Merge in the pthread library. This is the linuxthreads library taken from

glibc 2.1.3 and ported to work with uClibc by Stefan Soucek and Erik Andersen
(me).  Stefan has hacked things up such that linuxthreads runs on MMU-less
systems (tested only on arm-nommu).  Erik cleaned things up and made it work
properly as a shared library.
 -Erik

1 files changed, 1428 insertions, 0 deletions

diff --git a/libpthread/linuxthreads/linuxthreads.texi b/libpthread/linuxthreads/linuxthreads.texi
new file mode 100644
index 000000000..7a98103b3
--- /dev/null
+++ b/libpthread/linuxthreads/linuxthreads.texi
@@ -0,0 +1,1428 @@
+@node POSIX Threads
+@c @node POSIX Threads, , Top, Top
+@chapter POSIX Threads
+@c %MENU% The standard threads library
+
+@c This chapter needs more work bigtime. -zw
+
+This chapter describes the pthreads (POSIX threads) library.  This
+library provides support functions for multithreaded programs: thread
+primitives, synchronization objects, and so forth.  It also implements
+POSIX 1003.1b semaphores (not to be confused with System V semaphores).
+
+The threads operations (@samp{pthread_*}) do not use @var{errno}.
+Instead they return an error code directly.  The semaphore operations do
+use @var{errno}.
+
+@menu
+* Basic Thread Operations::     Creating, terminating, and waiting for threads.
+* Thread Attributes::           Tuning thread scheduling.
+* Cancellation::                Stopping a thread before it's done.
+* Cleanup Handlers::            Deallocating resources when a thread is
+                                  cancelled.
+* Mutexes::                     One way to synchronize threads.
+* Condition Variables::         Another way.
+* POSIX Semaphores::            And a third way.
+* Thread-Specific Data::        Variables with different values in
+                                  different threads.
+* Threads and Signal Handling:: Why you should avoid mixing the two, and
+                                  how to do it if you must.
+* Miscellaneous Thread Functions:: A grab bag of utility routines.
+@end menu
+
+@node Basic Thread Operations
+@section Basic Thread Operations
+
+These functions are the thread equivalents of @code{fork}, @code{exit},
+and @code{wait}.
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_create (pthread_t * @var{thread}, pthread_attr_t * @var{attr}, void * (*@var{start_routine})(void *), void * @var{arg})
+@code{pthread_create} creates a new thread of control that executes
+concurrently with the calling thread. The new thread calls the
+function @var{start_routine}, passing it @var{arg} as first argument. The
+new thread terminates either explicitly, by calling @code{pthread_exit},
+or implicitly, by returning from the @var{start_routine} function. The
+latter case is equivalent to calling @code{pthread_exit} with the result
+returned by @var{start_routine} as exit code.
+
+The @var{attr} argument specifies thread attributes to be applied to the
+new thread. @xref{Thread Attributes}, for details. The @var{attr}
+argument can also be @code{NULL}, in which case default attributes are
+used: the created thread is joinable (not detached) and has an ordinary
+(not realtime) scheduling policy.
+
+On success, the identifier of the newly created thread is stored in the
+location pointed by the @var{thread} argument, and a 0 is returned. On
+error, a non-zero error code is returned.
+
+This function may return the following errors:
+@table @code
+@item EAGAIN
+Not enough system resources to create a process for the new thread,
+or more than @code{PTHREAD_THREADS_MAX} threads are already active.
+@end table
+@end deftypefun
+
+@comment pthread.h
+@comment POSIX
+@deftypefun void pthread_exit (void *@var{retval})
+@code{pthread_exit} terminates the execution of the calling thread.  All
+cleanup handlers (@pxref{Cleanup Handlers}) that have been set for the
+calling thread with @code{pthread_cleanup_push} are executed in reverse
+order (the most recently pushed handler is executed first). Finalization
+functions for thread-specific data are then called for all keys that
+have non-@code{NULL} values associated with them in the calling thread
+(@pxref{Thread-Specific Data}).  Finally, execution of the calling
+thread is stopped.
+
+The @var{retval} argument is the return value of the thread. It can be
+retrieved from another thread using @code{pthread_join}.
+
+The @code{pthread_exit} function never returns.
+@end deftypefun
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_cancel (pthread_t @var{thread})
+
+@code{pthread_cancel} sends a cancellation request to the thread denoted
+by the @var{thread} argument.  If there is no such thread,
+@code{pthread_cancel} fails and returns @code{ESRCH}.  Otherwise it
+returns 0. @xref{Cancellation}, for details.
+@end deftypefun
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_join (pthread_t @var{th}, void **thread_@var{return})
+@code{pthread_join} suspends the execution of the calling thread until
+the thread identified by @var{th} terminates, either by calling
+@code{pthread_exit} or by being cancelled.
