[904] | 1 | <!-- ******************************************************** --> |
---|
| 2 | <!-- --> |
---|
| 3 | <!-- [History] --> |
---|
| 4 | <!-- Converted to DocBook: Katsuya Amako, Aug-2006 --> |
---|
| 5 | <!-- Changed by: Katsuya Amako, 4-Aug-1998 --> |
---|
| 6 | <!-- Changed by: Dennis Wright, 27-Nov-2001 --> |
---|
| 7 | <!-- Proof read by: Joe Chuma, 30-Jun-1999 --> |
---|
| 8 | <!-- --> |
---|
| 9 | <!-- ******************************************************** --> |
---|
| 10 | |
---|
| 11 | <!-- ******************* Section (Level#1) ****************** --> |
---|
| 12 | <sect1 id="sect.ObjPers"> |
---|
| 13 | <title> |
---|
| 14 | Object Persistency |
---|
| 15 | </title> |
---|
| 16 | |
---|
| 17 | <!-- ******************* Section (Level#2) ****************** --> |
---|
| 18 | <sect2 id="sect.ObjPers.PersG4"> |
---|
| 19 | <title> |
---|
| 20 | Persistency in Geant4 |
---|
| 21 | </title> |
---|
| 22 | |
---|
| 23 | <para> |
---|
| 24 | Object persistency is provided by Geant4 as an optional category, |
---|
| 25 | so that the user may run Geant4 with or without an object database |
---|
| 26 | management system (ODBMS). |
---|
| 27 | </para> |
---|
| 28 | |
---|
| 29 | <para> |
---|
| 30 | When a usual (transient) object is created in C++, the object is |
---|
| 31 | placed onto the application heap and it ceases to exist when the |
---|
| 32 | application terminates. Persistent objects, on the other hand, live |
---|
| 33 | beyond the termination of the application process and may then be |
---|
| 34 | accessed by other processes (in some cases, by processes on other |
---|
| 35 | machines). |
---|
| 36 | |
---|
| 37 | <figure id="fig.ObjPers_1"> |
---|
| 38 | <title> |
---|
| 39 | Persistent object. |
---|
| 40 | </title> |
---|
| 41 | <mediaobject> |
---|
| 42 | <imageobject role="fo"> |
---|
| 43 | <imagedata fileref="./AllResources/Detector/persistency.src/pobject.gif" |
---|
| 44 | format="JPG" contentwidth="7.0cm" align="center" /> |
---|
| 45 | </imageobject> |
---|
| 46 | <imageobject role="html"> |
---|
| 47 | <imagedata fileref="./AllResources/Detector/persistency.src/pobject.gif" |
---|
| 48 | format="JPG" align="center" /> |
---|
| 49 | </imageobject> |
---|
| 50 | </mediaobject> |
---|
| 51 | </figure> |
---|
| 52 | </para> |
---|
| 53 | |
---|
| 54 | <para> |
---|
| 55 | C++ does not have, as an intrinsic part of the language, the |
---|
| 56 | ability to store and retrieve persistent objects. Geant4 provides |
---|
| 57 | an abstract framework for persistency of hits, digits and |
---|
| 58 | events. |
---|
| 59 | </para> |
---|
| 60 | |
---|
| 61 | <para> |
---|
| 62 | Two examples demonstrating an implementation of object |
---|
| 63 | persistency using one of the tools accessible through the available |
---|
| 64 | interface, is provided in |
---|
| 65 | <literal>examples/extended/persistency</literal>. |
---|
| 66 | </para> |
---|
| 67 | |
---|
| 68 | </sect2> |
---|
| 69 | |
---|
| 70 | <!-- ******************* Section (Level#2) ****************** --> |
---|
| 71 | <sect2 id="sect.ObjPers.Reflex"> |
---|
| 72 | <title> |
---|
| 73 | Using Reflex for persistency of Geant4 objects |
---|
| 74 | </title> |
---|
| 75 | |
---|
| 76 | <para> |
---|
| 77 | Object persistency of Geant4 objects is also possible by the |
---|
| 78 | mean of the <ulink url="http://cern.ch/seal-reflex/"> |
---|
| 79 | Reflex library</ulink>. |
---|
| 80 | Reflex provides, in a non-intrusive way, reflection capabilities to C++ |
---|
| 81 | classes by generating "dictionary information" for them. Those |
---|
| 82 | dictionaries can then be loaded in memory allowing direct |
---|
| 83 | persistency of the given objects without any instrumentation of the |
---|
| 84 | code. The Reflex library is also part of |
---|
| 85 | <ulink url="http://root.cern.ch/"> |
---|
| 86 | ROOT</ulink> (since release <literal>v5.08</literal>). |
---|
| 87 | </para> |
---|
| 88 | |
---|
| 89 | <para> |
---|
| 90 | The basic steps that one needs to do in order to use Reflex with |
---|
| 91 | ROOT I/O for arbitrary C++ classes is: |
---|
| 92 | |
---|
| 93 | <orderedlist spacing="compact"> |
---|
| 94 | <listitem><para> |
---|
| 95 | Generate the dictionary for the given classes using the |
---|
| 96 | <literal>genreflex</literal> tool from ROOT (this usually is done by adding |
---|
| 97 | the appropriate command to the makefile) |
---|
| 98 | </para></listitem> |
---|
| 99 | <listitem><para> |
---|
| 100 | Add initialization of ROOT I/O and loading of the generated |
---|
| 101 | dictionary for the given classes in the appropriate part of the |
---|
| 102 | code |
---|
| 103 | </para></listitem> |
---|
| 104 | <listitem><para> |
---|
| 105 | Whenever the objects to be persistified are available, call the |
---|
| 106 | <literal>WriteObject</literal> method of <literal>TFile</literal> with |
---|
| 107 | the pointer to the appropriate object as argument (usually it is some sort |
---|
| 108 | of container, like <literal>std::vector</literal> containing the collection |
---|
| 109 | of objects to be persistified) |
---|
| 110 | </para></listitem> |
---|
| 111 | </orderedlist> |
---|
| 112 | </para> |
---|
| 113 | |
---|
| 114 | <para> |
---|
| 115 | The two examples (<literal>P01</literal> and <literal>P02</literal>) provided |
---|
| 116 | in <literal>examples/extended/persistency</literal> |
---|
| 117 | demonstrate how to perform object persistency using the |
---|
| 118 | Reflex mechanism in ROOT I/O for storing hits and geometry description. |
---|
| 119 | </para> |
---|
| 120 | |
---|
| 121 | |
---|
| 122 | </sect2> |
---|
| 123 | </sect1> |
---|