src/share/classes/java/security/AccessControlContext.java - toolchain/jdk/jdk9_jdk - Git at Google

 /*
  * Copyright (c) 1997, 2008, 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 java.security;

 import java.util.ArrayList;
 import java.util.List;
 import sun.security.util.Debug;
 import sun.security.util.SecurityConstants;

 /**
  * An AccessControlContext is used to make system resource access decisions
  * based on the context it encapsulates.
  *
  * <p>More specifically, it encapsulates a context and
  * has a single method, <code>checkPermission</code>,
  * that is equivalent to the <code>checkPermission</code> method
  * in the AccessController class, with one difference: The AccessControlContext
  * <code>checkPermission</code> method makes access decisions based on the
  * context it encapsulates,
  * rather than that of the current execution thread.
  *
  * <p>Thus, the purpose of AccessControlContext is for those situations where
  * a security check that should be made within a given context
  * actually needs to be done from within a
  * <i>different</i> context (for example, from within a worker thread).
  *
  * <p> An AccessControlContext is created by calling the
  * <code>AccessController.getContext</code> method.
  * The <code>getContext</code> method takes a "snapshot"
  * of the current calling context, and places
  * it in an AccessControlContext object, which it returns. A sample call is
  * the following:
  *
  * <pre>
  *   AccessControlContext acc = AccessController.getContext()
  * </pre>
  *
  * <p>
  * Code within a different context can subsequently call the
  * <code>checkPermission</code> method on the
  * previously-saved AccessControlContext object. A sample call is the
  * following:
  *
  * <pre>
  *   acc.checkPermission(permission)
  * </pre>
  *
  * @see AccessController
  *
  * @author Roland Schemers
  */

 public final class AccessControlContext {

     private ProtectionDomain context[];
     private boolean isPrivileged;

     // Note: This field is directly used by the virtual machine
     // native codes. Don't touch it.
     private AccessControlContext privilegedContext;

     private DomainCombiner combiner = null;

     private static boolean debugInit = false;
     private static Debug debug = null;

     static Debug getDebug()
     {
         if (debugInit)
             return debug;
         else {
             if (Policy.isSet()) {
                 debug = Debug.getInstance("access");
                 debugInit = true;
             }
             return debug;
         }
     }

     /**
      * Create an AccessControlContext with the given array of ProtectionDomains.
      * Context must not be null. Duplicate domains will be removed from the
      * context.
      *
      * @param context the ProtectionDomains associated with this context.
      * The non-duplicate domains are copied from the array. Subsequent
      * changes to the array will not affect this AccessControlContext.
      * @throws NullPointerException if <code>context</code> is <code>null</code>
      */
     public AccessControlContext(ProtectionDomain context[])
     {
         if (context.length == 0) {
             this.context = null;
         } else if (context.length == 1) {
             if (context[0] != null) {
                 this.context = context.clone();
             } else {
                 this.context = null;
             }
         } else {
             List<ProtectionDomain> v = new ArrayList<ProtectionDomain>(context.length);
             for (int i =0; i< context.length; i++) {
                 if ((context[i] != null) &&  (!v.contains(context[i])))
                     v.add(context[i]);
             }
             if (!v.isEmpty()) {
                 this.context = new ProtectionDomain[v.size()];
                 this.context = v.toArray(this.context);
             }
         }
     }

     /**
      * Create a new <code>AccessControlContext</code> with the given
      * <code>AccessControlContext</code> and <code>DomainCombiner</code>.
      * This constructor associates the provided
      * <code>DomainCombiner</code> with the provided
      * <code>AccessControlContext</code>.
      *
      * <p>
      *
      * @param acc the <code>AccessControlContext</code> associated
      *          with the provided <code>DomainCombiner</code>.
      *
      * @param combiner the <code>DomainCombiner</code> to be associated
      *          with the provided <code>AccessControlContext</code>.
      *
      * @exception NullPointerException if the provided
      *          <code>context</code> is <code>null</code>.
      *
      * @exception SecurityException if a security manager is installed and the
      *          caller does not have the "createAccessControlContext"
      *          {@link SecurityPermission}
      * @since 1.3
      */
     public AccessControlContext(AccessControlContext acc,
                                 DomainCombiner combiner) {

         SecurityManager sm = System.getSecurityManager();
         if (sm != null) {
             sm.checkPermission(SecurityConstants.CREATE_ACC_PERMISSION);
         }

         this.context = acc.context;