+
+If @var{thread_return} is not @code{NULL}, the return value of @var{th}
+is stored in the location pointed to by @var{thread_return}.  The return
+value of @var{th} is either the argument it gave to @code{pthread_exit},
+or @code{PTHREAD_CANCELED} if @var{th} was cancelled.
+
+The joined thread @code{th} must be in the joinable state: it must not
+have been detached using @code{pthread_detach} or the
+@code{PTHREAD_CREATE_DETACHED} attribute to @code{pthread_create}.
+
+When a joinable thread terminates, its memory resources (thread
+descriptor and stack) are not deallocated until another thread performs
+@code{pthread_join} on it. Therefore, @code{pthread_join} must be called
+once for each joinable thread created to avoid memory leaks.
+
+At most one thread can wait for the termination of a given
+thread. Calling @code{pthread_join} on a thread @var{th} on which
+another thread is already waiting for termination returns an error.
+
+@code{pthread_join} is a cancellation point. If a thread is canceled
+while suspended in @code{pthread_join}, the thread execution resumes
+immediately and the cancellation is executed without waiting for the
+@var{th} thread to terminate. If cancellation occurs during
+@code{pthread_join}, the @var{th} thread remains not joined.
+
+On success, the return value of @var{th} is stored in the location
+pointed to by @var{thread_return}, and 0 is returned. On error, one of
+the following values is returned:
+@table @code
+@item ESRCH
+No thread could be found corresponding to that specified by @var{th}.
+@item EINVAL
+The @var{th} thread has been detached, or another thread is already
+waiting on termination of @var{th}.
+@item EDEADLK
+The @var{th} argument refers to the calling thread.
+@end table
+@end deftypefun
+
+@node Thread Attributes
+@section Thread Attributes
+
+@comment pthread.h
+@comment POSIX
+
+Threads have a number of attributes that may be set at creation time.
+This is done by filling a thread attribute object @var{attr} of type
+@code{pthread_attr_t}, then passing it as second argument to
+@code{pthread_create}. Passing @code{NULL} is equivalent to passing a
+thread attribute object with all attributes set to their default values.
+
+Attribute objects are consulted only when creating a new thread.  The
+same attribute object can be used for creating several threads.
+Modifying an attribute object after a call to @code{pthread_create} does
+not change the attributes of the thread previously created.
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_attr_init (pthread_attr_t *@var{attr})
+@code{pthread_attr_init} initializes the thread attribute object
+@var{attr} and fills it with default values for the attributes. (The
+default values are listed below for each attribute.)
+
+Each attribute @var{attrname} (see below for a list of all attributes)
+can be individually set using the function
+@code{pthread_attr_set@var{attrname}} and retrieved using the function
+@code{pthread_attr_get@var{attrname}}.
+@end deftypefun
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_attr_destroy (pthread_attr_t *@var{attr})
+@code{pthread_attr_destroy} destroys the attribute object pointed to by
+@var{attr} releasing any resources associated with it.  @var{attr} is
+left in an undefined state, and you must not use it again in a call to
+any pthreads function until it has been reinitialized.
+@end deftypefun
+
+@findex pthread_attr_setinheritsched
+@findex pthread_attr_setschedparam
+@findex pthread_attr_setschedpolicy
+@findex pthread_attr_setscope
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_attr_set@var{attr} (pthread_attr_t *@var{obj}, int @var{value})
+Set attribute @var{attr} to @var{value} in the attribute object pointed
+to by @var{obj}.  See below for a list of possible attributes and the
+values they can take.
+
+On success, these functions return 0.  If @var{value} is not meaningful
+for the @var{attr} being modified, they will return the error code
+@code{EINVAL}.  Some of the functions have other failure modes; see
+below.
+@end deftypefun
+
+@findex pthread_attr_getinheritsched
+@findex pthread_attr_getschedparam
+@findex pthread_attr_getschedpolicy
+@findex pthread_attr_getscope
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_attr_get@var{attr} (const pthread_attr_t *@var{obj}, int *@var{value})
+Store the current setting of @var{attr} in @var{obj} into the variable
+pointed to by @var{value}.
+
+These functions always return 0.
+@end deftypefun
+
+The following thread attributes are supported:
+@table @samp
+@item detachstate
+Choose whether the thread is created in the joinable state (value
+@code{PTHREAD_CREATE_JOINABLE}) or in the detached state
+(@code{PTHREAD_CREATE_DETACHED}).  The default is
+@code{PTHREAD_CREATE_JOINABLE}.
+
+In the joinable state, another thread can synchronize on the thread
+termination and recover its termination code using @code{pthread_join},
+but some of the thread resources are kept allocated after the thread
+terminates, and reclaimed only when another thread performs
+@code{pthread_join} on that thread.
