CK_ELIDE(3)

okay bestie, welcome to ck_elide(3) — the lock elision wrappers page from Concurrency Kit, and I'm literally obsessed 💖. this is the one where locks get to be a little lazy (in a good way) and let your threads vibe concurrently. let's get into it, no cap.

🎀 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 💖

okay so these macros? they 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. and 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. it's giving "everybody retry together, periodt" 😭.

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/ 🌈

and that's the whole vibe, bestie 💅. this was the ck_elide(3) page, signed off with source/version vibes and dated July 13, 2013. — go forth and elide responsibly, mwah 🫶💖