         // we do not need to run the combine method on the
         // provided ACC.  it was already "combined" when the
         // context was originally retrieved.
         //
         // at this point in time, we simply throw away the old
         // combiner and use the newly provided one.
         this.combiner = combiner;
     }

     /**
      * package private for AccessController
      */
     AccessControlContext(ProtectionDomain context[], DomainCombiner combiner) {
         if (context != null) {
             this.context = context.clone();
         }
         this.combiner = combiner;
     }

     /**
      * package private constructor for AccessController.getContext()
      */

     AccessControlContext(ProtectionDomain context[],
                                  boolean isPrivileged)
     {
         this.context = context;
         this.isPrivileged = isPrivileged;
     }

     /**
      * Returns true if this context is privileged.
      */
     boolean isPrivileged()
     {
         return isPrivileged;
     }

     /**
      * get the assigned combiner from the privileged or inherited context
      */
     DomainCombiner getAssignedCombiner() {
         AccessControlContext acc;
         if (isPrivileged) {
             acc = privilegedContext;
         } else {
             acc = AccessController.getInheritedAccessControlContext();
         }
         if (acc != null) {
             return acc.combiner;
         }
         return null;
     }

     /**
      * Get the <code>DomainCombiner</code> associated with this
      * <code>AccessControlContext</code>.
      *
      * <p>
      *
      * @return the <code>DomainCombiner</code> associated with this
      *          <code>AccessControlContext</code>, or <code>null</code>
      *          if there is none.
      *
      * @exception SecurityException if a security manager is installed and
      *          the caller does not have the "getDomainCombiner"
      *          {@link SecurityPermission}
      * @since 1.3
      */
     public DomainCombiner getDomainCombiner() {

         SecurityManager sm = System.getSecurityManager();
         if (sm != null) {
             sm.checkPermission(SecurityConstants.GET_COMBINER_PERMISSION);
         }
         return combiner;
     }

     /**
      * Determines whether the access request indicated by the
      * specified permission should be allowed or denied, based on
      * the security policy currently in effect, and the context in
      * this object. The request is allowed only if every ProtectionDomain
      * in the context implies the permission. Otherwise the request is
      * denied.
      *
      * <p>
      * This method quietly returns if the access request
      * is permitted, or throws a suitable AccessControlException otherwise.
      *
      * @param perm the requested permission.
      *
      * @exception AccessControlException if the specified permission
      * is not permitted, based on the current security policy and the
      * context encapsulated by this object.
      * @exception NullPointerException if the permission to check for is null.
      */
     public void checkPermission(Permission perm)
         throws AccessControlException
     {
         boolean dumpDebug = false;

         if (perm == null) {
             throw new NullPointerException("permission can't be null");
         }
         if (getDebug() != null) {
             // If "codebase" is not specified, we dump the info by default.
             dumpDebug = !Debug.isOn("codebase=");
             if (!dumpDebug) {
                 // If "codebase" is specified, only dump if the specified code
                 // value is in the stack.
                 for (int i = 0; context != null && i < context.length; i++) {
                     if (context[i].getCodeSource() != null &&
                         context[i].getCodeSource().getLocation() != null &&
                         Debug.isOn("codebase=" + context[i].getCodeSource().getLocation().toString())) {
                         dumpDebug = true;
                         break;
                     }
                 }
             }

             dumpDebug &= !Debug.isOn("permission=") ||
                 Debug.isOn("permission=" + perm.getClass().getCanonicalName());

             if (dumpDebug && Debug.isOn("stack")) {
                 Thread.currentThread().dumpStack();
             }

             if (dumpDebug && Debug.isOn("domain")) {
                 if (context == null) {
                     debug.println("domain (context is null)");
                 } else {
                     for (int i=0; i< context.length; i++) {
                         debug.println("domain "+i+" "+context[i]);
                     }
                 }
             }
         }

         /*
          * iterate through the ProtectionDomains in the context.
          * Stop at the first one that doesn't allow the
          * requested permission (throwing an exception).
          *
          */

