Note: The __pthread_once definition in the new unified implementation in
this patch has been edited. The original version of the patch had an old
style declaration that was causing a -Werror=old-style-definition failure.
commit 36875b06e0ed7f137190b9228bef553adfc338ba
Author: Torvald Riegel <triegel@redhat.com>
Date: Wed May 8 16:35:10 2013 +0200
Fixed and unified pthread_once.
[BZ #15215] This unifies various pthread_once architecture-specific
implementations which were using the same algorithm with slightly different
implementations. It also adds missing memory barriers that are required for
correctness.
diff --git a/nptl/sysdeps/unix/sysv/linux/pthread_once.c b/nptl/sysdeps/unix/sysv/linux/pthread_once.c
new file mode 100644
index 0000000000000000..2684b660958361d4
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/pthread_once.c
@@ -0,0 +1,129 @@
+/* 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)
diff --git a/nptl/sysdeps/unix/sysv/linux/sparc/pthread_once.c b/nptl/sysdeps/unix/sysv/linux/sparc/pthread_once.c
deleted file mode 100644
index a2111756374174f2..0000000000000000
--- a/nptl/sysdeps/unix/sysv/linux/sparc/pthread_once.c
+++ /dev/null
@@ -1,93 +0,0 @@
-/* Copyright (C) 2003-2012 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>
-
-
-unsigned long int __fork_generation attribute_hidden;
-
-
-static void
-clear_once_control (void *arg)
-{
- pthread_once_t *once_control = (pthread_once_t *) arg;
-
- *once_control = 0;
- lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
-}
-
-
-int
-__pthread_once (once_control, init_routine)
- pthread_once_t *once_control;
- void (*init_routine) (void);
-{
- while (1)
- {
- int oldval, val, newval;
-
- val = *once_control;
- do
- {
- /* Check if the initialized has already been done. */
- if ((val & 2) != 0)
- return 0;
-
- oldval = val;
- newval = (oldval & 3) | __fork_generation | 1;
- val = atomic_compare_and_exchange_val_acq (once_control, newval,
- oldval);
- }
- while (__builtin_expect (val != oldval, 0));
-
- /* Check if another thread already runs the initializer. */
- if ((oldval & 1) != 0)
- {
- /* Check whether the initializer execution was interrupted
- by a fork. */
- if (((oldval ^ newval) & -4) == 0)
- {
- /* 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);
-
-
- /* Add one to *once_control. */
- atomic_increment (once_control);
-
- /* 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)
diff --git a/sysdeps/unix/sysv/linux/aarch64/nptl/pthread_once.c b/sysdeps/unix/sysv/linux/aarch64/nptl/pthread_once.c
deleted file mode 100644
index 0897e1e004ef3278..0000000000000000
--- a/sysdeps/unix/sysv/linux/aarch64/nptl/pthread_once.c
+++ /dev/null
@@ -1,90 +0,0 @@
-/* Copyright (C) 2004-2012 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/>. */
-
-#include "pthreadP.h"
-#include <lowlevellock.h>
-
-unsigned long int __fork_generation attribute_hidden;
-
-static void
-clear_once_control (void *arg)
-{
- pthread_once_t *once_control = (pthread_once_t *) arg;
-
- *once_control = 0;
- lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
-}
-
-int
-__pthread_once (pthread_once_t *once_control, void (*init_routine) (void))
-{
- for (;;)
- {
- int oldval;
- int newval;
-
- /* Pseudo code:
- newval = __fork_generation | 1;
- oldval = *once_control;
- if ((oldval & 2) == 0)
- *once_control = newval;
- Do this atomically.
