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      <year>2001</year><year>2017</year>
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    <title>CORBA System and User Defined Exceptions</title>
    <prepared></prepared>
    <docno></docno>
    <date>2000-12-19</date>
    <rev></rev>
    <file>ch_exceptions.xml</file>
  </header>

  <section>
    <title>System Exceptions</title>
    <p><c>Orber</c>, or any other <c>ORB</c>, may raise a <c>System Exceptions</c>.
      These exceptions contain status- and minor-fields and may not appear in the
      operations raises exception IDL-definition.</p>

    <section>
      <title>Status Field</title>
      <p>The status field indicates if the request was completed or not and will be
        assigned one of the following Erlang atoms:</p>
      <table>
        <row>
          <cell align="center" valign="middle"><em>Status</em></cell>
          <cell align="center" valign="middle"><em>Description</em></cell>
        </row>
        <row>
          <cell align="left" valign="middle">'COMPLETED_YES'</cell>
          <cell align="left" valign="middle">The operation was invoked on the target object but an error occurred after the object replied. This occur, for example, if a server replies but Orber is not able to marshal and send the reply to the  client ORB.</cell>
        </row>
        <row>
          <cell align="left" valign="middle">'COMPLETED_NO'</cell>
          <cell align="left" valign="middle">Orber failed to invoke the operation on the target object. This occur, for example, if the object no longer exists.</cell>
        </row>
        <row>
          <cell align="left" valign="middle">'COMPLETED_MAYBE'</cell>
          <cell align="left" valign="middle">Orber invoked the operation on the target object but an error occurred and it is impossible to decide if the request really reached the object or not.</cell>
        </row>
        <tcaption>System Exceptions Status</tcaption>
      </table>
    </section>

    <section>
      <title>Minor Field</title>
      <p>The minor field contains an integer (VMCID), which is related to a more
        specific reason why an invocation failed. The function 
        <c>orber:exception_info/1</c> can be used to map the minor code to a string. 
        Note, for VMCID:s not assigned by the OMG or Orber, the documentation
        for that particular ORB must be consulted.</p>
    </section>

    <section>
      <title>Supported System Exceptions</title>
      <p>The OMG CORBA specification defines the following exceptions:</p>
      <list type="bulleted">
        <item><em>'BAD_CONTEXT'</em> - if a request does not contain a correct
         context this exception is raised.</item>
        <item><em>'BAD_INV_ORDER'</em> - this exception indicates that operations
         has been invoked operations in the wrong order, which would cause,
         for example, a dead-lock.</item>
        <item><em>'BAD_OPERATION'</em> - raised if the target object exists, but
         that the invoked operation is not supported.</item>
        <item><em>'BAD_PARAM'</em> - is thrown if, for example, a parameter is out
         of range or otherwise considered illegal.</item>
        <item><em>'BAD_TYPECODE'</em> - if illegal type code is passed, for example,
         encapsulated in an any data type the <c>'BAD_TYPECODE'</c> exception
         will be raised.</item>
        <item><em>'BAD_QOS'</em> - raised whenever an object cannot support the 
         required quality of service.</item>
        <item><em>'CODESET_INCOMPATIBLE'</em> - raised if two ORB's cannot 
         communicate due to different representation of, for example, 
        <c>char</c> and/or <c>wchar</c>.</item>
        <item><em>'COMM_FAILURE'</em> - raised if an ORB is unable to setup 
         communication or it is lost while an operation is in progress.</item>
        <item><em>'DATA_CONVERSION'</em> - raised if an ORB cannot convert data 
         received to the native representation. See also the 
        <c>'CODESET_INCOMPATIBLE'</c> exception.</item>
        <item><em>'FREE_MEM'</em> - the ORB failed to free dynamic memory and 
         failed.</item>
        <item><em>'IMP_LIMIT'</em> - an implementation limit was exceeded in the
         ORB at run time. A object factory may, for example, limit the
         number of object clients are allowed to create.</item>
        <item><em>'INTERNAL'</em> - an internal failure occurred in an ORB, which
         is unrecognized. You may consider contacting the ORB providers 
         support.</item>
        <item><em>'INTF_REPOS'</em> - the ORB was not able to reach the interface
         repository, or some other failure relating to the interface 
         repository is detected.</item>
        <item><em>'INITIALIZE'</em> - the ORB initialization failed due to, for
         example, network or configuration error.</item>
        <item><em>'INVALID_TRANSACTION'</em> - is raised if the request carried an
         invalid transaction context.</item>
        <item><em>'INV_FLAG'</em> - an invalid flag was passed to an operation, 
         which caused, for example, a connection to be closed.</item>
        <item><em>'INV_IDENT'</em> - this exception indicates that an IDL 
         identifier is incorrect.</item>
        <item><em>'INV_OBJREF'</em> - this exception is raised if an object 
         reference is malformed or a nil reference (see 
         also corba:create_nil_objref/0).</item>
        <item><em>'INV_POLICY'</em> - the invocation cannot be made due to an
         incompatibility between policy overrides that apply to the
         particular invocation.</item>
        <item><em>'MARSHAL'</em> - this exception may be raised by the client- or
         server-side when either ORB is unable to marshal/unmarshal requests or
         replies.</item>
        <item><em>'NO_IMPLEMENT'</em> - if the operation exists but no implementation
         exists, this exception is raised.</item>
        <item><em>'NO_MEMORY'</em> - the ORB has run out of memory.</item>
        <item><em>'NO_PERMISSION'</em> - the caller has insufficient privileges, 
         such as, for example, bad <c>SSL</c> certificate.</item>
        <item><em>'NO_RESOURCES'</em> - a general platform resource limit 
         exceeded.</item>
        <item><em>'NO_RESPONSE'</em> - no response available of a deferred
         synchronous request.</item>
        <item><em>'OBJ_ADAPTER'</em> - indicates administrative mismatch; the object
         adapter is not able to associate an object with the implementation
         repository.</item>
        <item><em>'OBJECT_NOT_EXIST'</em> - the object have been disposed or 
         terminated; clients should remove all copies of the object reference
         and initiate desired recovery process.</item>
        <item><em>'PERSIST_STORE'</em> - the ORB was not able to establish a
         connection to its persistent storage or data contained in the
         the storage is corrupted.</item>
        <item><em>'REBIND'</em> - a request resulted in, for example, a 
        <c>'LOCATION_FORWARD'</c> message; if the policies are incompatible 
         this exception is raised.</item>
        <item><em>'TIMEOUT'</em> - raised if a request fail to complete within the 
         given time-limit.</item>
        <item><em>'TRANSACTION_MODE'</em> - a transaction policy mismatch detected.</item>
        <item><em>'TRANSACTION_REQUIRED'</em> - a transaction is required for the
         invoked operation but the request contained no transaction context.</item>
        <item><em>'TRANSACTION_ROLLEDBACK'</em> - the transaction associated with
         the request has already been rolled back or will be.</item>
        <item><em>'TRANSACTION_UNAVAILABLE'</em> - no transaction context can be
         supplied since the ORB is unable to contact the Transaction
         Service.</item>
        <item><em>'TRANSIENT'</em> - the ORB could not determine the current status
         of an object since it could not be reached. The error may be
         temporary.</item>
        <item><em>'UNKNOWN'</em> - is thrown if an implementation throws a 
         non-CORBA, or unrecognized, exception.</item>
      </list>
    </section>
  </section>

