htl: Make pthread_cond_destroy wait for threads to be woken

This allows to reuse the storage after calling pthread_cond_destroy.

* sysdeps/htl/bits/types/struct___pthread_cond.h (__pthread_cond):
Replace unused struct __pthread_condimpl *__impl field with unsigned int
__wrefs.
(__PTHREAD_COND_INITIALIZER): Update accordingly.
* sysdeps/htl/pt-cond-timedwait.c (__pthread_cond_timedwait_internal):
Register as waiter in __wrefs field. On unregistering, wake any pending
pthread_cond_destroy.
* sysdeps/htl/pt-cond-destroy.c (__pthread_cond_destroy): Register wake
request in __wrefs.
* nptl/Makefile (tests): Move tst-cond20 tst-cond21 to...
* sysdeps/pthread/Makefile (tests): ... here.
* nptl/tst-cond20.c nptl/tst-cond21.c: Move to...
* sysdeps/pthread/tst-cond20.c sysdeps/pthread/tst-cond21.c: ... here.

7 files changed, 215 insertions, 6 deletions

diff --git a/sysdeps/htl/bits/types/struct___pthread_cond.h b/sysdeps/htl/bits/types/struct___pthread_cond.h
index 150a37c..c040b17 100644
--- a/sysdeps/htl/bits/types/struct___pthread_cond.h
+++ b/sysdeps/htl/bits/types/struct___pthread_cond.h
@@ -27,12 +27,12 @@ struct __pthread_cond
   __pthread_spinlock_t __lock;
   struct __pthread *__queue;
   struct __pthread_condattr *__attr;
-  struct __pthread_condimpl *__impl;
+  unsigned int __wrefs;
   void *__data;
 };
 
 /* Initializer for a condition variable.  */
 #define __PTHREAD_COND_INITIALIZER \
-  { __PTHREAD_SPIN_LOCK_INITIALIZER, NULL, NULL, NULL, NULL }
+  { __PTHREAD_SPIN_LOCK_INITIALIZER, NULL, NULL, 0, NULL }
 
 #endif /* bits/types/struct___pthread_cond.h */
diff --git a/sysdeps/htl/pt-cond-destroy.c b/sysdeps/htl/pt-cond-destroy.c
index 0664f3f..722516a 100644
--- a/sysdeps/htl/pt-cond-destroy.c
+++ b/sysdeps/htl/pt-cond-destroy.c
@@ -22,14 +22,26 @@
 int
 __pthread_cond_destroy (pthread_cond_t *cond)
 {
-  int ret = 0;
+  /* Set the wake request flag. */
+  unsigned int wrefs = atomic_fetch_or_acquire (&cond->__wrefs, 1);
 
   __pthread_spin_wait (&cond->__lock);
   if (cond->__queue)
-    ret = EBUSY;
+    {
+      __pthread_spin_unlock (&cond->__lock);
+      return EBUSY;
+    }
   __pthread_spin_unlock (&cond->__lock);
 
-  return ret;
+  while (wrefs >> 1 != 0)
+    {
+      gsync_wait (__mach_task_self (), (vm_offset_t) &cond->__wrefs, wrefs,
+		  0, 0, 0);
+      wrefs = atomic_load_acquire (&cond->__wrefs);
+    }
+  /* The memory the condvar occupies can now be reused.  */
+
+  return 0;
 }
 
 weak_alias (__pthread_cond_destroy, pthread_cond_destroy);
diff --git a/sysdeps/htl/pt-cond-timedwait.c b/sysdeps/htl/pt-cond-timedwait.c
index a0ced9a..c05944d 100644
--- a/sysdeps/htl/pt-cond-timedwait.c
+++ b/sysdeps/htl/pt-cond-timedwait.c
@@ -144,6 +144,10 @@ __pthread_cond_timedwait_internal (pthread_cond_t *cond,
   /* Release MUTEX before blocking.  */
   __pthread_mutex_unlock (mutex);
 
+  /* Increase the waiter reference count.  Relaxed MO is sufficient because
+     we only need to synchronize when decrementing the reference count.  */
+  atomic_fetch_add_relaxed (&cond->__wrefs, 2);
+
   /* Block the thread.  */
   if (abstime != NULL)
     err = __pthread_timedblock (self, abstime, clock_id);
@@ -178,6 +182,13 @@ __pthread_cond_timedwait_internal (pthread_cond_t *cond,
     }
   __pthread_spin_unlock (&cond->__lock);
 
