1 /* Copyright (c) 2006-2018. The SimGrid Team. All rights reserved. */
3 /* This program is free software; you can redistribute it and/or modify it
4 * under the terms of the license (GNU LGPL) which comes with this package. */
6 #ifndef SIMGRID_S4U_MAILBOX_HPP
7 #define SIMGRID_S4U_MAILBOX_HPP
9 #include <xbt/string.hpp>
10 #include <simgrid/s4u/Actor.hpp>
17 /** @brief Mailboxes: Network rendez-vous points.
19 * <b>What are mailboxes?</b>
21 * Rendez-vous point for network communications, similar to URLs on
22 * which you could post and retrieve data. Actually, the mailboxes are
23 * not involved in the communication once it starts, but only to find
24 * the contact with which you want to communicate.
26 * Here are some mechanisms similar to the mailbox in other
27 * communication systems: The phone number, which allows the caller to
28 * find the receiver. The twitter hashtag, which help senders and
29 * receivers to find each others. In TCP, the pair {host name, host
30 * port} to which you can connect to find your interlocutor. In HTTP,
31 * URLs through which the clients can connect to the servers. In ZeroMQ
32 * and other queuing systems, the queues are used to match senders
35 * One big difference with most of these systems is that no actor is
36 * the exclusive owner of a mailbox, neither in sending nor in
37 * receiving. Many actors can send into and/or receive from the
38 * same mailbox. This is a big difference to the socket ports for
39 * example, that are definitely exclusive in receiving.
41 * Mailboxes can optionally have a @i receiver with `simgrid::s4u::Mailbox::set_receiver()`.
42 * It means that the data exchange starts as soon as the sender has
43 * done the `put()`, even before the corresponding `get()`
44 * (usually, it starts as soon as both `put()` and `get()` are posted).
45 * This is closer to the BSD semantic and can thus help to improve
46 * the timing accuracy, but this is not mandatory at all.
48 * A big difference with twitter hashtags is that SimGrid does not
49 * offer easy support to broadcast a given message to many
50 * receivers. So that would be like a twitter tag where each message
51 * is consumed by the first coming receiver.
53 * A big difference with the ZeroMQ queues is that you cannot filter
54 * on the data you want to get from the mailbox. To model such settings
55 * in SimGrid, you'd have one mailbox per potential topic, and subscribe
56 * to each topic individually with a `get_async()` on each mailbox.
57 * Then, use `Comm::wait_any()` to get the first message on any of the
58 * mailbox you are subscribed onto.
60 * The mailboxes are not located on the network, and you can access
61 * them without any latency. The network delay are only related to the
62 * location of the sender and receiver once the match between them is
63 * done on the mailbox. This is just like the phone number that you
64 * can use locally, and the geographical distance only comes into play
65 * once you start the communication by dialing this number.
67 * <b>How to use mailboxes?</b>
69 * Any existing mailbox can be retrieve from its name (which are
70 * unique strings, just like with twitter tags). This results in a
71 * versatile mechanism that can be used to build many different
74 * For something close to classical socket communications, use
75 * "hostname:port" as mailbox names, and make sure that only one actor
76 * reads into that mailbox. It's hard to build a perfectly realistic
77 * model of the TCP sockets, but most of the time, this system is too
78 * cumbersome for your simulations anyway. You probably want something
79 * simpler, that turns our to be easy to build with the mailboxes.
81 * Many SimGrid examples use a sort of yellow page system where the
82 * mailbox names are the name of the service (such as "worker",
83 * "master" or "reducer"). That way, you don't have to know where your
84 * peer is located to contact it. You don't even need its name. Its
85 * function is enough for that. This also gives you some sort of load
86 * balancing for free if more than one actor pulls from the mailbox:
87 * the first relevant actor that can deal with the request will handle
90 * <b>How are sends and receives matched?</b>
92 * The matching algorithm is as simple as a first come, first
93 * serve. When a new send arrives, it matches the oldest enqueued
94 * receive. If no receive is currently enqueued, then the incoming
95 * send is enqueued. As you can see, the mailbox cannot contain both
96 * send and receive requests: all enqueued requests must be of the
99 * <b>Declaring a receiving actor</b>
101 * The last twist is that by default in the simulator, the data starts
102 * to be exchanged only when both the sender and the receiver are
103 * declared while in real systems (such as TCP or MPI), the data
104 * starts to flow as soon as the sender posts it, even if the receiver
105 * did not post its recv() yet. This can obviously lead to bad
106 * simulation timings, as the simulated communications do not start at
107 * the exact same time than the real ones.
109 * If the simulation timings are very important to you, you can
110 * declare a specific receiver to a given mailbox (with the function
111 * setReceiver()). That way, any send() posted to that mailbox will
112 * start as soon as possible, and the data will already be there on
113 * the receiver host when the receiver actor posts its receive().
