/* Test program for a read-phase / write-phase explicit hand-over.

   Copyright (C) 2017-2018 Free Software Foundation, Inc.

   The GNU C Library is free software; you can redistribute it and/or

   modify it under the terms of the GNU Lesser General Public License as

   published by the Free Software Foundation; either version 2.1 of the

   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public

   License along with the GNU C Library; see the file COPYING.LIB.  If

   not, see <http://www.gnu.org/licenses/>.  */

#include <errno.h>

#include <error.h>

#include <pthread.h>

#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

#include <stdint.h>

#include <time.h>

#include <atomic.h>

#include <support/xthread.h>

/* We realy want to set threads to 2 to reproduce this issue. The goal

   is to have one primary writer and a single reader, and to hit the

   bug that happens in the interleaving of those two phase transitions.

   However, on most hardware, adding a second writer seems to help the

   interleaving happen slightly more often, say 20% of the time.  On a

   16 core ppc64 machine this fails 100% of the time with an unpatched

   glibc.  On a 8 core x86_64 machine this fails ~93% of the time, but

   it doesn't fail at all on a 4 core system, so having available

   unloaded cores makes a big difference in reproducibility.  On an 8

   core qemu/kvm guest the reproducer reliability drops to ~10%.  */

#define THREADS 3

#define KIND PTHREAD_RWLOCK_PREFER_READER_NP

static pthread_rwlock_t lock;

static int done = 0;

static void*

tf (void* arg)

{

  while (atomic_load_relaxed (&done) == 0)

    {

      int rcnt = 0;

      int wcnt = 100;

      if ((uintptr_t) arg == 0)

	{

	  rcnt = 1;

	  wcnt = 1;

	}

      do

	{

	  if (wcnt)

	    {

	      xpthread_rwlock_wrlock (&lock);

	      xpthread_rwlock_unlock (&lock);

	      wcnt--;

	  }

	  if (rcnt)

	    {

	      xpthread_rwlock_rdlock (&lock);

	      xpthread_rwlock_unlock (&lock);

	      rcnt--;

	  }

	}

      while ((atomic_load_relaxed (&done) == 0) && (rcnt + wcnt > 0));

    }

    return NULL;

}

static int

do_test (void)

{

  pthread_t thr[THREADS];

  int n;

  pthread_rwlockattr_t attr;

  xpthread_rwlockattr_init (&attr);

  xpthread_rwlockattr_setkind_np (&attr, KIND);

  xpthread_rwlock_init (&lock, &attr);

  /* Make standard error the same as standard output.  */

  dup2 (1, 2);

  /* Make sure we see all message, even those on stdout.  */

  setvbuf (stdout, NULL, _IONBF, 0);

  for (n = 0; n < THREADS; ++n)

    thr[n] = xpthread_create (NULL, tf, (void *) (uintptr_t) n);

  struct timespec delay;

  delay.tv_sec = 10;

  delay.tv_nsec = 0;

  nanosleep (&delay, NULL);

  atomic_store_relaxed (&done, 1);

  /* Wait for all the threads.  */

  for (n = 0; n < THREADS; ++n)

    xpthread_join (thr[n]);

  return 0;

}

#include <support/test-driver.c>