+
+In the detached state, the thread resources are immediately freed when
+it terminates, but @code{pthread_join} cannot be used to synchronize on
+the thread termination.
+
+A thread created in the joinable state can later be put in the detached
+thread using @code{pthread_detach}.
+
+@item schedpolicy
+Select the scheduling policy for the thread: one of @code{SCHED_OTHER}
+(regular, non-realtime scheduling), @code{SCHED_RR} (realtime,
+round-robin) or @code{SCHED_FIFO} (realtime, first-in first-out).
+The default is @code{SCHED_OTHER}.
+@c Not doc'd in our manual: FIXME.
+@c See @code{sched_setpolicy} for more information on scheduling policies.
+
+The realtime scheduling policies @code{SCHED_RR} and @code{SCHED_FIFO}
+are available only to processes with superuser privileges.
+@code{pthread_attr_setschedparam} will fail and return @code{ENOTSUP} if
+you try to set a realtime policy when you are unprivileged.
+
+The scheduling policy of a thread can be changed after creation with
+@code{pthread_setschedparam}.
+
+@item schedparam
+Change the scheduling parameter (the scheduling priority)
+for the thread.  The default is 0.
+
+This attribute is not significant if the scheduling policy is
+@code{SCHED_OTHER}; it only matters for the realtime policies
+@code{SCHED_RR} and @code{SCHED_FIFO}.
+
+The scheduling priority of a thread can be changed after creation with
+@code{pthread_setschedparam}.
+
+@item inheritsched
+Choose whether the scheduling policy and scheduling parameter for the
+newly created thread are determined by the values of the
+@var{schedpolicy} and @var{schedparam} attributes (value
+@code{PTHREAD_EXPLICIT_SCHED}) or are inherited from the parent thread
+(value @code{PTHREAD_INHERIT_SCHED}).  The default is
+@code{PTHREAD_EXPLICIT_SCHED}.
+
+@item scope
+Choose the scheduling contention scope for the created thread.  The
+default is @code{PTHREAD_SCOPE_SYSTEM}, meaning that the threads contend
+for CPU time with all processes running on the machine. In particular,
+thread priorities are interpreted relative to the priorities of all
+other processes on the machine. The other possibility,
+@code{PTHREAD_SCOPE_PROCESS}, means that scheduling contention occurs
+only between the threads of the running process: thread priorities are
+interpreted relative to the priorities of the other threads of the
+process, regardless of the priorities of other processes.
+
+@code{PTHREAD_SCOPE_PROCESS} is not supported in LinuxThreads.  If you
+try to set the scope to this value @code{pthread_attr_setscope} will
+fail and return @code{ENOTSUP}.
+@end table
+
+@node Cancellation
+@section Cancellation
+
+Cancellation is the mechanism by which a thread can terminate the
+execution of another thread. More precisely, a thread can send a
+cancellation request to another thread. Depending on its settings, the
+target thread can then either ignore the request, honor it immediately,
+or defer it till it reaches a cancellation point.  When threads are
+first created by @code{pthread_create}, they always defer cancellation
+requests.
+
+When a thread eventually honors a cancellation request, it behaves as if
+@code{pthread_exit(PTHREAD_CANCELED)} was called.  All cleanup handlers
+are executed in reverse order, finalization functions for
+thread-specific data are called, and finally the thread stops executing.
+If the cancelled thread was joinable, the return value
+@code{PTHREAD_CANCELED} is provided to whichever thread calls
+@var{pthread_join} on it. See @code{pthread_exit} for more information.
+
+Cancellation points are the points where the thread checks for pending
+cancellation requests and performs them.  The POSIX threads functions
+@code{pthread_join}, @code{pthread_cond_wait},
+@code{pthread_cond_timedwait}, @code{pthread_testcancel},
+@code{sem_wait}, and @code{sigwait} are cancellation points.  In
+addition, these system calls are cancellation points:
+
+@multitable @columnfractions .33 .33 .33
+@item @t{accept}	@tab @t{open}		@tab @t{sendmsg}
+@item @t{close}		@tab @t{pause}		@tab @t{sendto}
+@item @t{connect}	@tab @t{read}		@tab @t{system}
+@item @t{fcntl}		@tab @t{recv}		@tab @t{tcdrain}
+@item @t{fsync}		@tab @t{recvfrom}	@tab @t{wait}
+@item @t{lseek}		@tab @t{recvmsg}	@tab @t{waitpid}
+@item @t{msync}		@tab @t{send}		@tab @t{write}
+@item @t{nanosleep}
+@end multitable
+
+@noindent
+All library functions that call these functions (such as
+@code{printf}) are also cancellation points.