         /* if ctxt is null, all we had on the stack were system domains,
            or the first domain was a Privileged system domain. This
            is to make the common case for system code very fast */

         if (context == null)
             return;

         for (int i=0; i< context.length; i++) {
             if (context[i] != null &&  !context[i].implies(perm)) {
                 if (dumpDebug) {
                     debug.println("access denied " + perm);
                 }

                 if (Debug.isOn("failure") && debug != null) {
                     // Want to make sure this is always displayed for failure,
                     // but do not want to display again if already displayed
                     // above.
                     if (!dumpDebug) {
                         debug.println("access denied " + perm);
                     }
                     Thread.currentThread().dumpStack();
                     final ProtectionDomain pd = context[i];
                     final Debug db = debug;
                     AccessController.doPrivileged (new PrivilegedAction<Void>() {
                         public Void run() {
                             db.println("domain that failed "+pd);
                             return null;
                         }
                     });
                 }
                 throw new AccessControlException("access denied "+perm, perm);
             }
         }

         // allow if all of them allowed access
         if (dumpDebug) {
             debug.println("access allowed "+perm);
         }

         return;
     }

     /**
      * Take the stack-based context (this) and combine it with the
      * privileged or inherited context, if need be.
      */
     AccessControlContext optimize() {
         // the assigned (privileged or inherited) context
         AccessControlContext acc;
         if (isPrivileged) {
             acc = privilegedContext;
         } else {
             acc = AccessController.getInheritedAccessControlContext();
         }

         // this.context could be null if only system code is on the stack;
         // in that case, ignore the stack context
         boolean skipStack = (context == null);

         // acc.context could be null if only system code was involved;
         // in that case, ignore the assigned context
         boolean skipAssigned = (acc == null || acc.context == null);

         if (acc != null && acc.combiner != null) {
             // let the assigned acc's combiner do its thing
             return goCombiner(context, acc);
         }

         // optimization: if neither have contexts; return acc if possible
         // rather than this, because acc might have a combiner
         if (skipAssigned && skipStack) {
             return this;
         }

         // optimization: if there is no stack context; there is no reason
         // to compress the assigned context, it already is compressed
         if (skipStack) {
             return acc;
         }

         int slen = context.length;

         // optimization: if there is no assigned context and the stack length
         // is less then or equal to two; there is no reason to compress the
         // stack context, it already is
         if (skipAssigned && slen <= 2) {
             return this;
         }

         // optimization: if there is a single stack domain and that domain
         // is already in the assigned context; no need to combine
         if ((slen == 1) && (context[0] == acc.context[0])) {
             return acc;
         }

         int n = (skipAssigned) ? 0 : acc.context.length;

         // now we combine both of them, and create a new context
         ProtectionDomain pd[] = new ProtectionDomain[slen + n];

         // first copy in the assigned context domains, no need to compress
         if (!skipAssigned) {
             System.arraycopy(acc.context, 0, pd, 0, n);
         }

         // now add the stack context domains, discarding nulls and duplicates
     outer:
         for (int i = 0; i < context.length; i++) {
             ProtectionDomain sd = context[i];
             if (sd != null) {
                 for (int j = 0; j < n; j++) {
                     if (sd == pd[j]) {
                         continue outer;
                     }
                 }
                 pd[n++] = sd;
             }
         }

         // if length isn't equal, we need to shorten the array
         if (n != pd.length) {
             // optimization: if we didn't really combine anything
             if (!skipAssigned && n == acc.context.length) {
                 return acc;
             } else if (skipAssigned && n == slen) {
                 return this;
             }
             ProtectionDomain tmp[] = new ProtectionDomain[n];
             System.arraycopy(pd, 0, tmp, 0, n);
             pd = tmp;
         }

         //      return new AccessControlContext(pd, false);

         // Reuse existing ACC

         this.context = pd;
         this.combiner = null;
         this.isPrivileged = false;

         return this;
     }

     private AccessControlContext goCombiner(ProtectionDomain[] current,
                                         AccessControlContext assigned) {

         // the assigned ACC's combiner is not null --
         // let the combiner do its thing

         // XXX we could add optimizations to 'current' here ...

         if (getDebug() != null) {
             debug.println("AccessControlContext invoking the Combiner");
         }

         // No need to clone current and assigned.context
         // combine() will not update them
         ProtectionDomain[] combinedPds = assigned.combiner.combine(
             current, assigned.context);

         // return new AccessControlContext(combinedPds, assigned.combiner);