- */
- do
- {
- newval = __fork_generation | 1;
- oldval = *once_control;
- if (oldval & 2)
- break;
- } while (atomic_compare_and_exchange_val_acq (once_control, newval, oldval) != oldval);
-
- /* Check if the initializer has already been done. */
- if ((oldval & 2) != 0)
- return 0;
-
- /* Check if another thread already runs the initializer. */
- if ((oldval & 1) == 0)
- break;
-
- /* Check whether the initializer execution was interrupted by a fork. */
- if (oldval != newval)
- break;
-
- /* Same generation, some other thread was faster. Wait. */
- lll_futex_wait (once_control, oldval, 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);
-
- /* Say that the initialisation is done. */
- *once_control = __fork_generation | 2;
-
- /* Wake up all other threads. */
- lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
-
- return 0;
-}
-weak_alias (__pthread_once, pthread_once)
-hidden_def (__pthread_once)
diff --git a/sysdeps/unix/sysv/linux/arm/nptl/pthread_once.c b/sysdeps/unix/sysv/linux/arm/nptl/pthread_once.c
deleted file mode 100644
index 0c03f1c816a2fad5..0000000000000000
--- a/sysdeps/unix/sysv/linux/arm/nptl/pthread_once.c
+++ /dev/null
@@ -1,89 +0,0 @@
-/* Copyright (C) 2004-2012 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/>. */
-
-#include "pthreadP.h"
-#include <lowlevellock.h>
-
-unsigned long int __fork_generation attribute_hidden;
-
-static void
-clear_once_control (void *arg)
-{
- pthread_once_t *once_control = (pthread_once_t *) arg;
-
- *once_control = 0;
- lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
-}
-
-int
-__pthread_once (pthread_once_t *once_control, void (*init_routine) (void))
-{
- for (;;)
- {
- int oldval;
- int newval;
-
- /* Pseudo code:
- newval = __fork_generation | 1;
- oldval = *once_control;
- if ((oldval & 2) == 0)
- *once_control = newval;
- Do this atomically.
- */
- do
- {
- newval = __fork_generation | 1;
- oldval = *once_control;
- if (oldval & 2)
- break;
- } while (atomic_compare_and_exchange_val_acq (once_control, newval, oldval) != oldval);
-
- /* Check if the initializer has already been done. */
- if ((oldval & 2) != 0)
- return 0;
-
- /* Check if another thread already runs the initializer. */
- if ((oldval & 1) == 0)
- break;
-
- /* Check whether the initializer execution was interrupted by a fork. */
- if (oldval != newval)
- break;
-
- /* Same generation, some other thread was faster. Wait. */
- lll_futex_wait (once_control, oldval, 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);
-
- /* Say that the initialisation is done. */
- *once_control = __fork_generation | 2;
-
- /* Wake up all other threads. */
- lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
-
- return 0;
-}
-weak_alias (__pthread_once, pthread_once)
-hidden_def (__pthread_once)
diff --git a/sysdeps/unix/sysv/linux/ia64/nptl/pthread_once.c b/sysdeps/unix/sysv/linux/ia64/nptl/pthread_once.c
deleted file mode 100644
index 7730935dfec85ae6..0000000000000000
--- a/sysdeps/unix/sysv/linux/ia64/nptl/pthread_once.c
+++ /dev/null
@@ -1,93 +0,0 @@
-/* Copyright (C) 2003, 2004, 2007 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>
-
-
-unsigned long int __fork_generation attribute_hidden;
-
-
-static void
-clear_once_control (void *arg)
-{
- pthread_once_t *once_control = (pthread_once_t *) arg;
-
- *once_control = 0;
- lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
-}
-
-
-int
-__pthread_once (once_control, init_routine)
- pthread_once_t *once_control;
- void (*init_routine) (void);
-{
- while (1)
- {
- int oldval, val, newval;
-
- val = *once_control;
- do
- {
- /* Check if the initialized has already been done. */
- if ((val & 2) != 0)
- return 0;
-
- oldval = val;
- newval = (oldval & 3) | __fork_generation | 1;
- val = atomic_compare_and_exchange_val_acq (once_control, newval,
- oldval);
- }
- while (__builtin_expect (val != oldval, 0));
-
- /* Check if another thread already runs the initializer. */
- if ((oldval & 1) != 0)
- {
- /* Check whether the initializer execution was interrupted
- by a fork. */
- if (((oldval ^ newval) & -4) == 0)
- {
- /* 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);
-
-
- /* Add one to *once_control. */
- atomic_increment (once_control);
-
- /* 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)
diff --git a/sysdeps/unix/sysv/linux/m68k/nptl/pthread_once.c b/sysdeps/unix/sysv/linux/m68k/nptl/pthread_once.c
deleted file mode 100644
index 8d81db602eee601f..0000000000000000
--- a/sysdeps/unix/sysv/linux/m68k/nptl/pthread_once.c
+++ /dev/null
@@ -1,90 +0,0 @@
-/* Copyright (C) 2010-2012 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
- Contributed by Maxim Kuvyrkov <maxim@codesourcery.com>, 2010.
-
- 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>
-
-unsigned long int __fork_generation attribute_hidden;
-
-static void
-clear_once_control (void *arg)
-{
- pthread_once_t *once_control = (pthread_once_t *) arg;
-
- *once_control = 0;
- lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
-}
-
-int
-__pthread_once (pthread_once_t *once_control, void (*init_routine) (void))
-{
- for (;;)
- {
- int oldval;
- int newval;
-
- /* Pseudo code:
- newval = __fork_generation | 1;
- oldval = *once_control;
- if ((oldval & 2) == 0)
- *once_control = newval;
- Do this atomically.
