This patch is based on the below upstream commit.
It only includes relevant pthread_once bits.
commit 08192659bbeae149e7cb1f4c43547257f7099bb0
Author: Roland McGrath <roland@hack.frob.com>
Date: Mon Jul 7 09:28:38 2014 -0700
Get rid of nptl/sysdeps/ entirely!
diff --git a/nptl/pthread_once.c b/nptl/pthread_once.c
index ed1ea3498c397e5c..10c01d6023508e3c 100644
--- a/nptl/pthread_once.c
+++ b/nptl/pthread_once.c
@@ -1,6 +1,6 @@
-/* Copyright (C) 2002-2012 Free Software Foundation, Inc.
+/* Copyright (C) 2003-2014 Free Software Foundation, Inc.
This file is part of the GNU C Library.
- Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
+ Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
@@ -9,7 +9,7 @@
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
+ 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
@@ -18,37 +18,114 @@
#include "pthreadP.h"
#include <lowlevellock.h>
+#include <atomic.h>
+unsigned long int __fork_generation attribute_hidden;
-static int once_lock = LLL_LOCK_INITIALIZER;
+static void
+clear_once_control (void *arg)
+{
+ pthread_once_t *once_control = (pthread_once_t *) arg;
+
+ /* Reset to the uninitialized state here. We don't need a stronger memory
+ order because we do not need to make any other of our writes visible to
+ other threads that see this value: This function will be called if we
+ get interrupted (see __pthread_once), so all we need to relay to other
+ threads is the state being reset again. */
+ *once_control = 0;
+ lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
+}
+
+/* This is similar to a lock implementation, but we distinguish between three
+ states: not yet initialized (0), initialization finished (2), and
+ initialization in progress (__fork_generation | 1). If in the first state,
+ threads will try to run the initialization by moving to the second state;
+ the first thread to do so via a CAS on once_control runs init_routine,
+ other threads block.
+ When forking the process, some threads can be interrupted during the second
+ state; they won't be present in the forked child, so we need to restart
+ initialization in the child. To distinguish an in-progress initialization
+ from an interrupted initialization (in which case we need to reclaim the
+ lock), we look at the fork generation that's part of the second state: We
+ can reclaim iff it differs from the current fork generation.
+ XXX: This algorithm has an ABA issue on the fork generation: If an
+ initialization is interrupted, we then fork 2^30 times (30 bits of
+ once_control are used for the fork generation), and try to initialize
+ again, we can deadlock because we can't distinguish the in-progress and
+ interrupted cases anymore. */
int
__pthread_once (once_control, init_routine)
pthread_once_t *once_control;
void (*init_routine) (void);
{
- /* XXX Depending on whether the LOCK_IN_ONCE_T is defined use a
- global lock variable or one which is part of the pthread_once_t
- object. */
- if (*once_control == PTHREAD_ONCE_INIT)
+ while (1)
{
- lll_lock (once_lock, LLL_PRIVATE);
+ int oldval, val, newval;
- /* XXX This implementation is not complete. It doesn't take
- cancelation and fork into account. */
- if (*once_control == PTHREAD_ONCE_INIT)
+ /* We need acquire memory order for this load because if the value
+ signals that initialization has finished, we need to be see any
+ data modifications done during initialization. */
+ val = *once_control;
+ atomic_read_barrier();
+ do
{
- init_routine ();
+ /* Check if the initialization has already been done. */
+ if (__glibc_likely ((val & 2) != 0))
+ return 0;
+
+ oldval = val;
+ /* We try to set the state to in-progress and having the current
+ fork generation. We don't need atomic accesses for the fork
+ generation because it's immutable in a particular process, and
+ forked child processes start with a single thread that modified
+ the generation. */
+ newval = __fork_generation | 1;
+ /* We need acquire memory order here for the same reason as for the
+ load from once_control above. */
+ val = atomic_compare_and_exchange_val_acq (once_control, newval,
+ oldval);
+ }
+ while (__glibc_unlikely (val != oldval));
- *once_control = !PTHREAD_ONCE_INIT;
+ /* Check if another thread already runs the initializer. */
+ if ((oldval & 1) != 0)
+ {
+ /* Check whether the initializer execution was interrupted by a
+ fork. We know that for both values, bit 0 is set and bit 1 is
+ not. */
+ if (oldval == newval)
+ {
+ /* Same generation, some other thread was faster. Wait. */
+ lll_futex_wait (once_control, newval, LLL_PRIVATE);
+ continue;
+ }
}
- lll_unlock (once_lock, LLL_PRIVATE);
+ /* This thread is the first here. Do the initialization.
