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Adding some debugging help
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@ -2,7 +2,7 @@
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<meta name="GENERATOR" content="Mozilla/4.51 [en] (X11; U; Linux 2.0.36 i686) [Netscape]">
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<meta name="GENERATOR" content="Mozilla/4.51 [en] (WinNT; U) [Netscape]">
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<meta name="Author" content="Suresh Duddi">
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<title>XPCOM Code FAQ</title>
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</head>
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@ -85,22 +85,22 @@ is the order of creation of the ServiceManager, ComponentManager and Registry</h
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<blockquote>Init_XPCOM()
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<blockquote>
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<li>
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create the global component manager</li>
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create the global service manager</li>
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<li>
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create the global component manager and register as service with the global
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service manager</li>
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<li>
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RegisterFactory(...RegistryFactory...) Register the RegistryFactory()
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RegisterFactory(...RegistryFactory...) Register the RegistryFactory
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with the component manager so that new registry objects can be created.</li>
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</blockquote>
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Now the hard problem is when to trigger Init_XPCOM() There are two static
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objects nsComponentManager and nsServiceManager. Any function in either
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of them can be called first. Today nsServiceManager::GetService() is the
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first one that gets called. All the members of the static nsServiceManager
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use the nsGetGlobalServiceManager() to get to the global service manager.
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All members of the static nsComponentManager use the nsGetGlobalComponentManager()
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use the NS_GetGlobalServiceManager() to get to the global service manager.
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All members of the static nsComponentManager use the NS_GetGlobalComponentManager()
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to get to the global component manager. Hence if we trigger Init_XPCOM()
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from both NS_GetGlobalComponentManager() and NS_GetGlobalServiceManager()
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we will be safe.</blockquote>
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@ -144,38 +144,26 @@ of Shutting down a service.</font>
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<i><font color="#000000">When does a client use the service manager vs
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component manager</font></i></li>
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<br>
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<p>
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<br>
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<br>
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<p><font color="#000000">When a client knows that the component that they
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<br><font color="#000000">When a client knows that the component that they
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are trying to instantiate is a singleton, they need to call service manager
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instead of component manager. Clients dont have to worry about calling
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the ComponentManager at all in this case. The ServiceManager will take
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care of creating the instance if the first one doesn't exist already.</font>
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<br><font color="#000000">-</font>
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<br>
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<li>
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<i><font color="#000000">When does a client use the Component Manager as
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opposed to Service Manager</font></i></li>
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<br>
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<p>
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<br>
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<br>
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<p><font color="#000000">When a client wants a private instance of a component,
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<br><font color="#000000">When a client wants a private instance of a component,
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they call the Component Manager. From the Clients point of view, a new
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xpcom object creation happens everytime they call CreateInstance() Anything
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else is an implementation detail that the Client need not worry about.</font>
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<br><font color="#000000">-</font>
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<br>
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<li>
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<i><font color="#000000">How does a Client know that they have to instantiate
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a singleton</font></i></li>
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<br>
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<p>
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<br>
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<br>
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<p><font color="#000000">For now, the Client just has to know. There is
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<br><font color="#000000">For now, the Client just has to know. There is
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no way of telling which component is a Service and which isn't. In fact,
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in todays xpcom (Mar 1999) any component can be accessed as a Service.
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Use your judgement until there is a proper method or service manager is
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@ -184,17 +172,13 @@ Instances.</font>
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<p><b><font color="#CC0000">Need a solution for this. Email suggestion
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to <a href="mailto:warren@netscape.com,dp@netscape.com">warren@netscape.com,
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dp@netscape.com</a></font></b>
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<br><font color="#000000">-</font></ul>
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<br> </ul>
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<b><i><font color="#000000">Component</font></i></b>
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<ul>
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<li>
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<i><font color="#000000">Can a component enforce use only as a Service</font></i></li>
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<br>
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<p>
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<br>
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<br>
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<p><font color="#000000">No. The notion of the ServiceManager is available
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<br><font color="#000000">No. The notion of the ServiceManager is available
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only to Clients.</font>
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<p><font color="#000000">Note that at some points when a component wants
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another component, it actually behaves as a client and hence follows the
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@ -215,28 +199,20 @@ nsPrefFactory::CreateInstance()</a> and <a href="http://lxr.mozilla.org/se
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nsPref::GetInstance()</a> With this implementation, whether Clients get
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to it by calling nsIServiceManager::GetService() or nsIComponentManager::CreateInstance(),
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the same object will be returned hence guaranteeing singletonism.</ul>
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<font color="#000000">-</font>
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<li>
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<i><font color="#000000">Should a component do anything at creation to
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become a Service</font></i></li>
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<br><font color="#000000">No. Again, the notion of a ServiceManager is
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available only to Clients.</font>
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<br>
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<p>
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<br>
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<br>
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<p><font color="#000000">No. Again, the notion of a ServiceManager is available
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only to Clients.</font>
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<br><font color="#000000">-</font>
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<li>
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<i><font color="#000000">Can a component advertise that it is a service
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so clients can use it as one</font></i></li>
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<br>
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<p>
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<br>
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<br>
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<p>No. There isn't a way other than a comment in the interface of the header
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file.</ul>
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<br>No. There isn't a way other than a comment in the interface of the
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header file.</ul>
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</blockquote>
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<h4>
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@ -257,27 +233,28 @@ ProgIDs (not implemented yet).
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<li>
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<i>Should CreateInstance() calls use ProgID or CLSID</i></li>
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<br>
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<p>
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<p>ProgID is what Clients should use to CreateInstances. Clients should
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<br>ProgID is what Clients should use to CreateInstances. Clients should
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not even know about the CLSID unless they are hell bent on creating a particular
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implementation of a component.
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<br>-</ul>
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<br> </ul>
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<b><i>Component</i></b>
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<ul>
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<li>
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<i>Should Components register with both a CID and ProgID</i></li>
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<br>
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<p>
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<p>Absolutely.</ul>
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<br>Absolutely.</ul>
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</blockquote>
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<h4>
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<a NAME="How to debug components ?"></a>How to debug components ?</h4>
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<blockquote>Since components are dynamically loaded only on demand, debugging
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them could be a hard. Here are some tips to debugging components.
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<blockquote>XPCOM provides log output. To enable the logging:
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<blockquote><tt>setenv NSPR_LOG_MODULES nsComponentManager:5</tt>
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<br><tt>setenv NSPR_LOG_FILE xpcom.log</tt></blockquote>
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Start your application after setting the above environment variables. Debug
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log from xpcom would be in the file <tt>xpcom.log</tt>
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<p>Since components are dynamically loaded only on demand, debugging them
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could be a hard. Here are some tips to debugging components.
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<p><b><i>Windows: VC5.0 VC6.0</i></b>
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<ul>Include your component library in the Project->Settings, Additional
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Dll. drop down. After that breakpoints can be enabled.</ul>
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