liblttng-ust/futex.h

   1 #ifndef _LTTNG_UST_FUTEX_H
   2 #define _LTTNG_UST_FUTEX_H
   3
   4 /*
   5  * liblttng-ust/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 <errno.h>
  27 #include <stdint.h>
  28 #include <time.h>
  29 #include <sys/syscall.h>
  30
  31 #include "helper.h"
  32
  33 #ifdef __cplusplus
  34 extern "C" {
  35 #endif
  36
  37 #define FUTEX_WAIT              0
  38 #define FUTEX_WAKE              1
  39
  40 /*
  41  * sys_futex compatibility header.
  42  * Use *only* *either of* futex_noasync OR futex_async on a given address.
  43  *
  44  * futex_noasync cannot be executed in signal handlers, but ensures that
  45  * it will be put in a wait queue even in compatibility mode.
  46  *
  47  * futex_async is signal-handler safe for the wakeup. It uses polling
  48  * on the wait-side in compatibility mode.
  49  *
  50  * BEWARE: sys_futex() FUTEX_WAIT may return early if interrupted
  51  * (returns EINTR).
  52  */
  53
  54 LTTNG_HIDDEN
  55 extern int lttng_ust_compat_futex_noasync(int32_t *uaddr, int op, int32_t val,
  56                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3);
  57 LTTNG_HIDDEN
  58 extern int lttng_ust_compat_futex_async(int32_t *uaddr, int op, int32_t val,
  59                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3);
  60
  61 #if (defined(__linux__) && defined(__NR_futex))
  62
  63 #include <unistd.h>
  64 #include <errno.h>
  65 #include <urcu/compiler.h>
  66 #include <urcu/arch.h>
  67
  68 static inline int lttng_ust_futex(int32_t *uaddr, int op, int32_t val,
  69                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
  70 {
  71         return syscall(__NR_futex, uaddr, op, val, timeout,
  72                         uaddr2, val3);
  73 }
  74
  75 static inline int lttng_ust_futex_noasync(int32_t *uaddr, int op, int32_t val,
  76                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
  77 {
  78         int ret;
  79
  80         ret = lttng_ust_futex(uaddr, op, val, timeout, uaddr2, val3);
  81         if (caa_unlikely(ret < 0 && errno == ENOSYS)) {
  82                 /*
  83                  * The fallback on ENOSYS is the async-safe version of
  84                  * the compat futex implementation, because the
  85                  * async-safe compat implementation allows being used
  86                  * concurrently with calls to futex(). Indeed, sys_futex
  87                  * FUTEX_WAIT, on some architectures (mips and parisc),
  88                  * within a given process, spuriously return ENOSYS due
  89                  * to signal restart bugs on some kernel versions.
  90                  */
  91                 return lttng_ust_compat_futex_async(uaddr, op, val, timeout,
  92                                 uaddr2, val3);
  93         }
  94         return ret;
  95
  96 }
  97
  98 static inline int lttng_ust_futex_async(int32_t *uaddr, int op, int32_t val,
  99                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
 100 {
 101         int ret;
 102
 103         ret = lttng_ust_futex(uaddr, op, val, timeout, uaddr2, val3);
 104         if (caa_unlikely(ret < 0 && errno == ENOSYS)) {
 105                 return lttng_ust_compat_futex_async(uaddr, op, val, timeout,
 106                                 uaddr2, val3);
 107         }
 108         return ret;
 109 }
 110
 111 #elif defined(__FreeBSD__)
 112
 113 #include <sys/types.h>
 114 #include <sys/umtx.h>
 115
 116 static inline int lttng_ust_futex_async(int32_t *uaddr, int op, int32_t val,
 117                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
 118 {
 119         int umtx_op;
 120         void *umtx_uaddr = NULL, *umtx_uaddr2 = NULL;
 121         struct _umtx_time umtx_timeout = {
 122                 ._flags = UMTX_ABSTIME,
 123                 ._clockid = CLOCK_MONOTONIC,
 124         };
 125
 126         switch (op) {
 127         case FUTEX_WAIT:
 128                 /* On FreeBSD, a "u_int" is a 32-bit integer. */
 129                 umtx_op = UMTX_OP_WAIT_UINT;
 130                 if (timeout != NULL) {
 131                         umtx_timeout._timeout = *timeout;
 132                         umtx_uaddr = (void *) sizeof(umtx_timeout);
 133                         umtx_uaddr2 = (void *) &umtx_timeout;
 134                 }
 135                 break;
 136         case FUTEX_WAKE:
 137                 umtx_op = UMTX_OP_WAKE;
 138                 break;
 139         default:
 140                 errno = EINVAL;
 141                 return -1;
 142         }
 143
 144         return _umtx_op(uaddr, umtx_op, (uint32_t) val, umtx_uaddr,
 145                         umtx_uaddr2);
 146 }
 147
 148 static inline int lttng_ust_futex_noasync(int32_t *uaddr, int op, int32_t val,
 149                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
 150 {
 151         return lttng_ust_futex_async(uaddr, op, val, timeout, uaddr2, val3);
 152 }
 153
 154 #elif defined(__CYGWIN__)
 155
 156 /*
 157  * The futex_noasync compat code uses a weak symbol to share state across
 158  * different shared object which is not possible on Windows with the
 159  * Portable Executable format. Use the async compat code for both cases.
 160  */
 161 static inline int lttng_ust_futex_noasync(int32_t *uaddr, int op, int32_t val,
 162                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
 163 {
 164         return lttng_ust_compat_futex_async(uaddr, op, val, timeout, uaddr2, val3);
 165 }
 166
 167 static inline int lttng_ust_futex_async(int32_t *uaddr, int op, int32_t val,
 168                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
 169 {
 170         return lttng_ust_compat_futex_async(uaddr, op, val, timeout, uaddr2, val3);
 171 }
 172
 173 #else
 174
 175 static inline int lttng_ust_futex_noasync(int32_t *uaddr, int op, int32_t val,
 176                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
 177 {
 178         return lttng_ust_compat_futex_noasync(uaddr, op, val, timeout, uaddr2, val3);
 179 }
 180
 181 static inline int lttng_ust_futex_async(int32_t *uaddr, int op, int32_t val,
 182                 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
 183 {
 184         return lttng_ust_compat_futex_async(uaddr, op, val, timeout, uaddr2, val3);
 185 }
 186
 187 #endif
 188
 189 #ifdef __cplusplus
 190 }
 191 #endif
 192
 193 #endif /* _LTTNG_UST_FUTEX_H */