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<H3><A name="SCAJavabinding.erlang-%3Cbinding.erlang%3E"></A><binding.erlang></H3>
<P>The Tuscany Java SCA runtime supports Erlang using the <binding.erlang> SCDL extension. New Erlang based service can be provided using a <binding.erlang> element within a SCA <service>, existing Erlang object can be accessed using a <binding.erlang> element within a SCA <reference>.</P>
<UL>
<LI><A href="#SCAJavabinding.erlang-using"><B>Using Erlang binding</B></A>
<UL>
<LI><A href="#SCAJavabinding.erlang-requirements"><B>Requirements</B></A></LI>
<LI><A href="#SCAJavabinding.erlang-configuration"><B>Binding configuration</B></A></LI>
<LI><A href="#SCAJavabinding.erlang-interface"><B>Declaring interface</B></A></LI>
</UL>
</LI>
<LI><A href="#SCAJavabinding.erlang-messaging"><B>Details of message based RPC</B></A></LI>
<LI><A href="#SCAJavabinding.erlang-Exceptions"><B>Exceptions</B></A></LI>
<LI><A href="#SCAJavabinding.erlang-Samples"><B>Samples</B></A></LI>
</UL>
<P><A name="SCAJavabinding.erlang-using"></A></P>
<H2><A name="SCAJavabinding.erlang-UsingErlangbinding"></A>Using Erlang binding</H2>
<P>Basically SCA services can be exposed in two ways:</P>
<UL>
<LI>by Erlang <B>RPC</B> mechanism. In this case SCA component would act as Erlang module containing functions, based on components operations names.</LI>
<LI>by RPC realised using Erlang <B>messaging</B>. In this case for every operation named Erlang message box would be created - name of the box will correspond to operation name. After receiving message from Erlang node appropriate components operation will be invoked and result would be sent back to sender.</LI>
</UL>
<P>Similarly, SCA references can access Erlang modules in two ways:</P>
<UL>
<LI>using <B>RPC</B> mechanism. In this case SCA reference would be mapped to remote Erlang functions module, each operation would correspond to different function, basing on its name.</LI>
<LI>by RPC realised using Erlang <B>messaging</B>. In this case invoking operation on reference would cause sending Erlang message to named Erlang process - name would be the same as operation name. If operation has return value then return message will be expected.</LI>
</UL>
<P><A name="SCAJavabinding.erlang-requirements"></A></P>
<H4><A name="SCAJavabinding.erlang-Requirements"></A>Requirements</H4>
<P>Erlang binding is available since Apache Tuscany SCA Java 1.6, <B>source distribution only</B>. To use Erlang binding module you need to build Apache Tuscany by your own, please follow instructions contained in <B>BUILDING</B> file which can be found in source distribution root directory.</P>
<P>Erlang nodes need to communicate with <B>Erlang Port Mapper Daemon (EPMD)</B> which should be run locally. To run JUnit tests and samples for Tuscany Erlang modules you <B>need to have epmd binary</B> in your system path - epmd comes with Erlang/OTP distribution. See <A href="http://erlang.org/" class="external-link" rel="nofollow">http://erlang.org</A> for downloads.</P>
<P>Erlang samples and JUnit tests inside Tuscany spawns epmd process automatically, but if you are creating your own solution using Erlang binding <B>you need to provide running epmd process</B>.</P>
<P><A name="SCAJavabinding.erlang-configuration"></A></P>
<H4><A name="SCAJavabinding.erlang-Bindingconfiguration"></A>Binding configuration</H4>
<P>Binding configuration can take several attributes:</P>
<UL>
<LI><B>node</B> - name of the local (service side) or remote (reference side) Erlang node. Tuscany creates separate Erlang node for each service binding, so remember to provide unique node name for every service binding.</LI>
<LI><B>module</B> - specifies name of the module mapped to SCA component/reference. When using this attribute you can't use mbox="true" attribute.</LI>
<LI><B>mbox</B> - specifies whether binding would be realised using messaging based RPC ("true") or built-in Erlang RPC ("false"). Default (no value specified) is "false". When using mbox="true" you can't use module attribute.</LI>
