.. _S4U_doc:
+=================
The S4U Interface
=================
<br/>
The S4U interface (SimGrid for you) mixes the full power of SimGrid
-with the full power of C++. This is the prefered interface to describe
-abstract algorithms in the domains of Cloud, P2P, HPC, IoT and similar
+with the full power of C++. This is the preferred interface to describe
+abstract algorithms in the domains of Cloud, P2P, HPC, IoT, and similar
settings.
+-------------
Main Concepts
-------------
and other |Activities|_, so that they get reflected within the
simulator. These activities take place on resources such as |Hosts|_,
|Links|_ and |Storages|_. SimGrid predicts the time taken by each
-activity and orchestrates accordingly the actors waiting for the
+activity and orchestrates the actors accordingly, waiting for the
completion of these activities.
When **communicating**, data is not directly sent to other actors but
-posted onto a |Mailbox|_ that serve as rendez-vous point between
+posted onto a |Mailbox|_ that serves as a rendez-vous point between
communicating actors. This means that you don't need to know who you
-are talking to, you just put your communication `Send` request in a
-mailbox, and it will be matched with a complementary `Receive`
+are talking to, you just put your communication `Put` request in a
+mailbox, and it will be matched with a complementary `Get`
request. Alternatively, actors can interact through **classical
synchronization mechanisms** such as |Barrier|_, |Semaphore|_,
|Mutex|_ and |ConditionVariable|_.
- :ref:`class s4u::Link <exhale_class_classsimgrid_1_1s4u_1_1Link>`
Interconnecting hosts.
- :ref:`class s4u::NetZone <exhale_class_classsimgrid_1_1s4u_1_1NetZone>`:
- Sub-region of the platform, containing resources (Hosts, Link, etc).
+ Sub-region of the platform, containing resources (Hosts, Links, etc).
- :ref:`class s4u::Storage <exhale_class_classsimgrid_1_1s4u_1_1Storage>`
Resource on which actors can write and read data.
- :ref:`class s4u::VirtualMachine <exhale_class_classsimgrid_1_1s4u_1_1VirtualMachine>`:
.. |Mutex| replace:: **Mutex**
.. _Mutex: api/classsimgrid_1_1s4u_1_1Mutex.html
+
+----------
+Activities
+----------
+
+Activities represent the actions that consume a resource, such as a
+:ref:`s4u::Comm <exhale_class_classsimgrid_1_1s4u_1_1Comm>` that
+consumes the *transmiting power* of :ref:`s4u::Link
+<exhale_class_classsimgrid_1_1s4u_1_1Link>` resources.
+
+.......................
+Asynchronous Activities
+.......................
+
+Every activity can be either **blocking** or **asynchronous**. For
+example, :cpp:func:`s4u::Mailbox::put() <simgrid::s4u::Mailbox::put>`
+and :cpp:func:`s4u::Mailbox::get() <simgrid::s4u::Mailbox::get>`
+create blocking communications: the actor is blocked until the
+completion of that communication. Asynchronous communications do not
+block the actor during their execution but progress on their own.
+
+Once your asynchronous activity is started, you can test for its
+completion using :cpp:func:`s4u::Activity::test() <simgrid::s4u::Activity::test>`.
+This function returns ``true`` if the activity completed already.
+You can also use :cpp:func:`s4u::Activity::wait() <simgrid::s4u::Activity::wait>`
+to block until the completion of the activity. To wait for at most a given amount of time,
+use :cpp:func:`s4u::Activity::wait_for() <simgrid::s4u::Activity::wait_for>`.
+Finally, to wait at most until a specified time limit, use
+:cpp:func:`s4u::Activity::wait_until() <simgrid::s4u::Activity::wait_until>`.
+
+.. todo::
+
+ wait_for and wait_until are currently not implemented for Exec and Io activities.
+
+Every kind of activities can be asynchronous:
+
+ - :ref:`s4u::CommPtr <exhale_class_classsimgrid_1_1s4u_1_1Comm>` are created with
+ :cpp:func:`s4u::Mailbox::put_async() <simgrid::s4u::Mailbox::put_async>` and
+ :cpp:func:`s4u::Mailbox::get_async() <simgrid::s4u::Mailbox::get_async>`.
+ - :ref:`s4u::IoPtr <exhale_class_classsimgrid_1_1s4u_1_1Io>` are created with
+ :cpp:func:`s4u::Storage::read_async() <simgrid::s4u::Storage::read_async>` and
+ :cpp:func:`s4u::Storage::write_async() <simgrid::s4u::Storage::write_async>`.
+ - :ref:`s4u::ExecPtr <exhale_class_classsimgrid_1_1s4u_1_1Exec>` are created with
+ :cpp:func:`s4u::Host::exec_async() <simgrid::s4u::Host::exec_async>`.
+ - In the future, it will become possible to have asynchronous IPC
+ such as asynchronous mutex lock requests.
+
+The following example shows how to have several concurrent
+communications ongoing. First, you have to declare a vector in which
+we will store the ongoing communications. It is also useful to have a
+vector of mailboxes.
+
+.. literalinclude:: ../../examples/s4u/async-waitall/s4u-async-waitall.cpp
+ :language: c++
+ :start-after: init-begin
+ :end-before: init-end
+ :dedent: 4
+
+Then, you start all the communications that should occur concurrently with
+:cpp:func:`s4u::Mailbox::put_async() <simgrid::s4u::Mailbox::put_async>`.
+Finally, the actor waits for the completion of all of them at once
+with
+:cpp:func:`s4u::Comm::wait_all() <simgrid::s4u::Comm::wait_all>`.
+
+.. literalinclude:: ../../examples/s4u/async-waitall/s4u-async-waitall.cpp
+ :language: c++
+ :start-after: put-begin
+ :end-before: put-end
+ :dedent: 4
+
+
+.....................
+Activities Life cycle
+.....................
+
+Sometimes, you want to change the setting of an activity before it even starts.
