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<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>D-Bus FAQ</title><meta name="generator" content="DocBook XSL Stylesheets V1.74.3"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="article" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="index"></a>D-Bus FAQ</h2></div><div><div class="authorgroup"><div class="author"><h3 class="author"><span class="firstname">Havoc</span> <span class="surname">Pennington</span></h3><div class="affiliation"><span class="orgname">Red Hat, Inc.<br></span><div class="address"><p><br>
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<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>D-Bus FAQ</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="article" title="D-Bus FAQ"><div class="titlepage"><div><div><h2 class="title"><a name="index"></a>D-Bus FAQ</h2></div><div><div class="authorgroup"><div class="author"><h3 class="author"><span class="firstname">Havoc</span> <span class="surname">Pennington</span></h3><div class="affiliation"><span class="orgname">Red Hat, Inc.<br></span><div class="address"><p><br>
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����<code class="email"><<a class="email" href="mailto:hp@pobox.com">hp@pobox.com</a>></code><br>
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��</p></div></div></div><div class="author"><h3 class="author"><span class="firstname">David</span> <span class="othername">A</span> <span class="surname">Wheeler</span></h3></div></div></div><div><p class="releaseinfo">Version 0.3</p></div></div><hr></div><div class="qandaset"><dl><dt>1. <a href="#id2948247">
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��</p></div></div></div><div class="author"><h3 class="author"><span class="firstname">David</span> <span class="othername">A</span> <span class="surname">Wheeler</span></h3></div></div></div><div><p class="releaseinfo">Version 0.3</p></div></div><hr></div><div class="qandaset" title="Frequently Asked Questions"><a name="faq"></a><dl><dt>1. <a href="#id319467">
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</a></dt><dt>2. <a href="#id2948284">
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</a></dt><dt>2. <a href="#id322828">
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Is D-Bus stable/finished?
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</a></dt><dt>3. <a href="#id2982134">
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</a></dt><dt>3. <a href="#id322854">
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How is the reference implementation licensed? Can I use it in
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proprietary applications?
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</a></dt><dt>4. <a href="#id2942814">
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</a></dt><dt>4. <a href="#id319923">
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What is the difference between a bus name, and object path,
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</a></dt><dt>5. <a href="#service">
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How does D-Bus differ from [yet more IPC mechanisms]?
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</a></dt><dt>18. <a href="#which-ipc">
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Which IPC mechanism should I use?
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</a></dt><dt>19. <a href="#id2991686">
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</a></dt><dt>19. <a href="#id359012">
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How can I submit a bug or patch?
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</a></dt></dl><table border="0" summary="Q and A Set"><col align="left" width="1%"><tbody><tr class="question"><td align="left" valign="top"><a name="id2948247"></a><a name="id2948249"></a><p><b>1.</b></p></td><td align="left" valign="top"><p>
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</a></dt></dl><table border="0" width="100%" summary="Q and A Set"><col align="left" width="1%"><col><tbody><tr class="question" title="1."><td align="left" valign="top"><a name="id319467"></a><a name="id322798"></a><p><b>1.</b></p></td><td align="left" valign="top"><p>
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</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
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This is probably best answered by reading the D-Bus <a class="ulink" href="dbus-tutorial.html" target="_top">tutorial</a> or
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Phrased differently, D-Bus is 1) an interprocess communication (IPC) system and 2) some higher-level
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structure (lifecycle tracking, service activation, security policy) provided by two bus daemons,
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one systemwide and one per-user-session.
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</p></td></tr><tr class="question"><td align="left" valign="top"><a name="id2948284"></a><a name="id2948287"></a><p><b>2.</b></p></td><td align="left" valign="top"><p>
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</p></td></tr><tr class="question" title="2."><td align="left" valign="top"><a name="id322828"></a><a name="id322830"></a><p><b>2.</b></p></td><td align="left" valign="top"><p>
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Is D-Bus stable/finished?
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</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
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The low-level library "libdbus" and the protocol specification are considered
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have their own release schedules and degree of maturity, not linked to
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the low-level library and bus daemon release. Check the project page for
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the binding you're considering to understand that project's policies.
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</p></td></tr><tr class="question"><td align="left" valign="top"><a name="id2982134"></a><a name="id2982137"></a><p><b>3.</b></p></td><td align="left" valign="top"><p>
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</p></td></tr><tr class="question" title="3."><td align="left" valign="top"><a name="id322854"></a><a name="id322856"></a><p><b>3.</b></p></td><td align="left" valign="top"><p>
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How is the reference implementation licensed? Can I use it in
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proprietary applications?
