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18 The S4U interface (SimGrid for you) mixes the full power of SimGrid
19 with the full power of C++. This is the preferred interface to describe
20 abstract algorithms in the domains of Cloud, P2P, HPC, IoT, and similar
23 Since v3.20 (June 2018), S4U is definitely the way to go for long-term
24 projects. It is feature complete, but may still evolve slightly in the
25 future releases. It can already be used to do everything that can be
26 done in SimGrid, but you may have to adapt your code in future
27 releases. When this happens, compiling your code will produce
28 deprecation warnings for 4 releases (one year) before the removal of
30 If you want an API that will never ever evolve in the future, you
31 should use the deprecated MSG API instead.
36 A typical SimGrid simulation is composed of several |API_s4u_Actors|_, that
37 execute user-provided functions. The actors have to explicitly use the
38 S4U interface to express their :ref:`computation <API_s4u_Exec>`,
39 :ref:`communication <API_s4u_Comm>`, :ref:`disk usage <API_s4u_Io>`,
40 and other |API_s4u_Activities|_, so that they get reflected within the
41 simulator. These activities take place on resources such as |API_s4u_Hosts|_,
42 |API_s4u_Links|_ and |API_s4u_Storages|_. SimGrid predicts the time taken by each
43 activity and orchestrates the actors accordingly, waiting for the
44 completion of these activities.
47 When **communicating**, data is not directly sent to other actors but
48 posted onto a |API_s4u_Mailbox|_ that serves as a rendez-vous point between
49 communicating actors. This means that you don't need to know who you
50 are talking to, you just put your communication `Put` request in a
51 mailbox, and it will be matched with a complementary `Get`
52 request. Alternatively, actors can interact through **classical
53 synchronization mechanisms** such as |API_s4u_Barrier|_, |API_s4u_Semaphore|_,
54 |API_s4u_Mutex|_ and |API_s4u_ConditionVariable|_.
56 Each actor is located on a simulated |API_s4u_Host|_. Each host is located
57 itself in a |API_s4u_NetZone|_, that knows the networking path between one
58 resource to another. Each NetZone is included in another one, forming
59 a tree of NetZones which root zone contains the whole platform.
61 The :ref:`simgrid::s4u::this_actor <API_s4u_this_actor>` namespace
62 provides many helper functions to simplify the code of actors.
66 - :ref:`class s4u::Actor <API_s4u_Actor>`:
67 Active entities executing your application.
68 - :ref:`class s4u::Engine <API_s4u_Engine>`
69 Simulation engine (singleton).
70 - :ref:`class s4u::Mailbox <API_s4u_Mailbox>`
71 Communication rendez-vous.
73 - **Platform Elements**
75 - :ref:`class s4u::Host <API_s4u_Host>`:
76 Actor location, providing computational power.
77 - :ref:`class s4u::Link <API_s4u_Link>`
78 Interconnecting hosts.
79 - :ref:`class s4u::NetZone <API_s4u_NetZone>`:
80 Sub-region of the platform, containing resources (Hosts, Links, etc).
81 - :ref:`class s4u::Storage <API_s4u_Storage>`
82 Resource on which actors can write and read data.
83 - :ref:`class s4u::VirtualMachine <API_s4u_VirtualMachine>`:
84 Execution containers that can be moved between Hosts.
86 - **Activities** (:ref:`class s4u::Activity <API_s4u_Activity>`):
