   (SX_OWNER(x) >> SX_SHARERS_SHIFT)
    #define SX_SHARERS_LOCK(x)                                              \
            ((x) << SX_SHARERS_SHIFT | SX_LOCK_SHARED)
    #define SX_ONE_SHARER                   (1 << SX_SHARERS_SHIFT)
    
    #define SX_LOCK_UNLOCKED                SX_SHARERS_LOCK(0)
    #define SX_LOCK_DESTROYED                                               \
            (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)
    
    #ifdef _KERNEL
    
    /*
     * Function prototipes.  Routines that start with an underscore are not part
     * of the public interface and are wrappered with a macro.
     */
    void    sx_sysinit(void *arg);
   #define sx_init(sx, desc)       sx_init_flags((sx), (desc), 0)
   void    sx_init_flags(struct sx *sx, const char *description, int opts);
   void    sx_destroy(struct sx *sx);
   int     _sx_slock(struct sx *sx, int opts, const char *file, int line);
   int     _sx_xlock(struct sx *sx, int opts, const char *file, int line);
   int     _sx_try_slock(struct sx *sx, const char *file, int line);
   int     _sx_try_xlock(struct sx *sx, const char *file, int line);
   void    _sx_sunlock(struct sx *sx, const char *file, int line);
   void    _sx_xunlock(struct sx *sx, const char *file, int line);
   int     _sx_try_upgrade(struct sx *sx, const char *file, int line);
   void    _sx_downgrade(struct sx *sx, const char *file, int line);
   int     _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts,
               const char *file, int line);
   int     _sx_slock_hard(struct sx *sx, int opts, const char *file, int line);
   void    _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int
               line);
   void    _sx_sunlock_hard(struct sx *sx, const char *file, int line);
   #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
   void    _sx_assert(struct sx *sx, int what, const char *file, int line);
   #endif
   #ifdef DDB
   int     sx_chain(struct thread *td, struct thread **ownerp);
   #endif
   
   struct sx_args {
           struct sx       *sa_sx;
           const char      *sa_desc;
   };
   
   #define SX_SYSINIT(name, sxa, desc)                                     \
           static struct sx_args name##_args = {                           \
                   (sxa),                                                  \
                   (desc)                                                  \
           };                                                              \
           SYSINIT(name##_sx_sysinit, SI_SUB_LOCK, SI_ORDER_MIDDLE,        \
               sx_sysinit, &name##_args);                                  \
           SYSUNINIT(name##_sx_sysuninit, SI_SUB_LOCK, SI_ORDER_MIDDLE,    \
               sx_destroy, (sxa))
   
   /*
    * Full lock operations that are suitable to be inlined in non-debug kernels.
    * If the lock can't be acquired or released trivially then the work is
    * deferred to 'tougher' functions.
    */
   
   /* Acquire an exclusive lock. */
   static __inline int
   __sx_xlock(struct sx *sx, struct thread *td, int opts, const char *file,
       int line)
   {
           uintptr_t tid = (uintptr_t)td;
           int error = 0;
   
           if (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid))
                   error = _sx_xlock_hard(sx, tid, opts, file, line);
           else
                   lock_profile_obtain_lock_success(&sx->lock_object, 0, 0, file,
                       line);
   
           return (error);
   }
   
   /* Release an exclusive lock. */
   static __inline void
   __sx_xunlock(struct sx *sx, struct thread *td, const char *file, int line)
   {
           uintptr_t tid = (uintptr_t)td;
   
           if (!atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED))
                   _sx_xunlock_hard(sx, tid, file, line);
   }
   
   /* Acquire a shared lock. */
   static __inline int
   __sx_slock(struct sx *sx, int opts, const char *file, int line)
   {
           uintptr_t x = sx->sx_lock;
           int error = 0;
   
           if (!(x & SX_LOCK_SHARED) ||
               !atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER))
                   error = _sx_slock_hard(sx, opts, file, line);
   #ifdef LOCK_PROFILING_SHARED
           else if (SX_SHARERS(x) == 0)
                   lock_profile_obtain_lock_success(&sx->lock_object, 0, 0, file,
                       line);
   #endif
   
           return (error);
   }
   
   /*
    * Release a shared lock.  We can just drop a single shared lock so
    * long as we aren't trying to drop the last shared lock when other
    * threads are waiting for an exclusive lock.  This takes advantage of
    * the fact that an unlocked lock is encoded as a shared lock with a
    * count of 0.
    */
   static __inline void
   __sx_sunlock(struct sx *sx, const char *file, int line)
   {
           uintptr_t x = sx->sx_lock;
   
           if (x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS) ||
               !atomic_cmpset_ptr(&sx->sx_lock, x, x - SX_ONE_SHARER))
                   _sx_sunlock_hard(sx, file, line);
   }
   
