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56 | >Chapter 2. How to use the Linux Trace Toolkit Viewer's Reading Context</TD |
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77 | >2.3. Using the reading context</A |
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79 | ><P |
80 | > If you have read the tutorials about writing a text and a graphic module, you |
81 | should be fairly ready to use the information provided to your hook by the |
82 | reading API. |
83 | </P |
84 | ><P |
85 | > The data structures of the reading context are based on the gobject, a |
86 | object-oriented library from the glib. Some evolved types that are found in the |
87 | context also comes from the "glib" (GArray, GHashTable and so on). For detailed |
88 | information about "gobjects" and the "glib", see the <A |
89 | HREF="http://www.gtk.org" |
90 | TARGET="_top" |
91 | >www.gtk.org</A |
92 | > website. They provide a complete |
93 | API reference about the data types they provide. |
94 | </P |
95 | ><P |
96 | > The reading context is object oriented. It is described by the lttv/tracecontext.h |
97 | header. Is can be illustrated with this UML class diagram : |
98 | </P |
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108 | >Linux Trace Toolkit Viewer Reading Context Class Diagram</P |
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115 | > Though, for performance's sake, navigating through it is not as encapsulated as |
116 | it could. Consider the class attributes to be all public (no get/set functions). |
117 | Sometimes, iteration upon a specific element can be uneasy. For example, you may |
118 | have to get the number of tracefiles in a trace from the "vt" field of the trace |
119 | context to be able to iterate over all the tracefiles contained by the trace. |
120 | </P |
121 | ><P |
122 | > To facilitate the common operations on the reading context, LTTV now provides a |
123 | header that consists of simple macros : lttv/contextmacros.h. It gives an object |
124 | look-and-feel to the context classes. Simple "GET" macros can be used to easily |
125 | access the different fields are iterate over the elements (and get the total |
126 | number of elements too). |
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