87 The things that actors can do on resources
89 - :ref:`class s4u::Comm <API_s4u_Comm>`
90 Communication activity, started on Mailboxes and consuming links.
91 - :ref:`class s4u::Exec <API_s4u_Exec>`
92 Computation activity, started on Host and consuming CPU resources.
93 - :ref:`class s4u::Io <API_s4u_Io>`
94 I/O activity, started on and consumming Storages.
96 - **Synchronization Mechanisms**: Classical IPC that actors can use
98 - :ref:`class s4u::Barrier <API_s4u_Barrier>`
99 - :ref:`class s4u::ConditionVariable <API_s4u_ConditionVariable>`
100 - :ref:`class s4u::Mutex <API_s4u_Mutex>`
101 - :ref:`class s4u::Semaphore <API_s4u_Semaphore>`
104 .. |API_s4u_Actors| replace:: **Actors**
105 .. _API_s4u_Actors: #s4u-actor
107 .. |API_s4u_Activities| replace:: **Activities**
108 .. _API_s4u_Activities: #s4u-activity
110 .. |API_s4u_Hosts| replace:: **Hosts**
111 .. _API_s4u_Hosts: #s4u-host
113 .. |API_s4u_Links| replace:: **Links**
114 .. _API_s4u_Links: #s4u-link
116 .. |API_s4u_Storages| replace:: **Storages**
117 .. _API_s4u_Storages: #s4u-storage
119 .. |API_s4u_VirtualMachines| replace:: **VirtualMachines**
120 .. _API_s4u_VirtualMachines: #s4u-virtualmachine
122 .. |API_s4u_Host| replace:: **Host**
124 .. |API_s4u_Mailbox| replace:: **Mailbox**
126 .. |API_s4u_Mailboxes| replace:: **Mailboxes**
127 .. _API_s4u_Mailboxes: #s4u-mailbox
129 .. |API_s4u_NetZone| replace:: **NetZone**
131 .. |API_s4u_Barrier| replace:: **Barrier**
133 .. |API_s4u_Semaphore| replace:: **Semaphore**
135 .. |API_s4u_ConditionVariable| replace:: **ConditionVariable**
137 .. |API_s4u_Mutex| replace:: **Mutex**
141 .. include:: ../../examples/s4u/README.rst
146 Activities represent the actions that consume a resource, such as a
147 :ref:`s4u::Comm <API_s4u_Comm>` that consumes the *transmiting power* of
148 :ref:`s4u::Link <API_s4u_Link>` resources.
150 =======================
151 Asynchronous Activities
152 =======================
154 Every activity can be either **blocking** or **asynchronous**. For
155 example, :cpp:func:`s4u::Mailbox::put() <simgrid::s4u::Mailbox::put>`
156 and :cpp:func:`s4u::Mailbox::get() <simgrid::s4u::Mailbox::get>`
157 create blocking communications: the actor is blocked until the
158 completion of that communication. Asynchronous communications do not
159 block the actor during their execution but progress on their own.
161 Once your asynchronous activity is started, you can test for its
162 completion using :cpp:func:`s4u::Activity::test() <simgrid::s4u::Activity::test>`.
163 This function returns ``true`` if the activity completed already.
164 You can also use :cpp:func:`s4u::Activity::wait() <simgrid::s4u::Activity::wait>`
165 to block until the completion of the activity. To wait for at most a given amount of time,
166 use :cpp:func:`s4u::Activity::wait_for() <simgrid::s4u::Activity::wait_for>`.
167 Finally, to wait at most until a specified time limit, use
168 :cpp:func:`s4u::Activity::wait_until() <simgrid::s4u::Activity::wait_until>`.
172 wait_for and wait_until are currently not implemented for Exec and Io activities.
174 Every kind of activities can be asynchronous:
176 - :ref:`s4u::CommPtr <API_s4u_Comm>` are created with
177 :cpp:func:`s4u::Mailbox::put_async() <simgrid::s4u::Mailbox::put_async>` and
178 :cpp:func:`s4u::Mailbox::get_async() <simgrid::s4u::Mailbox::get_async>`.
179 - :ref:`s4u::IoPtr <API_s4u_Io>` are created with
180 :cpp:func:`s4u::Storage::read_async() <simgrid::s4u::Storage::read_async>` and
181 :cpp:func:`s4u::Storage::write_async() <simgrid::s4u::Storage::write_async>`.
182 - :ref:`s4u::ExecPtr <API_s4u_Exec>` are created with
183 :cpp:func:`s4u::Host::exec_async() <simgrid::s4u::Host::exec_async>`.
184 - In the future, it will become possible to have asynchronous IPC
185 such as asynchronous mutex lock requests.
187 The following example shows how to have several concurrent
188 communications ongoing. First, you have to declare a vector in which
189 we will store the ongoing communications. It is also useful to have a
192 .. literalinclude:: ../../examples/s4u/async-waitall/s4u-async-waitall.cpp
194 :start-after: init-begin
195 :end-before: init-end
198 Then, you start all the communications that should occur concurrently with
199 :cpp:func:`s4u::Mailbox::put_async() <simgrid::s4u::Mailbox::put_async>`.