+ Register a cleanup handler so that in case the thread gets
+ interrupted the initialization can be restarted. */
+ pthread_cleanup_push (clear_once_control, once_control);
+
+ init_routine ();
+
+ pthread_cleanup_pop (0);
+
+
+ /* Mark *once_control as having finished the initialization. We need
+ release memory order here because we need to synchronize with other
+ threads that want to use the initialized data. */
+ atomic_write_barrier();
+ *once_control = 2;
+
+ /* Wake up all other threads. */
+ lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
+ break;
}
return 0;
}
-strong_alias (__pthread_once, pthread_once)
+weak_alias (__pthread_once, pthread_once)
hidden_def (__pthread_once)
diff --git a/nptl/sysdeps/unix/sysv/linux/pthread_once.c b/nptl/sysdeps/unix/sysv/linux/pthread_once.c
deleted file mode 100644
index 2684b660958361d4..0000000000000000
--- a/nptl/sysdeps/unix/sysv/linux/pthread_once.c
+++ /dev/null
@@ -1,129 +0,0 @@
-/* Copyright (C) 2003-2014 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
- Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.
-
- 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/>. */
-
-#include "pthreadP.h"
-#include <lowlevellock.h>
-#include <atomic.h>
-
-
-unsigned long int __fork_generation attribute_hidden;
-
-
-static void
-clear_once_control (void *arg)
-{
- pthread_once_t *once_control = (pthread_once_t *) arg;
-
- /* Reset to the uninitialized state here. We don't need a stronger memory
- order because we do not need to make any other of our writes visible to
- other threads that see this value: This function will be called if we
- get interrupted (see __pthread_once), so all we need to relay to other
- threads is the state being reset again. */
- *once_control = 0;
- lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
-}
-
-
-/* This is similar to a lock implementation, but we distinguish between three
- states: not yet initialized (0), initialization finished (2), and
- initialization in progress (__fork_generation | 1). If in the first state,
- threads will try to run the initialization by moving to the second state;
- the first thread to do so via a CAS on once_control runs init_routine,
- other threads block.
- When forking the process, some threads can be interrupted during the second
- state; they won't be present in the forked child, so we need to restart
- initialization in the child. To distinguish an in-progress initialization
- from an interrupted initialization (in which case we need to reclaim the
- lock), we look at the fork generation that's part of the second state: We
- can reclaim iff it differs from the current fork generation.
- XXX: This algorithm has an ABA issue on the fork generation: If an
- initialization is interrupted, we then fork 2^30 times (30 bits of
- once_control are used for the fork generation), and try to initialize
- again, we can deadlock because we can't distinguish the in-progress and
- interrupted cases anymore. */
-int
-__pthread_once (pthread_once_t *once_control, void (*init_routine) (void))
-{
- while (1)
- {
- int oldval, val, newval;
-
- /* We need acquire memory order for this load because if the value
- signals that initialization has finished, we need to be see any
- data modifications done during initialization. */
- val = *once_control;
- atomic_read_barrier();
- do
- {
- /* Check if the initialization has already been done. */
- if (__glibc_likely ((val & 2) != 0))
- return 0;
-
- oldval = val;
- /* We try to set the state to in-progress and having the current
- fork generation. We don't need atomic accesses for the fork
- generation because it's immutable in a particular process, and
- forked child processes start with a single thread that modified
- the generation. */
- newval = __fork_generation | 1;
- /* We need acquire memory order here for the same reason as for the
- load from once_control above. */
- val = atomic_compare_and_exchange_val_acq (once_control, newval,
- oldval);
- }
- while (__glibc_unlikely (val != oldval));
-
- /* Check if another thread already runs the initializer. */
- if ((oldval & 1) != 0)
- {
- /* Check whether the initializer execution was interrupted by a
- fork. We know that for both values, bit 0 is set and bit 1 is
- not. */
- if (oldval == newval)
- {
- /* Same generation, some other thread was faster. Wait. */
- lll_futex_wait (once_control, newval, LLL_PRIVATE);
- continue;
- }
- }
-
- /* This thread is the first here. Do the initialization.
- Register a cleanup handler so that in case the thread gets
- interrupted the initialization can be restarted. */
- pthread_cleanup_push (clear_once_control, once_control);
-
- init_routine ();
-
- pthread_cleanup_pop (0);
-
-
- /* Mark *once_control as having finished the initialization. We need
- release memory order here because we need to synchronize with other
- threads that want to use the initialized data. */
- atomic_write_barrier();
- *once_control = 2;
-
- /* Wake up all other threads. */
- lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
- break;
- }
-
- return 0;
-}
-weak_alias (__pthread_once, pthread_once)
-hidden_def (__pthread_once)