lock.c revision 169695
1/* Copyright (C) 2005 Free Software Foundation, Inc. 2 Contributed by Richard Henderson <rth@redhat.com>. 3 4 This file is part of the GNU OpenMP Library (libgomp). 5 6 Libgomp is free software; you can redistribute it and/or modify it 7 under the terms of the GNU Lesser General Public License as published by 8 the Free Software Foundation; either version 2.1 of the License, or 9 (at your option) any later version. 10 11 Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY 12 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS 13 FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for 14 more details. 15 16 You should have received a copy of the GNU Lesser General Public License 17 along with libgomp; see the file COPYING.LIB. If not, write to the 18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, 19 MA 02110-1301, USA. */ 20 21/* As a special exception, if you link this library with other files, some 22 of which are compiled with GCC, to produce an executable, this library 23 does not by itself cause the resulting executable to be covered by the 24 GNU General Public License. This exception does not however invalidate 25 any other reasons why the executable file might be covered by the GNU 26 General Public License. */ 27 28/* This is a Linux specific implementation of the public OpenMP locking 29 primitives. This implementation uses atomic instructions and the futex 30 syscall. */ 31 32#include "libgomp.h" 33#include <string.h> 34#include <unistd.h> 35#include <sys/syscall.h> 36#include "futex.h" 37 38 39/* The internal gomp_mutex_t and the external non-recursive omp_lock_t 40 have the same form. Re-use it. */ 41 42void 43omp_init_lock (omp_lock_t *lock) 44{ 45 gomp_mutex_init (lock); 46} 47 48void 49omp_destroy_lock (omp_lock_t *lock) 50{ 51 gomp_mutex_destroy (lock); 52} 53 54void 55omp_set_lock (omp_lock_t *lock) 56{ 57 gomp_mutex_lock (lock); 58} 59 60void 61omp_unset_lock (omp_lock_t *lock) 62{ 63 gomp_mutex_unlock (lock); 64} 65 66int 67omp_test_lock (omp_lock_t *lock) 68{ 69 return __sync_bool_compare_and_swap (lock, 0, 1); 70} 71 72/* The external recursive omp_nest_lock_t form requires additional work. */ 73 74/* We need an integer to uniquely identify this thread. Most generally 75 this is the thread's TID, which ideally we'd get this straight from 76 the TLS block where glibc keeps it. Unfortunately, we can't get at 77 that directly. 78 79 If we don't support (or have disabled) TLS, one function call is as 80 good (or bad) as any other. Use the syscall all the time. 81 82 On an ILP32 system (defined here as not LP64), we can make do with 83 any thread-local pointer. Ideally we'd use the TLS base address, 84 since that requires the least amount of arithmetic, but that's not 85 always available directly. Make do with the gomp_thread pointer 86 since it's handy. */ 87 88#if !defined (HAVE_TLS) 89static inline int gomp_tid (void) 90{ 91 return syscall (SYS_gettid); 92} 93#elif !defined(__LP64__) 94static inline int gomp_tid (void) 95{ 96 return (int) gomp_thread (); 97} 98#else 99static __thread int tid_cache; 100static inline int gomp_tid (void) 101{ 102 int tid = tid_cache; 103 if (__builtin_expect (tid == 0, 0)) 104 tid_cache = tid = syscall (SYS_gettid); 105 return tid; 106} 107#endif 108 109 110void 111omp_init_nest_lock (omp_nest_lock_t *lock) 112{ 113 memset (lock, 0, sizeof (lock)); 114} 115 116void 117omp_destroy_nest_lock (omp_nest_lock_t *lock) 118{ 119} 120 121void 122omp_set_nest_lock (omp_nest_lock_t *lock) 123{ 124 int otid, tid = gomp_tid (); 125 126 while (1) 127 { 128 otid = __sync_val_compare_and_swap (&lock->owner, 0, tid); 129 if (otid == 0) 130 { 131 lock->count = 1; 132 return; 133 } 134 if (otid == tid) 135 { 136 lock->count++; 137 return; 138 } 139 140 futex_wait (&lock->owner, otid); 141 } 142} 143 144void 145omp_unset_nest_lock (omp_nest_lock_t *lock) 146{ 147 /* ??? Validate that we own the lock here. */ 148 149 if (--lock->count == 0) 150 { 151 __sync_lock_release (&lock->owner); 152 futex_wake (&lock->owner, 1); 153 } 154} 155 156int 157omp_test_nest_lock (omp_nest_lock_t *lock) 158{ 159 int otid, tid = gomp_tid (); 160 161 otid = __sync_val_compare_and_swap (&lock->owner, 0, tid); 162 if (otid == 0) 163 { 164 lock->count = 1; 165 return 1; 166 } 167 if (otid == tid) 168 return ++lock->count; 169 170 return 0; 171} 172 173ialias (omp_init_lock) 174ialias (omp_init_nest_lock) 175ialias (omp_destroy_lock) 176ialias (omp_destroy_nest_lock) 177ialias (omp_set_lock) 178ialias (omp_set_nest_lock) 179ialias (omp_unset_lock) 180ialias (omp_unset_nest_lock) 181ialias (omp_test_lock) 182ialias (omp_test_nest_lock) 183