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authorLukas Larsson <[email protected]>2014-01-08 18:54:15 +0100
committerLukas Larsson <[email protected]>2014-02-24 15:16:03 +0100
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ose: Create OSE application
Create an specific OSE application that mainly contains documentation around the OSE specific part of Erlang/OTP.
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+<?xml version="1.0" encoding="utf-8" ?>
+<!DOCTYPE chapter SYSTEM "chapter.dtd">
+
+<chapter>
+ <header>
+ <copyright>
+ <year>2013</year><year>2014</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>Interacting with Enea OSE</title>
+ <prepared>Lukas Larsson</prepared>
+ <docno></docno>
+ <date>2014-01-08</date>
+ <rev>A</rev>
+ <file>ose_signals_chapter.xml</file>
+ </header>
+
+ <marker id="introduction"></marker>
+ <section>
+ <title>Introduction</title>
+ <p>The main way which programs on Enea OSE interact is through the
+ usage of message passing, much the same way as Erlang processes
+ communicate. There are two ways in which an Erlang programmer can
+ interact with the signals sent from other Enea OSE processes; either
+ through the provided <c>ose</c> module, or by writing a custom linked-in
+ driver. This User's Guide describes and provides examples for both
+ approaches.
+ </p>
+ </section>
+
+ <marker id="erlang"></marker>
+ <section>
+ <title>Signals in Erlang</title>
+ </section>
+
+ <marker id="driver"></marker>
+ <section>
+ <title>Signals in a Linked-in driver</title>
+ <p>
+ Writing Linked-in drivers for OSE is very similar to how it is done
+ for Unix/Windows. It is only the way in which the driver subscribes
+ and consumed external events that is different. In Unix (and Windows)
+ file descriptiors (and Event Objects) are used to select on. On OSE
+ we use signals to deliver the same functionality. There are two large
+ differences between a signal and an fd.
+ </p>
+ <p>
+ In OSE it is not possible for a signal number to be a unique identifier
+ for a resource in the same way as an fd is. For example; let's say we
+ implement a driver that does an asynchronous hunt that uses signal
+ number 1234 as the hunt_sig. If we want to be able to have multiple
+ hunt ports running at the same time we have to have someway of routing
+ the signal to the correct port. This is achieved by supplying a secondary
+ id that can be retrieved through the meta-data or payload of the signal,
+ e.g:
+ <code>ErlDrvEvent event = erl_drv_ose_event_alloc(1234,port,resolver);</code>
+ The event you get back from
+ <seealso marker="ose_erl_driver#erl_drv_ose_event_alloc">
+ erl_drv_ose_event_alloc</seealso> can then be used by
+ <seealso marker="erts:erl_driver#driver_select">driver_select</seealso>
+ to subscribe to signals. The first argument is just the signal number
+ that we are interested in. The second is the id that we choose to use,
+ in this case the port id that we got in the
+ <seealso marker="erts:driver_entry#start">start</seealso> callback is
+ used. The third argument is a function pointer to a function that can
+ be used to figure out the id from a given signal. There is a complete
+ example of what this could look like in
+ <seealso marker="example">the next section</seealso>.
+ <note>It is very important to issue the driver_select call before
+ any of the signals you are interested in are sent. If driver_select
+ is called after the signal is sent, there is a high probability that it
+ will be lost.</note>
+ </p>
+ <p>
+ The other difference from unix is that in OSE the payload of the event
+ (i.e. the signal data) is already received when the ready_output/input
+ callbacks are called. This means that you access the data of a signal
+ by calling <seealso marker="ose_erl_driver#erl_drv_ose_get_signal">
+ erl_drv_ose_get_signal</seealso>. Additionally multiple signals might be
+ associated with the event, so you should call
+ <seealso marker="ose_erl_driver#erl_drv_ose_get_signal">
+ erl_drv_ose_get_signal</seealso> until <c>NULL</c> is returned.
+ </p>
+ </section>
+
+ <marker id="example"></marker>
+ <section>
+ <title>Example Linked-in driver</title>
+<code>#include "erl_driver.h"
+#include "ose.h"
+
+struct huntsig {
+ SIGSELECT signo;
+ ErlDrvPort port;
+};
+
+union SIGNAL {
+ SIGSELECT signo;
+ struct huntsig;
+}
+
+/* Here we have to get the id from the signal. In this case we use the
+ port id since we have control over the data structure of the signal.
+ It is however possible to use anything in here. The only restriction
+ is that the same id has to be used for all signals of the same number.*/
+ErlDrvOseEventId resolver(union SIGNAL *sig) {
+ return (ErlDrvOseEventId)sig->huntsig.port;
+}
+
+static int drv_init(void) { return 0; };
+
+static ErlDrvData drv_start(ErlDrvPort port, char *command) {
+ return (ErlDrvData)port;
+}
+
+static ErlDrvSSizeT control(ErlDrvData driver_data, unsigned int cmd,
+ char *buf, ErlDrvSizeT len,
+ char **rbuf, ErlDrvSizeT rlen) {
+ ErlDrvPort port = (ErlDrvPort)driver_data;
+
+ /* Create a new event to select on */
+ ErlDrvOseEvent evt = erl_drv_ose_event_alloc(1234,port,resolver);
+
+ /* Make sure to do the select call _BEFORE_ the signal arrives.
+ The signal might get lost if the hunt call is done before the
+ select. */
+ driver_select(port,evt,ERL_DRV_READ|ERL_DRV_USE,1);
+
+ union SIGNAL *sig = alloc(sizeof(union SIGNAL),1234);
+ sig->huntsig.port = port;
+ hunt("testprocess",0,NULL,&amp;sig);
+ return 0;
+}
+
+static void ready_input(ErlDrvData driver_data, ErlDrvEvent evt) {
+ /* Get the first signal payload from the event */
+ union SIGNAL *sig = erl_drv_ose_get_signal(evt);
+ ErlDrvPort port = (ErlDrvPort)driver_data;
+ while (sig != NULL) {
+ if (sig->signo == 1234) {
+ /* If it is our signal we send a message with the sender of the signal
+ to the controlling erlang process */
+ ErlDrvTermData reply[] = { ERL_DRV_UINT, (ErlDrvUInt)sender(&amp;sig) };
+ erl_drv_send_term(port,reply,sizeof(reply) / sizeof(reply[0]));
+ }
+
+ /* Cleanup the signal and deselect on the event.
+ Note that the event itself has to be free'd in the stop_select
+ callback. */
+ free_buf(&amp;sig);
+ driver_select(port,evt,ERL_DRV_READ|ERL_DRV_USE,0);
+
+ /* There could be more than one signal waiting in this event, so
+ we have to loop until sig == NULL */
+ sig = erl_drv_ose_get_signal(evt);
+ }
+}
+
+static void stop_select(ErlDrvEvent event, void *reserved)
+{
+ erl_drv_ose_event_free(event);
+}
+
+/**
+ * Setup the driver entry for the Erlang runtime
+ **/
+ErlDrvEntry ose_signal_driver_entry = {
+ .init = drv_init,
+ .start = drv_start,
+ .stop = drv_stop,
+ .ready_input = ready_input,
+ .driver_name = DRIVER_NAME,
+ .control = control,
+ .extended_marker = ERL_DRV_EXTENDED_MARKER,
+ .major_version = ERL_DRV_EXTENDED_MAJOR_VERSION,
+ .minor_version = ERL_DRV_EXTENDED_MINOR_VERSION,
+ .driver_flags = ERL_DRV_FLAG_USE_PORT_LOCKING,
+ .stop_select = stop_select
+};
+</code>
+ </section>
+
+</chapter>