X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/blobdiff_plain/39c935d6d5ee86d153f6f7e6a10d723ae7c57f6f..5ed37babb2fa9097abe82df299c0aa259ed84d5a:/src/kernel/activity/MutexImpl.hpp

diff --git a/src/kernel/activity/MutexImpl.hpp b/src/kernel/activity/MutexImpl.hpp
index fa291d3bb4..c7ba205702 100644
--- a/src/kernel/activity/MutexImpl.hpp
+++ b/src/kernel/activity/MutexImpl.hpp
@@ -1,4 +1,4 @@
-/* Copyright (c) 2012-2021. The SimGrid Team. All rights reserved.          */
+/* Copyright (c) 2012-2023. The SimGrid Team. All rights reserved.          */
 
 /* This program is free software; you can redistribute it and/or modify it
  * under the terms of the license (GNU LGPL) which comes with this package. */
@@ -6,36 +6,79 @@
 #ifndef SIMGRID_KERNEL_ACTIVITY_MUTEX_HPP
 #define SIMGRID_KERNEL_ACTIVITY_MUTEX_HPP
 
-#include "simgrid/s4u/ConditionVariable.hpp"
+#include "simgrid/s4u/Mutex.hpp"
+#include "src/kernel/activity/ActivityImpl.hpp"
 #include "src/kernel/actor/ActorImpl.hpp"
 #include <boost/intrusive/list.hpp>
 
-namespace simgrid {
-namespace kernel {
-namespace activity {
+namespace simgrid::kernel::activity {
+
+/** Mutex Acquisition: the act / process of acquiring the mutex.
+ *
+ * You can declare some interest on a mutex without being blocked waiting if it's already occupied.
+ * If it gets freed by its current owned, you become the new owner, even if you're still not blocked on it.
+ * 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.
+ *
+ * Afterward, when you do consider the lock, the test() or wait() operations are both non-blocking since you're the
+ * owner. People who declared interest in the mutex after you get stuck in the queue behind you.
+ *
+ *
+ * Splitting the locking process this way is interesting for symmetry with the other activities such as exec or
+ * communication that do have an async variant and could be mildly interesting to the users once exposed in S4U, but
+ * that's not the only reason. It's also very important to the MC world: the Mutex::lock_async() is always enabled
+ * (nothing can prevent you from adding yourself to the queue of potential owners) while Acquisition::wait() is
+ * persistent: it's not always enabled but once it gets enabled (because you're the owner), it remains enabled for ever.
+ *
+ * Mutex::lock() is not persistent: sometimes it's enabled if the mutex is free, and then it gets disabled if
+ * someone else locks the mutex, and then it becomes enabled again once the mutex is freed. This is why Mutex::lock()
+ * is not used in our MC computational model: we ban non-persistent transitions because they would make some
+ * computations much more complex.
+ *
+ * In particular, computing the extension of an unfolding's configuration is polynomial when you only have persistent
+ * transitions while it's O(2^n) when some of the transitions are non-persistent (you have to consider again all subsets
+ * of a set if some transitions may become disabled in between, while you don't have to reconsider them if you can reuse
+ * your previous computations).
+ */
+class XBT_PUBLIC MutexAcquisitionImpl : public ActivityImpl_T<MutexAcquisitionImpl> {
+  actor::ActorImpl* issuer_ = nullptr;
+  MutexImpl* mutex_         = nullptr;
+
+public:
+  MutexAcquisitionImpl(actor::ActorImpl* issuer, MutexImpl* mutex) : issuer_(issuer), mutex_(mutex) {}
+  MutexImplPtr get_mutex() { return mutex_; }
+  actor::ActorImpl* get_issuer() { return issuer_; }
+
+  bool test(actor::ActorImpl* issuer = nullptr) override;
+  void wait_for(actor::ActorImpl* issuer, double timeout) override;
+  void post() override
+  { /*no surf action*/
+  }
+  void finish() override;
+  void set_exception(actor::ActorImpl* issuer) override
+  { /* nothing to do */
+  }
+};
 
 class XBT_PUBLIC MutexImpl {
   std::atomic_int_fast32_t refcount_{1};
   s4u::Mutex piface_;
-  bool locked_ = false;
   actor::ActorImpl* owner_ = nullptr;
-  // List of sleeping actors:
-  actor::SynchroList sleeping_;
+  std::deque<MutexAcquisitionImplPtr> ongoing_acquisitions_;
+  static unsigned next_id_;
+  unsigned id_ = next_id_++;
+
+  friend MutexAcquisitionImpl;
 
 public:
   MutexImpl() : piface_(this) {}
   MutexImpl(MutexImpl const&) = delete;
   MutexImpl& operator=(MutexImpl const&) = delete;
 
-  void lock(actor::ActorImpl* issuer);
+  MutexAcquisitionImplPtr lock_async(actor::ActorImpl* issuer);
   bool try_lock(actor::ActorImpl* issuer);
   void unlock(actor::ActorImpl* issuer);
-  bool is_locked() const { return locked_; }
-
-  MutexImpl* ref();
-  void unref();
+  unsigned get_id() const { return id_; }
 
-  void remove_sleeping_actor(actor::ActorImpl& actor) { xbt::intrusive_erase(sleeping_, actor); }
   actor::ActorImpl* get_owner() const { return owner_; }
 
   // boost::intrusive_ptr<Mutex> support:
@@ -53,7 +96,5 @@ public:
 
   s4u::Mutex& mutex() { return piface_; }
 };
-} // namespace activity
-} // namespace kernel
-} // namespace simgrid
+} // namespace simgrid::kernel::activity
 #endif