HardenedBSD/share/man/man3/pthread_mutexattr.3

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.Dd October 27, 2023
.Dt PTHREAD_MUTEXATTR 3
.Os
.Sh NAME
.Nm pthread_mutexattr_init ,
.Nm pthread_mutexattr_destroy ,
.Nm pthread_mutexattr_setprioceiling ,
.Nm pthread_mutexattr_getprioceiling ,
.Nm pthread_mutexattr_setprotocol ,
.Nm pthread_mutexattr_getprotocol ,
.Nm pthread_mutexattr_setpshared ,
.Nm pthread_mutexattr_getpshared ,
.Nm pthread_mutexattr_setrobust ,
.Nm pthread_mutexattr_getrobust ,
.Nm pthread_mutexattr_settype ,
.Nm pthread_mutexattr_gettype
.Nd mutex attribute operations
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In pthread.h
.Ft int
.Fn pthread_mutexattr_init "pthread_mutexattr_t *attr"
.Ft int
.Fn pthread_mutexattr_destroy "pthread_mutexattr_t *attr"
.Ft int
.Fo pthread_mutexattr_setprioceiling
.Fa "pthread_mutexattr_t *attr" "int prioceiling"
.Fc
.Ft int
.Fo pthread_mutexattr_getprioceiling
.Fa "const pthread_mutexattr_t *attr" "int *prioceiling"
.Fc
.Ft int
.Fn pthread_mutexattr_setprotocol "pthread_mutexattr_t *attr" "int protocol"
.Ft int
.Fo pthread_mutexattr_getprotocol
.Fa "const pthread_mutexattr_t *restrict attr" "int *restrict protocol"
.Fc
.Ft int
.Fo pthread_mutexattr_setpshared
.Fa "pthread_mutexattr_t *attr" "int shared"
.Fc
.Ft int
.Fo pthread_mutexattr_getpshared
.Fa "const pthread_mutexattr_t *attr" "int *shared"
.Fc
.Ft int
.Fn pthread_mutexattr_setrobust "pthread_mutexattr_t *attr" "int robust"
.Ft int
.Fn pthread_mutexattr_getrobust "pthread_mutexattr_t *attr" "int *robust"
.Ft int
.Fn pthread_mutexattr_settype "pthread_mutexattr_t *attr" "int type"
.Ft int
.Fo pthread_mutexattr_gettype
.Fa "const pthread_mutexattr_t *restrict attr" "int *restrict type"
.Fc
.Sh DESCRIPTION
Mutex attributes are used to specify parameters to
.Fn pthread_mutex_init .
One attribute object can be used in multiple calls to
.Fn pthread_mutex_init ,
with or without modifications between calls.
.Pp
The
.Fn pthread_mutexattr_init
function initializes
.Fa attr
with all the default mutex attributes.
.Pp
The
.Fn pthread_mutexattr_destroy
function destroys
.Fa attr .
.Pp
The
.Fn pthread_mutexattr_setprioceiling
function sets the priority ceiling for the mutex, used
by threads executed under the
.Dv PTHREAD_PRIO_PROTECT
protocol.
.Pp
The
.Fn pthread_mutexattr_setprotocol
function specifies the protocol to be followed in utilizing mutexes.
The
.Fa protocol
argument can take one of the following values:
.Bl -tag -width PTHREAD_PRIO_PROTECT
.It PTHREAD_PRIO_NONE
Priority and scheduling of the thread owning this mutex is not
affected by its mutex ownership.
.It PTHREAD_PRIO_INHERIT
Request priority-inheritance protocol, where the thread owning the mutex
is executed at the highest priority among priorities of all threads waiting
on any mutex owned by this thread.
.It PTHREAD_PRIO_PROTECT
Request priority-inheritance protocol, where the thread owning the mutex
is executed at highest priority among priorities or priority ceilings of
all threads waiting on any mutex owned by this thread.
.El
.Pp
The
.Fn pthread_mutexattr_setpshared
function sets the process-shared attribute of
.Fa attr
to the value specified in
.Fa pshared .
The argument
.Fa pshared
may have one of the following values:
.Bl -tag -width ".Dv PTHREAD_PROCESS_PRIVATE"
.It Dv PTHREAD_PROCESS_PRIVATE
The mutex may only be used by threads in the same process as the one
that created the object.
.It Dv PTHREAD_PROCESS_SHARED
The mutex may be used by
threads in processes other than the one that created the object,
assuming other processes share access to the memory where the mutex
was allocated.
.El
See
.Xr libthr 3
for details of the implementation of the shared mutexes,
and their limitations.
.Pp
The
.Fn pthread_mutexattr_setrobust
function specifies robustness attribute of the mutex.
