1 /*
   2  * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled/precompiled.hpp"
  26 #include "runtime/orderAccess.hpp"
  27 #include "runtime/os.hpp"
  28 #include "waitBarrier_linux.hpp"
  29 #include <sys/syscall.h>
  30 #include <linux/futex.h>
  31 
  32 #define check_with_errno(check_type, cond, msg)                             \
  33   do {                                                                      \
  34     int err = errno;                                                        \
  35     check_type(cond, "%s; error='%s' (errno=%s)", msg, os::strerror(err),   \
  36                os::errno_name(err));                                        \
  37 } while (false)
  38 
  39 #define guarantee_with_errno(cond, msg) check_with_errno(guarantee, cond, msg)
  40 
  41 static int futex(volatile int *addr, int futex_op, int op_arg)
  42 {
  43   return syscall(SYS_futex, addr, futex_op, op_arg, NULL, NULL, 0);
  44 }
  45 
  46 void LinuxWaitBarrier::arm(int barrier_tag) {
  47   assert(_futex_barrier == 0, "Already armed");
  48   _futex_barrier = barrier_tag;
  49   OrderAccess::fence();
  50 }
  51 
  52 void LinuxWaitBarrier::wake() {
  53   assert(_futex_barrier != 0, "Not armed");
  54   _futex_barrier = 0;
  55   int s = futex(&_futex_barrier,
  56                 FUTEX_WAKE_PRIVATE,
  57                 INT_MAX /* wake a max of this many threads */);
  58   guarantee_with_errno(s > -1, "futex FUTEX_WAKE");
  59 }
  60 
  61 void LinuxWaitBarrier::wait(int barrier_tag) {
  62   assert(barrier_tag != 0, "Trying to wait on disarmed value");
  63   if (barrier_tag == 0 ||
  64       barrier_tag != _futex_barrier) {
  65     OrderAccess::fence();
  66     return;
  67   }
  68   do {
  69     int s = futex(&_futex_barrier,
  70                   FUTEX_WAIT_PRIVATE,
  71                   barrier_tag /* should be this tag */);
  72     guarantee_with_errno((s == 0) ||
  73                          (s == -1 && errno == EAGAIN) ||
  74                          (s == -1 && errno == EINTR),
  75                          "futex FUTEX_WAIT");
  76     // Return value 0: woken up, but re-check in case of spurious wakeup
  77     // Error EINTR: woken by signal, so re-check and re-wait if necessary.
  78     // Error EAGAIN: we are already disarmed and so will pass the check
  79   } while (barrier_tag == _futex_barrier);
  80 }