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/* Test of read-write locks in multithreaded situations.
   Copyright (C) 2005, 2008-2025 Free Software Foundation, Inc.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

/* Written by Bruno Haible <bruno@clisp.org>, 2005.  */

/* This test fails when writer starvation occurs
   <https://en.wikipedia.org/wiki/Readers%E2%80%93writers_problem>.
   It depends on the implementation of pthread rwlocks, cf.
   <https://gitweb.git.savannah.gnu.org/gitweb/?p=gnulib/maint-tools.git;a=tree;f=test-programs/pthread-rwlock>,
   as well as on the number of CPUs (because when there are >= 2*THREAD_COUNT
   CPUs, the checker threads are more "efficient" at not giving away the
   reader lock).
   A failure was seen with musl libc/riscv64 on a machine with 64 CPUs.  */

#include <config.h>

#if USE_ISOC_THREADS || USE_POSIX_THREADS || USE_ISOC_AND_POSIX_THREADS || USE_WINDOWS_THREADS

/* Whether to enable locking.
   Uncomment this to get a test program without locking, to verify that
   it crashes.  */
#define ENABLE_LOCKING 1

/* Whether to help the scheduler through explicit sched_yield().
   Uncomment this to see if the operating system has a fair scheduler.  */
#define EXPLICIT_YIELD 1

/* Whether to print debugging messages.  */
#define ENABLE_DEBUGGING 0

/* Number of simultaneous threads.  */
#define THREAD_COUNT 10

/* Number of operations performed in each thread.
   This is quite high, because with a smaller count, say 5000, we often get
   an "OK" result even without ENABLE_LOCKING (on Linux/x86).  */
#define REPEAT_COUNT 50000

#include <pthread.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#if EXPLICIT_YIELD
# include <sched.h>
#endif

#if HAVE_DECL_ALARM
# include <signal.h>
# include <unistd.h>
#endif

#include "macros.h"
#include "atomic-int-posix.h"

#if ENABLE_DEBUGGING
# define dbgprintf printf
#else
# define dbgprintf if (0) printf
#endif

#if EXPLICIT_YIELD
# define yield() sched_yield ()
#else
# define yield()
#endif

/* Returns a reference to the current thread as a pointer, for debugging.  */
#if defined __MVS__
  /* On IBM z/OS, pthread_t is a struct with an 8-byte '__' field.
     The first three bytes of this field appear to uniquely identify a
     pthread_t, though not necessarily representing a pointer.  */
# define pthread_self_pointer() (*((void **) pthread_self ().__))
#else
# define pthread_self_pointer() ((void *) (uintptr_t) pthread_self ())
#endif

#define ACCOUNT_COUNT 4

static int account[ACCOUNT_COUNT];

static int
random_account (void)
{
  return ((unsigned long) random () >> 3) % ACCOUNT_COUNT;
}

static void
check_accounts (void)
{
  int i, sum;

  sum = 0;
  for (i = 0; i < ACCOUNT_COUNT; i++)
    sum += account[i];
  if (sum != ACCOUNT_COUNT * 1000)
    abort ();
}


/* ----------------- Test read-write (non-recursive) locks ----------------- */

/* Test read-write locks by having several bank accounts and several threads
   which shuffle around money between the accounts and several other threads
   that check that all the money is still there.  */

static pthread_rwlock_t my_rwlock = PTHREAD_RWLOCK_INITIALIZER;

static void *
rwlock_mutator_thread (void *arg)
{
  int repeat;

  for (repeat = REPEAT_COUNT; repeat > 0; repeat--)
    {
      int i1, i2, value;

      dbgprintf ("Mutator %p before wrlock\n", pthread_self_pointer ());
      ASSERT (pthread_rwlock_wrlock (&my_rwlock) == 0);
      dbgprintf ("Mutator %p after  wrlock\n", pthread_self_pointer ());

      i1 = random_account ();
      i2 = random_account ();
      value = ((unsigned long) random () >> 3) % 10;
      account[i1] += value;
      account[i2] -= value;

      dbgprintf ("Mutator %p before unlock\n", pthread_self_pointer ());
      ASSERT (pthread_rwlock_unlock (&my_rwlock) == 0);
      dbgprintf ("Mutator %p after  unlock\n", pthread_self_pointer ());

      yield ();
    }

  dbgprintf ("Mutator %p dying.\n", pthread_self_pointer ());
  return NULL;
}

static struct atomic_int rwlock_checker_done;

static void *
rwlock_checker_thread (void *arg)
{
  while (get_atomic_int_value (&rwlock_checker_done) == 0)
    {
      dbgprintf ("Checker %p before check rdlock\n", pthread_self_pointer ());
      ASSERT (pthread_rwlock_rdlock (&my_rwlock) == 0);
      check_accounts ();
      ASSERT (pthread_rwlock_unlock (&my_rwlock) == 0);
      dbgprintf ("Checker %p after  check unlock\n", pthread_self_pointer ());

      yield ();
    }

  dbgprintf ("Checker %p dying.\n", pthread_self_pointer ());
  return NULL;
}

static void
test_rwlock (void)
{
  int i;
  pthread_t checkerthreads[THREAD_COUNT];
  pthread_t threads[THREAD_COUNT];

  /* Initialization.  */
  for (i = 0; i < ACCOUNT_COUNT; i++)
    account[i] = 1000;
  init_atomic_int (&rwlock_checker_done);
  set_atomic_int_value (&rwlock_checker_done, 0);

  /* Spawn the threads.  */
  for (i = 0; i < THREAD_COUNT; i++)
    ASSERT (pthread_create (&checkerthreads[i], NULL,
                            rwlock_checker_thread, NULL)
            == 0);
  for (i = 0; i < THREAD_COUNT; i++)
    ASSERT (pthread_create (&threads[i], NULL, rwlock_mutator_thread, NULL)
            == 0);

  /* Wait for the threads to terminate.  */
  for (i = 0; i < THREAD_COUNT; i++)
    ASSERT (pthread_join (threads[i], NULL) == 0);
  set_atomic_int_value (&rwlock_checker_done, 1);
  for (i = 0; i < THREAD_COUNT; i++)
    ASSERT (pthread_join (checkerthreads[i], NULL) == 0);
  check_accounts ();
}


/* -------------------------------------------------------------------------- */

int
main ()
{
#if HAVE_DECL_ALARM
  /* Declare failure if test takes too long, by using default abort
     caused by SIGALRM.  */
  int alarm_value = 600;
  signal (SIGALRM, SIG_DFL);
  alarm (alarm_value);
#endif

  printf ("Starting test_rwlock ..."); fflush (stdout);
  test_rwlock ();
  printf (" OK\n"); fflush (stdout);

  return test_exit_status;
}

#else

/* No multithreading available.  */

#include <stdio.h>

int
main ()
{
  fputs ("Skipping test: multithreading not enabled\n", stderr);
  return 77;
}

#endif
kc3-lang/gnulib/tests/test-pthread-rwlock.c

Commit

tests/test-pthread-rwlock.c