         // Reuse existing ACC
         this.context = combinedPds;
         this.combiner = assigned.combiner;
         this.isPrivileged = false;

         return this;
     }

     /**
      * Checks two AccessControlContext objects for equality.
      * Checks that <i>obj</i> is
      * an AccessControlContext and has the same set of ProtectionDomains
      * as this context.
      * <P>
      * @param obj the object we are testing for equality with this object.
      * @return true if <i>obj</i> is an AccessControlContext, and has the
      * same set of ProtectionDomains as this context, false otherwise.
      */
     public boolean equals(Object obj) {
         if (obj == this)
             return true;

         if (! (obj instanceof AccessControlContext))
             return false;

         AccessControlContext that = (AccessControlContext) obj;


         if (context == null) {
             return (that.context == null);
         }

         if (that.context == null)
             return false;

         if (!(this.containsAllPDs(that) && that.containsAllPDs(this)))
             return false;

         if (this.combiner == null)
             return (that.combiner == null);

         if (that.combiner == null)
             return false;

         if (!this.combiner.equals(that.combiner))
             return false;

         return true;
     }

     private boolean containsAllPDs(AccessControlContext that) {
         boolean match = false;
         //
         // ProtectionDomains within an ACC currently cannot be null
         // and this is enforced by the constructor and the various
         // optimize methods. However, historically this logic made attempts
         // to support the notion of a null PD and therefore this logic continues
         // to support that notion.
         ProtectionDomain thisPd;
         for (int i = 0; i < context.length; i++) {
             match = false;
             if ((thisPd = context[i]) == null) {
                 for (int j = 0; (j < that.context.length) && !match; j++) {
                     match = (that.context[j] == null);
                 }
             } else {
                 Class thisPdClass = thisPd.getClass();
                 ProtectionDomain thatPd;
                 for (int j = 0; (j < that.context.length) && !match; j++) {
                     thatPd = that.context[j];

                     // Class check required to avoid PD exposure (4285406)
                     match = (thatPd != null &&
                         thisPdClass == thatPd.getClass() && thisPd.equals(thatPd));
                 }
             }
             if (!match) return false;
         }
         return match;
     }
     /**
      * Returns the hash code value for this context. The hash code
      * is computed by exclusive or-ing the hash code of all the protection
      * domains in the context together.
      *
      * @return a hash code value for this context.
      */

     public int hashCode() {
         int hashCode = 0;

         if (context == null)
             return hashCode;

         for (int i =0; i < context.length; i++) {
             if (context[i] != null)
                 hashCode ^= context[i].hashCode();
         }
         return hashCode;
     }
 }
	/*
	* Copyright (c) 1997, 2008, 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 java.security;

	import java.util.ArrayList;
	import java.util.List;
	import sun.security.util.Debug;
	import sun.security.util.SecurityConstants;

	/**
	* An AccessControlContext is used to make system resource access decisions
	* based on the context it encapsulates.
	*
	* <p>More specifically, it encapsulates a context and
	* has a single method, <code>checkPermission</code>,
	* that is equivalent to the <code>checkPermission</code> method
	* in the AccessController class, with one difference: The AccessControlContext
	* <code>checkPermission</code> method makes access decisions based on the
	* context it encapsulates,
	* rather than that of the current execution thread.
	*
	* <p>Thus, the purpose of AccessControlContext is for those situations where
	* a security check that should be made within a given context
	* actually needs to be done from within a
	* <i>different</i> context (for example, from within a worker thread).
	*
	* <p> An AccessControlContext is created by calling the
	* <code>AccessController.getContext</code> method.
	* The <code>getContext</code> method takes a "snapshot"
	* of the current calling context, and places
	* it in an AccessControlContext object, which it returns. A sample call is
	* the following:
	*
	* <pre>
	* AccessControlContext acc = AccessController.getContext()
	* </pre>
	*
	* <p>
	* Code within a different context can subsequently call the
	* <code>checkPermission</code> method on the
	* previously-saved AccessControlContext object. A sample call is the
	* following:
	*
	* <pre>
	* acc.checkPermission(permission)
	* </pre>
	*
	* @see AccessController
	*
	* @author Roland Schemers
	*/

	public final class AccessControlContext {

	private ProtectionDomain context[];
	private boolean isPrivileged;

	// Note: This field is directly used by the virtual machine
	// native codes. Don't touch it.
	private AccessControlContext privilegedContext;

	private DomainCombiner combiner = null;

	private static boolean debugInit = false;
	private static Debug debug = null;

	static Debug getDebug()
	{
	if (debugInit)
	return debug;
	else {
	if (Policy.isSet()) {
	debug = Debug.getInstance("access");
	debugInit = true;
	}
	return debug;
	}
	}