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_setcancelstate (int @var{state}, int *@var{oldstate})
+@code{pthread_setcancelstate} changes the cancellation state for the
+calling thread -- that is, whether cancellation requests are ignored or
+not. The @var{state} argument is the new cancellation state: either
+@code{PTHREAD_CANCEL_ENABLE} to enable cancellation, or
+@code{PTHREAD_CANCEL_DISABLE} to disable cancellation (cancellation
+requests are ignored).
+
+If @var{oldstate} is not @code{NULL}, the previous cancellation state is
+stored in the location pointed to by @var{oldstate}, and can thus be
+restored later by another call to @code{pthread_setcancelstate}.
+
+If the @var{state} argument is not @code{PTHREAD_CANCEL_ENABLE} or
+@code{PTHREAD_CANCEL_DISABLE}, @code{pthread_setcancelstate} fails and
+returns @code{EINVAL}.  Otherwise it returns 0.
+@end deftypefun
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_setcanceltype (int @var{type}, int *@var{oldtype})
+@code{pthread_setcanceltype} changes the type of responses to
+cancellation requests for the calling thread: asynchronous (immediate)
+or deferred.  The @var{type} argument is the new cancellation type:
+either @code{PTHREAD_CANCEL_ASYNCHRONOUS} to cancel the calling thread
+as soon as the cancellation request is received, or
+@code{PTHREAD_CANCEL_DEFERRED} to keep the cancellation request pending
+until the next cancellation point. If @var{oldtype} is not @code{NULL},
+the previous cancellation state is stored in the location pointed to by
+@var{oldtype}, and can thus be restored later by another call to
+@code{pthread_setcanceltype}.
+
+If the @var{type} argument is not @code{PTHREAD_CANCEL_DEFERRED} or
+@code{PTHREAD_CANCEL_ASYNCHRONOUS}, @code{pthread_setcanceltype} fails
+and returns @code{EINVAL}.  Otherwise it returns 0.
+@end deftypefun
+
+@comment pthread.h
+@comment POSIX
+@deftypefun void pthread_testcancel (@var{void})
+@code{pthread_testcancel} does nothing except testing for pending
+cancellation and executing it. Its purpose is to introduce explicit
+checks for cancellation in long sequences of code that do not call
+cancellation point functions otherwise.
+@end deftypefun
+
+@node Cleanup Handlers
+@section Cleanup Handlers
+
+Cleanup handlers are functions that get called when a thread terminates,
+either by calling @code{pthread_exit} or because of
+cancellation. Cleanup handlers are installed and removed following a
+stack-like discipline.
+
+The purpose of cleanup handlers is to free the resources that a thread
+may hold at the time it terminates. In particular, if a thread exits or
+is cancelled while it owns a locked mutex, the mutex will remain locked
+forever and prevent other threads from executing normally. The best way
+to avoid this is, just before locking the mutex, to install a cleanup
+handler whose effect is to unlock the mutex. Cleanup handlers can be
+used similarly to free blocks allocated with @code{malloc} or close file
+descriptors on thread termination.
+
+Here is how to lock a mutex @var{mut} in such a way that it will be
+unlocked if the thread is canceled while @var{mut} is locked:
+
+@smallexample
+pthread_cleanup_push(pthread_mutex_unlock, (void *) &mut);
+pthread_mutex_lock(&mut);
+/* do some work */
+pthread_mutex_unlock(&mut);
+pthread_cleanup_pop(0);
+@end smallexample
+
+Equivalently, the last two lines can be replaced by
+
+@smallexample
+pthread_cleanup_pop(1);
+@end smallexample
+
+Notice that the code above is safe only in deferred cancellation mode
+(see @code{pthread_setcanceltype}). In asynchronous cancellation mode, a
+cancellation can occur between @code{pthread_cleanup_push} and
+@code{pthread_mutex_lock}, or between @code{pthread_mutex_unlock} and
+@code{pthread_cleanup_pop}, resulting in both cases in the thread trying
+to unlock a mutex not locked by the current thread. This is the main
+reason why asynchronous cancellation is difficult to use.
+
+If the code above must also work in asynchronous cancellation mode,
+then it must switch to deferred mode for locking and unlocking the
+mutex:
+
+@smallexample
+pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, &oldtype);
+pthread_cleanup_push(pthread_mutex_unlock, (void *) &mut);
+pthread_mutex_lock(&mut);
+/* do some work */
+pthread_cleanup_pop(1);
+pthread_setcanceltype(oldtype, NULL);
+@end smallexample
+
+The code above can be rewritten in a more compact and efficient way,
+using the non-portable functions @code{pthread_cleanup_push_defer_np}
+and @code{pthread_cleanup_pop_restore_np}:
+
+@smallexample
+pthread_cleanup_push_defer_np(pthread_mutex_unlock, (void *) &mut);
+pthread_mutex_lock(&mut);
+/* do some work */
+pthread_cleanup_pop_restore_np(1);
+@end smallexample
+
+@comment pthread.h
+@comment POSIX
+@deftypefun void pthread_cleanup_push (void (*@var{routine}) (void *), void *@var{arg})
+
+@code{pthread_cleanup_push} installs the @var{routine} function with
+argument @var{arg} as a cleanup handler. From this point on to the
+matching @code{pthread_cleanup_pop}, the function @var{routine} will be
+called with arguments @var{arg} when the thread terminates, either
+through @code{pthread_exit} or by cancellation. If several cleanup
+handlers are active at that point, they are called in LIFO order: the
+most recently installed handler is called first.
