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ck_elide(3)              BSD Library Functions Manual              ck_elide(3)

NAME
     CK_ELIDE_PROTOTYPE, CK_ELIDE_LOCK_ADAPTIVE, CK_ELIDE_UNLOCK_ADAPTIVE,
     CK_ELIDE_LOCK, CK_ELIDE_UNLOCK, CK_ELIDE_TRYLOCK_PROTOTYPE,
     CK_ELIDE_TRYLOCK -- lock elision wrappers

LIBRARY
     Concurrency Kit (libck, -lck)

SYNOPSIS
     #include <ck_elide.h>

     ck_elide_stat_t stat = CK_ELIDE_STAT_INITIALIZER;

     void
     ck_elide_stat_init(ck_elide_stat_t *);

     struct ck_elide_config config = CK_ELIDE_CONFIG_DEFAULT_INITIALIZER;

     struct ck_elide_config {
             unsigned short skip_busy;
             short retry_busy;
             unsigned short skip_other;
             short retry_other;
             unsigned short skip_conflict;
             short retry_conflict;
     };

     CK_ELIDE_PROTOTYPE(NAME, TYPE, LOCK_PREDICATE, LOCK_FUNCTION,
         UNLOCK_PREDICATE, UNLOCK_FUNCTION);

     CK_ELIDE_LOCK_ADAPTIVE(NAME, ck_elide_stat_t *, struct ck_elide_config *,
         TYPE *);

     CK_ELIDE_UNLOCK_ADAPTIVE(NAME, ck_elide_stat_t *, TYPE *);

     CK_ELIDE_LOCK(NAME, TYPE *);

     CK_ELIDE_UNLOCK(NAME, TYPE *);

     CK_ELIDE_TRYLOCK_PROTOTYPE(NAME, TYPE, LOCK_PREDICATE, TRYLOCK_FUNCTION);

DESCRIPTION
     These macros implement lock elision wrappers for a user-specified single-
     argument lock interface. The wrappers will attempt to elide lock acquisi-
     tion, allowing concurrent execution of critical sections that do not
     issue conflicting memory operations. If any threads have successfully
     elided a lock acquisition, conflicting memory operations will roll-back
     any side-effects of the critical section and force every thread to retry
     the lock acquisition regularly.

     CK_ELIDE_LOCK(), CK_ELIDE_UNLOCK(), CK_ELIDE_LOCK_ADAPTIVE(), and
     CK_ELIDE_UNLOCK_ADAPTIVE() macros require a previous CK_ELIDE_PROTOTYPE()
     with the same NAME.  Elision is attempted if the LOCK_PREDICATE function
     returns false. If LOCK_PREDICATE returns true then elision is aborted and
     LOCK_FUNCTION is executed instead. If any threads are in an elided criti-
     cal section, LOCK_FUNCTION must force them to rollback through a con-
     flicting memory operation.  The UNLOCK_PREDICATE function must return
     true if the lock is acquired by the caller, meaning that the lock was not
     successfully elided. If UNLOCK_PREDICATE returns true, then the
     UNLOCK_FUNCTION is executed. If RTM is unsupported (no CK_F_PR_RTM macro)
     then CK_ELIDE_LOCK() and CK_ELIDE_LOCK_ADAPTIVE() will immediately call
     LOCK_FUNCTION().  CK_ELIDE_UNLOCK() and CK_ELIDE_UNLOCK_ADAPTIVE() will
     immediately call UNLOCK_FUNCTION().

     CK_ELIDE_TRYLOCK() requires a previous CK_ELIDE_TRYLOCK_PROTOTYPE() with
     the same name.  Elision is attempted if the LOCK_PREDICATE function
     returns false. If LOCK_PREDICATE returns true or if elision fails then
     the operation is aborted. If RTM is unsupported (no CK_F_PR_RTM macro)
     then CK_ELIDE_TRYLOCK() will immediately call TRYLOCK_FUNCTION().

     CK_ELIDE_LOCK_ADAPTIVE() and CK_ELIDE_UNLOCK_ADAPTIVE() will adapt the
     elision behavior associated with lock operations according to the run-
     time behavior of the program. This behavior is defined by the
     ck_elide_config structure pointer passed to CK_ELIDE_LOCK_ADAPTIVE().  A
     thread-local ck_elide_stat structure must be passed to both
     CK_ELIDE_LOCK_ADAPTIVE() and CK_ELIDE_UNLOCK_ADAPTIVE().  This structure
     is expected to be unique for different workloads, may not be re-used in
     recursive acquisitions and must match the lifetime of the lock it is
     associated with. It is safe to mix adaptive calls with best-effort calls.

     Both ck_spinlock.h and ck_rwlock.h define ck_elide wrappers under the
     ck_spinlock and ck_rwlock namespace, respectively.