200 Finally, the actor waits for the completion of all of them at once
202 :cpp:func:`s4u::Comm::wait_all() <simgrid::s4u::Comm::wait_all>`.
204 .. literalinclude:: ../../examples/s4u/async-waitall/s4u-async-waitall.cpp
206 :start-after: put-begin
211 =====================
212 Activities Life cycle
213 =====================
215 Sometimes, you want to change the setting of an activity before it even starts.
217 .. todo:: write this section
224 Please also refer to the :ref:`API reference for s4u::Mailbox
231 |API_s4u_Mailboxes|_ are rendez-vous points for network communications,
232 similar to URLs on which you could post and retrieve data. Actually,
233 the mailboxes are not involved in the communication once it starts,
234 but only to find the contact with which you want to communicate.
236 They are similar to many common things: The phone number, which allows
237 the caller to find the receiver. The twitter hashtag, which help
238 senders and receivers to find each others. In TCP, the pair
239 ``{host name, host port}`` to which you can connect to find your peer.
240 In HTTP, URLs through which the clients can connect to the servers.
241 In ZeroMQ, the queues are used to match senders and receivers.
243 One big difference with most of these systems is that no actor is the
244 exclusive owner of a mailbox, neither in sending nor in receiving.
245 Many actors can send into and/or receive from the same mailbox. TCP
246 socket ports for example are shared on the sender side but exclusive
247 on the receiver side (only one process can receive from a given socket
248 at a given point of time).
250 A big difference with TCP sockets or MPI communications is that
251 communications do not start right away after a
252 :cpp:func:`Mailbox::put() <simgrid::s4u::Mailbox::put()>`, but wait
253 for the corresponding :cpp:func:`Mailbox::get() <simgrid::s4u::Mailbox::get()>`.
254 You can change this by :ref:`declaring a receiving actor <s4u_receiving_actor>`.
256 A big difference with twitter hashtags is that SimGrid does not
257 offer easy support to broadcast a given message to many
258 receivers. So that would be like a twitter tag where each message
259 is consumed by the first receiver.
261 A big difference with the ZeroMQ queues is that you cannot filter
262 on the data you want to get from the mailbox. To model such settings
263 in SimGrid, you'd have one mailbox per potential topic, and subscribe
264 to each topic individually with a
265 :cpp:func:`get_async() <simgrid::s4u::Mailbox::get_async()>` on each mailbox.
266 Then, use :cpp:func:`Comm::wait_any() <simgrid::s4u::Comm::wait_any()>`
267 to get the first message on any of the mailbox you are subscribed onto.
269 The mailboxes are not located on the network, and you can access
270 them without any latency. The network delay are only related to the
271 location of the sender and receiver once the match between them is
272 done on the mailbox. This is just like the phone number that you
273 can use locally, and the geographical distance only comes into play
274 once you start the communication by dialing this number.
276 =====================
277 How to use Mailboxes?
278 =====================
280 You can retrieve any existing mailbox from its name (which is a
281 unique string, just like a twitter tag). This results in a
282 versatile mechanism that can be used to build many different
285 To model classical socket communications, use "hostname:port" as
286 mailbox names, and make sure that only one actor reads into a given
287 mailbox. This does not make it easy to build a perfectly realistic
288 model of the TCP sockets, but in most cases, this system is too
289 cumbersome for your simulations anyway. You probably want something
290 simpler, that turns our to be easy to build with the mailboxes.
292 Many SimGrid examples use a sort of yellow page system where the
293 mailbox names are the name of the service (such as "worker",
294 "master" or "reducer"). That way, you don't have to know where your
295 peer is located to contact it. You don't even need its name. Its
296 function is enough for that. This also gives you some sort of load
297 balancing for free if more than one actor pulls from the mailbox:
298 the first actor that can deal with the request will handle it.
300 =========================================
301 How put() and get() Requests are Matched?
302 =========================================
304 The matching algorithm simple: first come, first serve. When a new
305 send arrives, it matches the oldest enqueued receive. If no receive is
306 currently enqueued, then the incoming send is enqueued. As you can
307 see, the mailbox cannot contain both send and receive requests: all
308 enqueued requests must be of the same sort.
