aboutsummaryrefslogtreecommitdiffstats
path: root/lib/ic/doc/src/ch_ic_protocol.xml
diff options
context:
space:
mode:
authorErlang/OTP <[email protected]>2009-11-20 14:54:40 +0000
committerErlang/OTP <[email protected]>2009-11-20 14:54:40 +0000
commit84adefa331c4159d432d22840663c38f155cd4c1 (patch)
treebff9a9c66adda4df2106dfd0e5c053ab182a12bd /lib/ic/doc/src/ch_ic_protocol.xml
downloadotp-84adefa331c4159d432d22840663c38f155cd4c1.tar.gz
otp-84adefa331c4159d432d22840663c38f155cd4c1.tar.bz2
otp-84adefa331c4159d432d22840663c38f155cd4c1.zip
The R13B03 release.OTP_R13B03
Diffstat (limited to 'lib/ic/doc/src/ch_ic_protocol.xml')
-rw-r--r--lib/ic/doc/src/ch_ic_protocol.xml233
1 files changed, 233 insertions, 0 deletions
diff --git a/lib/ic/doc/src/ch_ic_protocol.xml b/lib/ic/doc/src/ch_ic_protocol.xml
new file mode 100644
index 0000000000..678fdc766c
--- /dev/null
+++ b/lib/ic/doc/src/ch_ic_protocol.xml
@@ -0,0 +1,233 @@
+<?xml version="1.0" encoding="latin1" ?>
+<!DOCTYPE chapter SYSTEM "chapter.dtd">
+
+<chapter>
+ <header>
+ <copyright>
+ <year>2003</year><year>2009</year>
+ <holder>Ericsson AB. All Rights Reserved.</holder>
+ </copyright>
+ <legalnotice>
+ The contents of this file are subject to the Erlang Public License,
+ Version 1.1, (the "License"); you may not use this file except in
+ compliance with the License. You should have received a copy of the
+ Erlang Public License along with this software. If not, it can be
+ retrieved online at http://www.erlang.org/.
+
+ Software distributed under the License is distributed on an "AS IS"
+ basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+ the License for the specific language governing rights and limitations
+ under the License.
+
+ </legalnotice>
+
+ <title>IC Protocol</title>
+ <prepared></prepared>
+ <docno></docno>
+ <date>2003-12-11</date>
+ <rev>PA1</rev>
+ <file>ch_ic_protocol.xml</file>
+ </header>
+ <p>The purpose of this chapter is to explain the bits and bytes of the
+ IC protocol, which is a composition of the Erlang distribution protocol
+ and the Erlang/OTP gen_server protocol. If you do not intend to replace
+ the Erlang distribution protocol, or replace the gen_server protocol,
+ skip over this chapter.
+ </p>
+
+ <section>
+ <title>Introduction</title>
+ <p>The IDL Compiler (IC) transforms Interface Definition Language
+ (IDL) specifications files to interface code for Erlang, C, and
+ Java. The Erlang language mapping is described in the Orber
+ documentation, while the other mappings are described in the IC
+ documentation (they are of course in accordance with the CORBA C
+ and Java language mapping specifications, with some restrictions).
+ </p>
+ <p>The most important parts of an IDL specification are the operation
+ declarations. An operation defines what information a client
+ provides to a server, and what information (if any) the client
+ gets back from the server. We consider IDL operations and language
+ mappings in section 2.
+ </p>
+ <p>What we here call the IC protocol, is the description of messages
+ exchanged between IC end-points (client and servers). It is valid
+ for all IC back-ends, except the 'erl_plain' and 'erl_corba'
+ back-ends.
+ The IC protocol is in turn embedded into the Erlang gen_server
+ protocol, which is described below.
+ Finally, the gen_server protocol is embedded in the Erlang
+ distribution protocol. Pertinent parts of that protocol is
+ described further below.
+ </p>
+ </section>
+
+ <section>
+ <title>Language mappings and IDL operations</title>
+
+ <section>
+ <title>IDL Operations</title>
+ <p>An IDL operation is declared as follows:</p>
+ <code type="none">
+\011[oneway] RetType Op(in IType1 I1, in IType2 I2, ..., in ITypeN IN,
+\011out OType1 O1, out OType2 O2, ..., out OTypeM OM)
+\011N, M = 0, 1, 2, ...\011\011(2.1.1)
+ </code>
+ <p>`Op' is the operation name, RetType is the return type, and ITypei,
+ i = 1, 2, ..., N, and OTypej, j = 1, 2, ..., M, are the `in' types
+ and `out' types, respectively. The values I1, I2, ..., IN are
+ provided by the caller, and the value of RetType, and the values
+ O1, O2, ..., OM, are provided as results to the caller.
+ </p>
+ <p>The types can be any basic types or derived types declared in the
+ IDL specification of which the operation declaration is a part.
+ </p>
+ <p>If the RetType has the special name `void' there is no return
+ value (but there might still be result values O1, 02, ..., OM).
+ </p>
+ <p>The `in' and `out' parameters can be declared in any order, but
+ for clarity we have listed all `in' parameters before the `out'
+ parameters in the declaration above.
+ </p>
+ <p>If the keyword `oneway' is present, the operation is a cast, i.e.
+ there is no confirmation of the operation, and consequently there
+ must be no result values: RetType must be equal to `void', and M =
+ 0 must hold.
