.. _S4U_doc:
+=================
The S4U Interface
=================
abstract algorithms in the domains of Cloud, P2P, HPC, IoT and similar
settings.
+-------------
Main Concepts
-------------
.. |Mutex| replace:: **Mutex**
.. _Mutex: api/classsimgrid_1_1s4u_1_1Mutex.html
+
+----------
+Activities
+----------
+
+Activities represent the actions that consumes a resource, such as
+: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
+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 at most for a given period,
+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
+
+You then start all 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: send-begin
+ :end-before: send-end
+ :dedent: 4
+
+
+.....................
+Activities Life cycle
+.....................
+
+Sometimes, you want to change the setting of an activity before it even starts.
