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"
14 #include "src/simix/smx_private.hpp"
16 #include "ContextUnix.hpp"
18 XBT_LOG_EXTERNAL_DEFAULT_CATEGORY(simix_context);
20 /** Many integers are needed to store a pointer
22 * Support up to two ints. */
23 constexpr int CTX_ADDR_LEN = 2;
25 static_assert(sizeof(simgrid::kernel::context::UContext*) <= CTX_ADDR_LEN * sizeof(int),
26 "Ucontexts are not supported on this arch yet");
34 UContextFactory::UContextFactory() : SwappedContextFactory("UContextFactory") {}
35 UContextFactory::~UContextFactory() = default;
37 Context* UContextFactory::create_context(std::function<void()> code, void_pfn_smxprocess_t cleanup, smx_actor_t process)
40 return new_context<ParallelUContext>(std::move(code), cleanup, process, this);
42 return new_context<UContext>(std::move(code), cleanup, process, this);
48 UContext::UContext(std::function<void()> code, void_pfn_smxprocess_t cleanup_func, smx_actor_t process,
49 SwappedContextFactory* factory)
50 : SwappedContext(std::move(code), cleanup_func, process, factory)
52 /* if the user provided a function for the process then use it, otherwise it is the context for maestro */
54 getcontext(&this->uc_);
55 this->uc_.uc_link = nullptr;
56 this->uc_.uc_stack.ss_sp = sg_makecontext_stack_addr(this->stack_);
57 this->uc_.uc_stack.ss_size = sg_makecontext_stack_size(smx_context_usable_stack_size);
58 #if PTH_STACKGROWTH == -1
59 ASAN_ONLY(this->asan_stack_ = static_cast<char*>(this->stack_) + smx_context_usable_stack_size);
61 ASAN_ONLY(this->asan_stack_ = this->stack_);
63 UContext::make_ctx(&this->uc_, UContext::smx_ctx_sysv_wrapper, this);
65 if (process != nullptr && get_maestro() == nullptr)
70 if (MC_is_active() && has_code()) {
71 MC_register_stack_area(this->stack_, process, &(this->uc_), smx_context_usable_stack_size);
76 UContext::~UContext() = default;
78 // The name of this function is currently hardcoded in the code (as string).
79 // Do not change it without fixing those references as well.
80 void UContext::smx_ctx_sysv_wrapper(int i1, int i2)
82 // Rebuild the Context* pointer from the integers:
83 int ctx_addr[CTX_ADDR_LEN] = {i1, i2};
84 simgrid::kernel::context::UContext* context;
85 memcpy(&context, ctx_addr, sizeof context);
87 ASAN_FINISH_SWITCH(nullptr, &context->asan_ctx_->asan_stack_, &context->asan_ctx_->asan_stack_size_);
90 } catch (simgrid::kernel::context::Context::StopRequest const&) {
91 XBT_DEBUG("Caught a StopRequest");
92 } catch (simgrid::Exception const& e) {
93 XBT_INFO("Actor killed by an uncatched exception %s", simgrid::xbt::demangle(typeid(e).name()).get());
96 context->Context::stop();
97 ASAN_ONLY(context->asan_stop_ = true);
101 /** A better makecontext
103 * Makecontext expects integer arguments, we the context variable is decomposed into a serie of integers and each
104 * integer is passed as argument to makecontext.
106 void UContext::make_ctx(ucontext_t* ucp, void (*func)(int, int), UContext* arg)
108 int ctx_addr[CTX_ADDR_LEN]{};
109 memcpy(ctx_addr, &arg, sizeof arg);
110 makecontext(ucp, (void (*)())func, 2, ctx_addr[0], ctx_addr[1]);
113 void UContext::swap_into(SwappedContext* to_)
115 UContext* to = static_cast<UContext*>(to_);
116 ASAN_ONLY(void* fake_stack = nullptr);
117 ASAN_ONLY(to->asan_ctx_ = from);
118 ASAN_START_SWITCH(from->asan_stop_ ? nullptr : &fake_stack, to->asan_stack_, to->asan_stack_size_);
119 swapcontext(&this->uc_, &to->uc_);
120 ASAN_FINISH_SWITCH(fake_stack, &from->asan_ctx_->asan_stack_, &from->asan_ctx_->asan_stack_size_);
123 void UContext::stop()
131 void ParallelUContext::run_all()
135 /** Run one particular simulated process on the current thread.
137 * Only applied to the N first elements of the parmap array, where N is the amount of worker threads in the parmap.
138 * See ParallelUContext::run_all for details.
140 void ParallelUContext::resume()
142 // Save the thread number (my body) in an os-thread-specific area
143 worker_id_ = threads_working_.fetch_add(1, std::memory_order_relaxed);
144 // Save my current soul (either maestro, or one of the minions) in a permanent area
145 SwappedContext* worker_context = static_cast<SwappedContext*>(self());
146 workers_context_[worker_id_] = worker_context;
147 // Switch my soul and the actor's one
148 Context::set_current(this);
149 worker_context->swap_into(this);
150 // No body runs that soul anymore at this point, but it is stored in a safe place.
151 // When the executed actor will do a blocking action, SIMIX_process_yield() will call suspend(), below.
156 * This function is called when a simulated process wants to yield back to the maestro in a blocking simcall,
157 * ie in SIMIX_process_yield().
159 * Actually, it does not really yield back to maestro, but directly into the next executable actor.
161 * This makes the parmap::apply awkward (see ParallelUContext::run_all()) because it only apply regularly
162 * on the few first elements of the array, but it saves a lot of context switches back to maestro,
163 * and directly forth to the next executable actor.
165 void ParallelUContext::suspend()
167 // Get some more work to directly swap into the next executable actor instead of yielding back to the parmap
168 boost::optional<smx_actor_t> next_work = parmap_->next();
169 SwappedContext* next_context;
171 // There is a next soul to embody (ie, another executable actor)
172 XBT_DEBUG("Run next process");
173 next_context = static_cast<ParallelUContext*>(next_work.get()->context_);
175 // All actors were run, go back to the parmap context
176 XBT_DEBUG("No more processes to run");
177 // worker_id_ is the identity of my body, stored in thread_local when starting the scheduling round
178 next_context = workers_context_[worker_id_];
179 // When given that soul, the body will wait for the next scheduling round
182 // Get the next soul to run, either from another actor or the initial minion's one
183 Context::set_current(next_context);
184 this->swap_into(next_context);
187 XBT_PRIVATE ContextFactory* sysv_factory()
189 XBT_VERB("Activating SYSV context factory");
190 return new UContextFactory();
192 }}} // namespace simgrid::kernel::context