Back to index...

	/*
	* Copyright (c) 1999, 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. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* 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.
	*/

	package com.sun.tools.jdi;

	import com.sun.jdi.*;

	import java.lang.ref.WeakReference;
	import java.util.*;

	class VMState {
	private final VirtualMachineImpl vm;

	// Listeners
	private final List<WeakReference<VMListener>> listeners = new ArrayList<WeakReference<VMListener>>(); // synchronized (this)
	private boolean notifyingListeners = false; // synchronized (this)

	/*
	* Certain information can be cached only when the entire VM is
	* suspended and there are no pending resumes. The field below
	* is used to track whether there are pending resumes.
	*/
	private final Set<Integer> pendingResumeCommands = Collections.synchronizedSet(new HashSet<>());

	// This is cached only while the VM is suspended
	private static class Cache {
	List<ThreadGroupReference> groups = null; // cached Top Level ThreadGroups
	List<ThreadReference> threads = null; // cached Threads
	}

	private Cache cache = null; // synchronized (this)
	private static final Cache markerCache = new Cache();

	private void disableCache() {
	synchronized (this) {
	cache = null;
	}
	}

	private void enableCache() {
	synchronized (this) {
	cache = markerCache;
	}
	}

	private Cache getCache() {
	synchronized (this) {
	if (cache == markerCache) {
	cache = new Cache();
	}
	return cache;
	}
	}

	VMState(VirtualMachineImpl vm) {
	this.vm = vm;
	}

	/**
	* Is the VM currently suspended, for the purpose of caching?
	* Must be called synchronized on vm.state()
	*/
	boolean isSuspended() {
	return cache != null;
	}

	/*
	* A JDWP command has been completed (reply has been received).
	* Update data that tracks pending resume commands.
	*/
	void notifyCommandComplete(int id) {
	pendingResumeCommands.remove(id);
	}

	synchronized void freeze() {
	if (cache == null && (pendingResumeCommands.isEmpty())) {
	/*
	* No pending resumes to worry about. The VM is suspended
	* and additional state can be cached. Notify all
	* interested listeners.
	*/
	processVMAction(new VMAction(vm, VMAction.VM_SUSPENDED));
	enableCache();
	}
	}

	synchronized PacketStream thawCommand(CommandSender sender) {
	PacketStream stream = sender.send();
	pendingResumeCommands.add(stream.id());
	thaw();
	return stream;
	}

	/**
	* All threads are resuming
	*/
	void thaw() {
	thaw(null);
	}

	/**
	* Tell listeners to invalidate suspend-sensitive caches.
	* If resumingThread != null, then only that thread is being
	* resumed.
	*/
	synchronized void thaw(ThreadReference resumingThread) {
	if (cache != null) {
	if ((vm.traceFlags & VirtualMachine.TRACE_OBJREFS) != 0) {
	vm.printTrace("Clearing VM suspended cache");
	}
	disableCache();
	}
	processVMAction(new VMAction(vm, resumingThread, VMAction.VM_NOT_SUSPENDED));
	}

	private synchronized void processVMAction(VMAction action) {
	if (!notifyingListeners) {
	// Prevent recursion
	notifyingListeners = true;

	Iterator<WeakReference<VMListener>> iter = listeners.iterator();
	while (iter.hasNext()) {
	WeakReference<VMListener> ref = iter.next();
	VMListener listener = ref.get();
	if (listener != null) {
	boolean keep = true;
	switch (action.id()) {
	case VMAction.VM_SUSPENDED:
	keep = listener.vmSuspended(action);
	break;
	case VMAction.VM_NOT_SUSPENDED:
	keep = listener.vmNotSuspended(action);
	break;
	}
	if (!keep) {
	iter.remove();
	}
	} else {
	// Listener is unreachable; clean up
	iter.remove();
	}
	}

	notifyingListeners = false;
	}
	}

	synchronized void addListener(VMListener listener) {
	listeners.add(new WeakReference<VMListener>(listener));
	}

	synchronized boolean hasListener(VMListener listener) {
	Iterator<WeakReference<VMListener>> iter = listeners.iterator();
	while (iter.hasNext()) {
	WeakReference<VMListener> ref = iter.next();
	if (listener.equals(ref.get())) {
	return true;
	}
	}
	return false;
	}

	synchronized void removeListener(VMListener listener) {
	Iterator<WeakReference<VMListener>> iter = listeners.iterator();
	while (iter.hasNext()) {
	WeakReference<VMListener> ref = iter.next();
	if (listener.equals(ref.get())) {
	iter.remove();
	break;
	}
	}
	}

	List<ThreadReference> allThreads() {
	List<ThreadReference> threads = null;
	try {
	Cache local = getCache();

	if (local != null) {
	// may be stale when returned, but not provably so
	threads = local.threads;
	}
	if (threads == null) {
	threads = Arrays.asList((ThreadReference[])JDWP.VirtualMachine.AllThreads.
	process(vm).threads);
	if (local != null) {
	local.threads = threads;
	if ((vm.traceFlags & VirtualMachine.TRACE_OBJREFS) != 0) {
	vm.printTrace("Caching all threads (count = " +
	threads.size() + ") while VM suspended");
	}
	}
	}
	} catch (JDWPException exc) {
	throw exc.toJDIException();
	}
	return threads;
	}


	List<ThreadGroupReference> topLevelThreadGroups() {
	List<ThreadGroupReference> groups = null;
	try {
	Cache local = getCache();

	if (local != null) {
	groups = local.groups;
	}
	if (groups == null) {
	groups = Arrays.asList(
	(ThreadGroupReference[])JDWP.VirtualMachine.TopLevelThreadGroups.
	process(vm).groups);
	if (local != null) {
	local.groups = groups;
	if ((vm.traceFlags & VirtualMachine.TRACE_OBJREFS) != 0) {
	vm.printTrace(
	"Caching top level thread groups (count = " +
	groups.size() + ") while VM suspended");
	}
	}
	}
	} catch (JDWPException exc) {
	throw exc.toJDIException();
	}
	return groups;
	}

	}

Back to index...