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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | NOTES | SEE ALSO | COLOPHON |
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pthread_spin_init(3) Library Functions Manual pthread_spin_init(3)
pthread_spin_init, pthread_spin_destroy - initialize or destroy a
spin lock
POSIX threads library (libpthread, -lpthread)
#include <pthread.h>
int pthread_spin_init(pthread_spinlock_t *lock, int pshared);
int pthread_spin_destroy(pthread_spinlock_t *lock);
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:
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() 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 lock.
ENOMEM Insufficient memory to initialize the spin lock.
POSIX.1-2008.
glibc 2.2. POSIX.1-2001.
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 the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 pthread_spin_init(3)
Pages that refer to this page: pthread_spin_lock(3), pthreads(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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