+  /* If destruction is pending (i.e., the wake-request flag is nonzero) and we
+     are the last waiter (prior value of __wrefs was 1 << 1), then wake any
+     threads waiting in pthread_cond_destroy.  Release MO to synchronize with
+     these threads.  Don't bother clearing the wake-up request flag.  */
+  if ((atomic_fetch_add_release (&cond->__wrefs, -2)) == 3)
+    __gsync_wake (__mach_task_self (), (vm_offset_t) &cond->__wrefs, 0, 0);
+
   if (drain)
     __pthread_block (self);
 
diff --git a/sysdeps/mach/hurd/htl/pt-hurd-cond-timedwait.c b/sysdeps/mach/hurd/htl/pt-hurd-cond-timedwait.c
index 939ed56..4f63955 100644
--- a/sysdeps/mach/hurd/htl/pt-hurd-cond-timedwait.c
+++ b/sysdeps/mach/hurd/htl/pt-hurd-cond-timedwait.c
@@ -111,6 +111,10 @@ __pthread_hurd_cond_timedwait_internal (pthread_cond_t *cond,
       /* Release MUTEX before blocking.  */
       __pthread_mutex_unlock (mutex);
 
+  /* Increase the waiter reference count.  Relaxed MO is sufficient because
+     we only need to synchronize when decrementing the reference count.  */
+  atomic_fetch_add_relaxed (&cond->__wrefs, 2);
+
       /* Block the thread.  */
       if (abstime != NULL)
 	err = __pthread_timedblock (self, abstime, clock_id);
@@ -144,6 +148,13 @@ __pthread_hurd_cond_timedwait_internal (pthread_cond_t *cond,
 	__pthread_block (self);
     }
 
