xbt_free(stack_);
}
+/** Maestro wants to run all read_to_run actors */
+void SwappedContext::run_all()
+{
+ if (simix_global->process_to_run.empty())
+ return;
+ smx_actor_t first_process = simix_global->process_to_run.front();
+ process_index_ = 1;
+ /* execute the first process */
+ static_cast<SwappedContext*>(first_process->context_)->resume();
+}
+
+/** Maestro wants to yield back to a given actor */
+void SwappedContext::resume()
+{
+ // Maestro is always the calling thread of this function (ie, self() == maestro)
+ SwappedContext* old = static_cast<SwappedContext*>(self());
+ Context::set_current(this);
+ old->swap_into(this);
+}
+
+/** The actor wants to yield back to maestro */
void SwappedContext::suspend()
{
/* determine the next context */
process_index_++;
if (i < simix_global->process_to_run.size()) {
- /* execute the next process */
+ /* Actually swap into the next actor directly without transiting to maestro */
XBT_DEBUG("Run next process");
next_context = static_cast<SwappedContext*>(simix_global->process_to_run[i]->context_);
} else {
- /* all processes were run, return to maestro */
+ /* all processes were run, actually return to maestro */
XBT_DEBUG("No more process to run");
next_context = static_cast<SwappedContext*>(get_maestro());
}
this->swap_into(next_context);
}
-void SwappedContext::resume()
-{
- SwappedContext* old = static_cast<SwappedContext*>(self());
- Context::set_current(this);
- old->swap_into(this);
-}
-
-void SwappedContext::run_all()
-{
- if (simix_global->process_to_run.empty())
- return;
- smx_actor_t first_process = simix_global->process_to_run.front();
- process_index_ = 1;
- /* execute the first process */
- static_cast<SwappedContext*>(first_process->context_)->resume();
-}
} // namespace context
} // namespace kernel
} // namespace simgrid
{
UContext::set_maestro(nullptr);
if (parallel_)
- ParallelUContext::initialize();
+ SwappedContext::initialize();
}
UContextFactory::~UContextFactory()
{
if (parallel_)
- ParallelUContext::finalize();
+ SwappedContext::finalize();
}
Context* UContextFactory::create_context(std::function<void()> code, void_pfn_smxprocess_t cleanup, smx_actor_t process)
void ParallelUContext::run_all()
{
threads_working_ = 0;
- // Parmap_apply ensures that every working thread get an index in the process_to_run array (through an atomic
- // fetch_and_add), and runs the ParallelUContext::resume function on that index
- // We lazily create the parmap because the parmap creates context with simix_global->context_factory (which might not
- // be initialized when bootstrapping):
+ // We lazily create the parmap so that all options are actually processed when doing so.
if (parmap_ == nullptr)
parmap_ = new simgrid::xbt::Parmap<smx_actor_t>(SIMIX_context_get_nthreads(), SIMIX_context_get_parallel_mode());
+
+ // Usually, Parmap::apply() executes the provided function on all elements of the array.
+ // Here, the executed function does not return the control to the parmap before all the array is processed:
+ // - suspend() should switch back to the worker_context (either maestro or one of its minions) to return
+ // the control to the parmap. Instead, it uses parmap_->next() to steal another work, and does it directly.
+ // It only yields back to worker_context when the work array is exhausted.
+ // - So, resume() is only launched from the parmap for the first job of each minion.
parmap_->apply(
[](smx_actor_t process) {
ParallelUContext* context = static_cast<ParallelUContext*>(process->context_);
simix_global->process_to_run);
}
+/** Run one particular simulated process on the current thread.
+ *
+ * Only applied to the N first elements of the parmap array, where N is the amount of worker threads in the parmap.
+ * See ParallelUContext::run_all for details.
+ */
+void ParallelUContext::resume()
+{
+ // Save the thread number (my body) in an os-thread-specific area
+ worker_id_ = threads_working_.fetch_add(1, std::memory_order_relaxed);
+ // Save my current soul (either maestro, or one of the minions) in a permanent area
+ SwappedContext* worker_context = static_cast<SwappedContext*>(self());
+ workers_context_[worker_id_] = worker_context;
+ // Switch my soul and the actor's one
+ Context::set_current(this);
+ worker_context->swap_into(this);
+ // No body runs that soul anymore at this point, but it is stored in a safe place.
+ // When the executed actor will do a blocking action, SIMIX_process_yield() will call suspend(), below.
+}
+
/** Yield
*
- * This function is called when a simulated process wants to yield back to the maestro in a blocking simcall. This
- * naturally occurs within SIMIX_context_suspend(self->context), called from SIMIX_process_yield() Actually, it does not
- * really yield back to maestro, but into the next process that must be executed. If no one is to be executed, then it
- * yields to the initial soul that was in this working thread (that was saved in resume_parallel).
+ * This function is called when a simulated process wants to yield back to the maestro in a blocking simcall,
+ * ie in SIMIX_process_yield().
+ *
+ * Actually, it does not really yield back to maestro, but directly into the next executable actor.
+ *
+ * This makes the parmap::apply awkward (see ParallelUContext::run_all()) because it only apply regularly
+ * on the few first elements of the array, but it saves a lot of context switches back to maestro,
+ * and directly forth to the next executable actor.
*/
void ParallelUContext::suspend()
{
- /* determine the next context */
- // Get the next soul to embody now:
+ // Get some more work to directly swap into the next executable actor instead of yielding back to the parmap
boost::optional<smx_actor_t> next_work = parmap_->next();
SwappedContext* next_context;
if (next_work) {
- // There is a next soul to embody (ie, a next process to resume)
+ // There is a next soul to embody (ie, another executable actor)
XBT_DEBUG("Run next process");
next_context = static_cast<ParallelUContext*>(next_work.get()->context_);
} else {
- // All processes were run, go to the barrier
+ // All actors were run, go back to the parmap context
XBT_DEBUG("No more processes to run");
// worker_id_ is the identity of my body, stored in thread_local when starting the scheduling round
- // Deduce the initial soul of that body
next_context = workers_context_[worker_id_];
// When given that soul, the body will wait for the next scheduling round
}
+ // Get the next soul to run, either from another actor or the initial minion's one
Context::set_current(next_context);
- // Get the next soul to run, either simulated or initial minion's one:
this->swap_into(next_context);
}
-/** Run one particular simulated process on the current thread. */
-void ParallelUContext::resume()
-{
- // What is my containing body? Store its number in os-thread-specific area :
- worker_id_ = threads_working_.fetch_add(1, std::memory_order_relaxed);
- // Get my current soul:
- ParallelUContext* worker_context = static_cast<ParallelUContext*>(self());
- // Write down that this soul is hosted in that body (for now)
- workers_context_[worker_id_] = worker_context;
- // Write in simix that I switched my soul
- Context::set_current(this);
- // Actually do that using the relevant library call:
- worker_context->swap_into(this);
- // No body runs that soul anymore at this point. Instead the current body took the soul of simulated process The
- // simulated process wakes back after the call to "SIMIX_context_suspend(self->context);" within
- // smx_process.c::SIMIX_process_yield()
-
- // From now on, the simulated processes will change their soul with the next soul to execute (in suspend_parallel,
- // below). When nobody is to be executed in this scheduling round, the last simulated process will take back the
- // initial soul of the current working thread
-}
-
XBT_PRIVATE ContextFactory* sysv_factory()
{
XBT_VERB("Activating SYSV context factory");