<LI><B>cookie</B> - (optional) authentication token. Communicating nodes should have the same cookies. You can also provide cookie in .erlang.cookie file in users home directory (it's originally supported by Jinterface).</LI>
<LI><B>timeout</B> - (optional) specifies timeout (in milliseconds) for inactive connections. Timeouts will be disabled if attribute value is 0 or not provided.</LI>
<LI><B>serviceThreadPool</B> - (optional) for service side bindings only. Specifies maximum number of threads which will be handling clients. Default value is 20.</LI>
</UL>
<H5><A name="SCAJavabinding.erlang-Serviceconfigurationsamples"></A>Service configuration samples</H5>
<P><B>Sample based on RPC</B></P>
<P>Following sample exposes component as Erlang module named "HelloModule". Modules functions would be the same as in service interface - helloworld.HelloWorld. Node which will host this module will be named "HelloNodeModule".</P>
<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
<PRE class="code-java">
<service name=<SPAN class="code-quote">"HelloWorldService"</SPAN>>
<<SPAN class="code-keyword">interface</SPAN>.java <SPAN class="code-keyword">interface</SPAN>=<SPAN class="code-quote">"helloworld.HelloWorld"</SPAN>/>
<tuscany:binding.erlang node=<SPAN class="code-quote">"HelloNodeModule"</SPAN> module=<SPAN class="code-quote">"HelloModule"</SPAN>/>
</service>
</PRE>
</DIV></DIV>
<P><B>Sample based on messaging</B></P>
<P>Following sample exposes component as several message boxes - each box will correspond to each component operation. Node which will host those message boxes will be named "HelloNodeMbox".<BR>
Additional attributes are used:</P>
<UL>
<LI>cookie for authentication purposes - "secret string"</LI>
<LI>timeout (1 second) for disconnecting hanging clients</LI>
<LI>number of threads that handles clients (serviceThreadPool attribute) is set to 10.</LI>
</UL>
<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
<PRE class="code-java">
<service name=<SPAN class="code-quote">"HelloWorldService"</SPAN>>
<<SPAN class="code-keyword">interface</SPAN>.java <SPAN class="code-keyword">interface</SPAN>=<SPAN class="code-quote">"helloworld.HelloWorld"</SPAN>/>
<tuscany:binding.erlang node=<SPAN class="code-quote">"HelloNodeMbox"</SPAN> mbox=<SPAN class="code-quote">"<SPAN class="code-keyword">true</SPAN>"</SPAN> cookie=<SPAN class="code-quote">"secret string"</SPAN> timeout=<SPAN class="code-quote">"1000"</SPAN> serviceThreadPool=<SPAN class="code-quote">"10"</SPAN>/>
</service>
</PRE>
</DIV></DIV>
<H5><A name="SCAJavabinding.erlang-Referenceconfigurationsamples"></A>Reference configuration samples</H5>
<P><B>Sample based on RPC</B></P>
<P>Following sample uses remote Erlang module as reference. Configuration points to module named "HelloModule", hosted on "HelloNodeModule".<BR>
Additional attributes are used:</P>
<UL>
<LI>cookie for authentication purposes - "secret string"</LI>
<LI>timeout (1 second) for quitting from hanging server</LI>
</UL>
<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
<PRE class="code-java">
<reference name=<SPAN class="code-quote">"helloWorldReference"</SPAN>>
<tuscany:binding.erlang node=<SPAN class="code-quote">"HelloNodeModule"</SPAN> module=<SPAN class="code-quote">"HelloModule"</SPAN> cookie=<SPAN class="code-quote">"secret string"</SPAN> timeout=<SPAN class="code-quote">"1000"</SPAN>/>
</reference>
</PRE>
</DIV></DIV>
<P><B>Sample based on messaging</B></P>
<P>Following sample uses remote Erlang message boxes in RPC style. Message boxes with names the same as reference operations are available on "HelloNodeMbox".</P>
<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
<PRE class="code-java">
<reference name=<SPAN class="code-quote">"helloWorldReference"</SPAN>>
<tuscany:binding.erlang node=<SPAN class="code-quote">"HelloNodeMbox"</SPAN> mbox=<SPAN class="code-quote">"<SPAN class="code-keyword">true</SPAN>"</SPAN>/>
</reference>
</PRE>
</DIV></DIV>
<P><A name="SCAJavabinding.erlang-interface"></A></P>
<H4><A name="SCAJavabinding.erlang-Declaringinterface"></A>Declaring interface</H4>
<P>Following table describes mapping used between Java and Erlang types.</P>
