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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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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.LinkedBlockingQueue;
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/**
 * 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, true);
        this.opSessions = new Pool(this, false);
        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 AbstractQueue<Session> pool;
        private final int SESSION_MAX = 5;

        // Object session pools can contain unlimited sessions.
        // Operation session pools are limited and enforced by the queue.
        Pool(SessionManager mgr, boolean obj) {
            this.mgr = mgr;
            if (obj) {
                pool = new LinkedBlockingQueue<Session>();
            } else {
                pool = new LinkedBlockingQueue<Session>(SESSION_MAX);
            }
        }

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

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

        void release(Session session) {
            // Object session pools never return false, only Operation ones
            if (!pool.offer(session)) {
                mgr.closeSession(session);
                free();
            }
        }

        // Free any old operation session if this queue is full
        void free() {
            int n = SESSION_MAX;
            int i = 0;
            Session oldestSession;
            long time = System.currentTimeMillis();
            // Check if the session head is too old and continue through pool
            // 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);
            }
        }

    }

}