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</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
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use D-Bus</em></span>. If you're going to sue, you have to stop using
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the software. Read the licenses to determine their meaning, this FAQ
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entry is not intended to change the meaning or terms of the licenses.
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</p></td></tr><tr class="question"><td align="left" valign="top"><a name="id2942814"></a><a name="id2942816"></a><p><b>4.</b></p></td><td align="left" valign="top"><p>
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</p></td></tr><tr class="question" title="4."><td align="left" valign="top"><a name="id319923"></a><a name="id319925"></a><p><b>4.</b></p></td><td align="left" valign="top"><p>
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What is the difference between a bus name, and object path,
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</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
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interfaces, such as <code class="literal">org.freedesktop.DBus.Introspectable</code>,
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<code class="literal">org.freedesktop.BasicTextField</code>,
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<code class="literal">org.kde.RichTextDocument</code>.
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</p></td></tr><tr class="question"><td align="left" valign="top"><a name="service"></a><a name="id2942922"></a><p><b>5.</b></p></td><td align="left" valign="top"><p>
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</p></td></tr><tr class="question" title="5."><td align="left" valign="top"><a name="service"></a><a name="id320018"></a><p><b>5.</b></p></td><td align="left" valign="top"><p>
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What is a "service"?
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</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
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A service is a program that can be launched by the bus daemon
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In the D-Bus docs we try to use "service" only when talking about
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programs the bus knows how to launch, i.e. a service always has a
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</p></td></tr><tr class="question"><td align="left" valign="top"><a name="components"></a><a name="id2942954"></a><p><b>6.</b></p></td><td align="left" valign="top"><p>
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</p></td></tr><tr class="question" title="6."><td align="left" valign="top"><a name="components"></a><a name="id320045"></a><p><b>6.</b></p></td><td align="left" valign="top"><p>
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Is D-Bus a "component system"?
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</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
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It helps to keep these concepts separate in your mind:
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</p><div class="orderedlist"><ol type="1"><li><p>
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</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
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Object/component system
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</p></li><li class="listitem"><p>
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GUI control/widget embedding interfaces
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</p></li><li class="listitem"><p>
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Interprocess communication system or wire protocol
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</p></li></ol></div><p>
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from component/object systems, though perhaps a "plugin" tends to be a
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bundle of objects with a user-visible name and can be
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downloaded/packaged as a unit.
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</p></td></tr><tr class="question"><td align="left" valign="top"><a name="speed"></a><a name="id2947480"></a><p><b>7.</b></p></td><td align="left" valign="top"><p>
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</p></td></tr><tr class="question" title="7."><td align="left" valign="top"><a name="speed"></a><a name="id319564"></a><p><b>7.</b></p></td><td align="left" valign="top"><p>
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How fast is the D-Bus reference implementation?
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</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
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Of course it depends a bit on what you're doing.
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enable asynchronous communication and avoid round trips.
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This is frequently a more important performance issue
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</p></td></tr><tr class="question"><td align="left" valign="top"><a name="size"></a><a name="id2947540"></a><p><b>8.</b></p></td><td align="left" valign="top"><p>
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</p></td></tr><tr class="question" title="8."><td align="left" valign="top"><a name="size"></a><a name="id319610"></a><p><b>8.</b></p></td><td align="left" valign="top"><p>
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How large is the D-Bus reference implementation?
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</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
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A production build (with assertions, unit tests, and verbose logging
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A much, much smaller implementation would be possible by omitting out
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of memory handling, hardcoding a main loop (or always using blocking
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I/O), skipping validation, and otherwise simplifying things.
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</p></td></tr><tr class="question"><td align="left" valign="top"><a name="other-ipc"></a><a name="id2947571"></a><p><b>9.</b></p></td><td align="left" valign="top"><p>
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</p></td></tr><tr class="question" title="9."><td align="left" valign="top"><a name="other-ipc"></a><a name="id358326"></a><p><b>9.</b></p></td><td align="left" valign="top"><p>
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How does D-Bus differ from other interprocess communication
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or networking protocols?
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</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
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Note: the D-Bus mailing list subscribers are <span class="emphasis"><em>very much not
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interested</em></span> in debating which IPC system is the One True
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System. So if you want to discuss that, please use another forum.
