New pthread_barrier algorithm to fulfill barrier destruction requirements.

The previous barrier implementation did not fulfill the POSIX requirements
for when a barrier can be destroyed.  Specifically, it was possible that
threads that haven't noticed yet that their round is complete still access
the barrier's memory, and that those accesses can happen after the barrier
has been legally destroyed.
The new algorithm does not have this issue, and it avoids using a lock
internally.

1 files changed, 145 insertions, 0 deletions

diff --git a/nptl/tst-barrier5.c b/nptl/tst-barrier5.c
new file mode 100644
index 0000000000..b99bd00c5b
--- /dev/null
+++ b/nptl/tst-barrier5.c
@@ -0,0 +1,145 @@
+/* Copyright (C) 2004-2015 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   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; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* This tests the barrier reset mechanism.  */
+#include <errno.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <internaltypes.h>
+
+
+static pthread_barrier_t b1;
+static pthread_barrier_t b2;
+
+
+#define N 20
+#define ROUNDS_PER_RUN 20
+#define START ((BARRIER_IN_THRESHOLD / N - ROUNDS_PER_RUN / 2) * N)
+
+static void *
+tf (void *arg)
+{
+  int runs = 0;
+
+  while (runs++ < 30)
+    {
+      /* In each run, we execute a number of rounds and initialize the barrier
+	 so that we will go over the reset threshold with those rounds.  */
+      for (int rounds = 0; rounds < ROUNDS_PER_RUN; rounds++)
+	pthread_barrier_wait (&b1);
+
+      if (pthread_barrier_wait (&b1) == PTHREAD_BARRIER_SERIAL_THREAD)
+	{
+	  pthread_barrier_destroy (&b1);
+	  if (pthread_barrier_init (&b1, NULL, N) != 0)
+	    {
+	      puts ("tf: 1st barrier_init failed");
+	      exit (1);
+	    }
+	  puts ("b1 reinitialized");
+	  /* Trigger a reset.  */
+	  struct pthread_barrier *bar = (struct pthread_barrier *) &b1;
+	  bar->in = START;
+	  bar->out = START;
+	  /* We deliberately don't set bar->current_round so that we also
+	     test whether the helping for the updates of current_round
+	     works correctly.  */
+	}
+
+      /* Same as above, just for b2.  */
+      for (int rounds = 0; rounds < ROUNDS_PER_RUN; rounds++)
+	pthread_barrier_wait (&b2);
+
+      if (pthread_barrier_wait (&b2) == PTHREAD_BARRIER_SERIAL_THREAD)
+	{
+	  pthread_barrier_destroy (&b2);
+	  if (pthread_barrier_init (&b2, NULL, N) != 0)
+	    {
+	      puts ("tf: 2nd barrier_init failed");
+	      exit (1);
+	    }
+	  puts ("b2 reinitialized");
+	  /* Trigger a reset.  See above.  */
+	  struct pthread_barrier *bar = (struct pthread_barrier *) &b2;
+	  bar->in = START;
+	  bar->out = START;
+	}
+    }
+
+  return NULL;
+}
+
+
+static int
+do_test (void)
+{
+  pthread_attr_t at;
+  int cnt;
+
+  if (pthread_attr_init (&at) != 0)
+    {
+      puts ("attr_init failed");
+      return 1;
+    }
+
+  if (pthread_attr_setstacksize (&at, 1 * 1024 * 1024) != 0)
+    {
+      puts ("attr_setstacksize failed");
+      return 1;
+    }
+
+  if (pthread_barrier_init (&b1, NULL, N) != 0)
+    {
+      puts ("1st barrier_init failed");
+      return 1;
+    }
+
+  if (pthread_barrier_init (&b2, NULL, N) != 0)
+    {
+      puts ("2nd barrier_init failed");
+      return 1;
+    }
+
+  pthread_t th[N - 1];
+  for (cnt = 0; cnt < N - 1; ++cnt)
+    if (pthread_create (&th[cnt], &at, tf, NULL) != 0)
+      {
+	puts ("pthread_create failed");
+	return 1;
+      }
+
+  if (pthread_attr_destroy (&at) != 0)
+    {
+      puts ("attr_destroy failed");
+      return 1;
+    }
+
+  tf (NULL);
+
+  for (cnt = 0; cnt < N - 1; ++cnt)
+    if (pthread_join (th[cnt], NULL) != 0)
+      {
+	puts ("pthread_join failed");
+	return 1;
+      }
+
+  return 0;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"