95 lines
3.2 KiB
C++
95 lines
3.2 KiB
C++
/*
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* Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*
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*/
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#include "precompiled.hpp"
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#include "runtime/atomic.hpp"
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#include "runtime/orderAccess.hpp"
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#include "runtime/os.hpp"
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#include "utilities/waitBarrier_generic.hpp"
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#include "utilities/spinYield.hpp"
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void GenericWaitBarrier::arm(int barrier_tag) {
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assert(_barrier_tag == 0, "Already armed");
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assert(_waiters == 0, "We left a thread hanging");
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_barrier_tag = barrier_tag;
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_waiters = 0;
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OrderAccess::fence();
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}
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int GenericWaitBarrier::wake_if_needed() {
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assert(_barrier_tag == 0, "Not disarmed");
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int w = _waiters;
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if (w == 0) {
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// Load of _barrier_threads in caller must not pass the load of _waiters.
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OrderAccess::loadload();
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return 0;
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}
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assert(w > 0, "Bad counting");
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// We need an exact count which never goes below zero,
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// otherwise the semaphore may be signalled too many times.
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if (Atomic::cmpxchg(w - 1, &_waiters, w) == w) {
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_sem_barrier.signal();
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return w - 1;
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}
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return w;
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}
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void GenericWaitBarrier::disarm() {
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assert(_barrier_tag != 0, "Not armed");
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_barrier_tag = 0;
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// Loads of _barrier_threads/_waiters must not float above disarm store and
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// disarm store must not sink below.
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OrderAccess::fence();
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int left;
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SpinYield sp;
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do {
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left = GenericWaitBarrier::wake_if_needed();
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if (left == 0 && _barrier_threads > 0) {
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// There is no thread to wake but we still have barrier threads.
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sp.wait();
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}
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// We must loop here until there are no waiters or potential waiters.
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} while (left > 0 || _barrier_threads > 0);
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// API specifies disarm() must provide a trailing fence.
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OrderAccess::fence();
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}
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void GenericWaitBarrier::wait(int barrier_tag) {
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assert(barrier_tag != 0, "Trying to wait on disarmed value");
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if (barrier_tag != _barrier_tag) {
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// API specifies wait() must provide a trailing fence.
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OrderAccess::fence();
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return;
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}
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Atomic::add(1, &_barrier_threads);
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if (barrier_tag != 0 && barrier_tag == _barrier_tag) {
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Atomic::add(1, &_waiters);
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_sem_barrier.wait();
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// We help out with posting, but we need to do so before we decrement the
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// _barrier_threads otherwise we might wake threads up in next wait.
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GenericWaitBarrier::wake_if_needed();
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}
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Atomic::add(-1, &_barrier_threads);
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}
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