tests/test-rwlock1.c

   1 /* Test of glthread_rwlock_rdlock function.
   2    Copyright (C) 2017-2019 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program 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
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Bruno Haible <bruno@clisp.org>, 2005.
  18    Inspired by
  19    https://github.com/linux-test-project/ltp/blob/master/testcases/open_posix_testsuite/conformance/interfaces/pthread_rwlock_rdlock/2-2.c
  20    by Intel Corporation.  */
  21
  22 #include <config.h>
  23
  24 #include "glthread/lock.h"
  25
  26 #include <errno.h>
  27 #include <stdio.h>
  28 #include <stdlib.h>
  29 #include <unistd.h>
  30
  31 #include "glthread/thread.h"
  32 #include "glthread/yield.h"
  33
  34 /* Verify that in a situation where
  35      - an rwlock is taken by a reader and has a writer waiting,
  36      - an additional reader requests the lock,
  37      - the waiting writer and the requesting reader threads have the same
  38        priority,
  39    the requesting reader thread gets blocked, so that at some point the
  40    waiting writer can acquire the lock.
  41    Without such a guarantee, when there a N readers and each of the readers
  42    spends more than 1/Nth of the time with the lock held, there is a high
  43    probability that the waiting writer will not get the lock in a given finite
  44    time, a phenomenon called "writer starvation".
  45    Without such a guarantee, applications have a hard time avoiding writer
  46    starvation.
  47
  48    POSIX:2008 makes this requirement only for implementations that support TPS
  49    (Thread Priority Scheduling) and only for the scheduling policies SCHED_FIFO
  50    and SCHED_RR, see
  51    http://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_rwlock_rdlock.html
  52    but test verifies the guarantee regardless of TPS and regardless of
  53    scheduling policy.  */
  54
  55 #define SUCCEED() exit (0)
  56 #define FAILURE() exit (1)
  57 #define UNEXPECTED(n) (fprintf (stderr, "Unexpected outcome %d\n", n), abort ())
  58
  59 /* The main thread creates the waiting writer and the requesting reader threads
  60    in the default way; this guarantees that they have the same priority.
  61    We can reuse the main thread as first reader thread.  */
  62
  63 static gl_rwlock_t lock;
  64 static gl_thread_t reader1;
  65 static gl_thread_t writer;
  66 static gl_thread_t reader2;
  67 static gl_thread_t timer;
  68 /* Used to pass control from writer to reader2 and from reader2 to timer,
  69    as in a relay race.
  70    Passing control from one running thread to another running thread
  71    is most likely faster than to create the second thread.  */
  72 static gl_lock_t baton;
  73
  74 static void *
  75 timer_func (void *ignored)
  76 {
  77   /* Step 13 (can be before or after step 12):
  78      The timer thread takes the baton, then waits a moment to make sure
  79      it can tell whether the second reader thread is blocked at step 12.  */
  80   if (glthread_lock_lock (&baton))
  81     UNEXPECTED (13);
  82   usleep (100000);
  83   /* By the time we get here, it's clear that the second reader thread is
  84      blocked at step 12.  This is the desired behaviour.  */
  85   SUCCEED ();
  86 }
  87
  88 static void *
  89 reader2_func (void *ignored)
  90 {
  91   int err;
  92
  93   /* Step 8 (can be before or after step 7):
  94      The second reader thread takes the baton, then waits a moment to make sure
  95      the writer thread has reached step 7.  */
  96   if (glthread_lock_lock (&baton))
  97     UNEXPECTED (8);
  98   usleep (100000);
  99   /* Step 9 omitted.  */
 100   /* Step 10: Launch a timer, to test whether the next call blocks.  */
 101   if (glthread_create (&timer, timer_func, NULL))
 102     UNEXPECTED (10);
 103   /* Step 11: Release the baton.  */
 104   if (glthread_lock_unlock (&baton))
 105     UNEXPECTED (11);
 106   /* Step 12: The second reader thread requests the lock.  */
 107   err = glthread_rwlock_rdlock (&lock);
 108   if (err == 0)
 109     FAILURE ();
 110   else
 111     UNEXPECTED (12);
 112 }
 113
 114 static void *
 115 writer_func (void *ignored)
 116 {
 117   /* Step 4: Take the baton, so that the second reader thread does not go ahead
 118      too early.  */
 119   if (glthread_lock_lock (&baton))
 120     UNEXPECTED (4);
 121   /* Step 5: Create the second reader thread.  */
 122   if (glthread_create (&reader2, reader2_func, NULL))
 123     UNEXPECTED (5);
 124   /* Step 6: Release the baton.  */
 125   if (glthread_lock_unlock (&baton))
 126     UNEXPECTED (6);
 127   /* Step 7: The writer thread requests the lock.  */
 128   if (glthread_rwlock_wrlock (&lock))
 129     UNEXPECTED (7);
 130   return NULL;
 131 }
 132
 133 int
 134 main ()
 135 {
 136   reader1 = gl_thread_self ();
 137
 138   /* Step 1: The main thread initializes the lock and the baton.  */
 139   if (glthread_rwlock_init (&lock))
 140     UNEXPECTED (1);
 141   if (glthread_lock_init (&baton))
 142     UNEXPECTED (1);
 143   /* Step 2: The main thread acquires the lock as a reader.  */
 144   if (glthread_rwlock_rdlock (&lock))
 145     UNEXPECTED (2);
 146   /* Step 3: Create the writer thread.  */
 147   if (glthread_create (&writer, writer_func, NULL))
 148     UNEXPECTED (3);
 149   /* Job done.  Go to sleep.  */
 150   for (;;)
 151     {
 152       /* In cooperative threads implementations (Pth), give other threads
 153          a chance to run.  */
 154       gl_thread_yield ();
 155       sleep (1);
 156     }
 157 }