<DIV class="table-wrap">
<TABLE class="confluenceTable"><TBODY>
<TR>
<TH class="confluenceTh"> Java type </TH>
<TH class="confluenceTh"> Erlang type </TH>
</TR>
<TR>
<TD class="confluenceTd"> byte, short, char, int, long </TD>
<TD class="confluenceTd"> number - Erlang does not distinguish numbers size </TD>
</TR>
<TR>
<TD class="confluenceTd"> float, double </TD>
<TD class="confluenceTd"> Double - Erlang does not distinguish floating numbers size </TD>
</TR>
<TR>
<TD class="confluenceTd"> String </TD>
<TD class="confluenceTd"> Array of characters </TD>
</TR>
<TR>
<TD class="confluenceTd"> String annotated with @ErlangAtom (package org.apache.tuscany.sca.binding.erlang.meta) </TD>
<TD class="confluenceTd"> Atom </TD>
</TR>
<TR>
<TD class="confluenceTd"> array </TD>
<TD class="confluenceTd"> List </TD>
</TR>
<TR>
<TD class="confluenceTd"> User defined class with pubic no argument constructor and public fields of type from this table. </TD>
<TD class="confluenceTd"> Tuple </TD>
</TR>
</TBODY></TABLE>
</DIV>
<H5><A name="SCAJavabinding.erlang-Atomssample"></A>Atoms sample</H5>
<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
<PRE class="code-java">
<SPAN class="code-keyword">public</SPAN> <SPAN class="code-keyword">interface</SPAN> SomeInterface {
<SPAN class="code-comment">// Returns user defined class - tuple
</SPAN> TupleClass operation1();
<SPAN class="code-comment">// Returns list of characters and takes list of characters as an argument
</SPAN> <SPAN class="code-object">String</SPAN> operation2(<SPAN class="code-object">String</SPAN> argument);
<SPAN class="code-comment">// Returns atom and takes atom as an argument
</SPAN> @ErlangAtom
<SPAN class="code-object">String</SPAN> operation3(@ErlangAtom <SPAN class="code-object">String</SPAN> argument);
<SPAN class="code-comment">// Returns list of atoms
</SPAN> @ErlangAtom
<SPAN class="code-object">String</SPAN>[] operation4();
}
<SPAN class="code-comment">// Java class represents tuple which contains atom and list of characters.
</SPAN><SPAN class="code-keyword">public</SPAN> class TupleClass {
@EralngAtom
<SPAN class="code-keyword">public</SPAN> <SPAN class="code-object">String</SPAN> atom;
<SPAN class="code-keyword">public</SPAN> <SPAN class="code-object">String</SPAN> notAtom;
}
</PRE>
</DIV></DIV>
<H5><A name="SCAJavabinding.erlang-Tuplessample"></A>Tuples sample</H5>
<P>Following interface:</P>
<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
<PRE class="code-java">
<SPAN class="code-keyword">public</SPAN> class TupleClass1 {
<SPAN class="code-keyword">public</SPAN> <SPAN class="code-object">long</SPAN> field1;
<SPAN class="code-keyword">public</SPAN> TupleClass2 field2;
}
<SPAN class="code-keyword">public</SPAN> class TupleClass2 {
<SPAN class="code-keyword">public</SPAN> <SPAN class="code-object">long</SPAN> field1;
<SPAN class="code-keyword">public</SPAN> <SPAN class="code-object">double</SPAN> field2;
}
</PRE>
</DIV></DIV>
<P>will correspond to live tuple structure (using Erlang notation):</P>
<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
<PRE class="code-java">
{10, {10, 0.9}}
</PRE>
</DIV></DIV>
<P><A name="SCAJavabinding.erlang-messaging"></A></P>
<H2><A name="SCAJavabinding.erlang-DetailsofmessagebasedRPCcommunication"></A>Details of message based RPC communication</H2>
<P>RPC based on messaging uses messages for requests and responses.</P>
<UL>
<LI>For <B>service bindings</B> incoming messages should contain SCA operation arguments, formed in tuple. Operation result will be send in return message.</LI>
<LI>For <B>reference bindings</B> Tuscany creates message with content depending on attributes passed to reference operation. If reference operation has return value defined then Tuscany will wait for reply from remote process.</LI>
</UL>
<P>In Erlang messaging it's common technique for sender to provide it's PID at the beginning - it allows recipient to respond. In Tuscany every Erlang message is a tuple which contains operation arguments. This tuple is wrapped with tuple with PID.</P>
<H4><A name="SCAJavabinding.erlang-Overloadingoperations"></A>Overloading operations</H4>
