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 }