freebsd-dev/share/man/man3/pthread_mutex_timedlock.3
Konstantin Belousov 2a339d9e3d Add implementation of robust mutexes, hopefully close enough to the
intention of the POSIX IEEE Std 1003.1TM-2008/Cor 1-2013.

A robust mutex is guaranteed to be cleared by the system upon either
thread or process owner termination while the mutex is held.  The next
mutex locker is then notified about inconsistent mutex state and can
execute (or abandon) corrective actions.

The patch mostly consists of small changes here and there, adding
neccessary checks for the inconsistent and abandoned conditions into
existing paths.  Additionally, the thread exit handler was extended to
iterate over the userspace-maintained list of owned robust mutexes,
unlocking and marking as terminated each of them.

The list of owned robust mutexes cannot be maintained atomically
synchronous with the mutex lock state (it is possible in kernel, but
is too expensive).  Instead, for the duration of lock or unlock
operation, the current mutex is remembered in a special slot that is
also checked by the kernel at thread termination.

Kernel must be aware about the per-thread location of the heads of
robust mutex lists and the current active mutex slot.  When a thread
touches a robust mutex for the first time, a new umtx op syscall is
issued which informs about location of lists heads.

The umtx sleep queues for PP and PI mutexes are split between
non-robust and robust.

Somewhat unrelated changes in the patch:
1. Style.
2. The fix for proper tdfind() call use in umtxq_sleep_pi() for shared
   pi mutexes.
3. Removal of the userspace struct pthread_mutex m_owner field.
4. The sysctl kern.ipc.umtx_vnode_persistent is added, which controls
   the lifetime of the shared mutex associated with a vnode' page.

Reviewed by:	jilles (previous version, supposedly the objection was fixed)
Discussed with:	brooks, Martin Simmons <martin@lispworks.com> (some aspects)
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
2016-05-17 09:56:22 +00:00

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Groff

.\" Copyright (c) 2003 Michael Telahun Makonnen
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.\" $FreeBSD$
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.Dd April 29, 2016
.Dt PTHREAD_MUTEX_TIMEDLOCK 3
.Os
.Sh NAME
.Nm pthread_mutex_timedlock
.Nd lock a mutex without blocking indefinitely
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In pthread.h
.In time.h
.Ft int
.Fn pthread_mutex_timedlock "pthread_mutex_t *mutex" "const struct timespec *abs_timeout"
.Sh DESCRIPTION
The
.Fn pthread_mutex_timedlock
function will lock
.Fa mutex .
If it is already locked the calling thread will block until
the mutex becomes available or
the timeout,
specified by abs_timeout,
expires.
The time of the timeout is an absolute time and
is not relative to the current time.
.Sh RETURN VALUES
If successful,
.Fn pthread_mutex_timedlock
will return zero, otherwise an error number will be returned to
indicate the error.
.Sh ERRORS
The
.Fn pthread_mutex_timedlock
function will fail if:
.Bl -tag -width Er
.It Bq "Er ENOTRECOVERABLE"
The
.Fa mutex
was created with the protocol attribute having the
value PTHREAD_PRIO_PROTECT and
the calling thread's priority is higher than the
mutex's current priority ceiling.
.It Bq Er EINVAL
The process or thread would have blocked, and
.Fa abs_timeout
specified a nanosecond value less than zero or
greater than or equal to 1 billion.
.It Bq Er EINVAL
The
.Fa mutex
parameter is invalid.
.It Bq Er ETIMEDOUT
The
.Fa mutex
could not be locked before the timeout expired.
.It Bq Er EAGAIN
The
.Fa mutex
could not be acquired because the
maximum number of recursive locks for the
.Fa mutex
has been exceeded.
.It Bq Er EDEADLK
The current thread already owns the
.Fa mutex .
.It Bq Er EOWNERDEAD
The argument
.Fa mutex
points to a robust mutex and the previous owning thread terminated
while holding the mutex lock.
The lock was granted to the caller and it is up to the new owner
to make the state consistent.
.It Bq Er ENOTRECOVERABLE
The state protected by the
.Fa mutex
is not recoverable.
.El
.Sh SEE ALSO
.Xr pthread_mutex_consistent 3 ,
.Xr pthread_mutex_destroy 3 ,
.Xr pthread_mutex_init 3 ,
.Xr pthread_mutex_lock 3 ,
.Xr pthread_mutex_trylock 3 ,
.Xr pthread_mutex_unlock 3
.Sh STANDARDS
The
.Fn pthread_mutex_timedlock
function is expected to conform to
.St -p1003.1-96 .