pthread_mutex_lock(3T)pthread_mutex_lock(3T)NAMEpthread_mutex_lock(), pthread_mutex_trylock() - lock or attempt to lock
a mutex
SYNOPSISPARAMETERS
mutex Pointer to the mutex to be locked.
DESCRIPTION
The mutex object mutex is locked by calling the function. How the
calling thread acquires the mutex is dependent upon the type attribute
for the mutex. This operation returns with the mutex object referenced
by mutex in the locked state with the calling thread as its owner.
If the mutex type is deadlock detection is not provided. Attempting to
relock the mutex causes deadlock. If a thread attempts to unlock a
mutex that it has not locked or a mutex which is unlocked, undefined
behavior results.
If the mutex type is the mutex maintains the concept of an owner. If a
thread attempts to relock a mutex that it has already locked, an error
shall be returned. If a thread attempts to unlock a mutex that it has
not locked or a mutex that is unlocked, an error shall be returned.
If the mutex type is then the mutex maintains the concept of an owner
and a lock count. When a thread successfully acquires a mutex for the
first time, the count field shall be set to one. Every time a thread
relocks this mutex, the count field shall be incremented by one. Each
time the thread unlocks the mutex, the count field shall be decremented
by one. When the count field reaches zero, the mutex shall become
available for other threads to acquire. If a thread attempts to unlock
a mutex that it has not locked, an error shall be returned.
If the mutex type is deadlock detection is not provided. Attempting to
relock the mutex causes deadlock. A thread can unlock a mutex that it
has not locked. Attempting to unlock an unlocked mutex results in
undefined behavior.
If the mutex type is attempting to recursively lock the mutex results
in undefined behavior. Attempting to unlock the mutex if it was not
locked by the calling thread results in undefined behavior. Attempting
to unlocked the mutex if it is not locked results in undefined behav‐
ior.
The function is identical to the function except that if the mutex
object referenced by mutex cannot be acquired after one attempt, the
call returns immediately with an error.
If a signal is delivered to a thread waiting for a mutex, upon return
from the signal handler, the thread shall resume waiting for the mutex
as if it was not interrupted.
RETURN VALUE
Upon successful completion, and return zero. Otherwise, an error num‐
ber is returned to indicate the error (the variable is not set).
ERRORS
If any of the following occur, the and functions return the correspond‐
ing error number:
[EINVAL] mutex is a mutex and the caller's priority is
higher than mutex's priority ceiling.
If any of the following occur, the function returns the corresponding
error number:
[EBUSY] mutex is currently locked by another thread.
If any of the following occur, the and functions return the correspond‐
ing error number:
[EAGAIN] mutex could not be acquired because the maximum
number of recursive locks for mutex has been
exceeded. This error is not detected on HP-UX.
[EINVAL] mutex is not an initialized mutex.
[EFAULT] mutex parameter points to an illegal address.
If any of the following occur, the function returns the corresponding
error number:
[EDEADLK] The current thread already owns the mutex. This
error will be detected only for mutexes on HP-UX.
WARNINGS
A recursive mutex can be locked more than once by the same thread with‐
out causing that thread to deadlock. Undefined behavior may result if
the owner of a recursive mutex tries to lock the mutex too many times.
AUTHOR
and was derived from the IEEE POSIX P1003.1c standard and X/Open
SEE ALSOpthread_mutex_init(3T), pthread_mutex_destroy(3T),
pthread_mutex_unlock(3T).
STANDARDS CONFORMANCE
Pthread Library pthread_mutex_lock(3T)