<P>Overloading operations allows user to send message with different structure. Ie., in reference binding we could declare interface:</P>
<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
<PRE class="code-java">
<SPAN class="code-keyword">public</SPAN> <SPAN class="code-keyword">interface</SPAN> SomeInterface {
void someMbox(<SPAN class="code-object">String</SPAN> argument);
void someMbox(<SPAN class="code-object">String</SPAN> arg1, <SPAN class="code-object">String</SPAN> arg2);
}
</PRE>
</DIV></DIV>
<P>Invoking first <B>someMbox</B> operation would cause sending message addressed to <B>someMbox</B> message box. This message would contain one string value. Invoking second <B>someMbox</B> operation would cause sending message addressed also to <B>someMbox</B> message box, but message content would differ - now it would contain two string values.</P>
<H4><A name="SCAJavabinding.erlang-Servicesideexample"></A>Service side example</H4>
<P>For service defined by following interface:</P>
<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
<PRE class="code-java">
<SPAN class="code-keyword">public</SPAN> <SPAN class="code-object">String</SPAN> operation(<SPAN class="code-object">long</SPAN> arg1, @ErlangTuple arg2);
</PRE>
</DIV></DIV>
<P>expected Erlang message is (sample using Erlang notation):</P>
<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
<PRE class="code-java">
{SomePid, {10, AtomValue}}
</PRE>
</DIV></DIV>
<P>After receiving such formed message Tuscany is able to process it correctly, invoke SCA operation and send reply to PID provided as first element of outer tuple.</P>
<H4><A name="SCAJavabinding.erlang-Referencesideexample"></A>Reference side example</H4>
<P>For reference interface defined as:</P>
<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
<PRE class="code-java">
<SPAN class="code-keyword">public</SPAN> <SPAN class="code-object">String</SPAN> operation(<SPAN class="code-object">long</SPAN> arg1, @ErlangTuple <SPAN class="code-object">String</SPAN> arg2);
</PRE>
</DIV></DIV>
<P>executing it with following arguments:</P>
<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
<PRE class="code-java">
obj.operation(10, <SPAN class="code-quote">"AtomValue"</SPAN>);
</PRE>
</DIV></DIV>
<P>will make Tuscany to convert input arguments to Erlang tuple (using Erlang notation):</P>
<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
<PRE class="code-java">
{10, AtomValue}
</PRE>
</DIV></DIV>
<P>and wrap with tuple containing PID as follows (using Erlang notation):</P>
<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
<PRE class="code-java">
{SomePid, {10, AtomValue}}
</PRE>
</DIV></DIV>
<P>In this example Erlang message box would receive message and know PID for reply.</P>
<P><A name="SCAJavabinding.erlang-exceptions"></A></P>
<H2><A name="SCAJavabinding.erlang-Exceptions"></A>Exceptions</H2>
<P>While communicating with Erlang nodes (reference bindings) several error can be raised:</P>
<UL>
<LI>Function on remote Erlang doesn't exist</LI>
<LI>Connection problems</LI>
<LI>Others and unexpected errors</LI>
</UL>
<P>In case of error two things can happen:</P>
<UL>
<LI><B>Exception will be thrown</B>, only for operations which <B>declares exceptions</B></LI>
<LI><B>Problem will be logged</B>, only for operations with <B>no exception declared</B></LI>
</UL>
<P><A name="SCAJavabinding.erlang-samples"></A></P>
<H2><A name="SCAJavabinding.erlang-Samples"></A>Samples</H2>
<P>Samples can be found under sca/java/samples/:</P>
<UL>
<LI><B>helloworld-service-erlang</B></LI>
<LI><B>helloworld-reference-erlang</B></LI>
</UL>
<P>Samples use service and reference Erlang bindings realised via Erlang RPC. If you want to play with Erlang binding it's good place to start. Maybe you would like to experiment by changing communication model to message based?<BR>
For running instructions <B>please read README files</B>. You should also get familiar with <A href="#SCAJavabinding.erlang-requirements"><B>requirements</B></A>.</P></TD></TR></TBODY></TABLE>
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