  <section>
    <title>User Defined Exceptions</title>
    <p>User exceptions is defined in IDL-files and is listed in operations raises
      exception listing. For example, if we have the following IDL code:</p>
    <code type="none">
module MyModule {

  exception MyException {};
  exception MyExceptionMsg { string ExtraInfo; };

  interface MyInterface {

    void foo() 
      raises(MyException);

    void bar() 
      raises(MyException, MyExceptionMsg);

    void baz();
  };
};    
    </code>
  </section>

  <section>
    <title>Throwing Exceptions</title>
    <p>To be able to raise <c>MyException</c> or <c>MyExceptionMsg</c> exceptions, 
      the generated <c>MyModule.hrl</c> must be included, and typical usage is:</p>
    <code type="erl">
-module('MyModule_MyInterface_impl').
-include("MyModule.hrl").

bar(State) ->
    case TestingSomething of
        ok ->
           {reply, ok, State};
        {error, Reason} when list(Reason) ->
           corba:raise(#'MyModule_MyExceptionMsg'{'ExtraInfo' = Reason});
        error ->
           corba:raise(#'MyModule_MyException'{})
    end.
    </code>
  </section>

  <section>
    <title>Catching Exceptions</title>
    <p>Depending on which operation we invoke we must be able to handle:</p>
    <list type="bulleted">
      <item>foo - <c>MyException</c> or a system exception.</item>
      <item>bar - <c>MyException</c>, <c>MyExceptionMsg</c> or a system
       exception.</item>
      <item>baz - a system exception.</item>
    </list>
    <p>Catching and matching exceptions can bee done in different ways:</p>
    <code type="none">
    case catch 'MyModule_MyInterface':bar(MIReference) of
        ok ->
           %% The operation raised no exception.
           ok;
        {'EXCEPTION', #'MyModule_MyExceptionMsg'{'ExtraInfo' = Reason}} ->
           %% If we want to log the Reason we must extract 'ExtraInfo'.
           error_logger:error_msg("Operation 'bar' raised: ~p~n", [Reason]),
           ... do something ...;
        {'EXCEPTION', E} when record(E, 'OBJECT_NOT_EXIST') ->
           ... do something ...;
        {'EXCEPTION', E} ->
           ... do something ...
    end.
    </code>
  </section>
</chapter>