+  /* If destruction is pending (i.e., the wake-request flag is nonzero) and we
+     are the last waiter (prior value of __wrefs was 1 << 1), then wake any
+     threads waiting in pthread_cond_destroy.  Release MO to synchronize with
+     these threads.  Don't bother clearing the wake-up request flag.  */
+  if ((atomic_fetch_add_release (&cond->__wrefs, -2)) == 3)
+    __gsync_wake (__mach_task_self (), (vm_offset_t) &cond->__wrefs, 0, 0);
+
   /* Clear the hook, now that we are done blocking.  */
   ss->cancel_hook = NULL;
   /* Check the cancellation flag; we might have unblocked due to
diff --git a/sysdeps/pthread/Makefile b/sysdeps/pthread/Makefile
index 74dbca1..3dc8827 100644
--- a/sysdeps/pthread/Makefile
+++ b/sysdeps/pthread/Makefile
@@ -49,7 +49,7 @@ tests += tst-cnd-basic tst-mtx-trylock tst-cnd-broadcast \
 	 tst-cond1 tst-cond2 tst-cond3 tst-cond4 tst-cond5 tst-cond6 tst-cond7 \
 	 tst-cond8 tst-cond9 tst-cond10 tst-cond11 tst-cond12 tst-cond13 \
 	 tst-cond14 tst-cond15 tst-cond16 tst-cond17 tst-cond18 tst-cond19 \
-	 tst-cond23 tst-cond24 tst-cond25 tst-cond27 \
+	 tst-cond20 tst-cond21 tst-cond23 tst-cond24 tst-cond25 tst-cond27 \
 	 tst-cond-except \
 	 tst-join1 tst-join2 tst-join3 tst-join4 tst-join5 tst-join6 tst-join7 \
 	 tst-join8 tst-join9 tst-join10 tst-join11 tst-join12 tst-join13 \
diff --git a/sysdeps/pthread/tst-cond20.c b/sysdeps/pthread/tst-cond20.c
new file mode 100644
index 0000000..f4047c0
--- /dev/null
+++ b/sysdeps/pthread/tst-cond20.c
@@ -0,0 +1,172 @@
+/* Copyright (C) 2004-2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Jakub Jelinek <jakub@redhat.com>, 2004.
+
+   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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#define N 10
+#define ROUNDS 1000
+static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
+static pthread_cond_t cond2 = PTHREAD_COND_INITIALIZER;
+static pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER;
+static pthread_barrier_t b;
+static int count;
+
+static void *
+tf (void *p)
+{
+  int i;
+  for (i = 0; i < ROUNDS; ++i)
+    {
+      pthread_mutex_lock (&mut);
+
+      if (++count == N)
+	pthread_cond_signal (&cond2);
+
+#ifdef TIMED
+      struct timeval tv;
+      gettimeofday (&tv, NULL);
+      struct timespec ts;
+      /* Wait three seconds.  */
+      ts.tv_sec = tv.tv_sec + 3;
+      ts.tv_nsec = tv.tv_usec * 1000;
+      pthread_cond_timedwait (&cond, &mut, &ts);
+#else
+      pthread_cond_wait (&cond, &mut);
+#endif
+
+      pthread_mutex_unlock (&mut);
+
+      int err = pthread_barrier_wait (&b);
+      if (err != 0 && err != PTHREAD_BARRIER_SERIAL_THREAD)
+	{
+	  puts ("child: barrier_wait failed");
+	  exit (1);
+	}
+
+      err = pthread_barrier_wait (&b);
+      if (err != 0 && err != PTHREAD_BARRIER_SERIAL_THREAD)
+	{
+	  puts ("child: barrier_wait failed");
+	  exit (1);
+	}
+    }
+
+  return NULL;
+}
+
+
+static int
+do_test (void)
+{
+  if (pthread_barrier_init (&b, NULL, N + 1) != 0)
+    {
+      puts ("barrier_init failed");
+      return 1;
+    }
+
+  pthread_mutex_lock (&mut);
+
+  int i, j, err;
+  pthread_t th[N];
+  for (i = 0; i < N; ++i)
+    if ((err = pthread_create (&th[i], NULL, tf, NULL)) != 0)
+      {
+	printf ("cannot create thread %d: %s\n", i, strerror (err));
+	return 1;
+      }
+
+  for (i = 0; i < ROUNDS; ++i)
+    {
+      /* Make sure we discard spurious wake-ups.  */
+      do
+	pthread_cond_wait (&cond2, &mut);
+      while (count != N);
+
+      if (i & 1)
+        pthread_mutex_unlock (&mut);
+
+      if (i & 2)
+	pthread_cond_broadcast (&cond);
+      else if (i & 4)
+	for (j = 0; j < N; ++j)
+	  pthread_cond_signal (&cond);
+      else
+	{
+	  for (j = 0; j < (i / 8) % N; ++j)
+	    pthread_cond_signal (&cond);
+	  pthread_cond_broadcast (&cond);
+	}
+
+      if ((i & 1) == 0)
+        pthread_mutex_unlock (&mut);
+
+      err = pthread_cond_destroy (&cond);
+      if (err)
+	{
+	  printf ("pthread_cond_destroy failed: %s\n", strerror (err));
+	  return 1;
+	}
+
+      /* Now clobber the cond variable which has been successfully
+         destroyed above.  */
+      memset (&cond, (char) i, sizeof (cond));
+
+      err = pthread_barrier_wait (&b);
+      if (err != 0 && err != PTHREAD_BARRIER_SERIAL_THREAD)
+	{
+	  puts ("parent: barrier_wait failed");
+	  return 1;
+	}
+
+      pthread_mutex_lock (&mut);
+
+      err = pthread_barrier_wait (&b);
+      if (err != 0 && err != PTHREAD_BARRIER_SERIAL_THREAD)
+	{
+	  puts ("parent: barrier_wait failed");
+	  return 1;
+	}
+
+      count = 0;
+      err = pthread_cond_init (&cond, NULL);
+      if (err)
+	{
+	  printf ("pthread_cond_init failed: %s\n", strerror (err));
+	  return 1;
+	}
+    }
+
+  for (i = 0; i < N; ++i)
+    if ((err = pthread_join (th[i], NULL)) != 0)
+      {
+	printf ("failed to join thread %d: %s\n", i, strerror (err));
+	return 1;
+      }
+
+  puts ("done");
+
+  return 0;
+}
+
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/sysdeps/pthread/tst-cond21.c b/sysdeps/pthread/tst-cond21.c
new file mode 100644
index 0000000..89cb771
--- /dev/null
+++ b/sysdeps/pthread/tst-cond21.c
@@ -0,0 +1,3 @@
+#include <sys/time.h>
+#define TIMED 1
+#include "tst-cond20.c"