namespace simgrid {
namespace s4u {
-/** @brief Mailboxes
+/** @brief Mailboxes: Network rendez-vous points.
+ * @ingroup s4u_api
*
- * Rendez-vous point for network communications, similar to URLs on which you could post and retrieve data.
- * They are not network locations: you can post and retrieve on a given mailbox from anywhere on the network.
- * You can access any mailbox without any latency. The network delay are only related to the location of the
- * sender and receiver.
+ * @tableofcontents
+ *
+ * @section s4u_mb_what What are mailboxes
+ *
+ * Rendez-vous point for network communications, similar to URLs on
+ * which you could post and retrieve data. Actually, the mailboxes are
+ * not involved in the communication once it starts, but only to find
+ * the contact with which you want to communicate.
+
+ * Here are some mechanisms similar to the mailbox in other
+ * communication systems: The phone number, which allows the caller to
+ * find the receiver. The twitter hashtag, which help senders and
+ * receivers to find each others. In TCP, the pair {host name, host
+ * port} to which you can connect to find your interlocutor. In HTTP,
+ * URLs through which the clients can connect to the servers.
+ *
+ * One big difference with most of these systems is that usually, no
+ * actor is the exclusive owner of a mailbox, neither in sending nor
+ * in receiving. Many actors can send into and/or receive from the
+ * same mailbox. This is a big difference to the socket ports for
+ * example, that are definitely exclusive in receiving.
+ *
+ * A big difference with twitter hashtags is that SimGrid does not
+ * offer easy support to broadcast a given message to many
+ * receivers. So that would be like a twitter tag where each message
+ * is consumed by the first coming receiver.
+ *
+ * The mailboxes are not located on the network, and you can access
+ * them without any latency. The network delay are only related to the
+ * location of the sender and receiver once the match between them is
+ * done on the mailbox. This is just like the phone number that you
+ * can use locally, and the geographical distance only comes into play
+ * once you start the communication by dialling this number.
+ *
+ * @section s4u_mb_howto How to use mailboxes?
+ *
+ * Any existing mailbox can be retrieve from its name (which are
+ * unique strings, just like with twitter tags). This results in a
+ * versatile mechanism that can be used to build many different
+ * situations.
+ *
+ * For something close to classical socket communications, use
+ * "hostname:port" as mailbox names, and make sure that only one actor
+ * reads into that mailbox. It's hard to build a prefectly realistic
+ * model of the TCP sockets, but most of the time, this system is too
+ * cumbersome for your simulations anyway. You probably want something
+ * simpler, that turns our to be easy to build with the mailboxes.
+ *
+ * Many examples in the archive use a sort of yellow page system where
+ * the mailbox names are the name of the service (such as "worker",
+ * "master" or "reducer"). That way, you don't have to know where your
+ * peer is located to contact it. You don't even need its name. Its
+ * function is enough for that. This also gives you some sort of load
+ * balancing for free if more than one actor pulls from the mailbox:
+ * the first relevant actor that can deal with the request will handle
+ * it.
+ *
+ * @section s4u_mb_receiver Declaring a receiving actor
+ *
+ * The last twist is that by default in the simulator, the data starts
+ * to be exchanged only when both the sender and the receiver are
+ * declared while in real systems (such as TCP or MPI), the data
+ * starts to flow as soon as the sender posts it, even if the receiver
+ * did not post its recv() yet. This can obviously lead to bad
+ * simulation timings, as the simulated communications do not start at
+ * the exact same time than the real ones.
+ *
+ * If the simulation timings are very important to you, you can
+ * declare a specific receiver to a given mailbox (with the function
+ * setReceiver()). That way, any send() posted to that mailbox will
+ * start as soon as possible, and the data will already be there on
+ * the receiver host when the receiver actor posts its receive().
+ *
+ * @section s4u_mb_api The API
*/
XBT_PUBLIC_CLASS Mailbox {
friend Comm;
Mailbox(smx_mailbox_t mbox): pimpl_(mbox) {}
- // We don't have to manage the lifetime of mailboxes:
+ /** private function to manage the mailboxes' lifetime (see @ref s4u_raii) */
friend void intrusive_ptr_add_ref(Mailbox*) {}
+ /** private function to manage the mailboxes' lifetime (see @ref s4u_raii) */
friend void intrusive_ptr_release(Mailbox*) {}
public:
- smx_mailbox_t getImpl() { return pimpl_; } // FIXME: make me protected
-
+ /** private function, do not use. FIXME: make me protected */
+ smx_mailbox_t getImpl() { return pimpl_; }
- /** Get the name of that mailbox */
+ /** Gets the name of that mailbox */
const char *getName();
- /** Retrieve the mailbox associated to the given string (as a C string) */
+ /** Retrieve the mailbox associated to the given C string */
static MailboxPtr byName(const char *name);
- /** Retrieve the mailbox associated to the given string (as a C++ string) */
+ /** Retrieve the mailbox associated to the given C++ string */
static MailboxPtr byName(std::string name);
/** Returns whether the mailbox contains queued communications */
bool empty();
- /** Returns the first element in the queue, or nullptr if none is there */
+ /** Gets the first element in the queue (without dequeuing it), or nullptr if none is there */
smx_activity_t front();
- /** Declare that the specified process is a permanent receiver on that mailbox
+ /** Declare that the specified actor is a permanent receiver on that mailbox
*
* It means that the communications sent to this mailbox will start flowing to
* its host even before he does a recv(). This models the real behavior of TCP
* and MPI communications, amongst other.
*/
- void setReceiver(ActorPtr process);
+ void setReceiver(ActorPtr actor);
- /** Return the process declared as permanent receiver, or nullptr if none **/
+ /** Return the actor declared as permanent receiver, or nullptr if none **/
ActorPtr receiver();
};
