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package com.sun.corba.se.spi.extension ;

import org.omg.CORBA.Policy ;
import org.omg.CORBA.LocalObject ;
import com.sun.corba.se.impl.orbutil.ORBConstants ;


Policy used to implement servant caching optimization in the POA.
Creating a POA with an instance pol of this policy where
pol.getType() > NO_SERVANT_CACHING will cause the servant to be
looked up in the POA and cached in the LocalClientRequestDispatcher when
the ClientRequestDispatcher is colocated with the implementation of the
objref.  This greatly speeds up invocations at the cost of violating the
POA semantics.  In particular, every request to a particular objref
must be handled by the same servant.  Note that this is typically the
case for EJB implementations.


If servant caching is used, there are two different additional
features of the POA that are expensive:

    

  1. POA current semantics

  2. Proper handling of POA destroy.


POA current semantics requires maintaining a ThreadLocal stack of
invocation information that is always available for POACurrent operations.
Maintaining this stack is expensive on the timescale of optimized co-located
calls, so the option is provided to turn it off.  Similarly, causing
POA.destroy() calls to wait for all active calls in the POA to complete
requires careful tracking of the entry and exit of invocations in the POA.
Again, tracking this is somewhat expensive.

/** Policy used to implement servant caching optimization in the POA.
* Creating a POA with an instance pol of this policy where
* pol.getType() > NO_SERVANT_CACHING will cause the servant to be
* looked up in the POA and cached in the LocalClientRequestDispatcher when
* the ClientRequestDispatcher is colocated with the implementation of the
* objref.  This greatly speeds up invocations at the cost of violating the
* POA semantics.  In particular, every request to a particular objref
* must be handled by the same servant.  Note that this is typically the
* case for EJB implementations.
* <p>
* If servant caching is used, there are two different additional
* features of the POA that are expensive:
* <ol>
* <li>POA current semantics
* <li>Proper handling of POA destroy.
* </ol>
* POA current semantics requires maintaining a ThreadLocal stack of
* invocation information that is always available for POACurrent operations.
* Maintaining this stack is expensive on the timescale of optimized co-located
* calls, so the option is provided to turn it off.  Similarly, causing
* POA.destroy() calls to wait for all active calls in the POA to complete
* requires careful tracking of the entry and exit of invocations in the POA.
* Again, tracking this is somewhat expensive.
*/
public class ServantCachingPolicy extends LocalObject implements Policy
{
    
Do not cache servants in the ClientRequestDispatcher.  This will
always support the full POA semantics, including changing the
servant that handles requests on a particular objref.

/** Do not cache servants in the ClientRequestDispatcher.  This will
     * always support the full POA semantics, including changing the
     * servant that handles requests on a particular objref.
     */
    public static final int NO_SERVANT_CACHING = 0 ;

    
Perform servant caching, preserving POA current and POA destroy semantics.
We will use this as the new default, as the app server is making heavier use
now of POA facilities.

/** Perform servant caching, preserving POA current and POA destroy semantics.
    * We will use this as the new default, as the app server is making heavier use
    * now of POA facilities.
    */
    public static final int FULL_SEMANTICS = 1 ;

    
Perform servant caching, preservent only POA current semantics.
At least this level is required in order to support selection of ObjectCopiers
for co-located RMI-IIOP calls, as the current copier is stored in
OAInvocationInfo, which must be present on the stack inside the call.

/** Perform servant caching, preservent only POA current semantics.
    * At least this level is required in order to support selection of ObjectCopiers
    * for co-located RMI-IIOP calls, as the current copier is stored in
    * OAInvocationInfo, which must be present on the stack inside the call.
    */
    public static final int INFO_ONLY_SEMANTICS =  2 ;

    
Perform servant caching, not preserving POA current or POA destroy semantics.

/** Perform servant caching, not preserving POA current or POA destroy semantics.
    */
    public static final int MINIMAL_SEMANTICS = 3 ;

    private static ServantCachingPolicy policy = null ;
    private static ServantCachingPolicy infoOnlyPolicy = null ;
    private static ServantCachingPolicy minimalPolicy = null ;

    private int type ;

    public String typeToName()
    {
        switch (type) {
            case FULL_SEMANTICS:
                return "FULL" ;
            case INFO_ONLY_SEMANTICS:
                return "INFO_ONLY" ;
            case MINIMAL_SEMANTICS:
                return "MINIMAL" ;
            default:
                return "UNKNOWN(" + type + ")" ;
        }
    }

    public String toString()
    {
        return "ServantCachingPolicy[" + typeToName() + "]" ;
    }

    private ServantCachingPolicy( int type )
    {
        this.type = type ;
    }

    public int getType()
    {
        return type ;
    }

    
Return the default servant caching policy.

/** Return the default servant caching policy.
    */
    public synchronized static ServantCachingPolicy getPolicy()
    {
        return getFullPolicy() ;
    }

    public synchronized static ServantCachingPolicy getFullPolicy()
    {
        if (policy == null)
            policy = new ServantCachingPolicy( FULL_SEMANTICS ) ;

        return policy ;
    }

    public synchronized static ServantCachingPolicy getInfoOnlyPolicy()
    {
        if (infoOnlyPolicy == null)
            infoOnlyPolicy = new ServantCachingPolicy( INFO_ONLY_SEMANTICS ) ;

        return infoOnlyPolicy ;
    }

    public synchronized static ServantCachingPolicy getMinimalPolicy()
    {
        if (minimalPolicy == null)
            minimalPolicy = new ServantCachingPolicy( MINIMAL_SEMANTICS ) ;

        return minimalPolicy ;
    }

    public int policy_type ()
    {
        return ORBConstants.SERVANT_CACHING_POLICY ;
    }

    public org.omg.CORBA.Policy copy ()
    {
        return this ;
    }

    public void destroy ()
    {
        // NO-OP
    }
}