   /*
    * Public interface for lock operations.
    */
   #ifndef LOCK_DEBUG
   #error  "LOCK_DEBUG not defined, include <sys/lock.h> before <sys/sx.h>"
   #endif
   #if     (LOCK_DEBUG > 0) || defined(SX_NOINLINE)
   #define sx_xlock(sx)            (void)_sx_xlock((sx), 0, LOCK_FILE, LOCK_LINE)
   #define sx_xlock_sig(sx)                                                \
           _sx_xlock((sx), SX_INTERRUPTIBLE, LOCK_FILE, LOCK_LINE)
   #define sx_xunlock(sx)          _sx_xunlock((sx), LOCK_FILE, LOCK_LINE)
   #define sx_slock(sx)            (void)_sx_slock((sx), 0, LOCK_FILE, LOCK_LINE)
   #define sx_slock_sig(sx)                                                \
           _sx_slock((sx), SX_INTERRUPTIBLE, LOCK_FILE, LOCK_LINE)
   #define sx_sunlock(sx)          _sx_sunlock((sx), LOCK_FILE, LOCK_LINE)
   #else
   #define sx_xlock(sx)                                                    \
           (void)__sx_xlock((sx), curthread, 0, LOCK_FILE, LOCK_LINE)
   #define sx_xlock_sig(sx)                                                \
           __sx_xlock((sx), curthread, SX_INTERRUPTIBLE, LOCK_FILE, LOCK_LINE)
   #define sx_xunlock(sx)                                                  \
           __sx_xunlock((sx), curthread, LOCK_FILE, LOCK_LINE)
   #define sx_slock(sx)            (void)__sx_slock((sx), 0, LOCK_FILE, LOCK_LINE)
   #define sx_slock_sig(sx)                                                \
           __sx_slock((sx), SX_INTERRUPTIBLE, LOCK_FILE, LOCK_LINE)
   #define sx_sunlock(sx)          __sx_sunlock((sx), LOCK_FILE, LOCK_LINE)
   #endif  /* LOCK_DEBUG > 0 || SX_NOINLINE */
   #define sx_try_slock(sx)        _sx_try_slock((sx), LOCK_FILE, LOCK_LINE)
   #define sx_try_xlock(sx)        _sx_try_xlock((sx), LOCK_FILE, LOCK_LINE)
   #define sx_try_upgrade(sx)      _sx_try_upgrade((sx), LOCK_FILE, LOCK_LINE)
   #define sx_downgrade(sx)        _sx_downgrade((sx), LOCK_FILE, LOCK_LINE)
   
   /*
    * Return a pointer to the owning thread if the lock is exclusively
    * locked.
    */
   #define sx_xholder(sx)                                                  \
           ((sx)->sx_lock & SX_LOCK_SHARED ? NULL :                        \
           (struct thread *)SX_OWNER((sx)->sx_lock))
   
   #define sx_xlocked(sx)                                                  \
           (((sx)->sx_lock & ~(SX_LOCK_FLAGMASK & ~SX_LOCK_SHARED)) ==     \
               (uintptr_t)curthread)
   
   #define sx_unlock(sx) do {                                              \
           if (sx_xlocked(sx))                                             \
                   sx_xunlock(sx);                                         \
           else                                                            \
                   sx_sunlock(sx);                                         \
   } while (0)
   
   #define sx_sleep(chan, sx, pri, wmesg, timo)                            \
           _sleep((chan), &(sx)->lock_object, (pri), (wmesg), (timo))
   
   /*
    * Options passed to sx_init_flags().
    */
   #define SX_DUPOK                0x01
   #define SX_NOPROFILE            0x02
   #define SX_NOWITNESS            0x04
   #define SX_QUIET                0x08
   #define SX_ADAPTIVESPIN         0x10
   #define SX_RECURSE              0x20
   
   /*
    * Options passed to sx_*lock_hard().
    */
   #define SX_INTERRUPTIBLE        0x40
   
   #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
   #define SA_LOCKED               LA_LOCKED
   #define SA_SLOCKED              LA_SLOCKED
   #define SA_XLOCKED              LA_XLOCKED
   #define SA_UNLOCKED             LA_UNLOCKED
   #define SA_RECURSED             LA_RECURSED
   #define SA_NOTRECURSED          LA_NOTRECURSED
   
   /* Backwards compatability. */
   #define SX_LOCKED               LA_LOCKED
   #define SX_SLOCKED              LA_SLOCKED
   #define SX_XLOCKED              LA_XLOCKED
   #define SX_UNLOCKED             LA_UNLOCKED
   #define SX_RECURSED             LA_RECURSED
   #define SX_NOTRECURSED          LA_NOTRECURSED
   #endif
   
   #ifdef INVARIANTS
   #define sx_assert(sx, what)     _sx_assert((sx), (what), LOCK_FILE, LOCK_LINE)
   #else
   #define sx_assert(sx, what)
   #endif
   
   #endif /* _KERNEL */
   
   #endif /* !_SYS_SX_H_ */

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