It uses the `simgrid::simix::Process` as an opaque pimple:
-~~~
-class Process {
-private:
- std::atomic_int_fast32_t refcount_ { 1 };
- // The lifetime of the s4u::Actor is bound to the lifetime of the Process:
- simgrid::s4u::Actor actor_;
-public:
- Process() : actor_(this) {}
-
- // Reference count:
- friend void intrusive_ptr_add_ref(Process* process)
- {
- // Atomic operation! Do not split in two instructions!
- auto previous = (process->refcount_)++;
- xbt_assert(previous != 0);
- (void) previous;
- }
- friend void intrusive_ptr_release(Process* process)
- {
- // Atomic operation! Do not split in two instructions!
- auto count = --(process->refcount_);
- if (count == 0)
- delete process;
- }
-
- // [...]
-};
-
-smx_process_t SIMIX_process_ref(smx_process_t process)
-{
- if (process != nullptr)
- intrusive_ptr_add_ref(process);
- return process;
-}
-
-/** Decrease the refcount for this process */
-void SIMIX_process_unref(smx_process_t process)
-{
- if (process != nullptr)
- intrusive_ptr_release(process);
-}
-~~~
-
-@section simgrid_uhood_async Asynchronous operations
-
-@subsection simgrid_uhood_futures Futures
-
-The `simgrid::kernel::Future` class has been added to SimGrid as an abstraction
-to represent asynchronous operations in the SimGrid maestro. Its API is based
-on `std::experimental::future` from the [C++ Extensions for Concurrency Technical
-Specification](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0159r0.html):
-
- - `simgrid::kernel::Future<T>` represents the result an asynchronous operations
- in the simulation inside the SimGrid maestro/kernel;
-
- - `simgrid::kernel::Promise<T>` can be used to set the value of an assocaiated
- `simgrid::kernel::Future<T>`.
-
-The expected way to work with `simgrid::kernel::Future<T>` is to add a
-completion handler/continuation:
-
-~~~
-// This code is executed in the maestro context, we cannot block for the result
-// to be ready:
-simgrid::kernel::Future<std::vector<char>> result = simgrid::kernel::readFile(file);
-
-// Add a completion handler:
-result.then([file](simgrid::kernel::Future<std::vector<char>> result) {
- // At this point, the operation is complete and we can safely call .get():
- xbt_assert(result.is_ready());
- try {
- std::vector<char> data = result.get();
- XBT_DEBUG("Finished reading file %s: length %zu", file.c_str(), data.size());
- }
- // If the operation failed, .get() throws an exception:
- catch (std::runtime_error& e) {
- XBT_ERROR("Could not read file %s", file.c_str());
- }
-});
-~~~
-
-The SimGrid kernel cannot block so calling `.get()` or `.wait()` on a
-`simgrid::kernel::Future<T>` which is not ready will deadlock. In practice, the
-simulator detects this and aborts after reporting an error.
-
-In order to generate your own future, you might need to use a
-`simgrid::kernel::Promise<T>`. The promise is a one-way channel which can be
-used to set the result of an associated `simgrid::kernel::Future<T>`
-(with either `.set_value()` or `.set_exception()`):
-
-~~~
-simgrid::kernel::Future<void> kernel_wait_until(double date)
-{
- auto promise = std::make_shared<simgrid::kernel::Promise<void>>();
- auto future = promise->get_future();
- simgrid::simix::Timer::set(date, [promise] { promise->set_value(); });
- return future;
-}
-~~~
-
-Like the experimental futures, we support chaining `.then()` methods with
-automatic future unwrapping.
-You might want to look at some [tutorial on C++ futures](https://www.youtube.com/watch?v=mPxIegd9J3w&list=PLHTh1InhhwT75gykhs7pqcR_uSiG601oh&index=43)
-for more details and examples. Some operations of the proposed experimental
-futures are currently not implemented in our futures however such as
-`.wait_for()`, `.wait_until()`,
-[`shared_future`](http://en.cppreference.com/w/cpp/thread/shared_future),
-[`when_any()`](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0159r0.html#futures.when_any).
-
-@subsection simgrid_uhood_timer Timers
@section simgrid_uhood_mc Model Checker
