NAME

       pmemobj_mutex_zero(),  pmemobj_mutex_lock(),  pmemobj_mutex_timedlock(),  pmemobj_mutex_trylock(), pmemo‐
       bj_mutex_unlock(),

       pmemobj_rwlock_zero(),  pmemobj_rwlock_rdlock(),  pmemobj_rwlock_wrlock(),  pmemobj_rwlock_timedrdlock(),
       pmemobj_rwlock_timedwrlock(),  pmemobj_rwlock_tryrdlock(), pmemobj_rwlock_trywrlock(), pmemobj_rwlock_un‐
       lock(),

       pmemobj_cond_zero(), pmemobj_cond_broadcast(),  pmemobj_cond_signal(),  pmemobj_cond_timedwait(),  pmemo‐
       bj_cond_wait() - pmemobj synchronization primitives

SYNOPSIS

              #include <libpmemobj.h>

              void pmemobj_mutex_zero(PMEMobjpool *pop, PMEMmutex *mutexp);
              int pmemobj_mutex_lock(PMEMobjpool *pop, PMEMmutex *mutexp);
              int pmemobj_mutex_timedlock(PMEMobjpool *pop, PMEMmutex *restrict mutexp,
                  const struct timespec *restrict abs_timeout);
              int pmemobj_mutex_trylock(PMEMobjpool *pop, PMEMmutex *mutexp);
              int pmemobj_mutex_unlock(PMEMobjpool *pop, PMEMmutex *mutexp);

              void pmemobj_rwlock_zero(PMEMobjpool *pop, PMEMrwlock *rwlockp);
              int pmemobj_rwlock_rdlock(PMEMobjpool *pop, PMEMrwlock *rwlockp);
              int pmemobj_rwlock_wrlock(PMEMobjpool *pop, PMEMrwlock *rwlockp);
              int pmemobj_rwlock_timedrdlock(PMEMobjpool *pop, PMEMrwlock *restrict rwlockp,
                  const struct timespec *restrict abs_timeout);
              int pmemobj_rwlock_timedwrlock(PMEMobjpool *pop, PMEMrwlock *restrict rwlockp,
                  const struct timespec *restrict abs_timeout);
              int pmemobj_rwlock_tryrdlock(PMEMobjpool *pop, PMEMrwlock *rwlockp);
              int pmemobj_rwlock_trywrlock(PMEMobjpool *pop, PMEMrwlock *rwlockp);
              int pmemobj_rwlock_unlock(PMEMobjpool *pop, PMEMrwlock *rwlockp);

              void pmemobj_cond_zero(PMEMobjpool *pop, PMEMcond *condp);
              int pmemobj_cond_broadcast(PMEMobjpool *pop, PMEMcond *condp);
              int pmemobj_cond_signal(PMEMobjpool *pop, PMEMcond *condp);
              int pmemobj_cond_timedwait(PMEMobjpool *pop, PMEMcond *restrict condp,
                  PMEMmutex *restrict mutexp, const struct timespec *restrict abs_timeout);
              int pmemobj_cond_wait(PMEMobjpool *pop, PMEMcond *restrict condp,
                  PMEMmutex *restrict mutexp);

DESCRIPTION

       libpmemobj(7)  provides  several  types of synchronization primitives designed to be used with persistent
       memory.  The pmem-aware lock implementation is based on the standard POSIX Threads Library, as  described
       in  pthread_mutex_init(3), pthread_rwlock_init(3) and pthread_cond_init(3).  Pmem-aware locks provide se‐
       mantics similar to standard pthread locks, except that they are embedded in pmem-resident objects and are
       considered initialized by zeroing them.  Therefore, locks  allocated  with  pmemobj_zalloc(3)  or  pmemo‐
       bj_tx_zalloc(3)  do  not  require  another  initialization  step.  For performance reasons, they are also
       padded up to 64 bytes (cache line size).

       On FreeBSD, since all pthread locks are dynamically allocated, while the lock object is still  padded  up
       to 64 bytes for consistency with Linux, only the pointer to the lock is embedded in the pmem-resident ob‐
       ject.  libpmemobj(7) transparently manages freeing of the locks when the pool is closed.

       The  fundamental  property of pmem-aware locks is their automatic reinitialization every time the persis‐
       tent object store pool is opened.  Thus, all the pmem-aware locks  may  be  considered  initialized  (un‐
       locked)  immediately  after the pool is opened, regardless of their state at the time the pool was closed
       for the last time.

       Pmem-aware mutexes, read/write locks and condition variables must be declared with the PMEMmutex,  PMEMr‐
       wlock, or PMEMcond type, respectively.

       The pmemobj_mutex_zero() function explicitly initializes the pmem-aware mutex mutexp by zeroing it.  Ini‐
       tialization  is  not  necessary  if the object containing the mutex has been allocated using pmemobj_zal‐
       loc(3) or pmemobj_tx_zalloc(3).

