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<concept xml:lang="en" id="GUID-A95CDFDE-285F-5DE2-AADE-29B2B9663757"><title>The object index</title><prolog><metadata><keywords/></metadata></prolog><conbody><p>An object index is used to generate handle-numbers for reference counting objects. </p> <p>An object index is an instance of a <xref href="GUID-70824EE4-9E01-3AC0-9318-4B521A1FDD5E.dita"><apiname>CObjectIx</apiname></xref> class. </p> <p>An object index acts as a collector of reference counting objects but, unlike an object container, it does not act as a container for them. The difference is emphasised by the fact that removing a reference counting object from its object container causes that reference counting object to be <i>destroyed</i>, while removing it from an object index causes it to be <i>closed</i>. </p> <p>An object index can hold reference counting objects which belong to different object containers. The same reference counting object can also be added to an object index any number of times; each is regarded as a different instance of that object and each instance generates a different handle-number. </p> <p> <xref href="GUID-70824EE4-9E01-3AC0-9318-4B521A1FDD5E.dita#GUID-70824EE4-9E01-3AC0-9318-4B521A1FDD5E/GUID-03EC7FEC-030F-3F4E-9FF1-669284626DF5"><apiname>CObjectIx::AddL()</apiname></xref> adds a reference counting object to an object index, and is the way in which a unique handle-number can be generated for that object. A handle-number is the way in which an object which is owned or managed by another thread or process can be identified. For example, on the server side, the object representing a thread (a <codeph>DThread</codeph>) maintains an object index for all objects which are open in that thread. Semaphores, mutexes and other threads are examples. Typically, user code running in that thread will have handles, <codeph>RHandleBase</codeph> derived types, open on those objects. </p> <p>The following drawing shows the idea. </p> <fig id="GUID-139E5A87-1E6E-5102-AE60-A707EFC5AD5D"><image href="GUID-6BA9989F-6D45-5D77-BC79-DE4B5DD35A6C_d0e219996_href.png" placement="inline"/></fig> <p>An object index is implemented as an array where each element of the array contains a pointer to the reference counting object. An object index can index up to 32,768 (0x8000) reference counting objects. </p> <p>See also: </p> <ul><li id="GUID-3BD162E5-C0A7-5D42-94E3-6E2A0468749A"><p> <xref href="GUID-70824EE4-9E01-3AC0-9318-4B521A1FDD5E.dita"><apiname>CObjectIx</apiname></xref> </p> </li> <li id="GUID-C7108AB5-3F32-5F1D-B15F-E6DBE5CF9809"><p> <xref href="GUID-72761B3C-ECB6-34B2-87ED-C972E479357A.dita"><apiname>CObjectConIx</apiname></xref> </p> </li> <li id="GUID-00290334-9DA4-5FC0-874A-CD839027FD28"><p> <xref href="GUID-DE901A59-C714-356A-9490-C4E9C9F186DB.dita"><apiname>CObjectCon</apiname></xref> </p> </li> <li id="GUID-25EBCB93-A34E-57C3-BD33-B20398FD3CC0"><p> <xref href="GUID-9230EF62-376A-389C-B720-7C1EDCB7EA97.dita"><apiname>CObject</apiname></xref> </p> </li> </ul> </conbody></concept>