| 1 | <html><head><title></title><!-- Changed by: Katsuya Amako, 4-Aug-1998 --><!-- Changed by: Dennis Wright, 27-Nov-2001 --><!-- Proof read by: Joe Chuma, 30-Jun-1999 --></head><body> |
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| 2 | <table width="100%"><tbody><tr> |
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| 3 | <td> |
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| 4 | <a href="http://geant4.web.cern.ch/geant4/G4UsersDocuments/Overview/html/index.html"> |
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| 5 | <img src="persistency_files/Overview.gif" alt="Overview"></a> |
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| 6 | <a href="http://geant4.web.cern.ch/geant4/G4UsersDocuments/UsersGuides/ForApplicationDeveloper/html/Detector/index.html"> |
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| 7 | <img src="persistency_files/Contents.gif" alt="Contents"></a> |
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| 8 | <a href="http://geant4.web.cern.ch/geant4/G4UsersDocuments/UsersGuides/ForApplicationDeveloper/html/Detector/digitization.html"> |
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| 9 | <img src="persistency_files/Previous.gif" alt="Previous"></a> |
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| 10 | <a href="http://geant4.web.cern.ch/geant4/G4UsersDocuments/UsersGuides/ForApplicationDeveloper/html/Detector/parallelWorld.html"> |
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| 11 | <img src="persistency_files/NextGR.gif" alt="Next"></a> |
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| 12 | </td> |
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| 13 | <td align="right"> |
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| 14 | <font color="#238e23" size="-1"> |
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| 15 | <b>Geant4 User's Guide</b> |
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| 16 | <br> |
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| 17 | <b>For Application Developers</b> |
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| 18 | <br> |
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| 19 | <b>Detector Definition and Response</b> |
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| 20 | </font> |
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| 21 | </td> |
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| 22 | </tr></tbody></table> |
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| 23 | <br><br> |
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| 24 | |
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| 25 | <p align="center"> |
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| 26 | <font color="#238e23" size="+3"> |
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| 27 | <b>4.6 Object Persistency</b> |
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| 28 | </font> |
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| 29 | <br><br> |
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| 30 | |
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| 31 | </p><hr align="center" size="7"> |
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| 32 | <p> |
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| 33 | |
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| 34 | <a name="4.6.1"> |
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| 35 | <h2>4.6.1 Persistency in Geant4</h2></a> |
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| 36 | |
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| 37 | Object persistency is provided by Geant4 as an optional category, so that the |
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| 38 | user may run Geant4 with or without an object database management system |
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| 39 | (ODBMS). |
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| 40 | |
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| 41 | </p><p>When a usual (transient) object is created in C++, the object is placed |
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| 42 | onto the application heap and it ceases to exist when the application |
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| 43 | terminates. Persistent objects, on the other hand, live beyond the |
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| 44 | termination of the application process and may then be accessed by other |
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| 45 | processes (in some cases, by processes on other machines). |
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| 46 | </p><center><img src="persistency.src/pobject.gif" height="212" width="290"></center> |
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| 47 | |
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| 48 | |
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| 49 | <p>C++ does not have, as an intrinsic part of the language, the ability to |
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| 50 | store and retrieve persistent objects. Geant4 provides an abstract framework |
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| 51 | for persistency of hits, digits and events. |
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| 52 | </p><p> |
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| 53 | An example which demonstrates an implementation of object persistency using one |
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| 54 | of the tools accessible through the available interface, is provided in |
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| 55 | <tt>examples/extended/persistency</tt>. |
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| 56 | |
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| 57 | </p><p> |
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| 58 | |
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| 59 | <a name="4.6.2"> |
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| 60 | <h2>4.6.2 Using Reflex for persistency of Geant4 objects</h2></a> |
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| 61 | <p> |
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| 62 | Object persistency of Geant4 objects is also possible by the mean of the |
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| 63 | <b>Reflex</b> library <a href="#Reflex">[1]</a>. Reflex provides, in a |
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| 64 | non-intrusive way, reflection capabilities to C++ classes by generating |
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| 65 | "dictionary information" for them. Those dictionaries can then be loaded |
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| 66 | in memory allowing direct persistency of the given objects without any |
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| 67 | instrumentation of the code. The Reflex library is also part of ROOT |
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| 68 | <a href="#Root">[2]</a> (since release <tt>v5.08</tt>). |
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| 69 | </p> |
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| 70 | <p> |
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| 71 | The basic steps that one needs to do in order to use Reflex with ROOT I/O |
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| 72 | for arbitrary C++ classes is: |
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| 73 | <ol> |
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| 74 | <li>Generate the dictionary for the given classes using the |
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| 75 | <tt>genreflex</tt> tool from ROOT (this usually is done |
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| 76 | by adding the appropriate command to the makefile)</li> |
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| 77 | <li>Add initialization of ROOT I/O and loading of the generated |
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| 78 | dictionary for the given classes in the appropriate part of the |
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| 79 | code</li> |
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| 80 | <li>Whenever the objects to be persistified are available, call the |
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| 81 | <tt>WriteObject</tt> method of <tt>TFile</tt> with the pointer to the |
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| 82 | appropriate object as argument (usually it is some sort of container, |
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| 83 | like <tt>std::vector</tt> containing the collection of objects to be |
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| 84 | persistified)</li> |
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| 85 | </ol> |
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| 86 | The example provided in <tt>examples/extended/persistency</tt> |
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| 87 | demonstrates an implementation of object persistency using the Reflex |
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| 88 | mechanism in ROOT I/O. |
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| 89 | |
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| 90 | </p><p> |
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| 91 | |
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| 92 | <hr> |
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| 93 | <p> |
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| 94 | <table> |
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| 95 | <tr><td valign=top><a name="Reflex">[1]</a> |
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| 96 | <td><a href="http://cern.ch/seal-reflex/">http://cern.ch/seal-reflex</a> |
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| 97 | <tr><td valign=top><a name="Root">[2]</a> |
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| 98 | <td><a href="http://root.cern.ch/">http://root.cern.ch</a> |
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| 99 | </table> |
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| 100 | </p> |
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| 101 | |
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| 102 | <hr> |
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| 103 | <a href="http://cern.ch/geant4/G4UsersDocuments/Authors/html/subjectsToAuthors.html"> |
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| 104 | <i>About the authors</i></a> |
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| 105 | |
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| 106 | |
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| 107 | </body></html> |
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