118 class XBT_PUBLIC Mailbox {
119 friend simgrid::s4u::Comm;
120 friend simgrid::kernel::activity::MailboxImpl;
122 simgrid::kernel::activity::MailboxImpl* pimpl_;
124 explicit Mailbox(kernel::activity::MailboxImpl * mbox) : pimpl_(mbox) {}
126 /** private function to manage the mailboxes' lifetime (see @ref s4u_raii) */
127 friend void intrusive_ptr_add_ref(Mailbox*) {}
128 /** private function to manage the mailboxes' lifetime (see @ref s4u_raii) */
129 friend void intrusive_ptr_release(Mailbox*) {}
131 /** private function, do not use. FIXME: make me protected */
132 kernel::activity::MailboxImpl* get_impl() { return pimpl_; }
134 /** @brief Retrieves the name of that mailbox as a C++ string */
135 const simgrid::xbt::string& get_name() const;
136 /** @brief Retrieves the name of that mailbox as a C string */
137 const char* get_cname() const;
139 /** Retrieve the mailbox associated to the given name */
140 static MailboxPtr by_name(std::string name);
142 /** Returns whether the mailbox contains queued communications */
145 /** Check if there is a communication going on in a mailbox. */
148 /** Check if there is a communication ready to be consumed from a mailbox. */
151 /** Gets the first element in the queue (without dequeuing it), or nullptr if none is there */
152 smx_activity_t front();
154 /** Declare that the specified actor is a permanent receiver on that mailbox
156 * It means that the communications sent to this mailbox will start flowing to
157 * its host even before he does a recv(). This models the real behavior of TCP
158 * and MPI communications, amongst other. It will improve the accuracy of
159 * predictions, in particular if your application exhibits swarms of small messages.
161 * SimGrid does not enforces any kind of ownership over the mailbox. Even if a receiver
162 * was declared, any other actors can still get() data from the mailbox. The timings
163 * will then probably be off tracks, so you should strive on your side to not get data
164 * from someone else's mailbox.
166 void set_receiver(ActorPtr actor);
168 /** Return the actor declared as permanent receiver, or nullptr if none **/
169 ActorPtr get_receiver();
171 /** Creates (but don't start) a data emission to that mailbox */
173 /** Creates (but don't start) a data emission to that mailbox */
174 CommPtr put_init(void* data, uint64_t simulated_size_in_bytes);
175 /** Creates and start a data emission to that mailbox */
176 CommPtr put_async(void* data, uint64_t simulated_size_in_bytes);
178 /** Blocking data emission */
179 void put(void* payload, uint64_t simulated_size_in_bytes);
180 /** Blocking data emission with timeout */
181 void put(void* payload, uint64_t simulated_size_in_bytes, double timeout);
183 /** Creates (but don't start) a data reception onto that mailbox */
185 /** Creates and start an async data reception to that mailbox */
186 CommPtr get_async(void** data);
188 /** Blocking data reception */
189 void* get(); // FIXME: make a typed template version
190 /** Blocking data reception with timeout */
191 void* get(double timeout);
193 // Deprecated functions
194 /** @deprecated Mailbox::set_receiver() */
195 XBT_ATTRIB_DEPRECATED_v323("Please use Mailbox::set_receiver()") void setReceiver(ActorPtr actor)
199 /** @deprecated Mailbox::get_receiver() */
200 XBT_ATTRIB_DEPRECATED_v323("Please use Mailbox::get_receiver()") ActorPtr getReceiver() { return get_receiver(); }
201 /** @deprecated Mailbox::get_name() */
202 XBT_ATTRIB_DEPRECATED_v323("Please use Mailbox::get_name()") const simgrid::xbt::string& getName() const
206 /** @deprecated Mailbox::get_cname() */
207 XBT_ATTRIB_DEPRECATED_v323("Please use Mailbox::get_cname()") const char* getCname() const { return get_cname(); }
208 /** @deprecated Mailbox::get_impl() */
209 XBT_ATTRIB_DEPRECATED_v323("Please use Mailbox::get_impl()") kernel::activity::MailboxImpl* getImpl()
213 /** @deprecated Mailbox::by_name() */
214 XBT_ATTRIB_DEPRECATED_v323("Please use Mailbox::by_name()") static MailboxPtr byName(const char* name)
216 return by_name(name);
218 /** @deprecated Mailbox::by_name() */
219 XBT_ATTRIB_DEPRECATED_v323("Please use Mailbox::by_name()") static MailboxPtr byName(std::string name)
221 return by_name(name);
225 }} // namespace simgrid::s4u
227 #endif /* SIMGRID_S4U_MAILBOX_HPP */