1 /* Copyright (c) 2009-2018. 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 /* \file UContext.cpp Context switching with ucontexts from System V */
8 #include "context_private.hpp"
11 #include "simgrid/Exception.hpp"
12 #include "src/mc/mc_ignore.hpp"
13 #include "src/simix/ActorImpl.hpp"
15 #include "ContextUnix.hpp"
17 XBT_LOG_EXTERNAL_DEFAULT_CATEGORY(simix_context);
19 /** Many integers are needed to store a pointer
21 * Support up to two ints. */
22 constexpr int CTX_ADDR_LEN = 2;
24 static_assert(sizeof(simgrid::kernel::context::UContext*) <= CTX_ADDR_LEN * sizeof(int),
25 "Ucontexts are not supported on this arch yet");
33 UContextFactory::UContextFactory() : ContextFactory("UContextFactory"), parallel_(SIMIX_context_is_parallel())
35 UContext::setMaestro(nullptr);
37 #if HAVE_THREAD_CONTEXTS
38 ParallelUContext::initialize();
40 xbt_die("No thread support for parallel context execution");
45 UContextFactory::~UContextFactory()
47 #if HAVE_THREAD_CONTEXTS
49 ParallelUContext::finalize();
53 Context* UContextFactory::create_context(std::function<void()> code, void_pfn_smxprocess_t cleanup, smx_actor_t process)
55 #if HAVE_THREAD_CONTEXTS
57 return new_context<ParallelUContext>(std::move(code), cleanup, process);
60 return new_context<SerialUContext>(std::move(code), cleanup, process);
63 /* This function is called by maestro at the beginning of a scheduling round to get all working threads executing some
64 * stuff It is much easier to understand what happens if you see the working threads as bodies that swap their soul for
65 * the ones of the simulated processes that must run.
67 void UContextFactory::run_all()
69 #if HAVE_THREAD_CONTEXTS
71 ParallelUContext::run_all();
74 SerialUContext::run_all();
79 UContext* UContext::maestro_context_ = nullptr;
81 UContext::UContext(std::function<void()> code, void_pfn_smxprocess_t cleanup_func, smx_actor_t process)
82 : Context(std::move(code), cleanup_func, process)
84 /* if the user provided a function for the process then use it, otherwise it is the context for maestro */
86 this->stack_ = SIMIX_context_stack_new();
87 getcontext(&this->uc_);
88 this->uc_.uc_link = nullptr;
89 this->uc_.uc_stack.ss_sp = sg_makecontext_stack_addr(this->stack_);
90 this->uc_.uc_stack.ss_size = sg_makecontext_stack_size(smx_context_usable_stack_size);
91 #if PTH_STACKGROWTH == -1
92 ASAN_ONLY(this->asan_stack_ = static_cast<char*>(this->stack_) + smx_context_usable_stack_size);
94 ASAN_ONLY(this->asan_stack_ = this->stack_);
96 UContext::make_ctx(&this->uc_, UContext::smx_ctx_sysv_wrapper, this);
98 if (process != nullptr && maestro_context_ == nullptr)
99 maestro_context_ = this;
103 if (MC_is_active() && has_code()) {
104 MC_register_stack_area(this->stack_, process, &(this->uc_), smx_context_usable_stack_size);
109 UContext::~UContext()
111 SIMIX_context_stack_delete(this->stack_);
114 // The name of this function is currently hardcoded in the code (as string).
115 // Do not change it without fixing those references as well.
116 void UContext::smx_ctx_sysv_wrapper(int i1, int i2)
118 // Rebuild the Context* pointer from the integers:
119 int ctx_addr[CTX_ADDR_LEN] = {i1, i2};
120 simgrid::kernel::context::UContext* context;
121 memcpy(&context, ctx_addr, sizeof context);
123 ASAN_FINISH_SWITCH(nullptr, &context->asan_ctx_->asan_stack_, &context->asan_ctx_->asan_stack_size_);
126 } catch (simgrid::kernel::context::Context::StopRequest const&) {
127 XBT_DEBUG("Caught a StopRequest");
128 } catch (simgrid::HostFailureException const&) {
129 XBT_DEBUG("Caught an HostFailureException");
131 context->Context::stop();
132 ASAN_ONLY(context->asan_stop_ = true);
136 /** A better makecontext
138 * Makecontext expects integer arguments, we the context variable is decomposed into a serie of integers and each
139 * integer is passed as argument to makecontext.
