## Mutexes and condition variables
-## Mutexes
-
-SimGrid has had a C-based API for mutexes and condition variables for
-some time. These mutexes are different from the standard
-system-level mutex (`std::mutex`, `pthread_mutex_t`, etc.) because
-they work at simulation-level. Locking on a simulation mutex does
-not block the thread directly but makes a simcall
-(`simcall_mutex_lock()`) which asks the simulation kernel to wake the calling
-actor when it can get ownership of the mutex. Blocking directly at the
-OS level would deadlock the simulation.
-
-Reusing the C++ standard API for our simulation mutexes has many
-benefits:
-
- * it makes it easier for people familiar with the `std::mutex` to
- understand and use SimGrid mutexes;
-
- * we can benefit from a proven API;
-
- * we can reuse from generic library code in SimGrid.
-
-We defined a reference-counted `Mutex` class for this (which supports
-the [`Lockable`](http://en.cppreference.com/w/cpp/concept/Lockable)
-requirements, see
-[`[thread.req.lockable.req]`](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4296.pdf#page=1175)
-in the C++14 standard):
-
-@code{cpp}
-class Mutex {
- friend ConditionVariable;
-private:
- friend simgrid::simix::Mutex;
- simgrid::simix::Mutex* mutex_;
- Mutex(simgrid::simix::Mutex* mutex) : mutex_(mutex) {}
-public:
-
- friend void intrusive_ptr_add_ref(Mutex* mutex);
- friend void intrusive_ptr_release(Mutex* mutex);
- using Ptr = boost::intrusive_ptr<Mutex>;
-
- // No copy:
- Mutex(Mutex const&) = delete;
- Mutex& operator=(Mutex const&) = delete;
-
- static Ptr createMutex();
-
-public:
- void lock();
- void unlock();
- bool try_lock();
-};
-@endcode
-
-The methods are simply wrappers around existing simcalls:
-
-@code{cpp}
-void Mutex::lock()
-{
- simcall_mutex_lock(mutex_);
-}
-@endcode
-
-Using the same API as `std::mutex` (`Lockable`) means we can use existing
-C++-standard code such as `std::unique_lock<Mutex>` or
-`std::lock_guard<Mutex>` for exception-safe mutex handling[^lock]:
-
-@code{cpp}
-{
- std::lock_guard<simgrid::s4u::Mutex> lock(*mutex);
- sum += 1;
-}
-@endcode
-
### Condition Variables
Similarly SimGrid already had simulation-level condition variables
