pthread_spin_init(3) Library Functions Manual pthread_spin_init(3)
NAME
pthread_spin_init, pthread_spin_destroy - initialize or destroy a spin
lock
LIBRARY
POSIX threads library (libpthread, -lpthread)
SYNOPSIS
#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
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(). (Attempt-
ing 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 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. De-
stroying 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() on copies of the ob-
ject referred to by lock is undefined.
RETURN VALUE
On success, there functions return zero. On failure, they return an er-
ror 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.
STANDARDS
POSIX.1-2008.
HISTORY
glibc 2.2. 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 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)
Linux man-pages 6.9.1 2024-05-02 pthread_spin_init(3)
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