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PTHREAD_SPIN_INIT(3)       Linux Programmer's Manual      PTHREAD_SPIN_INIT(3)

NAME
       pthread_spin_init,  pthread_spin_destroy - initialize or destroy a spin
       lock

SYNOPSIS
       #include <pthread.h>

       int pthread_spin_init(pthread_spinlock_t *lock, int pshared);
       int pthread_spin_destroy(pthread_spinlock_t *lock);

       Compile and link with -pthread.

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       pthread_spin_init(), pthread_spin_destroy():
           _POSIX_C_SOURCE >= 200112L

DESCRIPTION
       General note: Most programs should use mutexes instead of  spin  locks.
       Spin  locks are primarily useful in conjunction with real-time schedul-
       ing policies.  See NOTES.

       The pthread_spin_init() function allocates any resources  required  for
       the  use  of the spin lock referred to by lock and initializes the lock
       to be in the unlocked state.  The pshared argument must have one of the
       following values:

       PTHREAD_PROCESS_PRIVATE
              The  spin  lock is to be operated on only by threads in the same
              process as the thread that calls pthread_spin_init().  (Attempt-
              ing  to  share  the spin lock between processes results in unde-
              fined behavior.)

       PTHREAD_PROCESS_SHARED
              The spin lock may be operated on by any thread  in  any  process
              that  has  access  to  the memory containing the lock (i.e., the
              lock may be in a shared memory object that is shared among  mul-
              tiple processes).

       Calling  pthread_spin_init()  on a spin lock that has already been ini-
       tialized results in undefined behavior.

       The pthread_spin_destroy() function destroys a  previously  initialized
       spin  lock,  freeing  any  resources that were allocated for that lock.
       Destroying a spin lock that has not been previously been initialized or
       destroying  a  spin lock while another thread holds the lock results in
       undefined behavior.

       Once a spin lock has been destroyed, performing any  operation  on  the
       lock  other than once more initializing it with pthread_spin_init() re-
       sults in undefined behavior.

       The result  of  performing  operations  such  as  pthread_spin_lock(3),
       pthread_spin_unlock(3),  and  pthread_spin_destroy(3)  on copies of the
       object referred to by lock is undefined.

RETURN VALUE
       On success, there functions return zero.  On failure,  they  return  an
       error number.  In the event that pthread_spin_init() fails, the lock is
       not initialized.

ERRORS
       pthread_spin_init() may fail with the following errors:

       EAGAIN The system has insufficient resources to initialize a  new  spin
              lock.

       ENOMEM Insufficient memory to initialize the spin lock.

VERSIONS
       These functions first appeared in glibc in version 2.2.

CONFORMING TO
       POSIX.1-2001.

       Support for process-shared spin locks is a POSIX option.  The option is
       supported in the glibc implementation.

NOTES
       Spin locks should be employed in conjunction with real-time  scheduling
       policies  (SCHED_FIFO,  or  possibly SCHED_RR).  Use of spin locks with
       nondeterministic scheduling policies such as SCHED_OTHER probably indi-
       cates  a design mistake.  The problem is that if a thread operating un-
       der such a policy is scheduled off the CPU while it holds a spin  lock,
       then  other threads will waste time spinning on the lock until the lock
       holder is once more rescheduled and releases the lock.

       If threads create a deadlock  situation  while  employing  spin  locks,
       those threads will spin forever consuming CPU time.

       User-space spin locks are not applicable as a general locking solution.
       They are, by definition, prone to priority inversion and unbounded spin
       times.  A programmer using spin locks must be exceptionally careful not
       only in the code, but also in terms  of  system  configuration,  thread
       placement, and priority assignment.

SEE ALSO
       pthread_mutex_init(3), pthread_mutex_lock(3), pthread_spin_lock(3),
       pthread_spin_unlock(3), pthreads(7)

COLOPHON
       This page is part of release 5.05 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

Linux                             2017-09-30              PTHREAD_SPIN_INIT(3)
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON