namespace simgrid {
namespace s4u {
-/** @brief Mailboxes: Network rendez-vous points.
- * @ingroup s4u_api
- *
- * @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 SimGrid examples 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_matching How are sends and receives matched?
- *
- * The matching algorithm is as simple as a first come, first
- * serve. When a new send arrives, it matches the oldest enqueued
- * receive. If no receive is currently enqueued, then the incomming
- * send is enqueued. As you can see, the mailbox cannot contain both
- * send and receive requests: all enqueued requests must be of the
- * same sort.
- *
- * @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
- */
+/** @brief Mailboxes: Network rendez-vous points. */
class XBT_PUBLIC Mailbox {
- friend Comm;
+ friend simgrid::s4u::Comm;
friend simgrid::kernel::activity::MailboxImpl;
simgrid::kernel::activity::MailboxImpl* pimpl_;
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:
/** private function, do not use. FIXME: make me protected */
kernel::activity::MailboxImpl* get_impl() { return pimpl_; }
/** Check if there is a communication going on in a mailbox. */
bool listen();
+ /** Check if there is a communication ready to be consumed from a mailbox. */
+ bool ready();
+
/** Gets the first element in the queue (without dequeuing it), or nullptr if none is there */
smx_activity_t front();
/** 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.
+ * its host even before it does a get(). This models the real behavior of TCP
+ * and MPI communications, amongst other. It will improve the accuracy of
+ * predictions, in particular if your application exhibits swarms of small messages.
+ *
+ * SimGrid does not enforces any kind of ownership over the mailbox. Even if a receiver
+ * was declared, any other actors can still get() data from the mailbox. The timings
+ * will then probably be off tracks, so you should strive on your side to not get data
+ * from someone else's mailbox.
+ *
+ * Note that being permanent receivers of a mailbox prevents actors to be garbage-collected.
+ * If your simulation creates many short-lived actors that marked as permanent receiver, you
+ * should call mailbox->set_receiver(nullptr) by the end of the actors so that their memory gets
+ * properly reclaimed. This call should be at the end of the actor's function, not in a on_exit
+ * callback.
*/
void set_receiver(ActorPtr actor);
/** Return the actor declared as permanent receiver, or nullptr if none **/
ActorPtr get_receiver();
- /** Creates (but don't start) a data emission to that mailbox */
+ /** Creates (but don't start) a data transmission to that mailbox */
CommPtr put_init();
- /** Creates (but don't start) a data emission to that mailbox */
+ /** Creates (but don't start) a data transmission to that mailbox */
CommPtr put_init(void* data, uint64_t simulated_size_in_bytes);
- /** Creates and start a data emission to that mailbox */
+ /** Creates and start a data transmission to that mailbox */
CommPtr put_async(void* data, uint64_t simulated_size_in_bytes);
- /** Blocking data emission */
+ /** Blocking data transmission */
void put(void* payload, uint64_t simulated_size_in_bytes);
- /** Blocking data emission with timeout */
+ /** Blocking data transmission with timeout */
void put(void* payload, uint64_t simulated_size_in_bytes, double timeout);
/** Creates (but don't start) a data reception onto that mailbox */
void* get(double timeout);
// Deprecated functions
+#ifndef DOXYGEN
/** @deprecated Mailbox::set_receiver() */
XBT_ATTRIB_DEPRECATED_v323("Please use Mailbox::set_receiver()") void setReceiver(ActorPtr actor)
{
{
return by_name(name);
}
+#endif
};
}} // namespace simgrid::s4u