	/**
	* Create an AccessControlContext with the given array of ProtectionDomains.
	* Context must not be null. Duplicate domains will be removed from the
	* context.
	*
	* @param context the ProtectionDomains associated with this context.
	* The non-duplicate domains are copied from the array. Subsequent
	* changes to the array will not affect this AccessControlContext.
	* @throws NullPointerException if <code>context</code> is <code>null</code>
	*/
	public AccessControlContext(ProtectionDomain context[])
	{
	if (context.length == 0) {
	this.context = null;
	} else if (context.length == 1) {
	if (context[0] != null) {
	this.context = context.clone();
	} else {
	this.context = null;
	}
	} else {
	List<ProtectionDomain> v = new ArrayList<ProtectionDomain>(context.length);
	for (int i =0; i< context.length; i++) {
	if ((context[i] != null) && (!v.contains(context[i])))
	v.add(context[i]);
	}
	if (!v.isEmpty()) {
	this.context = new ProtectionDomain[v.size()];
	this.context = v.toArray(this.context);
	}
	}
	}

	/**
	* Create a new <code>AccessControlContext</code> with the given
	* <code>AccessControlContext</code> and <code>DomainCombiner</code>.
	* This constructor associates the provided
	* <code>DomainCombiner</code> with the provided
	* <code>AccessControlContext</code>.
	*
	* <p>
	*
	* @param acc the <code>AccessControlContext</code> associated
	* with the provided <code>DomainCombiner</code>.
	*
	* @param combiner the <code>DomainCombiner</code> to be associated
	* with the provided <code>AccessControlContext</code>.
	*
	* @exception NullPointerException if the provided
	* <code>context</code> is <code>null</code>.
	*
	* @exception SecurityException if a security manager is installed and the
	* caller does not have the "createAccessControlContext"
	* {@link SecurityPermission}
	* @since 1.3
	*/
	public AccessControlContext(AccessControlContext acc,
	DomainCombiner combiner) {

	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	sm.checkPermission(SecurityConstants.CREATE_ACC_PERMISSION);
	}

	this.context = acc.context;

	// we do not need to run the combine method on the
	// provided ACC. it was already "combined" when the
	// context was originally retrieved.
	//
	// at this point in time, we simply throw away the old
	// combiner and use the newly provided one.
	this.combiner = combiner;
	}

	/**
	* package private for AccessController
	*/
	AccessControlContext(ProtectionDomain context[], DomainCombiner combiner) {
	if (context != null) {
	this.context = context.clone();
	}
	this.combiner = combiner;
	}

	/**
	* package private constructor for AccessController.getContext()
	*/

	AccessControlContext(ProtectionDomain context[],
	boolean isPrivileged)
	{
	this.context = context;
	this.isPrivileged = isPrivileged;
	}

	/**
	* Returns true if this context is privileged.
	*/
	boolean isPrivileged()
	{
	return isPrivileged;
	}

	/**
	* get the assigned combiner from the privileged or inherited context
	*/
	DomainCombiner getAssignedCombiner() {
	AccessControlContext acc;
	if (isPrivileged) {
	acc = privilegedContext;
	} else {
	acc = AccessController.getInheritedAccessControlContext();
	}
	if (acc != null) {
	return acc.combiner;
	}
	return null;
	}

	/**
	* Get the <code>DomainCombiner</code> associated with this
	* <code>AccessControlContext</code>.
	*
	* <p>
	*
	* @return the <code>DomainCombiner</code> associated with this
	* <code>AccessControlContext</code>, or <code>null</code>
	* if there is none.
	*
	* @exception SecurityException if a security manager is installed and
	* the caller does not have the "getDomainCombiner"
	* {@link SecurityPermission}
	* @since 1.3
	*/
	public DomainCombiner getDomainCombiner() {

	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	sm.checkPermission(SecurityConstants.GET_COMBINER_PERMISSION);
	}
	return combiner;
	}

