urcu/futex.h

   1 #ifndef _URCU_FUTEX_H
   2 #define _URCU_FUTEX_H
   3
   4 /*
   5  * urcu-futex.h
   6  *
   7  * Userspace RCU - sys_futex/compat_futex header.
   8  *
   9  * Copyright 2011-2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  10  *
  11  * This library is free software; you can redistribute it and/or
  12  * modify it under the terms of the GNU Lesser General Public
  13  * License as published by the Free Software Foundation; either
  14  * version 2.1 of the License, or (at your option) any later version.
  15  *
  16  * This library is distributed in the hope that it will be useful,
  17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  19  * Lesser General Public License for more details.
  20  *
  21  * You should have received a copy of the GNU Lesser General Public
  22  * License along with this library; if not, write to the Free Software
  23  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  24  */
  25
  26 #include <urcu/config.h>
  27 #include <stdint.h>
  28
  29 #ifdef __cplusplus
  30 extern "C" {
  31 #endif
  32
  33 #define FUTEX_WAIT              0
  34 #define FUTEX_WAKE              1
  35
  36 /*
  37  * sys_futex compatibility header.
  38  * Use *only* *either of* futex_noasync OR futex_async on a given address.
  39  *
  40  * futex_noasync cannot be executed in signal handlers, but ensures that
  41  * it will be put in a wait queue even in compatibility mode.
  42  *
  43  * futex_async is signal-handler safe for the wakeup. It uses polling
  44  * on the wait-side in compatibility mode.
  45  *
  46  * BEWARE: sys_futex() FUTEX_WAIT may return early if interrupted
  47  * (returns EINTR).
  48  */
  49
  50 extern int compat_futex_noasync(int32_t *uaddr, int op, int32_t val,
  51                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3);
  52 extern int compat_futex_async(int32_t *uaddr, int op, int32_t val,
  53                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3);
  54
  55 #ifdef CONFIG_RCU_HAVE_FUTEX
  56
  57 #include <unistd.h>
  58 #include <errno.h>
  59 #include <urcu/compiler.h>
  60 #include <urcu/arch.h>
  61
  62 static inline int futex(int32_t *uaddr, int op, int32_t val,
  63                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
  64 {
  65         return syscall(__NR_futex, uaddr, op, val, timeout,
  66                         uaddr2, val3);
  67 }
  68
  69 static inline int futex_noasync(int32_t *uaddr, int op, int32_t val,
  70                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
  71 {
  72         int ret;
  73
  74         ret = futex(uaddr, op, val, timeout, uaddr2, val3);
  75         if (caa_unlikely(ret < 0 && errno == ENOSYS)) {
  76                 /*
  77                  * The fallback on ENOSYS is the async-safe version of
  78                  * the compat futex implementation, because the
  79                  * async-safe compat implementation allows being used
  80                  * concurrently with calls to futex(). Indeed, sys_futex
  81                  * FUTEX_WAIT, on some architectures (mips and parisc),
  82                  * within a given process, spuriously return ENOSYS due
  83                  * to signal restart bugs on some kernel versions.
  84                  */
  85                 return compat_futex_async(uaddr, op, val, timeout,
  86                                 uaddr2, val3);
  87         }
  88         return ret;
  89
  90 }
  91
  92 static inline int futex_async(int32_t *uaddr, int op, int32_t val,
  93                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
  94 {
  95         int ret;
  96
  97         ret = futex(uaddr, op, val, timeout, uaddr2, val3);
  98         if (caa_unlikely(ret < 0 && errno == ENOSYS)) {
  99                 return compat_futex_async(uaddr, op, val, timeout,
 100                                 uaddr2, val3);
 101         }
 102         return ret;
 103 }
 104
 105 #elif defined(__CYGWIN__)
 106
 107 /*
 108  * The futex_noasync compat code uses a weak symbol to share state across
 109  * different shared object which is not possible on Windows with the
 110  * Portable Executable format. Use the async compat code for both cases.
 111  */
 112 static inline int futex_noasync(int32_t *uaddr, int op, int32_t val,
 113                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
 114 {
 115         return compat_futex_async(uaddr, op, val, timeout, uaddr2, val3);
 116 }
 117
 118 static inline int futex_async(int32_t *uaddr, int op, int32_t val,
 119                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
 120 {
 121         return compat_futex_async(uaddr, op, val, timeout, uaddr2, val3);
 122 }
 123
 124 #else
 125
 126 static inline int futex_noasync(int32_t *uaddr, int op, int32_t val,
 127                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
 128 {
 129         return compat_futex_noasync(uaddr, op, val, timeout, uaddr2, val3);
 130 }
 131
 132 static inline int futex_async(int32_t *uaddr, int op, int32_t val,
 133                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
 134 {
 135         return compat_futex_async(uaddr, op, val, timeout, uaddr2, val3);
 136 }
 137
 138 #endif
 139
 140 #ifdef __cplusplus
 141 }
 142 #endif
 143
 144 #endif /* _URCU_FUTEX_H */