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144 lines
5.3 KiB
HTML
144 lines
5.3 KiB
HTML
<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
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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/4.61 [en] (X11; U; Linux 2.0.36 i686) [Netscape]">
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</head>
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<body>
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<center>
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<h2>
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Component Loaders</h2></center>
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<center>Brendan Eich <<a href="mailto:brendan@mozilla.org">brendan@mozilla.org</a>>
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<br>John Bandauer <<a href="mailto:jband@netscape.com">jband@netscape.com</a>>
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<br>Mike McCabe <<a href="mailto:mccabe@netscape.com">mccabe@netscape.com</a>>
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<br>Mike Shaver <<a href="mailto:shaver@mozilla.org">shaver@mozilla.org</a>>
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<br>Suresh Duddi <<a href="mailto:dp@netscape.com">dp@netscape.com</a>></center>
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<h3>
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Scope of document</h3>
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<ul>
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<li>
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Component Developers</li>
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<li>
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Clients of XPCOM (for information only)</li>
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</ul>
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<h3>
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Why Component Loaders</h3>
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Currently XPCOM requires all component to be packaged in DLLs and uses
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the dynamic loading mechanism available with each platform to accomplish
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instantiation of component. This method doesn't blend well with say components
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written in java or javascript and packaged different from a DLL. Hence
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the proposal for Component Loaders.
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<br>
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<h3>
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Component Loaders</h3>
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XPCOM in its simplest form can be viewed as creating instances of objects
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given a CONTRACTID or ClassID. How it does this instantiation is specific to
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XPCOM and opaque to clients of XPCOM.
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<p>Internally XPCOM maps the passed in CONTRACTID to a CID and then the CID
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maps into a DLL name. XPCOM loads the DLL assuming the dynamic loading
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mechanism to create a factory. Then, asks the factory to create a particular
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instance. Here are roughly the steps involved:
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<ol>
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<li>
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CreateInstance(..., CONTRACTID,...)</li>
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<li>
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Map CONTRACTID to CID</li>
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<li>
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Map CID to DLL</li>
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<li>
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factory = Dynamically Load DLL to create Factory</li>
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<li>
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Use Factory to create object instance</li>
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</ol>
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The proposal for Component Loaders is to get XPCOM to delegate the loading
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to a component loader:
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<ul>
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<li>
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CreateInstance(..., CONTRACTID,...)</li>
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<li>
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Map CONTRACTID to CID</li>
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<li>
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<font color="#990000">Map CID to ComponentType</font></li>
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<li>
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<font color="#990000">If ComponentType is DLL</font></li>
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<ul>
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<li>
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factory = Dynamically Load DLL to create Factory</li>
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</ul>
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<li>
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<font color="#990000">else</font></li>
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<ul>
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<li>
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<font color="#990000">ComponentLoaderServiceCONTRACTID = "<i>@mozilla.org/xpcom/component-loader;1?type=</i>"
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+ ComponentType <sup><a href="#* ContractID syntax might change">*</a></sup></font></li>
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<li>
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<font color="#990000">loaderInstance = GetService(..., ComponentLoaderServiceCONTRACTID,...)</font></li>
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<li>
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<font color="#990000">factory = loaderInstance->CreateFactory(..., componentLocation,...)</font></li>
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</ul>
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<li>
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Use Factory to create object instance</li>
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<h4>
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Format of ComponentType</h4>
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ComponentType is assumed to be mimetype.
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<h4>
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Component Registration</h4>
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Registration of components in DLLs wont change. ComponentType of DLL is
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assumed here. To facilitate registration of components with specifc component
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types, the component manager will provide the following API:
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<p><tt><font color="#990000">RegisterComponentWithType(const nsCID &aClass,</font></tt>
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<br><tt><font color="#990000">
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const char *aClassName,</font></tt>
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<br><tt><font color="#990000">
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const char *aContractID,</font></tt>
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<br><tt><font color="#990000">
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const char *aComponentType,</font></tt>
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<br><tt><font color="#990000">
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const char *aComponentLocation,</font></tt>
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<br><tt><font color="#990000">
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PRBool aReplace,</font></tt>
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<br><tt><font color="#990000">
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PRBool aPersist);</font></tt>
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<br>
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<br>
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<h4>
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Component Loader Service Registration</h4>
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Since the loader is just another component with a special contractid, there
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is no special registration of the component loader. Component Loaders
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use either the RegisterComponent() api if they are a DLL (most common)
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or use RegisterComponentWithType() api if they are themselves of a particular
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type (very rare).</ul>
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<h3>
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Autoregistration of non DLL Components and Component Loaders</h3>
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<Need to figure this out>
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<br>
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<p><a NAME="* ContractID syntax might change"></a><sup><a href="#* ContractID syntax might change">*</a></sup>
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ContractID syntax might change
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<br>
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<hr WIDTH="100%">
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<br><i><font size=-1>Last Modified: 1 Aug 1999 Suresh Duddi <<a href="mailto:dp@netscape.com">dp@netscape.com</a>></font></i>
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<br>
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</body>
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</html>
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