- */
- do
- {
- newval = __fork_generation | 1;
- oldval = *once_control;
- if (oldval & 2)
- break;
- } while (atomic_compare_and_exchange_val_acq (once_control, newval, oldval) != oldval);
-
- /* Check if the initializer has already been done. */
- if ((oldval & 2) != 0)
- return 0;
-
- /* Check if another thread already runs the initializer. */
- if ((oldval & 1) == 0)
- break;
-
- /* Check whether the initializer execution was interrupted by a fork. */
- if (oldval != newval)
- break;
-
- /* Same generation, some other thread was faster. Wait. */
- lll_futex_wait (once_control, oldval, 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);
-
- /* Say that the initialisation is done. */
- *once_control = __fork_generation | 2;
-
- /* Wake up all other threads. */
- lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
-
- return 0;
-}
-weak_alias (__pthread_once, pthread_once)
-hidden_def (__pthread_once)
diff --git a/sysdeps/unix/sysv/linux/mips/nptl/pthread_once.c b/sysdeps/unix/sysv/linux/mips/nptl/pthread_once.c
deleted file mode 100644
index 308da8bbce0c3800..0000000000000000
--- a/sysdeps/unix/sysv/linux/mips/nptl/pthread_once.c
+++ /dev/null
@@ -1,93 +0,0 @@
-/* Copyright (C) 2003-2012 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>
-
-
-unsigned long int __fork_generation attribute_hidden;
-
-
-static void
-clear_once_control (void *arg)
-{
- pthread_once_t *once_control = (pthread_once_t *) arg;
-
- *once_control = 0;
- lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
-}
-
-
-int
-__pthread_once (once_control, init_routine)
- pthread_once_t *once_control;
- void (*init_routine) (void);
-{
- while (1)
- {
- int oldval, val, newval;
-
- val = *once_control;
- do
- {
- /* Check if the initialized has already been done. */
- if ((val & 2) != 0)
- return 0;
-
- oldval = val;
- newval = (oldval & 3) | __fork_generation | 1;
- val = atomic_compare_and_exchange_val_acq (once_control, newval,
- oldval);
- }
- while (__builtin_expect (val != oldval, 0));
-
- /* Check if another thread already runs the initializer. */
- if ((oldval & 1) != 0)
- {
- /* Check whether the initializer execution was interrupted
- by a fork. */
- if (((oldval ^ newval) & -4) == 0)
- {
- /* 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);
-
-
- /* Add one to *once_control. */
- atomic_increment (once_control);
-
- /* 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)
diff --git a/sysdeps/unix/sysv/linux/tile/nptl/pthread_once.c b/sysdeps/unix/sysv/linux/tile/nptl/pthread_once.c
deleted file mode 100644
index 93ac29b24c440b2c..0000000000000000
--- a/sysdeps/unix/sysv/linux/tile/nptl/pthread_once.c
+++ /dev/null
@@ -1,94 +0,0 @@
-/* Copyright (C) 2011-2012 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
- Contributed by Chris Metcalf <cmetcalf@tilera.com>, 2011.
- Based on work 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 <nptl/pthreadP.h>
-#include <lowlevellock.h>
-
-
-unsigned long int __fork_generation attribute_hidden;
-
-
-static void
-clear_once_control (void *arg)
-{
- pthread_once_t *once_control = (pthread_once_t *) arg;
-
- *once_control = 0;
- lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
-}
-
-
-int
-__pthread_once (once_control, init_routine)
- pthread_once_t *once_control;
- void (*init_routine) (void);
-{
- while (1)
- {
- int oldval, val, newval;
-
- val = *once_control;
- do
- {
- /* Check if the initialized has already been done. */
- if ((val & 2) != 0)
- return 0;
-
- oldval = val;
- newval = (oldval & 3) | __fork_generation | 1;
- val = atomic_compare_and_exchange_val_acq (once_control, newval,
- oldval);
- }
- while (__builtin_expect (val != oldval, 0));
-
- /* Check if another thread already runs the initializer. */
- if ((oldval & 1) != 0)
- {
- /* Check whether the initializer execution was interrupted
- by a fork. */
- if (((oldval ^ newval) & -4) == 0)
- {
- /* 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);
-
-
- /* Add one to *once_control. */
- atomic_increment (once_control);
-
- /* 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)