nptl/tst-rwlock15.c

   1 /* Copyright (C) 2015-2023 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 /* This tests that a writer that is preferred -- but times out due to a
  19    reader being present -- does not miss to wake other readers blocked on the
  20    writer's pending lock acquisition.  */
  21
  22 #include <errno.h>
  23 #include <pthread.h>
  24 #include <stdio.h>
  25 #include <stdlib.h>
  26 #include <time.h>
  27
  28 /* The bug existed in the code that strictly prefers writers over readers.  */
  29 static pthread_rwlock_t r = PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP;
  30
  31 static void *
  32 writer (void *arg)
  33 {
  34   struct timespec ts;
  35   if (clock_gettime (CLOCK_REALTIME, &ts) != 0)
  36     {
  37       puts ("clock_gettime failed");
  38       exit (EXIT_FAILURE);
  39     }
  40   ts.tv_sec += 1;
  41   int e = pthread_rwlock_timedwrlock (&r, &ts);
  42   if (e != ETIMEDOUT)
  43     {
  44       puts ("timedwrlock did not time out");
  45       exit (EXIT_FAILURE);
  46     }
  47   return NULL;
  48 }
  49
  50 static void *
  51 reader (void *arg)
  52 {
  53   /* This isn't a reliable way to get the interleaving we need (because a
  54      failed trylock doesn't synchronize with the writer, and because we could
  55      try to lock after the writer has already timed out).  However, both will
  56      just lead to false positives.  */
  57   int e;
  58   while ((e = pthread_rwlock_tryrdlock (&r)) != EBUSY)
  59     {
  60       if (e != 0)
  61         exit (EXIT_FAILURE);
  62       pthread_rwlock_unlock (&r);
  63     }
  64   e = pthread_rwlock_rdlock (&r);
  65   if (e != 0)
  66     {
  67       puts ("reader rdlock failed");
  68       exit (EXIT_FAILURE);
  69     }
  70   pthread_rwlock_unlock (&r);
  71   return NULL;
  72 }
  73
  74
  75 static int
  76 do_test (void)
  77 {
  78   /* Grab a rdlock, then create a writer and a reader, and wait until they
  79      finished.  */
  80
  81   if (pthread_rwlock_rdlock (&r) != 0)
  82     {
  83       puts ("initial rdlock failed");
  84       return 1;
  85     }
  86
  87   pthread_t thw;
  88   if (pthread_create (&thw, NULL, writer, NULL) != 0)
  89     {
  90       puts ("create failed");
  91       return 1;
  92     }
  93   pthread_t thr;
  94   if (pthread_create (&thr, NULL, reader, NULL) != 0)
  95     {
  96       puts ("create failed");
  97       return 1;
  98     }
  99
 100   if (pthread_join (thw, NULL) != 0)
 101     {
 102       puts ("writer join failed");
 103       return 1;
 104     }
 105   if (pthread_join (thr, NULL) != 0)
 106     {
 107       puts ("reader join failed");
 108       return 1;
 109     }
 110
 111   return 0;
 112 }
 113
 114
 115 #define TEST_FUNCTION do_test ()
 116 #include "../test-skeleton.c"