include/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 #include <time.h>
  29
  30 #ifdef __cplusplus
  31 extern "C" {
  32 #endif
  33
  34 #define FUTEX_WAIT              0
  35 #define FUTEX_WAKE              1
  36
  37 /*
  38  * sys_futex compatibility header.
  39  * Use *only* *either of* futex_noasync OR futex_async on a given address.
  40  *
  41  * futex_noasync cannot be executed in signal handlers, but ensures that
  42  * it will be put in a wait queue even in compatibility mode.
  43  *
  44  * futex_async is signal-handler safe for the wakeup. It uses polling
  45  * on the wait-side in compatibility mode.
  46  *
  47  * BEWARE: sys_futex() FUTEX_WAIT may return early if interrupted
  48  * (returns EINTR).
  49  */
  50
  51 extern int compat_futex_noasync(int32_t *uaddr, int op, int32_t val,
  52                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3);
  53 extern int compat_futex_async(int32_t *uaddr, int op, int32_t val,
  54                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3);
  55
  56 #ifdef CONFIG_RCU_HAVE_FUTEX
  57
  58 #include <unistd.h>
  59 #include <errno.h>
  60 #include <urcu/compiler.h>
  61 #include <urcu/arch.h>
  62
  63 static inline int futex(int32_t *uaddr, int op, int32_t val,
  64                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
  65 {
  66         return syscall(__NR_futex, uaddr, op, val, timeout,
  67                         uaddr2, val3);
  68 }
  69
  70 static inline int futex_noasync(int32_t *uaddr, int op, int32_t val,
  71                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
  72 {
  73         int ret;
  74
  75         ret = futex(uaddr, op, val, timeout, uaddr2, val3);
  76         if (caa_unlikely(ret < 0 && errno == ENOSYS)) {
  77                 /*
  78                  * The fallback on ENOSYS is the async-safe version of
  79                  * the compat futex implementation, because the
  80                  * async-safe compat implementation allows being used
  81                  * concurrently with calls to futex(). Indeed, sys_futex
  82                  * FUTEX_WAIT, on some architectures (mips and parisc),
  83                  * within a given process, spuriously return ENOSYS due
  84                  * to signal restart bugs on some kernel versions.
  85                  */
  86                 return compat_futex_async(uaddr, op, val, timeout,
  87                                 uaddr2, val3);
  88         }
  89         return ret;
  90
  91 }
  92
  93 static inline int futex_async(int32_t *uaddr, int op, int32_t val,
  94                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
  95 {
  96         int ret;
  97
  98         ret = futex(uaddr, op, val, timeout, uaddr2, val3);
  99         if (caa_unlikely(ret < 0 && errno == ENOSYS)) {
 100                 return compat_futex_async(uaddr, op, val, timeout,
 101                                 uaddr2, val3);
 102         }
 103         return ret;
 104 }
 105
 106 #elif defined(__CYGWIN__)
 107
 108 /*
 109  * The futex_noasync compat code uses a weak symbol to share state across
 110  * different shared object which is not possible on Windows with the
 111  * Portable Executable format. Use the async compat code for both cases.
 112  */
 113 static inline int futex_noasync(int32_t *uaddr, int op, int32_t val,
 114                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
 115 {
 116         return compat_futex_async(uaddr, op, val, timeout, uaddr2, val3);
 117 }
 118
 119 static inline int futex_async(int32_t *uaddr, int op, int32_t val,
 120                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
 121 {
 122         return compat_futex_async(uaddr, op, val, timeout, uaddr2, val3);
 123 }
 124
 125 #else
 126
 127 static inline int futex_noasync(int32_t *uaddr, int op, int32_t val,
 128                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
 129 {
 130         return compat_futex_noasync(uaddr, op, val, timeout, uaddr2, val3);
 131 }
 132
 133 static inline int futex_async(int32_t *uaddr, int op, int32_t val,
 134                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
 135 {
 136         return compat_futex_async(uaddr, op, val, timeout, uaddr2, val3);
 137 }
 138
 139 #endif
 140
 141 #ifdef __cplusplus
 142 }
 143 #endif
 144
 145 #endif /* _URCU_FUTEX_H */