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NAME |LIBRARY |SYNOPSIS |DESCRIPTION |RETURN VALUE |ERRORS |STANDARDS |HISTORY |NOTES |SEE ALSO |COLOPHON | |
pthread_spin_init(3) Library Functions Manualpthread_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, intpshared);int pthread_spin_destroy(pthread_spinlock_t *lock); Feature Test Macro Requirements for glibc (seefeature_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. Thepthread_spin_init() function allocates any resources required for the use of the spin lock referred to bylock and initializes the lock to be in the unlocked state. Thepshared 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 callspthread_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). Callingpthread_spin_init() on a spin lock that has already been initialized results in undefined behavior. Thepthread_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 withpthread_spin_init() results in undefined behavior. The result of performing operations such aspthread_spin_lock(3),pthread_spin_unlock(3), andpthread_spin_destroy() oncopies of the object referred to bylock is undefined.
On success, there functions return zero. On failure, they return an error number. In the event thatpthread_spin_init() fails, the lock is not initialized.
pthread_spin_init() may fail with the following errors:EAGAINThe system has insufficient resources to initialize a new spin lock.ENOMEMInsufficient 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 possiblySCHED_RR). Use of spin locks with nondeterministic scheduling policies such asSCHED_OTHERprobably 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 arenot 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 theman-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 isnot part of the original manual page), send a mail to man-pages@man7.orgLinux man-pages 6.15 2025-05-17pthread_spin_init(3)Pages that refer to this page:pthread_spin_lock(3), pthreads(7)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |