pthread_spin_init

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
       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:

       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().
              (Attempting to share the spin lock between processes results in
              undefined 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
              multiple processes).

       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(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
       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.

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 5.03 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)