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</p></td></tr><tr class="question"><td align="left" valign="top"><a name="corba"></a><a name="id2947661"></a><p><b>10.</b></p></td><td align="left" valign="top"><p>
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</p></td></tr><tr class="question" title="10."><td align="left" valign="top"><a name="corba"></a><a name="id358398"></a><p><b>10.</b></p></td><td align="left" valign="top"><p>
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How does D-Bus differ from CORBA?
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</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
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Start by reading <a class="xref" href="#other-ipc" title="Question">Q:�9</a>.
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Start by reading <a class="xref" href="#other-ipc" title="9.">Q:�9</a>.
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<a class="ulink" href="http://www.omg.org" target="_top">CORBA</a> is designed to support
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object-oriented IPC between objects, automatically marshalling
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On a more trivial note, D-Bus involves substantially fewer acronyms
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</p></td></tr><tr class="question"><td align="left" valign="top"><a name="xmlrpcsoap"></a><a name="id2942203"></a><p><b>11.</b></p></td><td align="left" valign="top"><p>
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</p></td></tr><tr class="question" title="11."><td align="left" valign="top"><a name="xmlrpcsoap"></a><a name="id319108"></a><p><b>11.</b></p></td><td align="left" valign="top"><p>
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How does D-Bus differ from XML-RPC and SOAP?
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</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
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Start by reading <a class="xref" href="#other-ipc" title="Question">Q:�9</a>.
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Start by reading <a class="xref" href="#other-ipc" title="9.">Q:�9</a>.
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In <a class="ulink" href="http://www.w3.org/TR/SOAP/" target="_top">SOAP</a> and <a class="ulink" href="http://www.xmlrpc.com" target="_top">XML-RPC</a>, RPC calls are transformed
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into an XML-based format, then sent over the wire (typically using the
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supports lifecycle tracking of other applications connected
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to the bus. With XML-RPC and SOAP, typically each method call
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exists in isolation and has its own HTTP connection.
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</p></td></tr><tr class="question"><td align="left" valign="top"><a name="dce"></a><a name="id2942264"></a><p><b>12.</b></p></td><td align="left" valign="top"><p>
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</p></td></tr><tr class="question" title="12."><td align="left" valign="top"><a name="dce"></a><a name="id358723"></a><p><b>12.</b></p></td><td align="left" valign="top"><p>
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How does D-Bus differ from DCE?
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</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
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Start by reading <a class="xref" href="#other-ipc" title="Question">Q:�9</a>.
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Start by reading <a class="xref" href="#other-ipc" title="9.">Q:�9</a>.
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<a class="ulink" href="http://www.opengroup.org/dce/" target="_top">Distributed Computing
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Environment (DCE)</a> is an industry-standard vendor-neutral
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a distributed time service. As the name implies, DCE is intended for
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use in a large, multi-computer distributed application. D-Bus would
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not be well-suited for this.
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</p></td></tr><tr class="question"><td align="left" valign="top"><a name="dcom"></a><a name="id2943326"></a><p><b>13.</b></p></td><td align="left" valign="top"><p>
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</p></td></tr><tr class="question" title="13."><td align="left" valign="top"><a name="dcom"></a><a name="id358763"></a><p><b>13.</b></p></td><td align="left" valign="top"><p>
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How does D-Bus differ from DCOM and COM?
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</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
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Start by reading <a class="xref" href="#other-ipc" title="Question">Q:�9</a>.
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Start by reading <a class="xref" href="#other-ipc" title="9.">Q:�9</a>.
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Comparing D-Bus to COM is apples and oranges;
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see <a class="xref" href="#components" title="Question">Q:�6</a>.
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see <a class="xref" href="#components" title="6.">Q:�6</a>.
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DCOM (distributed COM) is a Windows IPC system designed for use with
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the COM object system. It's similar in some ways to DCE and CORBA.
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</p></td></tr><tr class="question"><td align="left" valign="top"><a name="internet-communications-engine"></a><a name="id2943371"></a><p><b>14.</b></p></td><td align="left" valign="top"><p>
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</p></td></tr><tr class="question" title="14."><td align="left" valign="top"><a name="internet-communications-engine"></a><a name="id358799"></a><p><b>14.</b></p></td><td align="left" valign="top"><p>
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How does D-Bus differ from ZeroC's Internet Communications Engine (Ice)
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</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
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Start by reading <a class="xref" href="#other-ipc" title="Question">Q:�9</a>.
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Start by reading <a class="xref" href="#other-ipc" title="9.">Q:�9</a>.