310 .. _s4u_receiving_actor:
312 ===========================
313 Declaring a Receiving Actor
314 ===========================
316 The last twist is that by default in the simulator, the data starts
317 to be exchanged only when both the sender and the receiver are
318 declared (it waits until both :cpp:func:`put() <simgrid::s4u::Mailbox::put()>`
319 and :cpp:func:`get() <simgrid::s4u::Mailbox::get()>` are posted).
320 In TCP, since you establish connexions beforehand, the data starts to
321 flow as soon as the sender posts it, even if the receiver did not post
322 its :cpp:func:`recv() <simgrid::s4u::Mailbox::recv()>` yet.
324 To model this in SimGrid, you can declare a specific receiver to a
325 given mailbox (with the function
326 :cpp:func:`set_receiver() <simgrid::s4u::Mailbox::set_receiver()>`).
327 That way, any :cpp:func:`put() <simgrid::s4u::Mailbox::put()>`
328 posted to that mailbox will start as soon as possible, and the data
329 will already be there on the receiver host when the receiver actor
330 posts its :cpp:func:`get() <simgrid::s4u::Mailbox::get()>`
335 For sake of simplicity, we use `RAII
336 <https://en.wikipedia.org/wiki/Resource_Acquisition_Is_Initialization>`_
337 everywhere in S4U. This is an idiom where resources are automatically
338 managed through the context. Provided that you never manipulate
339 objects of type Foo directly but always FooPtr references (which are
340 defined as `boost::intrusive_ptr
341 <http://www.boost.org/doc/libs/1_61_0/libs/smart_ptr/intrusive_ptr.html>`_
342 <Foo>), you will never have to explicitely release the resource that
343 you use nor to free the memory of unused objects.
345 Here is a little example:
351 simgrid::s4u::MutexPtr mutex = simgrid::s4u::Mutex::create(); // Too bad we cannot use `new`
353 mutex->lock(); // use the mutex as a simple reference
357 } // The mutex gets automatically freed because the only existing reference gets out of scope
362 .. _API_s4u_this_actor:
364 =========================
365 namespace s4u::this_actor
366 =========================
368 .. doxygennamespace:: simgrid::s4u::this_actor
369 .. _API_s4u_Activity:
375 .. doxygenclass:: simgrid::s4u::Activity
386 .. doxygentypedef:: ActorPtr
388 .. doxygenclass:: simgrid::s4u::Actor
399 .. doxygentypedef:: BarrierPtr
401 .. doxygenclass:: simgrid::s4u::Barrier
412 .. doxygentypedef:: CommPtr
414 .. doxygenclass:: simgrid::s4u::Comm
419 .. _API_s4u_ConditionVariable:
421 ======================
422 s4u::ConditionVariable
423 ======================
425 .. doxygentypedef:: ConditionVariablePtr
427 .. doxygenclass:: simgrid::s4u::ConditionVariable
438 .. doxygenclass:: simgrid::s4u::Engine
449 .. doxygentypedef:: ExecPtr
451 .. doxygenclass:: simgrid::s4u::Exec
462 .. doxygenclass:: simgrid::s4u::Host
473 .. doxygentypedef:: IoPtr
475 .. doxygenclass:: simgrid::s4u::Io
486 .. doxygenclass:: simgrid::s4u::Link
497 Please also refer to the :ref:`full doc on s4u::Mailbox <s4u_mailbox>`.
499 .. doxygentypedef:: MailboxPtr
501 .. doxygenclass:: simgrid::s4u::Mailbox
512 .. doxygentypedef:: MutexPtr
514 .. doxygenclass:: simgrid::s4u::Mutex
525 .. doxygenclass:: simgrid::s4u::NetZone
530 .. _API_s4u_Semaphore:
536 .. doxygentypedef:: SemaphorePtr
538 .. doxygenclass:: simgrid::s4u::Semaphore
549 .. doxygenclass:: simgrid::s4u::Storage
554 .. _API_s4u_VirtualMachine:
560 .. doxygenclass:: simgrid::s4u::VirtualMachine