1*062c5bc4SJason Schmidlapp /*
2*062c5bc4SJason Schmidlapp * pthread_rwlock_check_need_init.c
3*062c5bc4SJason Schmidlapp *
4*062c5bc4SJason Schmidlapp * Description:
5*062c5bc4SJason Schmidlapp * This translation unit implements read/write lock primitives.
6*062c5bc4SJason Schmidlapp *
7*062c5bc4SJason Schmidlapp * --------------------------------------------------------------------------
8*062c5bc4SJason Schmidlapp *
9*062c5bc4SJason Schmidlapp * Pthreads-embedded (PTE) - POSIX Threads Library for embedded systems
10*062c5bc4SJason Schmidlapp * Copyright(C) 2008 Jason Schmidlapp
11*062c5bc4SJason Schmidlapp *
12*062c5bc4SJason Schmidlapp * Contact Email: jschmidlapp@users.sourceforge.net
13*062c5bc4SJason Schmidlapp *
14*062c5bc4SJason Schmidlapp *
15*062c5bc4SJason Schmidlapp * Based upon Pthreads-win32 - POSIX Threads Library for Win32
16*062c5bc4SJason Schmidlapp * Copyright(C) 1998 John E. Bossom
17*062c5bc4SJason Schmidlapp * Copyright(C) 1999,2005 Pthreads-win32 contributors
18*062c5bc4SJason Schmidlapp *
19*062c5bc4SJason Schmidlapp * Contact Email: rpj@callisto.canberra.edu.au
20*062c5bc4SJason Schmidlapp *
21*062c5bc4SJason Schmidlapp * The original list of contributors to the Pthreads-win32 project
22*062c5bc4SJason Schmidlapp * is contained in the file CONTRIBUTORS.ptw32 included with the
23*062c5bc4SJason Schmidlapp * source code distribution. The list can also be seen at the
24*062c5bc4SJason Schmidlapp * following World Wide Web location:
25*062c5bc4SJason Schmidlapp * http://sources.redhat.com/pthreads-win32/contributors.html
26*062c5bc4SJason Schmidlapp *
27*062c5bc4SJason Schmidlapp * This library is free software; you can redistribute it and/or
28*062c5bc4SJason Schmidlapp * modify it under the terms of the GNU Lesser General Public
29*062c5bc4SJason Schmidlapp * License as published by the Free Software Foundation; either
30*062c5bc4SJason Schmidlapp * version 2 of the License, or (at your option) any later version.
31*062c5bc4SJason Schmidlapp *
32*062c5bc4SJason Schmidlapp * This library is distributed in the hope that it will be useful,
33*062c5bc4SJason Schmidlapp * but WITHOUT ANY WARRANTY; without even the implied warranty of
34*062c5bc4SJason Schmidlapp * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
35*062c5bc4SJason Schmidlapp * Lesser General Public License for more details.
36*062c5bc4SJason Schmidlapp *
37*062c5bc4SJason Schmidlapp * You should have received a copy of the GNU Lesser General Public
38*062c5bc4SJason Schmidlapp * License along with this library in the file COPYING.LIB;
39*062c5bc4SJason Schmidlapp * if not, write to the Free Software Foundation, Inc.,
40*062c5bc4SJason Schmidlapp * 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
41*062c5bc4SJason Schmidlapp */
42*062c5bc4SJason Schmidlapp
43*062c5bc4SJason Schmidlapp
44*062c5bc4SJason Schmidlapp #include "pthread.h"
45*062c5bc4SJason Schmidlapp #include "implement.h"
46*062c5bc4SJason Schmidlapp
47*062c5bc4SJason Schmidlapp int
pte_rwlock_check_need_init(pthread_rwlock_t * rwlock)48*062c5bc4SJason Schmidlapp pte_rwlock_check_need_init (pthread_rwlock_t * rwlock)
49*062c5bc4SJason Schmidlapp {
50*062c5bc4SJason Schmidlapp int result = 0;
51*062c5bc4SJason Schmidlapp
52*062c5bc4SJason Schmidlapp /*
53*062c5bc4SJason Schmidlapp * The following guarded test is specifically for statically
54*062c5bc4SJason Schmidlapp * initialised rwlocks (via PTHREAD_RWLOCK_INITIALIZER).
55*062c5bc4SJason Schmidlapp *
56*062c5bc4SJason Schmidlapp * Note that by not providing this synchronisation we risk
57*062c5bc4SJason Schmidlapp * introducing race conditions into applications which are
58*062c5bc4SJason Schmidlapp * correctly written.
59*062c5bc4SJason Schmidlapp *
60*062c5bc4SJason Schmidlapp * Approach
61*062c5bc4SJason Schmidlapp * --------
62*062c5bc4SJason Schmidlapp * We know that static rwlocks will not be PROCESS_SHARED
63*062c5bc4SJason Schmidlapp * so we can serialise access to internal state using
64*062c5bc4SJason Schmidlapp * critical sections rather than mutexes.
65*062c5bc4SJason Schmidlapp *
66*062c5bc4SJason Schmidlapp * If using a single global lock slows applications down too much,
67*062c5bc4SJason Schmidlapp * multiple global locks could be created and hashed on some random
68*062c5bc4SJason Schmidlapp * value associated with each mutex, the pointer perhaps. At a guess,
69*062c5bc4SJason Schmidlapp * a good value for the optimal number of global locks might be
70*062c5bc4SJason Schmidlapp * the number of processors + 1.
71*062c5bc4SJason Schmidlapp *
72*062c5bc4SJason Schmidlapp */
73*062c5bc4SJason Schmidlapp
74*062c5bc4SJason Schmidlapp
75*062c5bc4SJason Schmidlapp pte_osMutexLock (pte_rwlock_test_init_lock);
76*062c5bc4SJason Schmidlapp
77*062c5bc4SJason Schmidlapp /*
78*062c5bc4SJason Schmidlapp * We got here possibly under race
79*062c5bc4SJason Schmidlapp * conditions. Check again inside the critical section
80*062c5bc4SJason Schmidlapp * and only initialise if the rwlock is valid (not been destroyed).
81*062c5bc4SJason Schmidlapp * If a static rwlock has been destroyed, the application can
82*062c5bc4SJason Schmidlapp * re-initialise it only by calling pthread_rwlock_init()
83*062c5bc4SJason Schmidlapp * explicitly.
84*062c5bc4SJason Schmidlapp */
85*062c5bc4SJason Schmidlapp if (*rwlock == PTHREAD_RWLOCK_INITIALIZER)
86*062c5bc4SJason Schmidlapp {
87*062c5bc4SJason Schmidlapp result = pthread_rwlock_init (rwlock, NULL);
88*062c5bc4SJason Schmidlapp }
89*062c5bc4SJason Schmidlapp else if (*rwlock == NULL)
90*062c5bc4SJason Schmidlapp {
91*062c5bc4SJason Schmidlapp /*
92*062c5bc4SJason Schmidlapp * The rwlock has been destroyed while we were waiting to
93*062c5bc4SJason Schmidlapp * initialise it, so the operation that caused the
94*062c5bc4SJason Schmidlapp * auto-initialisation should fail.
95*062c5bc4SJason Schmidlapp */
96*062c5bc4SJason Schmidlapp result = EINVAL;
97*062c5bc4SJason Schmidlapp }
98*062c5bc4SJason Schmidlapp
99*062c5bc4SJason Schmidlapp pte_osMutexUnlock(pte_rwlock_test_init_lock);
100*062c5bc4SJason Schmidlapp
101*062c5bc4SJason Schmidlapp return result;
102*062c5bc4SJason Schmidlapp }
103