+ </p>
+ <p>Otherwise the operation is a call, i.e. it is confirmed (or else
+ an exception is raised).
+ </p>
+ <p>Note carefully that an operation declared without `oneway' is
+ always a call, even if RetType is `void' and M = 0.
+ </p>
+ </section>
+
+ <section>
+ <title>Language Mappings</title>
+ <p>There are several CORBA Language Mapping specifications. These are
+ about mapping interfaces to various programming languages. IC
+ supports the CORBA C and Java mapping specifications, and the
+ Erlang language mapping specified in the Orber documentation.
+ </p>
+ <p>Excerpt from "6.4 Basic OMG IDL Types" in the Orber User's Guide:
+ </p>
+ <list type="bulleted">
+ <item>
+ <p>Functions with return type void will return the atom ok.</p>
+ </item>
+ </list>
+ <p>Excerpt from "6.13 Invocations of Operations" in the Orber User's
+ Guide:
+ </p>
+ <list type="bulleted">
+ <item>
+ <p>A function call will invoke an operation. The first parameter
+ of the function should be the object reference and then all in
+ and inout parameters follow in the same order as specified in
+ the IDL specification. The result will be a return value
+ unless the function has inout or out parameters specified; in
+ which case, a tuple of the return value, followed by the
+ parameters will be returned.</p>
+ </item>
+ </list>
+ <p>Hence the function that is mapped from an IDL operation to Erlang
+ always have a return value (an Erlang function always has). That
+ fact has influenced the IC protocol, in that there is always a
+ return value (which is 'ok' if the return type was declared 'void'). </p>
+ </section>
+ </section>
+
+ <section>
+ <title>IC Protocol</title>
+ <p>Given the operation declaration (2.1.1) the IC protocol maps to
+ messages as follows, defined in terms of Erlang terms.
+ </p>
+
+ <section>
+ <title>Call (Request/Reply, i.e. not oneway)</title>
+ <code type="none">
+ request:\011\011 Op\011\011\011atom()\011\011N = 0\011
+\011\011\011 {Op, I1, I2, ..., IN}\011tuple()\011\011N > 0
+\011\011\011\011\011\011\011\011(3.1.1)
+
+ reply:\011\011 Ret\011\011\011\011\011M = 0
+\011\011\011 {Ret, O1, O2, ..., OM}\011\011\011M > 0
+\011\011\011\011\011\011\011\011(3.1.2) </code>
+ <p><em>Notice:</em> Even if the RetType of the operation Op is
+ declared to be 'void', a return value 'ok' is returned in
+ the reply message. That
+ return value is of no significance, and is therefore ignored (note
+ however that a C server back-end returns the atom 'void' instead
+ of 'ok').
+ </p>
+ </section>
+
+ <section>
+ <title>Cast (oneway)</title>
+ <code type="none">
+
+ notification:\011Op\011\011\011atom()\011\011N = 0
+\011\011\011{Op, I1, I2, ..., IN}\011tuple()\011\011N > 0
+\011\011\011\011\011\011\011\011(3.2.1) </code>
+ <p>(There is of course no return message).
+ </p>
+ </section>
+ </section>
+
+ <section>
+ <title>Gen_server Protocol</title>
+ <p>Most of the IC generated code deals with encoding and decoding the
+ gen_server protocol.
+ </p>
+
+ <section>
+ <title>Call</title>
+ <code type="none">
+
+ request:\011{'$gen_call', {self(), Ref}, Request}\011\011(4.1.1)
+
+ reply:\011{Ref, Reply}\011\011\011\011\011(4.1.2) </code>
+ <p>where Request and Reply are the messages defined in the previous
+ chapter.
+ </p>
+ </section>
+
+ <section>
+ <title>Cast</title>
+ <code type="none">
+ notification: {'$gen_cast', Notification}\011\011(4.2.1) </code>
+ <p>where Notification is the message defined in the previous chapter.
+ </p>
+ </section>
+ </section>
+
+ <section>
+ <title>Erlang Distribution Protocol</title>
+ <p>Messages (of interest here) between Erlang nodes are of the form: </p>
+ <code type="none">
+ Len(4), Type(1), CtrlBin(N), MsgBin(M)\011\011\011(5.1) </code>
+ <p>Type is equal to 112 = PASS_THROUGH.
+ </p>
+ <p>CtrlBin and MsgBin are Erlang terms in binary form (as if created
+ by term_to_binary/1), whence for each of them the first byte is
+ equal to 131 = VERSION_MAGIC.
+ </p>
+ <p>CtrlBin (of interest here) contains the SEND and REG_SEND control
+ messages, which are binary forms of the Erlang terms</p>
+ <code type="none">
+\011{2, Cookie, ToPid} ,\011\011\011\011\011(5.2) </code>
+ <p>and</p>
+ <code type="none">
+\011{6, FromPid, Cookie, ToName} ,\011\011\011\011(5.3) </code>
+ <p>respectively.
+ </p>
+ <p>The CtrlBin(N) message is read and written by erl_interface code
+ (C), j_interface code (Java), or the Erlang distribution
+ implementation, which are invoked from IC generated code.
+ </p>
+ <p>The MsgBin(N) is the "real" message, i.e. of the form described
+ in the previous section.
+ </p>
+ </section>
+</chapter>
+