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diff --git a/system/doc/reference_manual/ports.xml b/system/doc/reference_manual/ports.xml new file mode 100644 index 0000000000..4847dd67cd --- /dev/null +++ b/system/doc/reference_manual/ports.xml @@ -0,0 +1,159 @@ +<?xml version="1.0" encoding="latin1" ?> +<!DOCTYPE chapter SYSTEM "chapter.dtd"> + +<chapter> + <header> + <copyright> + <year>2004</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>Ports and Port Drivers</title> + <prepared></prepared> + <docno></docno> + <date></date> + <rev></rev> + <file>ports.xml</file> + </header> + <p>Examples of how to use ports and port drivers can be found in + <em>Interoperability Tutorial</em>. The BIFs mentioned are as usual + documented in <c>erlang(3)</c>.</p> + + <section> + <title>Ports</title> + <p><em>Ports</em> provide the basic mechanism for communication + with the external world, from Erlang's point of view. They + provide a byte-oriented interface to an external program. When a + port has been created, Erlang can communicate with it by sending + and receiving lists of bytes, including binaries.</p> + <p>The Erlang process which creates a port is said to be + the <em>port owner</em>, or the <em>connected process</em> of + the port. All communication to and from the port should go via + the port owner. If the port owner terminates, so will the port + (and the external program, if it is written correctly).</p> + <p>The external program resides in another OS process. By default, + it should read from standard input (file descriptor 0) and write + to standard output (file descriptor 1). The external program + should terminate when the port is closed.</p> + </section> + + <section> + <title>Port Drivers</title> + <p>It is also possible to write a driver in C according to certain + principles and dynamically link it to the Erlang runtime system. + The linked-in driver looks like a port from the Erlang + programmer's point of view and is called a <em>port driver</em>.</p> + <warning> + <p>An erroneous port driver will cause the entire Erlang runtime + system to leak memory, hang or crash.</p> + </warning> + <p>Port drivers are documented in <c>erl_driver(4)</c>, + <c>driver_entry(1)</c> and <c>erl_ddll(3)</c>.</p> + </section> + + <section> + <title>Port BIFs</title> + <p>To create a port:</p> + <table> + <row> + <cell align="left" valign="middle"><c>open_port(PortName, PortSettings</c></cell> + <cell align="left" valign="middle">Returns a port identifier <c>Port</c>as the result of opening a new Erlang port. Messages can be sent to and received from a port identifier, just like a pid. Port identifiers can also be linked to or registered under a name using <c>link/1</c>and <c>register/2</c>.</cell> + </row> + <tcaption>Port Creation BIF.</tcaption> + </table> + <p><c>PortName</c> is usually a tuple <c>{spawn,Command}</c>, where + the string <c>Command</c> is the name of the external program. + The external program runs outside the Erlang workspace unless a + port driver with the name <c>Command</c> is found. If found, that + driver is started.</p> + <p><c>PortSettings</c> is a list of settings (options) for the port. + The list typically contains at least a tuple <c>{packet,N}</c> + which specifies that data sent between the port and the external + program are preceded by an N-byte length indicator. Valid values + for N are 1, 2 or 4. If binaries should be used instead of lists + of bytes, the option <c>binary</c> must be included.</p> + <p>The port owner <c>Pid</c> can communicate with the port + <c>Port</c> by sending and receiving messages. (In fact, any + process can send the messages to the port, but the messages from + the port always go to the port owner).</p> + <p>Below, <c>Data</c> must be an I/O list. An I/O list is a binary + or a (possibly deep) list of binaries or integers in the range + 0..255.</p> + <table> + <row> + <cell align="left" valign="middle"><c>{Pid,{command,Data}}</c></cell> + <cell align="left" valign="middle">Sends <c>Data</c>to the port.</cell> + </row> + <row> + <cell align="left" valign="middle"><c>{Pid,close}</c></cell> + <cell align="left" valign="middle">Closes the port. Unless the port is already closed, the port replies with <c>{Port,closed}</c>when all buffers have been flushed and the port really closes.</cell> + </row> + <row> + <cell align="left" valign="middle"><c>{Pid,{connect,NewPid}}</c></cell> + <cell align="left" valign="middle">Sets the port owner of <c>Port</c>to <c>NewPid</c>. Unless the port is already closed, the port replies with<c>{Port,connected}</c>to the old port owner. Note that the old port owner is still linked to the port, but the new port owner is not.</cell> + </row> + <tcaption>Messages Sent To a Port.</tcaption> + </table> + <table> + <row> + <cell align="left" valign="middle"><c>{Port,{data,Data}}</c></cell> + <cell align="left" valign="middle"><c>Data</c>is received from the external program.</cell> + </row> + <row> + <cell align="left" valign="middle"><c>{Port,closed}</c></cell> + <cell align="left" valign="middle">Reply to <c>Port ! {Pid,close}</c>.</cell> + </row> + <row> + <cell align="left" valign="middle"><c>{Port,connected}</c></cell> + <cell align="left" valign="middle">Reply to <c>Port ! {Pid,{connect,NewPid}}</c></cell> + </row> + <row> + <cell align="left" valign="middle"><c>{'EXIT',Port,Reason}</c></cell> + <cell align="left" valign="middle">If the port has terminated for some reason.</cell> + </row> + <tcaption>Messages Received From a Port.</tcaption> + </table> + <p>Instead of sending and receiving messages, there are also a + number of BIFs that can be used. These can be called by any + process, not only the port owner.</p> + <table> + <row> + <cell align="left" valign="middle"><c>port_command(Port,Data)</c></cell> + <cell align="left" valign="middle">Sends <c>Data</c>to the port.</cell> + </row> + <row> + <cell align="left" valign="middle"><c>port_close(Port)</c></cell> + <cell align="left" valign="middle">Closes the port.</cell> + </row> + <row> + <cell align="left" valign="middle"><c>port_connect(Port,NewPid)</c></cell> + <cell align="left" valign="middle">Sets the port owner of <c>Port</c>to <c>NewPid</c>. The old port owner <c>Pid</c>stays linked to the port and have to call <c>unlink(Port)</c>if this is not desired.</cell> + </row> + <row> + <cell align="left" valign="middle"><c>erlang:port_info(Port,Item)</c></cell> + <cell align="left" valign="middle">Returns information as specified by <c>Item</c>.</cell> + </row> + <row> + <cell align="left" valign="middle"><c>erlang:ports()</c></cell> + <cell align="left" valign="middle">Returns a list of all ports on the current node.</cell> + </row> + <tcaption>Port BIFs.</tcaption> + </table> + <p>There are some additional BIFs that only apply to port drivers: + <c>port_control/3</c> and <c>erlang:port_call/3</c>.</p> + </section> +</chapter> + |