+@end deftypefun
+
+@comment pthread.h
+@comment POSIX
+@deftypefun void pthread_cleanup_pop (int @var{execute})
+@code{pthread_cleanup_pop} removes the most recently installed cleanup
+handler. If the @var{execute} argument is not 0, it also executes the
+handler, by calling the @var{routine} function with arguments
+@var{arg}. If the @var{execute} argument is 0, the handler is only
+removed but not executed.
+@end deftypefun
+
+Matching pairs of @code{pthread_cleanup_push} and
+@code{pthread_cleanup_pop} must occur in the same function, at the same
+level of block nesting.  Actually, @code{pthread_cleanup_push} and
+@code{pthread_cleanup_pop} are macros, and the expansion of
+@code{pthread_cleanup_push} introduces an open brace @code{@{} with the
+matching closing brace @code{@}} being introduced by the expansion of the
+matching @code{pthread_cleanup_pop}.
+
+@comment pthread.h
+@comment GNU
+@deftypefun void pthread_cleanup_push_defer_np (void (*@var{routine}) (void *), void *@var{arg})
+@code{pthread_cleanup_push_defer_np} is a non-portable extension that
+combines @code{pthread_cleanup_push} and @code{pthread_setcanceltype}.
+It pushes a cleanup handler just as @code{pthread_cleanup_push} does,
+but also saves the current cancellation type and sets it to deferred
+cancellation. This ensures that the cleanup mechanism is effective even
+if the thread was initially in asynchronous cancellation mode.
+@end deftypefun
+
+@comment pthread.h
+@comment GNU
+@deftypefun void pthread_cleanup_pop_restore_np (int @var{execute})
+@code{pthread_cleanup_pop_restore_np} pops a cleanup handler introduced
+by @code{pthread_cleanup_push_defer_np}, and restores the cancellation
+type to its value at the time @code{pthread_cleanup_push_defer_np} was
+called.
+@end deftypefun
+
+@code{pthread_cleanup_push_defer_np} and
+@code{pthread_cleanup_pop_restore_np} must occur in matching pairs, at
+the same level of block nesting.
+
+The sequence
+
+@smallexample
+pthread_cleanup_push_defer_np(routine, arg);
+...
+pthread_cleanup_pop_defer_np(execute);
+@end smallexample
+
+@noindent
+is functionally equivalent to (but more compact and efficient than)
+
+@smallexample
+@{
+  int oldtype;
+  pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, &oldtype);
+  pthread_cleanup_push(routine, arg);
+  ...
+  pthread_cleanup_pop(execute);
+  pthread_setcanceltype(oldtype, NULL);
+@}
+@end smallexample
+
+
+@node Mutexes
+@section Mutexes
+
+A mutex is a MUTual EXclusion device, and is useful for protecting
+shared data structures from concurrent modifications, and implementing
+critical sections and monitors.
+
+A mutex has two possible states: unlocked (not owned by any thread),
+and locked (owned by one thread). A mutex can never be owned by two
+different threads simultaneously. A thread attempting to lock a mutex
+that is already locked by another thread is suspended until the owning
+thread unlocks the mutex first.
+
+None of the mutex functions is a cancellation point, not even
+@code{pthread_mutex_lock}, in spite of the fact that it can suspend a
+thread for arbitrary durations. This way, the status of mutexes at
+cancellation points is predictable, allowing cancellation handlers to
+unlock precisely those mutexes that need to be unlocked before the
+thread stops executing. Consequently, threads using deferred
+cancellation should never hold a mutex for extended periods of time.
+
+It is not safe to call mutex functions from a signal handler.  In
+particular, calling @code{pthread_mutex_lock} or
+@code{pthread_mutex_unlock} from a signal handler may deadlock the
+calling thread.
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_mutex_init (pthread_mutex_t *@var{mutex}, const pthread_mutexattr_t *@var{mutexattr})
+
+@code{pthread_mutex_init} initializes the mutex object pointed to by
+@var{mutex} according to the mutex attributes specified in @var{mutexattr}.
+If @var{mutexattr} is @code{NULL}, default attributes are used instead.
+
+The LinuxThreads implementation supports only one mutex attribute,
+the @var{mutex kind}, which is either ``fast'', ``recursive'', or
+``error checking''. The kind of a mutex determines whether
+it can be locked again by a thread that already owns it.
