New pthread rwlock that is more scalable.

This replaces the pthread rwlock with a new implementation that uses a
more scalable algorithm (primarily through not using a critical section
anymore to make state changes).  The fast path for rdlock acquisition and
release is now basically a single atomic read-modify write or CAS and a few
branches.  See nptl/pthread_rwlock_common.c for details.

	* nptl/DESIGN-rwlock.txt: Remove.
	* nptl/lowlevelrwlock.sym: Remove.
	* nptl/Makefile: Add new tests.
	* nptl/pthread_rwlock_common.c: New file.  Contains the new rwlock.
	* nptl/pthreadP.h (PTHREAD_RWLOCK_PREFER_READER_P): Remove.
	(PTHREAD_RWLOCK_WRPHASE, PTHREAD_RWLOCK_WRLOCKED,
	PTHREAD_RWLOCK_RWAITING, PTHREAD_RWLOCK_READER_SHIFT,
	PTHREAD_RWLOCK_READER_OVERFLOW, PTHREAD_RWLOCK_WRHANDOVER,
	PTHREAD_RWLOCK_FUTEX_USED): New.
	* nptl/pthread_rwlock_init.c (__pthread_rwlock_init): Adapt to new
	implementation.
	* nptl/pthread_rwlock_rdlock.c (__pthread_rwlock_rdlock_slow): Remove.
	(__pthread_rwlock_rdlock): Adapt.
	* nptl/pthread_rwlock_timedrdlock.c
	(pthread_rwlock_timedrdlock): Adapt.
	* nptl/pthread_rwlock_timedwrlock.c
	(pthread_rwlock_timedwrlock): Adapt.
	* nptl/pthread_rwlock_trywrlock.c (pthread_rwlock_trywrlock): Adapt.
	* nptl/pthread_rwlock_tryrdlock.c (pthread_rwlock_tryrdlock): Adapt.
	* nptl/pthread_rwlock_unlock.c (pthread_rwlock_unlock): Adapt.
	* nptl/pthread_rwlock_wrlock.c (__pthread_rwlock_wrlock_slow): Remove.
	(__pthread_rwlock_wrlock): Adapt.
	* nptl/tst-rwlock10.c: Adapt.
	* nptl/tst-rwlock11.c: Adapt.
	* nptl/tst-rwlock17.c: New file.
	* nptl/tst-rwlock18.c: New file.
	* nptl/tst-rwlock19.c: New file.
	* nptl/tst-rwlock2b.c: New file.
	* nptl/tst-rwlock8.c: Adapt.
	* nptl/tst-rwlock9.c: Adapt.
	* sysdeps/aarch64/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/arm/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/hppa/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/ia64/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/m68k/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/microblaze/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/mips/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/nios2/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/s390/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/sh/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/sparc/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/tile/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* sysdeps/unix/sysv/linux/alpha/bits/pthreadtypes.h
	(pthread_rwlock_t): Adapt.
	* sysdeps/unix/sysv/linux/powerpc/bits/pthreadtypes.h
	(pthread_rwlock_t): Adapt.
	* sysdeps/x86/bits/pthreadtypes.h (pthread_rwlock_t): Adapt.
	* nptl/nptl-printers.py (): Adapt.
	* nptl/nptl_lock_constants.pysym: Adapt.
	* nptl/test-rwlock-printers.py: Adapt.
	* nptl/test-rwlockattr-printers.c: Adapt.
	* nptl/test-rwlockattr-printers.py: Adapt.

1 files changed, 127 insertions, 0 deletions

diff --git a/nptl/tst-rwlock19.c b/nptl/tst-rwlock19.c
new file mode 100644
index 0000000..746d84d
--- /dev/null
+++ b/nptl/tst-rwlock19.c
@@ -0,0 +1,127 @@
+/* Test rdlock overflow.
+   Copyright (C) 2000-2017 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 <time.h>
+#include <unistd.h>
+#include <pthreadP.h>
+
+
+#define NREADERS 15
+#define READTRIES 5000
+
+#define DELAY   1000000
+
+static pthread_rwlock_t lock = PTHREAD_RWLOCK_INITIALIZER;
+static int eagain_returned = 0;
+static int success_returned = 0;
+
+static void *
+reader_thread (void *nr)
+{
+  struct timespec delay;
+  int n;
+
+  delay.tv_sec = 0;
+  delay.tv_nsec = DELAY;
+
+  for (n = 0; n < READTRIES; ++n)
+    {
+      int err = pthread_rwlock_rdlock (&lock);
+      if (err == EAGAIN)
+	{
+	  atomic_store_relaxed (&eagain_returned, 1);
+	  continue;
+	}
+      else if (err == 0)
+	atomic_store_relaxed (&success_returned, 1);
+      else
+	{
+	  puts ("rdlock failed");
+	  exit (1);
+	}
+
+      nanosleep (&delay, NULL);
+
+      if (pthread_rwlock_unlock (&lock) != 0)
+	{
+	  puts ("unlock for reader failed");
+	  exit (1);
+	}
+    }
+
+  return NULL;
+}
+
+
+static int
+do_test (void)
+{
+  pthread_t thrd[NREADERS];
+  int n;
+  void *res;
+
+  /* Set the rwlock so that it's close to a reader overflow.
+     PTHREAD_RWLOCK_WRPHASE and PTHREAD_RWLOCK_WRLOCK are zero initially.  */
+  unsigned int readers = PTHREAD_RWLOCK_READER_OVERFLOW
+      - ((NREADERS / 3) << PTHREAD_RWLOCK_READER_SHIFT);
+  lock.__data.__readers = readers;
+
+  for (n = 0; n < NREADERS; ++n)
+    if (pthread_create (&thrd[n], NULL, reader_thread,
+			(void *) (long int) n) != 0)
+      {
+	puts ("reader create failed");
+	exit (1);
+      }
+
+  /* Wait for all the threads.  */
+  for (n = 0; n < NREADERS; ++n)
+    if (pthread_join (thrd[n], &res) != 0)
+      {
+	puts ("reader join failed");
+	exit (1);
+      }
+
+  if (atomic_load_relaxed (&eagain_returned) == 0)
+    {
+      puts ("EAGAIN has never been returned");
+      exit (1);
+    }
+
+  if (atomic_load_relaxed (&success_returned) == 0)
+    {
+      puts ("rdlock was never successfully acquired");
+      exit (1);
+    }
+
+  if (lock.__data.__readers != readers)
+    {
+      puts ("__readers in rwlock differs from initial value");
+      exit (1);
+    }
+
+  return 0;
+}
+
+#define TIMEOUT 30
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"