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