+The default kind is ``fast''.
+
+Variables of type @code{pthread_mutex_t} can also be initialized
+statically, using the constants @code{PTHREAD_MUTEX_INITIALIZER} (for
+fast mutexes), @code{PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP} (for
+recursive mutexes), and @code{PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP}
+(for error checking mutexes).
+
+@code{pthread_mutex_init} always returns 0.
+@end deftypefun
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_mutex_lock (pthread_mutex_t *mutex))
+@code{pthread_mutex_lock} locks the given mutex. If the mutex is
+currently unlocked, it becomes locked and owned by the calling thread,
+and @code{pthread_mutex_lock} returns immediately. If the mutex is
+already locked by another thread, @code{pthread_mutex_lock} suspends the
+calling thread until the mutex is unlocked.
+
+If the mutex is already locked by the calling thread, the behavior of
+@code{pthread_mutex_lock} depends on the kind of the mutex. If the mutex
+is of the ``fast'' kind, the calling thread is suspended.  It will
+remain suspended forever, because no other thread can unlock the mutex.
+If  the mutex is of the ``error checking'' kind, @code{pthread_mutex_lock}
+returns immediately with the error code @code{EDEADLK}.  If the mutex is
+of the ``recursive'' kind, @code{pthread_mutex_lock} succeeds and
+returns immediately, recording the number of times the calling thread
+has locked the mutex. An equal number of @code{pthread_mutex_unlock}
+operations must be performed before the mutex returns to the unlocked
+state.
+@end deftypefun
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_mutex_trylock (pthread_mutex_t *@var{mutex})
+@code{pthread_mutex_trylock} behaves identically to
+@code{pthread_mutex_lock}, except that it does not block the calling
+thread if the mutex is already locked by another thread (or by the
+calling thread in the case of a ``fast'' mutex). Instead,
+@code{pthread_mutex_trylock} returns immediately with the error code
+@code{EBUSY}.
+@end deftypefun
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_mutex_unlock (pthread_mutex_t *@var{mutex})
+@code{pthread_mutex_unlock} unlocks the given mutex. The mutex is
+assumed to be locked and owned by the calling thread on entrance to
+@code{pthread_mutex_unlock}. If the mutex is of the ``fast'' kind,
+@code{pthread_mutex_unlock} always returns it to the unlocked state. If
+it is of the ``recursive'' kind, it decrements the locking count of the
+mutex (number of @code{pthread_mutex_lock} operations performed on it by
+the calling thread), and only when this count reaches zero is the mutex
+actually unlocked.
+
+On ``error checking'' mutexes, @code{pthread_mutex_unlock} actually
+checks at run-time that the mutex is locked on entrance, and that it was
+locked by the same thread that is now calling
+@code{pthread_mutex_unlock}.  If these conditions are not met,
+@code{pthread_mutex_unlock} returns @code{EPERM}, and the mutex remains
+unchanged.  ``Fast'' and ``recursive'' mutexes perform no such checks,
+thus allowing a locked mutex to be unlocked by a thread other than its
+owner. This is non-portable behavior and must not be relied upon.
+@end deftypefun
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_mutex_destroy (pthread_mutex_t *@var{mutex})
+@code{pthread_mutex_destroy} destroys a mutex object, freeing the
+resources it might hold. The mutex must be unlocked on entrance. In the
+LinuxThreads implementation, no resources are associated with mutex
+objects, thus @code{pthread_mutex_destroy} actually does nothing except
+checking that the mutex is unlocked.
+
+If the mutex is locked by some thread, @code{pthread_mutex_destroy}
+returns @code{EBUSY}.  Otherwise it returns 0.
+@end deftypefun
+
+If any of the above functions (except @code{pthread_mutex_init})
+is applied to an uninitialized mutex, they will simply return
+@code{EINVAL} and do nothing.
+
+A shared global variable @var{x} can be protected by a mutex as follows:
+
+@smallexample
+int x;
+pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER;
+@end smallexample
+
+All accesses and modifications to @var{x} should be bracketed by calls to
+@code{pthread_mutex_lock} and @code{pthread_mutex_unlock} as follows:
+
+@smallexample
+pthread_mutex_lock(&mut);
+/* operate on x */
+pthread_mutex_unlock(&mut);
+@end smallexample
+
+Mutex attributes can be specified at mutex creation time, by passing a
+mutex attribute object as second argument to @code{pthread_mutex_init}.
+Passing @code{NULL} is equivalent to passing a mutex attribute object
+with all attributes set to their default values.
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_mutexattr_init (pthread_mutexattr_t *@var{attr})
+@code{pthread_mutexattr_init} initializes the mutex attribute object
+@var{attr} and fills it with default values for the attributes.
