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

       pthread_spin_init, pthread_spin_destroy - initialize or destroy a spin

       #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

       General note: Most programs should use mutexes instead of spin locks.
       Spin locks are primarily useful in conjunction with real-time scheduling
       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:

              The spin lock is to be operated on only by threads in the same
              process as the thread that calls pthread_spin_init().  (Attempting
              to share the spin lock between processes results in undefined

              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 multiple

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

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

       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.

       pthread_spin_init() may fail with the following errors:

       EAGAIN The system has insufficient resources to initialize a new spin

       ENOMEM Insufficient memory to initialize the spin lock.

       These functions first appeared in glibc in version 2.2.


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

       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
       indicates a design mistake.  The problem is that if a thread operating
       under 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.

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

       This page is part of release 5.10 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

Linux                              2020-06-09               PTHREAD_SPIN_INIT(3)