	/**
	* Determines whether the access request indicated by the
	* specified permission should be allowed or denied, based on
	* the security policy currently in effect, and the context in
	* this object. The request is allowed only if every ProtectionDomain
	* in the context implies the permission. Otherwise the request is
	* denied.
	*
	* <p>
	* This method quietly returns if the access request
	* is permitted, or throws a suitable AccessControlException otherwise.
	*
	* @param perm the requested permission.
	*
	* @exception AccessControlException if the specified permission
	* is not permitted, based on the current security policy and the
	* context encapsulated by this object.
	* @exception NullPointerException if the permission to check for is null.
	*/
	public void checkPermission(Permission perm)
	throws AccessControlException
	{
	boolean dumpDebug = false;

	if (perm == null) {
	throw new NullPointerException("permission can't be null");
	}
	if (getDebug() != null) {
	// If "codebase" is not specified, we dump the info by default.
	dumpDebug = !Debug.isOn("codebase=");
	if (!dumpDebug) {
	// If "codebase" is specified, only dump if the specified code
	// value is in the stack.
	for (int i = 0; context != null && i < context.length; i++) {
	if (context[i].getCodeSource() != null &&
	context[i].getCodeSource().getLocation() != null &&
	Debug.isOn("codebase=" + context[i].getCodeSource().getLocation().toString())) {
	dumpDebug = true;
	break;
	}
	}
	}

	dumpDebug &= !Debug.isOn("permission=") \|\|
	Debug.isOn("permission=" + perm.getClass().getCanonicalName());

	if (dumpDebug && Debug.isOn("stack")) {
	Thread.currentThread().dumpStack();
	}

	if (dumpDebug && Debug.isOn("domain")) {
	if (context == null) {
	debug.println("domain (context is null)");
	} else {
	for (int i=0; i< context.length; i++) {
	debug.println("domain "+i+" "+context[i]);
	}
	}
	}
	}

	/*
	* iterate through the ProtectionDomains in the context.
	* Stop at the first one that doesn't allow the
	* requested permission (throwing an exception).
	*
	*/

	/* if ctxt is null, all we had on the stack were system domains,
	or the first domain was a Privileged system domain. This
	is to make the common case for system code very fast */

	if (context == null)
	return;

	for (int i=0; i< context.length; i++) {
	if (context[i] != null && !context[i].implies(perm)) {
	if (dumpDebug) {
	debug.println("access denied " + perm);
	}

	if (Debug.isOn("failure") && debug != null) {
	// Want to make sure this is always displayed for failure,
	// but do not want to display again if already displayed
	// above.
	if (!dumpDebug) {
	debug.println("access denied " + perm);
	}
	Thread.currentThread().dumpStack();
	final ProtectionDomain pd = context[i];
	final Debug db = debug;
	AccessController.doPrivileged (new PrivilegedAction<Void>() {
	public Void run() {
	db.println("domain that failed "+pd);
	return null;
	}
	});
	}
	throw new AccessControlException("access denied "+perm, perm);
	}
	}

	// allow if all of them allowed access
	if (dumpDebug) {
	debug.println("access allowed "+perm);
	}

	return;
	}

	/**
	* Take the stack-based context (this) and combine it with the
	* privileged or inherited context, if need be.
	*/
	AccessControlContext optimize() {
	// the assigned (privileged or inherited) context
	AccessControlContext acc;
	if (isPrivileged) {
	acc = privilegedContext;
	} else {
	acc = AccessController.getInheritedAccessControlContext();
	}

	// this.context could be null if only system code is on the stack;
	// in that case, ignore the stack context
	boolean skipStack = (context == null);

	// acc.context could be null if only system code was involved;
	// in that case, ignore the assigned context
	boolean skipAssigned = (acc == null \|\| acc.context == null);

	if (acc != null && acc.combiner != null) {
	// let the assigned acc's combiner do its thing
	return goCombiner(context, acc);
	}

	// optimization: if neither have contexts; return acc if possible
	// rather than this, because acc might have a combiner
	if (skipAssigned && skipStack) {
	return this;
	}

	// optimization: if there is no stack context; there is no reason
	// to compress the assigned context, it already is compressed
	if (skipStack) {
	return acc;
	}

	int slen = context.length;

	// optimization: if there is no assigned context and the stack length
	// is less then or equal to two; there is no reason to compress the
	// stack context, it already is
	if (skipAssigned && slen <= 2) {
	return this;
	}

	// optimization: if there is a single stack domain and that domain
	// is already in the assigned context; no need to combine
	if ((slen == 1) && (context[0] == acc.context[0])) {
	return acc;
	}

	int n = (skipAssigned) ? 0 : acc.context.length;

