ose: Create OSE application

Create an specific OSE application that mainly contains documentation
around the OSE specific part of Erlang/OTP.

1 files changed, 197 insertions, 0 deletions

diff --git a/lib/ose/doc/src/ose_signals_chapter.xml b/lib/ose/doc/src/ose_signals_chapter.xml
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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>