EXAMPLES
     This example utilizes built-in lock elision facilities in ck_rwlock and
     ck_spinlock.

           #include <ck_rwlock.h>
           #include <ck_spinlock.h>

           static ck_rwlock_t rw = CK_RWLOCK_INITIALIZER;
           static struct ck_elide_config rw_config =
               CK_ELIDE_CONFIG_DEFAULT_INITIALIZER;
           static __thread ck_elide_stat_t rw_stat =
               CK_ELIDE_STAT_INITIALIZER;

           static ck_spinlock_t spinlock = CK_SPINLOCK_INITIALIZER;
           static struct ck_elide_config spinlock_config =
               CK_ELIDE_CONFIG_DEFAULT_INITIALIZER;
           static __thread ck_elide_stat_t spinlock_stat =
               CK_ELIDE_STAT_INITIALIZER;

           void
           function(void)
           {

                   /* Lock-unlock write-side lock in weak best-effort manner. */
                   CK_ELIDE_LOCK(ck_rwlock_write, &rw);
                   CK_ELIDE_UNLOCK(ck_rwlock_write, &rw);

                   /* Attempt to acquire the write-side lock. */
                   if (CK_ELIDE_TRYLOCK(ck_rwlock_write, &rw) == true)
                           CK_ELIDE_UNLOCK(ck_rwlock_write, &rw);

                   /* Lock-unlock read-side lock in weak best-effort manner. */
                   CK_ELIDE_LOCK(ck_rwlock_read, &rw);
                   CK_ELIDE_UNLOCK(ck_rwlock_read, &rw);

                   /* Attempt to acquire the read-side lock. */
                   if (CK_ELIDE_TRYLOCK(ck_rwlock_read, &rw) == true)
                           CK_ELIDE_UNLOCK(ck_rwlock_read, &rw);

                   /* Lock-unlock write-side lock in an adaptive manner. */
                   CK_ELIDE_LOCK_ADAPTIVE(ck_rwlock_write, &rw_stat,
                       &rw_config, &rw);
                   CK_ELIDE_UNLOCK_ADAPTIVE(ck_rwlock_write, &rw_stat,
                       &rw_config, &rw);

                   /* Lock-unlock read-side lock in an adaptive manner. */
                   CK_ELIDE_LOCK_ADAPTIVE(ck_rwlock_read, &rw_stat,
                       &rw_config, &rw);
                   CK_ELIDE_UNLOCK_ADAPTIVE(ck_rwlock_read, &rw_stat,
                       &rw_config, &rw);

                   /* Lock-unlock spinlock in weak best-effort manner. */
                   CK_ELIDE_LOCK(ck_spinlock, &spinlock);
                   CK_ELIDE_UNLOCK(ck_spinlock, &spinlock);

                   /* Attempt to acquire the lock. */
                   if (CK_ELIDE_TRYLOCK(ck_spinlock, &lock) == true)
                           CK_ELIDE_UNLOCK(ck_spinlock, &spinlock);

                   /* Lock-unlock spinlock in an adaptive manner. */
                   CK_ELIDE_LOCK_ADAPTIVE(ck_spinlock, &spinlock_stat,
                       &spinlock_config, &spinlock);
                   CK_ELIDE_UNLOCK_ADAPTIVE(ck_spinlock, &spinlock_stat,
                       &spinlock_config, &spinlock);
           }

     In this example, user-defined locking functions are provided an elision
     implementation.

           /* Assume lock_t has been previously defined. */
           #include <ck_elide.h>

           /*
            * This function returns true if the lock is unavailable at the time
            * it was called or false if the lock is available.
            */
           bool is_locked(lock_t *);

           /*
            * This function acquires the supplied lock.
            */
           void lock(lock_t *);

           /*
            * This function releases the lock.
            */
           void unlock(lock_t *);

           CK_ELIDE_PROTOTYPE(my_lock, lock_t, is_locked, lock, is_locked, unlock)

           static lock_t lock;

           void
           function(void)
           {

                   CK_ELIDE_LOCK(my_lock, &lock);
                   CK_ELIDE_UNLOCK(my_lock, &lock);
           }

SEE ALSO
     ck_rwlock(3), ck_spinlock(3)

     Ravi Rajwar and James R. Goodman. 2001. Speculative lock elision:
     enabling highly concurrent multithreaded execution. In Proceedings of the
     34th annual ACM/IEEE international symposium on Microarchitecture (MICRO
     34). IEEE Computer Society, Washington, DC, USA, 294-305.

     Additional information available at http://en.wikipedia.org/wiki/Transac-
     tional_Synchronization_Extensions and http://concurrencykit.org/

                                July 13, 2013.