+
+This function always returns 0.
+@end deftypefun
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_mutexattr_destroy (pthread_mutexattr_t *@var{attr})
+@code{pthread_mutexattr_destroy} destroys a mutex attribute object,
+which must not be reused until it is
+reinitialized. @code{pthread_mutexattr_destroy} does nothing in the
+LinuxThreads implementation.
+
+This function always returns 0.
+@end deftypefun
+
+LinuxThreads supports only one mutex attribute: the mutex kind, which is
+either @code{PTHREAD_MUTEX_FAST_NP} for ``fast'' mutexes,
+@code{PTHREAD_MUTEX_RECURSIVE_NP} for ``recursive'' mutexes, or
+@code{PTHREAD_MUTEX_ERRORCHECK_NP} for ``error checking'' mutexes.  As
+the @code{NP} suffix indicates, this is a non-portable extension to the
+POSIX standard and should not be employed in portable programs.
+
+The mutex kind determines what happens if a thread attempts to lock a
+mutex it already owns with @code{pthread_mutex_lock}. If the mutex is of
+the ``fast'' kind, @code{pthread_mutex_lock} simply suspends the calling
+thread forever.  If the mutex is of the ``error checking'' kind,
+@code{pthread_mutex_lock} returns immediately with the error code
+@code{EDEADLK}.  If the mutex is of the ``recursive'' kind, the call to
+@code{pthread_mutex_lock} returns immediately with a success return
+code. The number of times the thread owning the mutex has locked it is
+recorded in the mutex. The owning thread must call
+@code{pthread_mutex_unlock} the same number of times before the mutex
+returns to the unlocked state.
+
+The default mutex kind is ``fast'', that is, @code{PTHREAD_MUTEX_FAST_NP}.
+
+@comment pthread.h
+@comment GNU
+@deftypefun int pthread_mutexattr_setkind_np (pthread_mutexattr_t *@var{attr}, int @var{kind})
+@code{pthread_mutexattr_setkind_np} sets the mutex kind attribute in
+@var{attr} to the value specified by @var{kind}.
+
+If @var{kind} is not @code{PTHREAD_MUTEX_FAST_NP},
+@code{PTHREAD_MUTEX_RECURSIVE_NP}, or
+@code{PTHREAD_MUTEX_ERRORCHECK_NP}, this function will return
+@code{EINVAL} and leave @var{attr} unchanged.
+@end deftypefun
+
+@comment pthread.h
+@comment GNU
+@deftypefun int pthread_mutexattr_getkind_np (const pthread_mutexattr_t *@var{attr}, int *@var{kind})
+@code{pthread_mutexattr_getkind_np} retrieves the current value of the
+mutex kind attribute in @var{attr} and stores it in the location pointed
+to by @var{kind}.
+
+This function always returns 0.
+@end deftypefun
+
+@node Condition Variables
+@section Condition Variables
+
+A condition (short for ``condition variable'') is a synchronization
+device that allows threads to suspend execution until some predicate on
+shared data is satisfied. The basic operations on conditions are: signal
+the condition (when the predicate becomes true), and wait for the
+condition, suspending the thread execution until another thread signals
+the condition.
+
+A condition variable must always be associated with a mutex, to avoid
+the race condition where a thread prepares to wait on a condition
+variable and another thread signals the condition just before the first
+thread actually waits on it.
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_cond_init (pthread_cond_t *@var{cond}, pthread_condattr_t *cond_@var{attr})
+
+@code{pthread_cond_init} initializes the condition variable @var{cond},
+using the condition attributes specified in @var{cond_attr}, or default
+attributes if @var{cond_attr} is @code{NULL}. The LinuxThreads
+implementation supports no attributes for conditions, hence the
+@var{cond_attr} parameter is actually ignored.
+
+Variables of type @code{pthread_cond_t} can also be initialized
+statically, using the constant @code{PTHREAD_COND_INITIALIZER}.
+
+This function always returns 0.
+@end deftypefun
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_cond_signal (pthread_cond_t *@var{cond})
+@code{pthread_cond_signal} restarts one of the threads that are waiting
+on the condition variable @var{cond}. If no threads are waiting on
+@var{cond}, nothing happens. If several threads are waiting on
+@var{cond}, exactly one is restarted, but it is not specified which.
+
+This function always returns 0.
+@end deftypefun
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_cond_broadcast (pthread_cond_t *@var{cond})
+@code{pthread_cond_broadcast} restarts all the threads that are waiting
+on the condition variable @var{cond}. Nothing happens if no threads are
+waiting on @var{cond}.
+
+This function always returns 0.