Possible values for the
.Fa robust
argument are
.Bl -tag -width PTHREAD_MUTEX_STALLED
.It PTHREAD_MUTEX_STALLED
No special actions are taken if the thread owning the mutex is terminated
without unlocking the mutex lock.
This can lead to deadlocks if no other thread can unlock the mutex.
This is the default value.
.It PTHREAD_MUTEX_ROBUST
If the process containing the owning thread of a robust mutex, or owning
thread, terminates while holding the mutex lock, the next thread that
acquires the mutex is notified about the termination
by the return value
.Ev EOWNERDEAD
from the locking function.
Then, either
.Xr pthread_mutex_consistent 3
can be used to repair the mutex lock state, or
.Xr pthread_mutex_unlock 3
can unlock the mutex lock but also put it an unusable state,
where all further attempts to acquire it result in the
.Ev ENOTRECOVERABLE
error.
.El
.Pp
The
.Fn pthread_mutexattr_settype
function sets the type of the mutex.
The type affects the behavior of calls which lock and unlock the mutex.
The possible values for the
.Fa type
argument are
.Bl -tag -width PTHREAD_MUTEX_ERRORCHECK
.It PTHREAD_MUTEX_NORMAL
Both recursive locking, and unlocking when the lock is not owned by the current
thread, cause an error to be returned from the corresponding functions.
This matches
.Dv PTHREAD_MUTEX_ERRORCHECK
but somewhat contradicts the behavior mandated by POSIX.
.It PTHREAD_MUTEX_ERRORCHECK
Both recursive locking, and unlocking when the lock is not owned by the current
thread, cause an error returned from the corresponding functions.
.It PTHREAD_MUTEX_RECURSIVE
Recursive locking is allowed.
Attempt to unlock when current thread is not an owner of the lock causes
an error to be returned.
.It PTHREAD_MUTEX_DEFAULT
The
.Fx
implementation maps this type to
.Dv PTHREAD_MUTEX_ERRORCHECK
type.
.El
.Pp
The
.Fn pthread_mutexattr_get*
functions copy the value of the attribute that corresponds to each function name
to the location pointed to by the second function parameter.
.Sh RETURN VALUES
If successful, these functions return 0.
Otherwise, an error number is returned to indicate the error.
.Sh ERRORS
The
.Fn pthread_mutexattr_init
function will fail if:
.Bl -tag -width Er
.It Bq Er ENOMEM
Out of memory.
.El
.Pp
The
.Fn pthread_mutexattr_destroy
function will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
Invalid value for
.Fa attr .
.El
.Pp
The
.Fn pthread_mutexattr_setprioceiling
function will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
Invalid value for
.Fa attr ,
or invalid value for
.Fa prioceiling .
.El
.Pp
The
.Fn pthread_mutexattr_getprioceiling
function will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
Invalid value for
.Fa attr .
.El
.Pp
The
.Fn pthread_mutexattr_setprotocol
function will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
Invalid value for
.Fa attr ,
or invalid value for
.Fa protocol .
.El
.Pp
The
.Fn pthread_mutexattr_getprotocol
function will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
Invalid value for
.Fa attr .
.El
.Pp
The
.Fn pthread_mutexattr_setpshared
function will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
Invalid value for
.Fa attr ,
or invalid value for
.Fa shared .
.El
.Pp
The
.Fn pthread_mutexattr_getpshared
function will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
Invalid value for
.Fa attr .
.El
.Pp
The
.Fn pthread_mutexattr_settype
function will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
Invalid value for
.Fa attr ,
or invalid value for
.Fa type .
.El
.Pp
The
.Fn pthread_mutexattr_gettype
function will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
Invalid value for
.Fa attr .
.El
.Pp
The
.Fn pthread_mutexattr_setrobust
function will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
Invalid value for
.Fa attr ,
or invalid value for
.Fa robust .
.El
.Pp
The
.Fn pthread_mutexattr_getrobust
function will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
Invalid value for
.Fa attr .
.El
.Sh SEE ALSO
.Xr libthr 3 ,
.Xr pthread_mutex_init 3
.Sh STANDARDS
The
.Fn pthread_mutexattr_init
and
.Fn pthread_mutexattr_destroy
functions conform to
.St -p1003.1-96
.Pp
The
.Fn pthread_mutexattr_setprioceiling ,
.Fn pthread_mutexattr_getprioceiling ,
.Fn pthread_mutexattr_setprotocol ,
.Fn pthread_mutexattr_getprotocol ,
.Fn pthread_mutexattr_setpshared ,
.Fn pthread_mutexattr_getpshared ,
.Fn pthread_mutexattr_settype ,
and
.Fn pthread_mutexattr_gettype
functions conform to
.St -susv2 .
The
.Fn pthread_mutexattr_setrobust
and
.Fn pthread_mutexattr_getrobust
functions conform to
.St -susv4 .