	// now we combine both of them, and create a new context
	ProtectionDomain pd[] = new ProtectionDomain[slen + n];

	// first copy in the assigned context domains, no need to compress
	if (!skipAssigned) {
	System.arraycopy(acc.context, 0, pd, 0, n);
	}

	// now add the stack context domains, discarding nulls and duplicates
	outer:
	for (int i = 0; i < context.length; i++) {
	ProtectionDomain sd = context[i];
	if (sd != null) {
	for (int j = 0; j < n; j++) {
	if (sd == pd[j]) {
	continue outer;
	}
	}
	pd[n++] = sd;
	}
	}

	// if length isn't equal, we need to shorten the array
	if (n != pd.length) {
	// optimization: if we didn't really combine anything
	if (!skipAssigned && n == acc.context.length) {
	return acc;
	} else if (skipAssigned && n == slen) {
	return this;
	}
	ProtectionDomain tmp[] = new ProtectionDomain[n];
	System.arraycopy(pd, 0, tmp, 0, n);
	pd = tmp;
	}

	// return new AccessControlContext(pd, false);

	// Reuse existing ACC

	this.context = pd;
	this.combiner = null;
	this.isPrivileged = false;

	return this;
	}

	private AccessControlContext goCombiner(ProtectionDomain[] current,
	AccessControlContext assigned) {

	// the assigned ACC's combiner is not null --
	// let the combiner do its thing

	// XXX we could add optimizations to 'current' here ...

	if (getDebug() != null) {
	debug.println("AccessControlContext invoking the Combiner");
	}

	// No need to clone current and assigned.context
	// combine() will not update them
	ProtectionDomain[] combinedPds = assigned.combiner.combine(
	current, assigned.context);

	// return new AccessControlContext(combinedPds, assigned.combiner);

	// Reuse existing ACC
	this.context = combinedPds;
	this.combiner = assigned.combiner;
	this.isPrivileged = false;

	return this;
	}

	/**
	* Checks two AccessControlContext objects for equality.
	* Checks that <i>obj</i> is
	* an AccessControlContext and has the same set of ProtectionDomains
	* as this context.
	* <P>
	* @param obj the object we are testing for equality with this object.
	* @return true if <i>obj</i> is an AccessControlContext, and has the
	* same set of ProtectionDomains as this context, false otherwise.
	*/
	public boolean equals(Object obj) {
	if (obj == this)
	return true;

	if (! (obj instanceof AccessControlContext))
	return false;

	AccessControlContext that = (AccessControlContext) obj;


	if (context == null) {
	return (that.context == null);
	}

	if (that.context == null)
	return false;

	if (!(this.containsAllPDs(that) && that.containsAllPDs(this)))
	return false;

	if (this.combiner == null)
	return (that.combiner == null);

	if (that.combiner == null)
	return false;

	if (!this.combiner.equals(that.combiner))
	return false;

	return true;
	}

	private boolean containsAllPDs(AccessControlContext that) {
	boolean match = false;
	//
	// ProtectionDomains within an ACC currently cannot be null
	// and this is enforced by the constructor and the various
	// optimize methods. However, historically this logic made attempts
	// to support the notion of a null PD and therefore this logic continues
	// to support that notion.
	ProtectionDomain thisPd;
	for (int i = 0; i < context.length; i++) {
	match = false;
	if ((thisPd = context[i]) == null) {
	for (int j = 0; (j < that.context.length) && !match; j++) {
	match = (that.context[j] == null);
	}
	} else {
	Class thisPdClass = thisPd.getClass();
	ProtectionDomain thatPd;
	for (int j = 0; (j < that.context.length) && !match; j++) {
	thatPd = that.context[j];

	// Class check required to avoid PD exposure (4285406)
	match = (thatPd != null &&
	thisPdClass == thatPd.getClass() && thisPd.equals(thatPd));
	}
	}
	if (!match) return false;
	}
	return match;
	}
	/**
	* Returns the hash code value for this context. The hash code
	* is computed by exclusive or-ing the hash code of all the protection
	* domains in the context together.
	*
	* @return a hash code value for this context.
	*/

	public int hashCode() {
	int hashCode = 0;

	if (context == null)
	return hashCode;

	for (int i =0; i < context.length; i++) {
	if (context[i] != null)
	hashCode ^= context[i].hashCode();
	}
	return hashCode;
	}
	}