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");
33 Context* UContextFactory::create_context(std::function<void()> code, void_pfn_smxprocess_t cleanup, smx_actor_t process)
36 return new_context<ParallelUContext>(std::move(code), cleanup, process, this);
38 return new_context<UContext>(std::move(code), cleanup, process, this);
44 UContext::UContext(std::function<void()> code, void_pfn_smxprocess_t cleanup_func, smx_actor_t process,
45 SwappedContextFactory* factory)
46 : SwappedContext(std::move(code), cleanup_func, process, factory)
48 /* if the user provided a function for the process then use it, otherwise it is the context for maestro */
50 getcontext(&this->uc_);
51 this->uc_.uc_link = nullptr;
52 this->uc_.uc_stack.ss_sp = sg_makecontext_stack_addr(this->stack_);
53 this->uc_.uc_stack.ss_size = sg_makecontext_stack_size(smx_context_usable_stack_size);
54 #if PTH_STACKGROWTH == -1
55 ASAN_ONLY(this->asan_stack_ = static_cast<char*>(this->stack_) + smx_context_usable_stack_size);
57 ASAN_ONLY(this->asan_stack_ = this->stack_);
59 UContext::make_ctx(&this->uc_, UContext::smx_ctx_sysv_wrapper, this);
61 if (process != nullptr && get_maestro() == nullptr)
66 if (MC_is_active() && has_code()) {
67 MC_register_stack_area(this->stack_, process, &(this->uc_), smx_context_usable_stack_size);
72 UContext::~UContext() = default;
74 // The name of this function is currently hardcoded in the code (as string).
75 // Do not change it without fixing those references as well.
76 void UContext::smx_ctx_sysv_wrapper(int i1, int i2)
78 // Rebuild the Context* pointer from the integers:
79 int ctx_addr[CTX_ADDR_LEN] = {i1, i2};
80 simgrid::kernel::context::UContext* context;
81 memcpy(&context, ctx_addr, sizeof context);
83 ASAN_FINISH_SWITCH(nullptr, &context->asan_ctx_->asan_stack_, &context->asan_ctx_->asan_stack_size_);
86 } catch (simgrid::kernel::context::Context::StopRequest const&) {
87 XBT_DEBUG("Caught a StopRequest");
88 } catch (simgrid::Exception const& e) {
89 XBT_INFO("Actor killed by an uncatched exception %s", simgrid::xbt::demangle(typeid(e).name()).get());
92 context->Context::stop();
93 ASAN_ONLY(context->asan_stop_ = true);
97 /** A better makecontext
99 * Makecontext expects integer arguments, we the context variable is decomposed into a serie of integers and each
100 * integer is passed as argument to makecontext.
102 void UContext::make_ctx(ucontext_t* ucp, void (*func)(int, int), UContext* arg)
104 int ctx_addr[CTX_ADDR_LEN]{};
105 memcpy(ctx_addr, &arg, sizeof arg);
106 makecontext(ucp, (void (*)())func, 2, ctx_addr[0], ctx_addr[1]);
109 void UContext::swap_into(SwappedContext* to_)
111 UContext* to = static_cast<UContext*>(to_);
112 ASAN_ONLY(void* fake_stack = nullptr);
113 ASAN_ONLY(to->asan_ctx_ = from);
114 ASAN_START_SWITCH(from->asan_stop_ ? nullptr : &fake_stack, to->asan_stack_, to->asan_stack_size_);
115 swapcontext(&this->uc_, &to->uc_);
116 ASAN_FINISH_SWITCH(fake_stack, &from->asan_ctx_->asan_stack_, &from->asan_ctx_->asan_stack_size_);
121 /** Run one particular simulated process on the current thread.
123 * Only applied to the N first elements of the parmap array, where N is the amount of worker threads in the parmap.
124 * See ParallelUContext::run_all for details.
126 void ParallelUContext::resume()
128 // Save the thread number (my body) in an os-thread-specific area
129 worker_id_ = threads_working_.fetch_add(1, std::memory_order_relaxed);
130 // Save my current soul (either maestro, or one of the minions) in a permanent area
131 SwappedContext* worker_context = static_cast<SwappedContext*>(self());
132 workers_context_[worker_id_] = worker_context;
133 // Switch my soul and the actor's one
134 Context::set_current(this);
135 worker_context->swap_into(this);
136 // No body runs that soul anymore at this point, but it is stored in a safe place.
137 // When the executed actor will do a blocking action, SIMIX_process_yield() will call suspend(), below.
142 * This function is called when a simulated process wants to yield back to the maestro in a blocking simcall,
143 * ie in SIMIX_process_yield().
145 * Actually, it does not really yield back to maestro, but directly into the next executable actor.
147 * This makes the parmap::apply awkward (see ParallelUContext::run_all()) because it only apply regularly
148 * on the few first elements of the array, but it saves a lot of context switches back to maestro,
149 * and directly forth to the next executable actor.
151 void ParallelUContext::suspend()
153 // Get some more work to directly swap into the next executable actor instead of yielding back to the parmap
154 boost::optional<smx_actor_t> next_work = parmap_->next();
155 SwappedContext* next_context;
157 // There is a next soul to embody (ie, another executable actor)
158 XBT_DEBUG("Run next process");
159 next_context = static_cast<ParallelUContext*>(next_work.get()->context_);
161 // All actors were run, go back to the parmap context
162 XBT_DEBUG("No more processes to run");
163 // worker_id_ is the identity of my body, stored in thread_local when starting the scheduling round
164 next_context = workers_context_[worker_id_];
165 // When given that soul, the body will wait for the next scheduling round
168 // Get the next soul to run, either from another actor or the initial minion's one
169 Context::set_current(next_context);
170 this->swap_into(next_context);
173 XBT_PRIVATE ContextFactory* sysv_factory()
175 XBT_VERB("Activating SYSV context factory");
176 return new UContextFactory();
178 }}} // namespace simgrid::kernel::context