1 /* Copyright (c) 2006-2017. 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
12 #include <xbt/string.hpp>
14 #include <simgrid/s4u/forward.hpp>
15 #include <simgrid/s4u/Actor.hpp>
20 /** @brief Mailboxes: Network rendez-vous points.
25 * @section s4u_mb_what What are mailboxes
27 * Rendez-vous point for network communications, similar to URLs on
28 * which you could post and retrieve data. Actually, the mailboxes are
29 * not involved in the communication once it starts, but only to find
30 * the contact with which you want to communicate.
32 * Here are some mechanisms similar to the mailbox in other
33 * communication systems: The phone number, which allows the caller to
34 * find the receiver. The twitter hashtag, which help senders and
35 * receivers to find each others. In TCP, the pair {host name, host
36 * port} to which you can connect to find your interlocutor. In HTTP,
37 * URLs through which the clients can connect to the servers.
39 * One big difference with most of these systems is that usually, no
40 * actor is the exclusive owner of a mailbox, neither in sending nor
41 * in receiving. Many actors can send into and/or receive from the
42 * same mailbox. This is a big difference to the socket ports for
43 * example, that are definitely exclusive in receiving.
45 * A big difference with twitter hashtags is that SimGrid does not
46 * offer easy support to broadcast a given message to many
47 * receivers. So that would be like a twitter tag where each message
48 * is consumed by the first coming receiver.
50 * The mailboxes are not located on the network, and you can access
51 * them without any latency. The network delay are only related to the
52 * location of the sender and receiver once the match between them is
53 * done on the mailbox. This is just like the phone number that you
54 * can use locally, and the geographical distance only comes into play
55 * once you start the communication by dialling this number.
57 * @section s4u_mb_howto How to use mailboxes?
59 * Any existing mailbox can be retrieve from its name (which are
60 * unique strings, just like with twitter tags). This results in a
61 * versatile mechanism that can be used to build many different
64 * For something close to classical socket communications, use
65 * "hostname:port" as mailbox names, and make sure that only one actor
66 * reads into that mailbox. It's hard to build a prefectly realistic
67 * model of the TCP sockets, but most of the time, this system is too
68 * cumbersome for your simulations anyway. You probably want something
69 * simpler, that turns our to be easy to build with the mailboxes.
71 * Many SimGrid examples use a sort of yellow page system where the
72 * mailbox names are the name of the service (such as "worker",
73 * "master" or "reducer"). That way, you don't have to know where your
74 * peer is located to contact it. You don't even need its name. Its
75 * function is enough for that. This also gives you some sort of load
76 * balancing for free if more than one actor pulls from the mailbox:
77 * the first relevant actor that can deal with the request will handle
80 * @section s4u_mb_matching How are sends and receives matched?
82 * The matching algorithm is as simple as a first come, first
83 * serve. When a new send arrives, it matches the oldest enqueued
84 * receive. If no receive is currently enqueued, then the incomming
85 * send is enqueued. As you can see, the mailbox cannot contain both
86 * send and receive requests: all enqueued requests must be of the
89 * @section s4u_mb_receiver Declaring a receiving actor
91 * The last twist is that by default in the simulator, the data starts
92 * to be exchanged only when both the sender and the receiver are
93 * declared while in real systems (such as TCP or MPI), the data
94 * starts to flow as soon as the sender posts it, even if the receiver
95 * did not post its recv() yet. This can obviously lead to bad
96 * simulation timings, as the simulated communications do not start at
97 * the exact same time than the real ones.
99 * If the simulation timings are very important to you, you can
100 * declare a specific receiver to a given mailbox (with the function
101 * setReceiver()). That way, any send() posted to that mailbox will
102 * start as soon as possible, and the data will already be there on
103 * the receiver host when the receiver actor posts its receive().
105 * @section s4u_mb_api The API
107 XBT_PUBLIC_CLASS Mailbox {
109 friend simgrid::s4u::Engine;
110 friend simgrid::kernel::activity::MailboxImpl;
112 simgrid::kernel::activity::MailboxImpl* pimpl_;
114 explicit Mailbox(kernel::activity::MailboxImpl * mbox) : pimpl_(mbox) {}
116 /** private function to manage the mailboxes' lifetime (see @ref s4u_raii) */
117 friend void intrusive_ptr_add_ref(Mailbox*) {}
118 /** private function to manage the mailboxes' lifetime (see @ref s4u_raii) */
119 friend void intrusive_ptr_release(Mailbox*) {}
121 /** private function, do not use. FIXME: make me protected */
122 kernel::activity::MailboxImpl* getImpl() { return pimpl_; }
124 /** @brief Retrieves the name of that mailbox as a C++ string */
125 const simgrid::xbt::string& getName() const;
126 /** @brief Retrieves the name of that mailbox as a C string */
127 const char* getCname() const;
129 /** Retrieve the mailbox associated to the given C string */
130 static MailboxPtr byName(const char *name);
132 /** Retrieve the mailbox associated to the given C++ string */
133 static MailboxPtr byName(std::string name);
135 /** Returns whether the mailbox contains queued communications */
138 /** Check if there is a communication going on in a mailbox. */
141 /** Gets the first element in the queue (without dequeuing it), or nullptr if none is there */
142 smx_activity_t front();
144 /** Declare that the specified actor is a permanent receiver on that mailbox
146 * It means that the communications sent to this mailbox will start flowing to
147 * its host even before he does a recv(). This models the real behavior of TCP
148 * and MPI communications, amongst other.
150 void setReceiver(ActorPtr actor);
152 /** Return the actor declared as permanent receiver, or nullptr if none **/
153 ActorPtr getReceiver();
155 /** Creates (but don't start) a data emission to that mailbox */
157 /** Creates (but don't start) a data emission to that mailbox */
158 CommPtr put_init(void* data, uint64_t simulatedSizeInBytes);
159 /** Creates and start a data emission to that mailbox */
160 CommPtr put_async(void* data, uint64_t simulatedSizeInBytes);
162 /** Blocking data emission */
163 void put(void* payload, uint64_t simulatedSizeInBytes);
164 /** Blocking data emission with timeout */
165 void put(void* payload, uint64_t simulatedSizeInBytes, double timeout);
167 /** Creates (but don't start) a data reception onto that mailbox */
169 /** Creates and start an async data reception to that mailbox */
170 CommPtr get_async(void** data);
172 /** Blocking data reception */
174 /** Blocking data reception with timeout */
175 void* get(double timeout);
178 }} // namespace simgrid::s4u
180 #endif /* SIMGRID_S4U_MAILBOX_HPP */