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	/*
	* Copyright (c) 2003, 2014, 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 sun.security.pkcs11;

	import java.util.*;

	import java.security.ProviderException;

	import sun.security.util.Debug;

	import sun.security.pkcs11.wrapper.*;
	import static sun.security.pkcs11.wrapper.PKCS11Constants.*;

	import java.util.concurrent.ConcurrentLinkedDeque;
	import java.util.concurrent.atomic.AtomicInteger;

	/**
	* Session manager. There is one session manager object per PKCS#11
	* provider. It allows code to checkout a session, release it
	* back to the pool, or force it to be closed.
	*
	* The session manager pools sessions to minimize the number of
	* C_OpenSession() and C_CloseSession() that have to be made. It
	* maintains two pools: one for "object" sessions and one for
	* "operation" sessions.
	*
	* The reason for this separation is how PKCS#11 deals with session objects.
	* It defines that when a session is closed, all objects created within
	* that session are destroyed. In other words, we may never close a session
	* while a Key created it in is still in use. We would like to keep the
	* number of such sessions low. Note that we occasionally want to explicitly
	* close a session, see P11Signature.
	*
	* NOTE that sessions obtained from this class SHOULD be returned using
	* either releaseSession() or closeSession() using a finally block when
	* not needed anymore. Otherwise, they will be left for cleanup via the
	* PhantomReference mechanism when GC kicks in, but it's best not to rely
	* on that since GC may not run timely enough since the native PKCS11 library
	* is also consuming memory.
	*
	* Note that sessions are automatically closed when they are not used for a
	* period of time, see Session.
	*
	* @author Andreas Sterbenz
	* @since 1.5
	*/
	final class SessionManager {

	private final static int DEFAULT_MAX_SESSIONS = 32;

	private final static Debug debug = Debug.getInstance("pkcs11");

	// token instance
	private final Token token;

	// maximum number of sessions to open with this token
	private final int maxSessions;

	// total number of active sessions
	private AtomicInteger activeSessions = new AtomicInteger();

	// pool of available object sessions
	private final Pool objSessions;

	// pool of available operation sessions
	private final Pool opSessions;

	// maximum number of active sessions during this invocation, for debugging
	private int maxActiveSessions;
	private Object maxActiveSessionsLock;

	// flags to use in the C_OpenSession() call
	private final long openSessionFlags;

	SessionManager(Token token) {
	long n;
	if (token.isWriteProtected()) {
	openSessionFlags = CKF_SERIAL_SESSION;
	n = token.tokenInfo.ulMaxSessionCount;
	} else {
	openSessionFlags = CKF_SERIAL_SESSION \| CKF_RW_SESSION;
	n = token.tokenInfo.ulMaxRwSessionCount;
	}
	if (n == CK_EFFECTIVELY_INFINITE) {
	n = Integer.MAX_VALUE;
	} else if ((n == CK_UNAVAILABLE_INFORMATION) \|\| (n < 0)) {
	// choose an arbitrary concrete value
	n = DEFAULT_MAX_SESSIONS;
	}
	maxSessions = (int)Math.min(n, Integer.MAX_VALUE);
	this.token = token;
	this.objSessions = new Pool(this);
	this.opSessions = new Pool(this);
	if (debug != null) {
	maxActiveSessionsLock = new Object();
	}
	}

	// returns whether only a fairly low number of sessions are
	// supported by this token.
	boolean lowMaxSessions() {
	return (maxSessions <= DEFAULT_MAX_SESSIONS);
	}

	Session getObjSession() throws PKCS11Exception {
	Session session = objSessions.poll();
	if (session != null) {
	return ensureValid(session);
	}
	session = opSessions.poll();
	if (session != null) {
	return ensureValid(session);
	}
	session = openSession();
	return ensureValid(session);
	}

	Session getOpSession() throws PKCS11Exception {
	Session session = opSessions.poll();
	if (session != null) {
	return ensureValid(session);
	}
	// create a new session rather than re-using an obj session
	// that avoids potential expensive cancels() for Signatures & RSACipher
	if (maxSessions == Integer.MAX_VALUE \|\|
	activeSessions.get() < maxSessions) {
	session = openSession();
	return ensureValid(session);
	}
	session = objSessions.poll();
	if (session != null) {
	return ensureValid(session);
	}
	throw new ProviderException("Could not obtain session");
	}

	private Session ensureValid(Session session) {
	session.id();
	return session;
	}

	Session killSession(Session session) {
	if ((session == null) \|\| (token.isValid() == false)) {
	return null;
	}
	if (debug != null) {
	String location = new Exception().getStackTrace()[2].toString();
	System.out.println("Killing session (" + location + ") active: "
	+ activeSessions.get());
	}
	closeSession(session);
	return null;
	}

	Session releaseSession(Session session) {
	if ((session == null) \|\| (token.isValid() == false)) {
	return null;
	}

	if (session.hasObjects()) {
	objSessions.release(session);
	} else {
	opSessions.release(session);
	}
	return null;
	}

	void demoteObjSession(Session session) {
	if (token.isValid() == false) {
	return;
	}
	if (debug != null) {
	System.out.println("Demoting session, active: " +
	activeSessions.get());
	}
	boolean present = objSessions.remove(session);
	if (present == false) {
	// session is currently in use
	// will be added to correct pool on release, nothing to do now
	return;
	}
	opSessions.release(session);
	}

	private Session openSession() throws PKCS11Exception {
	if ((maxSessions != Integer.MAX_VALUE) &&
	(activeSessions.get() >= maxSessions)) {
	throw new ProviderException("No more sessions available");
	}

	long id = token.p11.C_OpenSession
	(token.provider.slotID, openSessionFlags, null, null);
	Session session = new Session(token, id);
	activeSessions.incrementAndGet();
	if (debug != null) {
	synchronized(maxActiveSessionsLock) {
	if (activeSessions.get() > maxActiveSessions) {
	maxActiveSessions = activeSessions.get();
	if (maxActiveSessions % 10 == 0) {
	System.out.println("Open sessions: " + maxActiveSessions);
	}
	}
	}
	}
	return session;
	}

	private void closeSession(Session session) {
	session.close();
	activeSessions.decrementAndGet();
	}

	public static final class Pool {

	private final SessionManager mgr;

	private final ConcurrentLinkedDeque<Session> pool;

	Pool(SessionManager mgr) {
	this.mgr = mgr;
	pool = new ConcurrentLinkedDeque<Session>();
	}

	boolean remove(Session session) {
	return pool.remove(session);
	}

	Session poll() {
	return pool.pollLast();
	}

	void release(Session session) {
	pool.offer(session);
	if (session.hasObjects()) {
	return;
	}

	int n = pool.size();
	if (n < 5) {
	return;
	}

	Session oldestSession;
	long time = System.currentTimeMillis();
	int i = 0;
	// Check if the session head is too old and continue through queue
	// until only one is left.
	do {
	oldestSession = pool.peek();
	if (oldestSession == null \|\| oldestSession.isLive(time) \|\|
	!pool.remove(oldestSession)) {
	break;
	}

	i++;
	mgr.closeSession(oldestSession);
	} while ((n - i) > 1);

	if (debug != null) {
	System.out.println("Closing " + i + " idle sessions, active: "
	+ mgr.activeSessions);
	}
	}

	}

	}

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