pthread_spin_init, pthread_spin_destroy - initialize or destroy a spin lock
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
_POSIX_C_SOURCE >= 200112L
: Most programs should use mutexes instead of spin locks.
Spin locks are primarily useful in conjunction with real-time scheduling
policies. See NOTES.
() 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
- 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.)
- 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).
() on a spin lock that has already been
initialized results in undefined behavior.
() 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
The result of performing operations such as pthread_spin_lock
(3), and pthread_spin_destroy
of the object referred to by lock
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
() may fail with the following errors:
- The system has insufficient resources to initialize a new spin lock.
- 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
, or possibly SCHED_RR
). Use of spin locks with
nondeterministic scheduling policies such as SCHED_OTHER
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