+@end deftypefun
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_cond_wait (pthread_cond_t *@var{cond}, pthread_mutex_t *@var{mutex})
+@code{pthread_cond_wait} atomically unlocks the @var{mutex} (as per
+@code{pthread_unlock_mutex}) and waits for the condition variable
+@var{cond} to be signaled. The thread execution is suspended and does
+not consume any CPU time until the condition variable is signaled. The
+@var{mutex} must be locked by the calling thread on entrance to
+@code{pthread_cond_wait}. Before returning to the calling thread,
+@code{pthread_cond_wait} re-acquires @var{mutex} (as per
+@code{pthread_lock_mutex}).
+
+Unlocking the mutex and suspending on the condition variable is done
+atomically. Thus, if all threads always acquire the mutex before
+signaling the condition, this guarantees that the condition cannot be
+signaled (and thus ignored) between the time a thread locks the mutex
+and the time it waits on the condition variable.
+
+This function always returns 0.
+@end deftypefun
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_cond_timedwait (pthread_cond_t *@var{cond}, pthread_mutex_t *@var{mutex}, const struct timespec *@var{abstime})
+@code{pthread_cond_timedwait} atomically unlocks @var{mutex} and waits
+on @var{cond}, as @code{pthread_cond_wait} does, but it also bounds the
+duration of the wait. If @var{cond} has not been signaled before time
+@var{abstime}, the mutex @var{mutex} is re-acquired and
+@code{pthread_cond_timedwait} returns the error code @code{ETIMEDOUT}.
+The wait can also be interrupted by a signal; in that case
+@code{pthread_cond_timedwait} returns @code{EINTR}.
+
+The @var{abstime} parameter specifies an absolute time, with the same
+origin as @code{time} and @code{gettimeofday}: an @var{abstime} of 0
+corresponds to 00:00:00 GMT, January 1, 1970.
+@end deftypefun
+
+@comment pthread.h
+@comment POSIX
+@deftypefun int pthread_cond_destroy (pthread_cond_t *@var{cond})
+@code{pthread_cond_destroy} destroys the condition variable @var{cond},
+freeing the resources it might hold.  If any threads are waiting on the
+condition variable, @code{pthread_cond_destroy} leaves @var{cond}
+untouched and returns @code{EBUSY}.  Otherwise it returns 0, and
+@var{cond} must not be used again until it is reinitialized.
+
+In the LinuxThreads implementation, no resources are associated with
+condition variables, so @code{pthread_cond_destroy} actually does
+nothing.
+@end deftypefun
+
+@code{pthread_cond_wait} and @code{pthread_cond_timedwait} are
+cancellation points. If a thread is cancelled while suspended in one of
+these functions, the thread immediately resumes execution, relocks the
+mutex specified by  @var{mutex}, and finally executes the cancellation.
+Consequently, cleanup handlers are assured that @var{mutex} is locked
+when they are called.
+
+It is not safe to call the condition variable functions from a signal
+handler. In particular, calling @code{pthread_cond_signal} or
+@code{pthread_cond_broadcast} from a signal handler may deadlock the
+calling thread.
+
+Consider two shared variables @var{x} and @var{y}, protected by the
+mutex @var{mut}, and a condition variable @var{cond} that is to be
+signaled whenever @var{x} becomes greater than @var{y}.
+
+@smallexample
+int x,y;
+pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER;
+pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
+@end smallexample
+
+Waiting until @var{x} is greater than @var{y} is performed as follows:
+
+@smallexample
+pthread_mutex_lock(&mut);
+while (x <= y) @{
+        pthread_cond_wait(&cond, &mut);
+@}
+/* operate on x and y */
+pthread_mutex_unlock(&mut);
+@end smallexample
+
+Modifications on @var{x} and @var{y} that may cause @var{x} to become greater than
+@var{y} should signal the condition if needed:
+
+@smallexample
+pthread_mutex_lock(&mut);
+/* modify x and y */
+if (x > y) pthread_cond_broadcast(&cond);
+pthread_mutex_unlock(&mut);
+@end smallexample
+
+If it can be proved that at most one waiting thread needs to be waken
+up (for instance, if there are only two threads communicating through
+@var{x} and @var{y}), @code{pthread_cond_signal} can be used as a slightly more
+efficient alternative to @code{pthread_cond_broadcast}. In doubt, use
+@code{pthread_cond_broadcast}.
+
+To wait for @var{x} to becomes greater than @var{y} with a timeout of 5
+seconds, do:
+
+@smallexample
+struct timeval now;
+struct timespec timeout;
+int retcode;
+
+pthread_mutex_lock(&mut);
+gettimeofday(&now);
+timeout.tv_sec = now.tv_sec + 5;
+timeout.tv_nsec = now.tv_usec * 1000;
+retcode = 0;
+while (x <= y && retcode != ETIMEDOUT) @{
+        retcode = pthread_cond_timedwait(&cond, &mut, &timeout);
+@}
+if (retcode == ETIMEDOUT) @{
+        /* timeout occurred */