       The pmemobj_mutex_lock() function locks the pmem-aware mutex mutexp.  If the mutex is already locked, the
       calling thread will block until the mutex becomes available.  If this is the first use of the mutex since
       the opening of the pool pop, the mutex is automatically reinitialized and then locked.

       pmemobj_mutex_timedlock() performs the same action as pmemobj_mutex_lock(),  but  will  not  wait  beyond
       abs_timeout to obtain the lock before returning.

       The  pmemobj_mutex_trylock()  function  locks  pmem-aware  mutex mutexp.  If the mutex is already locked,
       pthread_mutex_trylock() will not block waiting for the mutex, but will return an error.  If this  is  the
       first  use  of  the mutex since the opening of the pool pop, the mutex is automatically reinitialized and
       then locked.

       The pmemobj_mutex_unlock() function unlocks the pmem-aware mutex mutexp.  Undefined behavior follows if a
       thread tries to unlock a mutex that has not been locked by it, or if a thread tries to  release  a  mutex
       that is already unlocked or has not been initialized.

       The  pmemobj_rwlock_zero()  function  is  used  to  explicitly  initialize the pmem-aware read/write lock
       rwlockp by zeroing it.  Initialization is not necessary if the object containing the lock has been  allo‐
       cated using pmemobj_zalloc(3) or pmemobj_tx_zalloc(3).

       The  pmemobj_rwlock_rdlock()  function  acquires  a  read  lock on rwlockp, provided that the lock is not
       presently held for writing and no writer threads are presently blocked on the lock.   If  the  read  lock
       cannot  be acquired immediately, the calling thread blocks until it can acquire the lock.  If this is the
       first use of the lock since the opening of the pool pop, the lock is automatically reinitialized and then
       acquired.

       pmemobj_rwlock_timedrdlock() performs the same action as pmemobj_rwlock_rdlock(), but will not  wait  be‐
       yond  abs_timeout to obtain the lock before returning.  A thread may hold multiple concurrent read locks.
       If so, pmemobj_rwlock_unlock() must be called once for each lock obtained.  The results  of  acquiring  a
       read lock while the calling thread holds a write lock are undefined.

       The  pmemobj_rwlock_wrlock()  function  blocks until a write lock can be acquired against read/write lock
       rwlockp.  If this is the first use of the lock since the opening of the pool pop, the lock  is  automati‐
       cally reinitialized and then acquired.

       pmemobj_rwlock_timedwrlock() performs the same action, but will not wait beyond abs_timeout to obtain the
       lock before returning.

       The pmemobj_rwlock_tryrdlock() function performs the same action as pmemobj_rwlock_rdlock(), but does not
       block  if  the  lock cannot be immediately obtained.  The results are undefined if the calling thread al‐
       ready holds the lock at the time the call is made.

       The pmemobj_rwlock_trywrlock() function performs the same action as pmemobj_rwlock_wrlock(), but does not
       block if the lock cannot be immediately obtained.  The results are undefined if the  calling  thread  al‐
       ready holds the lock at the time the call is made.

       The pmemobj_rwlock_unlock() function is used to release the read/write lock previously obtained by pmemo‐
       bj_rwlock_rdlock(), pmemobj_rwlock_wrlock(), pthread_rwlock_tryrdlock(), or pmemobj_rwlock_trywrlock().

       The  pmemobj_cond_zero() function explicitly initializes the pmem-aware condition variable condp by zero‐
       ing it.  Initialization is not necessary if the object containing the condition variable has  been  allo‐
       cated using pmemobj_zalloc(3) or pmemobj_tx_zalloc(3).

       The difference between pmemobj_cond_broadcast() and pmemobj_cond_signal() is that the former unblocks all
       threads  waiting  for  the  condition variable, whereas the latter blocks only one waiting thread.  If no
       threads are waiting on condp, neither function has any effect.  If more than one thread is blocked  on  a
       condition  variable, the used scheduling policy determines the order in which threads are unblocked.  The
       same mutex used for waiting must be held  while  calling  either  function.   Although  neither  function
       strictly enforces this requirement, undefined behavior may follow if the mutex is not held.

       The  pmemobj_cond_timedwait() and pmemobj_cond_wait() functions block on a condition variable.  They must
       be called with mutex mutexp locked by the calling thread, or undefined behavior results.  These functions
       atomically release mutex mutexp and cause the calling thread to block on the  condition  variable  condp;
       atomically here means “atomically with respect to access by another thread to the mutex and then the con‐
       dition  variable”.   That  is,  if  another  thread is able to acquire the mutex after the about-to-block
       thread has released it, then a subsequent call to pmemobj_cond_broadcast()  or  pmemobj_cond_signal()  in
       that  thread will behave as if it were issued after the about-to-block thread has blocked.  Upon success‐
       ful return, the mutex will be locked and owned by the calling thread.

RETURN VALUE

       The pmemobj_mutex_zero(), pmemobj_rwlock_zero() and pmemobj_cond_zero() functions return no value.

       Other locking functions return 0 on success.  Otherwise, an error number will be returned to indicate the
       error.

SEE ALSO

       pmemobj_tx_zalloc(3),       pmemobj_zalloc(3),        pthread_cond_init(3),        pthread_mutex_init(3),
       pthread_rwlock_init(3), libpmem(7), libpmemobj(7) and <https://pmem.io>