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The <a class="ulink" href="http://www.zeroc.com/ice.html" target="_top"> Internet
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Communications Engine (Ice)</a> is a powerful IPC mechanism more
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on the level of SOAP or CORBA than D-Bus. Ice has a "dual-license"
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business around it; i.e. you can use it under the GPL, or pay for a
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proprietary license.
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</p></td></tr><tr class="question"><td align="left" valign="top"><a name="inter-client-exchange"></a><a name="id2943411"></a><p><b>15.</b></p></td><td align="left" valign="top"><p>
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</p></td></tr><tr class="question" title="15."><td align="left" valign="top"><a name="inter-client-exchange"></a><a name="id358832"></a><p><b>15.</b></p></td><td align="left" valign="top"><p>
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How does D-Bus differ from Inter-Client Exchange (ICE)?
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</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
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<a class="ulink" href="http://www.x.org/X11R6.8.1/docs/ICE/ice.pdf" target="_top">ICE</a>
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DCOP and XSMP are the only two widely-used applications of ICE,
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and both could in principle be replaced by D-Bus. (Though whether
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GNOME and KDE will bother is an open question.)
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</p></td></tr><tr class="question"><td align="left" valign="top"><a name="dcop"></a><a name="id2943460"></a><p><b>16.</b></p></td><td align="left" valign="top"><p>
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</p></td></tr><tr class="question" title="16."><td align="left" valign="top"><a name="dcop"></a><a name="id358871"></a><p><b>16.</b></p></td><td align="left" valign="top"><p>
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How does D-Bus differ from DCOP?
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</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
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Start by reading <a class="xref" href="#other-ipc" title="Question">Q:�9</a>.
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Start by reading <a class="xref" href="#other-ipc" title="9.">Q:�9</a>.
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D-Bus is intentionally pretty similar to <a class="ulink" href="http://developer.kde.org/documentation/library/kdeqt/dcop.html" target="_top">DCOP</a>,
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and can be thought of as a "DCOP the next generation" suitable for
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DCOP's implementation to use D-Bus internally (so that GNOME and KDE
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would end up using exactly the same bus). See the KDE mailing list
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archives for some of these discussions.
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</p></td></tr><tr class="question"><td align="left" valign="top"><a name="yet-more-ipc"></a><a name="id2991587"></a><p><b>17.</b></p></td><td align="left" valign="top"><p>
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</p></td></tr><tr class="question" title="17."><td align="left" valign="top"><a name="yet-more-ipc"></a><a name="id358929"></a><p><b>17.</b></p></td><td align="left" valign="top"><p>
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How does D-Bus differ from [yet more IPC mechanisms]?
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</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
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Start by reading <a class="xref" href="#other-ipc" title="Question">Q:�9</a>.
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Start by reading <a class="xref" href="#other-ipc" title="9.">Q:�9</a>.
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There are countless uses of network sockets in the world. <a class="ulink" href="http://www.mbus.org/" target="_top">MBUS</a>, Sun ONC/RPC, Jabber/XMPP,
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SIP, are some we can think of quickly.
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</p></td></tr><tr class="question"><td align="left" valign="top"><a name="which-ipc"></a><a name="id2991622"></a><p><b>18.</b></p></td><td align="left" valign="top"><p>
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</p></td></tr><tr class="question" title="18."><td align="left" valign="top"><a name="which-ipc"></a><a name="id358962"></a><p><b>18.</b></p></td><td align="left" valign="top"><p>
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Which IPC mechanism should I use?
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</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
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Start by reading <a class="xref" href="#other-ipc" title="Question">Q:�9</a>.
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Start by reading <a class="xref" href="#other-ipc" title="9.">Q:�9</a>.
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If you're writing an Internet or Intranet application, XML-RPC or SOAP
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work for many people. These are standard, available for most
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to search the list archives is probably to use
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an Internet engine such as Google. On Google,
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include "site:freedesktop.org" in your search.
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</p></td></tr><tr class="question"><td align="left" valign="top"><a name="id2991686"></a><a name="id2991688"></a><p><b>19.</b></p></td><td align="left" valign="top"><p>
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</p></td></tr><tr class="question" title="19."><td align="left" valign="top"><a name="id359012"></a><a name="id359014"></a><p><b>19.</b></p></td><td align="left" valign="top"><p>
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How can I submit a bug or patch?
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</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
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The D-Bus <a class="ulink" href="http://dbus.freedesktop.org" target="_top">web site</a>
added
removed
doc/dbus-faq.html