141 void UContext::make_ctx(ucontext_t* ucp, void (*func)(int, int), UContext* arg)
143 int ctx_addr[CTX_ADDR_LEN]{};
144 memcpy(ctx_addr, &arg, sizeof arg);
145 makecontext(ucp, (void (*)())func, 2, ctx_addr[0], ctx_addr[1]);
148 inline void UContext::swap(UContext* from, UContext* to)
150 ASAN_ONLY(void* fake_stack = nullptr);
151 ASAN_ONLY(to->asan_ctx_ = from);
152 ASAN_START_SWITCH(from->asan_stop_ ? nullptr : &fake_stack, to->asan_stack_, to->asan_stack_size_);
153 swapcontext(&from->uc_, &to->uc_);
154 ASAN_FINISH_SWITCH(fake_stack, &from->asan_ctx_->asan_stack_, &from->asan_ctx_->asan_stack_size_);
157 void UContext::stop()
165 unsigned long SerialUContext::process_index_; /* index of the next process to run in the list of runnable processes */
167 void SerialUContext::suspend()
169 /* determine the next context */
170 SerialUContext* next_context;
171 unsigned long int i = process_index_;
174 if (i < simix_global->process_to_run.size()) {
175 /* execute the next process */
176 XBT_DEBUG("Run next process");
177 next_context = static_cast<SerialUContext*>(simix_global->process_to_run[i]->context_);
179 /* all processes were run, return to maestro */
180 XBT_DEBUG("No more process to run");
181 next_context = static_cast<SerialUContext*>(UContext::getMaestro());
183 SIMIX_context_set_current(next_context);
184 UContext::swap(this, next_context);
187 void SerialUContext::resume()
189 SIMIX_context_set_current(this);
190 UContext::swap(UContext::getMaestro(), this);
193 void SerialUContext::run_all()
195 if (simix_global->process_to_run.empty())
197 smx_actor_t first_process = simix_global->process_to_run.front();
199 static_cast<SerialUContext*>(first_process->context_)->resume();
204 #if HAVE_THREAD_CONTEXTS
206 simgrid::xbt::Parmap<smx_actor_t>* ParallelUContext::parmap_;
207 std::atomic<uintptr_t> ParallelUContext::threads_working_; /* number of threads that have started their work */
208 thread_local uintptr_t ParallelUContext::worker_id_; /* thread-specific storage for the thread id */
209 std::vector<ParallelUContext*> ParallelUContext::workers_context_; /* space to save the worker's context
212 void ParallelUContext::initialize()
215 workers_context_.clear();
216 workers_context_.resize(SIMIX_context_get_nthreads(), nullptr);
219 void ParallelUContext::finalize()
223 workers_context_.clear();
226 void ParallelUContext::run_all()
228 threads_working_ = 0;
229 // Parmap_apply ensures that every working thread get an index in the process_to_run array (through an atomic
230 // fetch_and_add), and runs the ParallelUContext::resume function on that index
232 // We lazily create the parmap because the parmap creates context with simix_global->context_factory (which might not
233 // be initialized when bootstrapping):
234 if (parmap_ == nullptr)
235 parmap_ = new simgrid::xbt::Parmap<smx_actor_t>(SIMIX_context_get_nthreads(), SIMIX_context_get_parallel_mode());
237 [](smx_actor_t process) {
238 ParallelUContext* context = static_cast<ParallelUContext*>(process->context_);
241 simix_global->process_to_run);
246 * This function is called when a simulated process wants to yield back to the maestro in a blocking simcall. This
247 * naturally occurs within SIMIX_context_suspend(self->context), called from SIMIX_process_yield() Actually, it does not
248 * really yield back to maestro, but into the next process that must be executed. If no one is to be executed, then it
249 * yields to the initial soul that was in this working thread (that was saved in resume_parallel).
251 void ParallelUContext::suspend()
253 /* determine the next context */
254 // Get the next soul to embody now:
255 boost::optional<smx_actor_t> next_work = parmap_->next();
256 ParallelUContext* next_context;
258 // There is a next soul to embody (ie, a next process to resume)
259 XBT_DEBUG("Run next process");
260 next_context = static_cast<ParallelUContext*>(next_work.get()->context_);
262 // All processes were run, go to the barrier
263 XBT_DEBUG("No more processes to run");
264 // worker_id_ is the identity of my body, stored in thread_local when starting the scheduling round
265 // Deduce the initial soul of that body
266 next_context = workers_context_[worker_id_];
267 // When given that soul, the body will wait for the next scheduling round
270 SIMIX_context_set_current(next_context);
271 // Get the next soul to run, either simulated or initial minion's one:
272 UContext::swap(this, next_context);
275 /** Run one particular simulated process on the current thread. */
276 void ParallelUContext::resume()
278 // What is my containing body? Store its number in os-thread-specific area :
279 worker_id_ = threads_working_.fetch_add(1, std::memory_order_relaxed);
280 // Get my current soul:
281 ParallelUContext* worker_context = static_cast<ParallelUContext*>(SIMIX_context_self());
282 // Write down that this soul is hosted in that body (for now)
283 workers_context_[worker_id_] = worker_context;
284 // Write in simix that I switched my soul
285 SIMIX_context_set_current(this);
286 // Actually do that using the relevant library call:
287 UContext::swap(worker_context, this);
288 // No body runs that soul anymore at this point. Instead the current body took the soul of simulated process The
289 // simulated process wakes back after the call to "SIMIX_context_suspend(self->context);" within
290 // smx_process.c::SIMIX_process_yield()
292 // From now on, the simulated processes will change their soul with the next soul to execute (in suspend_parallel,
293 // below). When nobody is to be executed in this scheduling round, the last simulated process will take back the
294 // initial soul of the current working thread
299 XBT_PRIVATE ContextFactory* sysv_factory()
301 XBT_VERB("Activating SYSV context factory");
302 return new UContextFactory();
304 }}} // namespace simgrid::kernel::context