1 /* Copyright (c) 2012-2022. The SimGrid Team. All rights reserved. */
3 /* This program is free software; you can redistribute it and/or modify it
4 * under the terms of the license (GNU LGPL) which comes with this package. */
6 #ifndef SIMGRID_KERNEL_ACTIVITY_MUTEX_HPP
7 #define SIMGRID_KERNEL_ACTIVITY_MUTEX_HPP
9 #include "simgrid/s4u/Mutex.hpp"
10 #include "src/kernel/activity/ActivityImpl.hpp"
11 #include "src/kernel/actor/ActorImpl.hpp"
12 #include <boost/intrusive/list.hpp>
14 namespace simgrid::kernel::activity {
16 /** Mutex Acquisition: the act / process of acquiring the mutex.
18 * You can declare some interest on a mutex without being blocked waiting if it's already occupied.
19 * If it gets freed by its current owned, you become the new owner, even if you're still not blocked on it.
20 * Nobody can lock it behind your back or overpass you in the queue in any way, even if you're still not blocked on it.
22 * Afterward, when you do consider the lock, the test() or wait() operations are both non-blocking since you're the
23 * owner. People who declared interest in the mutex after you get stuck in the queue behind you.
26 * Splitting the locking process this way is interesting for symmetry with the other activities such as exec or
27 * communication that do have an async variant and could be mildly interesting to the users once exposed in S4U, but
28 * that's not the only reason. It's also very important to the MC world: the Mutex::lock_async() is always enabled
29 * (nothing can prevent you from adding yourself to the queue of potential owners) while Acquisition::wait() is
30 * persistent: it's not always enabled but once it gets enabled (because you're the owner), it remains enabled for ever.
32 * Mutex::lock() is not persistent: sometimes it's enabled if the mutex is free, and then it gets disabled if
33 * someone else locks the mutex, and then it becomes enabled again once the mutex is freed. This is why Mutex::lock()
34 * is not used in our MC computational model: we ban non-persistent transitions because they would make some
35 * computations much more complex.
37 * In particular, computing the extension of an unfolding's configuration is polynomial when you only have persistent
38 * transitions while it's O(2^n) when some of the transitions are non-persistent (you have to consider again all subsets
39 * of a set if some transitions may become disabled in between, while you don't have to reconsider them if you can reuse
40 * your previous computations).
42 class XBT_PUBLIC MutexAcquisitionImpl : public ActivityImpl_T<MutexAcquisitionImpl> {
43 actor::ActorImpl* issuer_ = nullptr;
44 MutexImpl* mutex_ = nullptr;
47 MutexAcquisitionImpl(actor::ActorImpl* issuer, MutexImpl* mutex) : issuer_(issuer), mutex_(mutex) {}
48 MutexImplPtr get_mutex() { return mutex_; }
49 actor::ActorImpl* get_issuer() { return issuer_; }
51 bool test(actor::ActorImpl* issuer = nullptr) override;
52 void wait_for(actor::ActorImpl* issuer, double timeout) override;
56 void finish() override;
57 void set_exception(actor::ActorImpl* issuer) override
62 class XBT_PUBLIC MutexImpl {
63 std::atomic_int_fast32_t refcount_{1};
65 actor::ActorImpl* owner_ = nullptr;
66 std::deque<MutexAcquisitionImplPtr> ongoing_acquisitions_;
67 static unsigned next_id_;
68 unsigned id_ = next_id_++;
70 friend MutexAcquisitionImpl;
73 MutexImpl() : piface_(this) {}
74 MutexImpl(MutexImpl const&) = delete;
75 MutexImpl& operator=(MutexImpl const&) = delete;
77 MutexAcquisitionImplPtr lock_async(actor::ActorImpl* issuer);
78 bool try_lock(actor::ActorImpl* issuer);
79 void unlock(actor::ActorImpl* issuer);
80 unsigned get_id() const { return id_; }
82 actor::ActorImpl* get_owner() const { return owner_; }
84 // boost::intrusive_ptr<Mutex> support:
85 friend void intrusive_ptr_add_ref(MutexImpl* mutex)
87 XBT_ATTRIB_UNUSED auto previous = mutex->refcount_.fetch_add(1);
88 xbt_assert(previous != 0);
91 friend void intrusive_ptr_release(MutexImpl* mutex)
93 if (mutex->refcount_.fetch_sub(1) == 1)
97 s4u::Mutex& mutex() { return piface_; }
99 } // namespace simgrid::kernel::activity