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 acquisition, 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 critical section, LOCK_FUNCTION must force them to rollback through a conflicting 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/Transactional_Synchronization_Extensions and http://concurrencykit.org/