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/*
* Copyright (c) 2015, 2020, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
#include "precompiled.hpp"
#include "gc/z/zAddress.inline.hpp"
#include "gc/z/zForwarding.inline.hpp"
#include "gc/z/zStat.hpp"
#include "gc/z/zUtils.inline.hpp"
#include "utilities/align.hpp"
//
// Reference count states:
//
// * If the reference count is zero, it will never change again.
//
// * If the reference count is positive, it can be both retained
// (increased) and released (decreased).
//
// * If the reference count is negative, is can only be released
// (increased). A negative reference count means that one or more
// threads are waiting for one or more other threads to release
// their references.
//
// The reference lock is used for waiting until the reference
// count has become zero (released) or negative one (claimed).
//
static const ZStatCriticalPhase ZCriticalPhaseRelocationStall("Relocation Stall");
bool ZForwarding::retain_page() {
for (;;) {
const int32_t ref_count = Atomic::load_acquire(&_ref_count);
if (ref_count == 0) {
// Released
return false;
}
if (ref_count < 0) {
// Claimed
const bool success = wait_page_released();
assert(success, "Should always succeed");
return false;
}
if (Atomic::cmpxchg(&_ref_count, ref_count, ref_count + 1) == ref_count) {
// Retained
return true;
}
}
}
ZPage* ZForwarding::claim_page() {
for (;;) {
const int32_t ref_count = Atomic::load(&_ref_count);
assert(ref_count > 0, "Invalid state");
// Invert reference count
if (Atomic::cmpxchg(&_ref_count, ref_count, -ref_count) != ref_count) {
continue;
}
// If the previous reference count was 1, then we just changed it to -1,
// and we have now claimed the page. Otherwise we wait until it is claimed.
if (ref_count != 1) {
ZLocker<ZConditionLock> locker(&_ref_lock);
while (Atomic::load_acquire(&_ref_count) != -1) {
_ref_lock.wait();
}
}
return _page;
}
}
void ZForwarding::release_page() {
for (;;) {
const int32_t ref_count = Atomic::load(&_ref_count);
assert(ref_count != 0, "Invalid state");
if (ref_count > 0) {
// Decrement reference count
if (Atomic::cmpxchg(&_ref_count, ref_count, ref_count - 1) != ref_count) {
continue;
}
// If the previous reference count was 1, then we just decremented
// it to 0 and we should signal that the page is now released.
if (ref_count == 1) {
// Notify released
ZLocker<ZConditionLock> locker(&_ref_lock);
_ref_lock.notify_all();
}
} else {
// Increment reference count
if (Atomic::cmpxchg(&_ref_count, ref_count, ref_count + 1) != ref_count) {
continue;
}
// If the previous reference count was -2 or -1, then we just incremented it
// to -1 or 0, and we should signal the that page is now claimed or released.
if (ref_count == -2 || ref_count == -1) {
// Notify claimed or released
ZLocker<ZConditionLock> locker(&_ref_lock);
_ref_lock.notify_all();
}
}
return;
}
}
bool ZForwarding::wait_page_released() const {
if (Atomic::load_acquire(&_ref_count) != 0) {
ZStatTimer timer(ZCriticalPhaseRelocationStall);
ZLocker<ZConditionLock> locker(&_ref_lock);
while (Atomic::load_acquire(&_ref_count) != 0) {
if (_ref_abort) {
return false;
}
_ref_lock.wait();
}
}
return true;
}
ZPage* ZForwarding::detach_page() {
// Wait until released
if (Atomic::load_acquire(&_ref_count) != 0) {
ZLocker<ZConditionLock> locker(&_ref_lock);
while (Atomic::load_acquire(&_ref_count) != 0) {
_ref_lock.wait();
}
}
// Detach and return page
ZPage* const page = _page;
_page = NULL;
return page;
}
void ZForwarding::abort_page() {
ZLocker<ZConditionLock> locker(&_ref_lock);
assert(Atomic::load(&_ref_count) > 0, "Invalid state");
assert(!_ref_abort, "Invalid state");
_ref_abort = true;
_ref_lock.notify_all();
}
void ZForwarding::verify() const {
guarantee(_ref_count != 0, "Invalid reference count");
guarantee(_page != NULL, "Invalid page");
uint32_t live_objects = 0;
size_t live_bytes = 0;
for (ZForwardingCursor i = 0; i < _entries.length(); i++) {
const ZForwardingEntry entry = at(&i);
if (!entry.populated()) {
// Skip empty entries
continue;
}
// Check from index
guarantee(entry.from_index() < _page->object_max_count(), "Invalid from index");
// Check for duplicates
for (ZForwardingCursor j = i + 1; j < _entries.length(); j++) {
const ZForwardingEntry other = at(&j);
if (!other.populated()) {
// Skip empty entries
continue;
}
guarantee(entry.from_index() != other.from_index(), "Duplicate from");
guarantee(entry.to_offset() != other.to_offset(), "Duplicate to");
}
const uintptr_t to_addr = ZAddress::good(entry.to_offset());
const size_t size = ZUtils::object_size(to_addr);
const size_t aligned_size = align_up(size, _page->object_alignment());
live_bytes += aligned_size;
live_objects++;
}
// Verify number of live objects and bytes
_page->verify_live(live_objects, live_bytes);
}
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