- \ref GRAS_tut_tour_simpledata_use
- \ref GRAS_tut_tour_simpledata_example
- \ref GRAS_tut_tour_simpledata_recap
-
+
<hr>
\section GRAS_tut_tour_simpledata_intro Introduction
The platforms targeted by GRAS complicate the data transfers since the
machines may well be heterogeneous. You may want to exchange data between a
regular x86 machine (Intel and assimilated) and amd64 machine or even a ppc
-machine (Mac).
+machine (Mac).
The first problem comes from the fact that C datatypes are not always of the
same size depending on the processor. On 32 bits machines (such as x86 and
Simply, when you declare a message type with gras_msgtype_declare(), you
should provide a description of the payload data type as last argument. GRAS
will serialize the data, send it on the socket, convert it on need and
-deserialize it for you automatically.
+deserialize it for you automatically.
That means that any given message type can only convey a payload of a
predefined type. You cannot have a message type sometimes conveying an
a segfault. Try passing too few parameters to printf with regard to the
format string if you want an example. Moreover, since you can convey
structures, it is easy to overcome this limitation: if you want several
-arguments, simply pack them into a structure before doing so.
+arguments, simply pack them into a structure before doing so.
There is absolutely no limitation on the type of data you can exchange in
GRAS. If you can build a C representation of your data, you can exchange it
- int
- long int
- long long int
-
+
For all these types, there is three variant: signed, unsigned and the
version where it is not specified. For example, "signed char", "char" and
"unsigned char" are all GRAS predefined datatype. The use of the unqualified
over the network and are thus predefined)
- #xbt_peer_t (a datatype describing a peer. There is a plenty of situation
in which you want to exchange data of this type, so this is also predefined)
-
+
\section GRAS_tut_tour_simpledata_example Back to our example
We will now modify our example to add some data to the "hello" and the
"kill" messages. "hello" will convey a string being displayed in the logs
while "kill" will convey an double indicating the number of seconds to wait
-before dying.
+before dying.
The first thing is to modify the message declarations to specify that they
convey a payload. Of course, all nodes have to agree on message definitions,
the network, converted and deserialized, but really, you can consider that
it's the exact copy of your variable. So, to retrieve the content, you have
to cast the <tt>void*</tt> pointer to a pointer on your datatype, and then
-derefence it.
+derefence it.
So, it you want to retrieve a double, you have to cast the pointer using
<tt>(double*)</tt>, and then dereference the obtained pointer by adding a
