com.yahoo.memory

Class DefaultMemoryRequestServer

java.lang.Object

com.yahoo.memory.DefaultMemoryRequestServer

All Implemented Interfaces:

MemoryRequestServer

public final class DefaultMemoryRequestServer
extends Object
implements MemoryRequestServer

This is a simple implementation of the MemoryRequestServer that creates space on the Java heap for the requesting application. This capability is only available for direct, off-heap allocated memory.

Using this default implementation could be something like the following:

 class OffHeap {
   WritableMemory mem;
   MemoryRequestServer memReqSvr = null;

   void add(Object something) {

     if (outOfSpace) { // determine if out-of-space
       long spaceNeeded = ...

       //Acquire the MemoryRequestServer from the direct Memory the first time.
       //Once acquired, this can be reused if more memory is needed later.
       //This is required for the default implementation because it returns memory on heap
       // and on-heap memory does not carry a reference to the MemoryRequestServer.
       memReqSvr = (memReqSvr == null) ? mem.getMemoryRequestServer() : memReqSvr;

       //Request bigger memory
       WritableMemory newMem = memReqSvr.request(spaceNeeded);

       //Copy your data from the current memory to the new one and resize
       moveAndResize(mem, newMem);

       //You are done with the old memory, so request close.
       //Note that it is up to the owner of the WritableDirectHandle whether or not to
       // actually close the resource.
       memReqSvr.requestClose(mem, newMem);

       mem = newMem; //update your reference to memoty
     }

     //continue with the add process
   }
 }
 

Author:

Lee Rhodes

Constructor Summary

Constructors

Constructor and Description
DefaultMemoryRequestServer()

Method Summary

Modifier and Type	Method and Description
WritableMemory	request(long capacityBytes) Request new WritableMemory with the given capacity.
void	requestClose(WritableMemory memToRelease, WritableMemory newMemory) Request close the AutoCloseable resource.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DefaultMemoryRequestServer

public DefaultMemoryRequestServer()

Method Detail

request

public WritableMemory request(long capacityBytes)

Request new WritableMemory with the given capacity.

By default this allocates new memory requests on the Java heap.

Specified by:

request in interface MemoryRequestServer

Parameters:

capacityBytes - The capacity being requested.

Returns:

new WritableMemory with the given capacity.

requestClose

public void requestClose(WritableMemory memToRelease,
                         WritableMemory newMemory)

Request close the AutoCloseable resource. This may be ignored depending on the application implementation.

This method does nothing in this default implementation because it is application specific. This method must be overridden to explicitly close if desired. Otherwise, the AutoCloseable will eventually close the resource.

Specified by:

requestClose in interface MemoryRequestServer

Parameters:

memToRelease - the relevant WritbleMemory to be considered for closing.

newMemory - the newly allocated WritableMemory. This is returned from the client for the convenience of the resource owner. It is optional and may be null.