From 0ecb606cb6cf65de1d9fc8a919bceb4be476c602 Mon Sep 17 00:00:00 2001 From: Jakub Jelinek Date: Thu, 12 Jul 2007 18:26:36 +0000 Subject: 2.5-18.1 --- nptl/lowlevellock.h | 90 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 90 insertions(+) create mode 100644 nptl/lowlevellock.h (limited to 'nptl/lowlevellock.h') diff --git a/nptl/lowlevellock.h b/nptl/lowlevellock.h new file mode 100644 index 0000000000..338da39990 --- /dev/null +++ b/nptl/lowlevellock.h @@ -0,0 +1,90 @@ +/* Low level locking macros used in NPTL implementation. Stub version. + Copyright (C) 2002 Free Software Foundation, Inc. + This file is part of the GNU C Library. + Contributed by Ulrich Drepper , 2002. + + 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, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA + 02111-1307 USA. */ + +#include + + +/* Implement generic mutex. Basic futex syscall support is required: + + lll_futex_wait(futex, value) - call sys_futex with FUTEX_WAIT + and third parameter VALUE + + lll_futex_wake(futex, value) - call sys_futex with FUTEX_WAKE + and third parameter VALUE +*/ + + +/* Mutex lock counter: + bit 31 clear means unlocked; + bit 31 set means locked. + + All code that looks at bit 31 first increases the 'number of + interested threads' usage counter, which is in bits 0-30. + + All negative mutex values indicate that the mutex is still locked. */ + + +static inline void +__generic_mutex_lock (int *mutex) +{ + unsigned int v; + + /* Bit 31 was clear, we got the mutex. (this is the fastpath). */ + if (atomic_bit_test_set (mutex, 31) == 0) + return; + + atomic_increment (mutex); + + while (1) + { + if (atomic_bit_test_set (mutex, 31) == 0) + { + atomic_decrement (mutex); + return; + } + + /* We have to wait now. First make sure the futex value we are + monitoring is truly negative (i.e. locked). */ + v = *mutex; + if (v >= 0) + continue; + + lll_futex_wait (mutex, v); + } +} + + +static inline void +__generic_mutex_unlock (int *mutex) +{ + /* Adding 0x80000000 to the counter results in 0 if and only if + there are not other interested threads - we can return (this is + the fastpath). */ + if (atomic_add_zero (mutex, 0x80000000)) + return; + + /* There are other threads waiting for this mutex, wake one of them + up. */ + lll_futex_wake (mutex, 1); +} + + +#define lll_mutex_lock(futex) __generic_mutex_lock (&(futex)) +#define lll_mutex_unlock(futex) __generic_mutex_unlock (&(futex)) -- cgit 1.4.1