1 /* Copyright (c) 2009-2017. 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 <ucontext.h> /* context relative declarations */
11 #include "src/mc/mc_ignore.h"
12 #include "src/simix/ActorImpl.hpp"
13 #include "src/simix/smx_private.h"
14 #include "xbt/parmap.hpp"
16 /** Many integers are needed to store a pointer
18 * This is a bit paranoid about sizeof(smx_ctx_sysv_t) not being a multiple
19 * of sizeof(int), but it doesn't harm. */
20 #define CTX_ADDR_LEN \
21 (sizeof(void*) / sizeof(int) + \
22 !!(sizeof(void*) % sizeof(int)))
24 /** A better makecontext
26 * Makecontext expects integer arguments, we the context
27 * variable is decomposed into a serie of integers and
28 * each integer is passed as argument to makecontext. */
29 static void simgrid_makecontext(ucontext_t* ucp, void (*func)(int first, ...), void* arg)
31 int ctx_addr[CTX_ADDR_LEN];
32 memcpy(ctx_addr, &arg, sizeof(void*));
33 switch (CTX_ADDR_LEN) {
35 makecontext(ucp, (void (*)())func, 1, ctx_addr[0]);
38 makecontext(ucp, (void (*)()) func, 2, ctx_addr[0], ctx_addr[1]);
41 xbt_die("Ucontexts are not supported on this arch yet (addr len = %zu/%zu = %zu)", sizeof(void*), sizeof(int), CTX_ADDR_LEN);
45 XBT_LOG_EXTERNAL_DEFAULT_CATEGORY(simix_context);
52 class ParallelUContext;
53 class UContextFactory;
56 #if HAVE_THREAD_CONTEXTS
57 static simgrid::xbt::Parmap<smx_actor_t>* sysv_parmap;
58 static simgrid::kernel::context::ParallelUContext** sysv_workers_context; /* space to save the worker's context in each thread */
59 static uintptr_t sysv_threads_working; /* number of threads that have started their work */
60 static xbt_os_thread_key_t sysv_worker_id_key; /* thread-specific storage for the thread id */
62 static unsigned long sysv_process_index = 0; /* index of the next process to run in the
63 * list of runnable processes */
64 static simgrid::kernel::context::UContext* sysv_maestro_context;
65 static bool sysv_parallel;
67 // The name of this function is currently hardcoded in the code (as string).
68 // Do not change it without fixing those references as well.
69 static void smx_ctx_sysv_wrapper(int first, ...);
75 class UContext : public Context {
77 ucontext_t uc_; /* the ucontext that executes the code */
78 char *stack_ = nullptr; /* the thread stack */
80 friend UContextFactory;
81 UContext(std::function<void()> code,
82 void_pfn_smxprocess_t cleanup_func, smx_actor_t process);
86 class SerialUContext : public UContext {
88 SerialUContext(std::function<void()> code,
89 void_pfn_smxprocess_t cleanup_func, smx_actor_t process)
90 : UContext(std::move(code), cleanup_func, process)
93 void suspend() override;
97 class ParallelUContext : public UContext {
99 ParallelUContext(std::function<void()> code,
100 void_pfn_smxprocess_t cleanup_func, smx_actor_t process)
101 : UContext(std::move(code), cleanup_func, process)
103 void stop() override;
104 void suspend() override;
108 class UContextFactory : public ContextFactory {
111 friend SerialUContext;
112 friend ParallelUContext;
115 ~UContextFactory() override;
116 Context* create_context(std::function<void()> code,
117 void_pfn_smxprocess_t cleanup, smx_actor_t process) override;
118 void run_all() override;
121 XBT_PRIVATE ContextFactory* sysv_factory()
123 XBT_VERB("Activating SYSV context factory");
124 return new UContextFactory();
127 UContextFactory::UContextFactory() : ContextFactory("UContextFactory")
129 if (SIMIX_context_is_parallel()) {
130 sysv_parallel = true;
131 #if HAVE_THREAD_CONTEXTS /* To use parallel ucontexts a thread pool is needed */
132 int nthreads = SIMIX_context_get_nthreads();
133 sysv_parmap = nullptr;
134 sysv_workers_context = xbt_new(ParallelUContext*, nthreads);
135 sysv_maestro_context = nullptr;
136 xbt_os_thread_key_create(&sysv_worker_id_key);
138 THROWF(arg_error, 0, "No thread support for parallel context execution");
141 sysv_parallel = false;
145 UContextFactory::~UContextFactory()
147 #if HAVE_THREAD_CONTEXTS
149 xbt_free(sysv_workers_context);
153 /* This function is called by maestro at the beginning of a scheduling round to get all working threads executing some stuff
154 * It is much easier to understand what happens if you see the working threads as bodies that swap their soul for the
155 * ones of the simulated processes that must run.
157 void UContextFactory::run_all()
160 #if HAVE_THREAD_CONTEXTS
161 sysv_threads_working = 0;
162 // Parmap_apply ensures that every working thread get an index in the
163 // process_to_run array (through an atomic fetch_and_add),
164 // and runs the smx_ctx_sysv_resume_parallel function on that index
166 // We lazily create the parmap because the parmap creates context
167 // with simix_global->context_factory (which might not be initialized
168 // when bootstrapping):
169 if (sysv_parmap == nullptr)
171 new simgrid::xbt::Parmap<smx_actor_t>(SIMIX_context_get_nthreads(), SIMIX_context_get_parallel_mode());
174 [](smx_actor_t process) {
175 ParallelUContext* context = static_cast<ParallelUContext*>(process->context);
178 simix_global->process_to_run);
180 xbt_die("You asked for a parallel execution, but you don't have any threads.");
184 if (simix_global->process_to_run.empty())
187 smx_actor_t first_process = simix_global->process_to_run.front();
188 sysv_process_index = 1;
189 SerialUContext* context = static_cast<SerialUContext*>(first_process->context);
194 Context* UContextFactory::create_context(std::function<void()> code,
195 void_pfn_smxprocess_t cleanup, smx_actor_t process)
198 return new_context<ParallelUContext>(std::move(code), cleanup, process);
200 return new_context<SerialUContext>(std::move(code), cleanup, process);
203 UContext::UContext(std::function<void()> code,
204 void_pfn_smxprocess_t cleanup_func, smx_actor_t process)
205 : Context(std::move(code), cleanup_func, process)
207 /* if the user provided a function for the process then use it, otherwise it is the context for maestro */
209 this->stack_ = (char*) SIMIX_context_stack_new();
210 getcontext(&this->uc_);
211 this->uc_.uc_link = nullptr;
212 this->uc_.uc_stack.ss_sp = sg_makecontext_stack_addr(this->stack_);
213 this->uc_.uc_stack.ss_size = sg_makecontext_stack_size(smx_context_usable_stack_size);
214 simgrid_makecontext(&this->uc_, smx_ctx_sysv_wrapper, this);
216 if (process != nullptr && sysv_maestro_context == nullptr)
217 sysv_maestro_context = this;
221 if (MC_is_active() && has_code()) {
222 MC_register_stack_area(this->stack_, process,
223 &(this->uc_), smx_context_usable_stack_size);
228 UContext::~UContext()
230 SIMIX_context_stack_delete(this->stack_);
233 }}} // namespace simgrid::kernel::context
235 static void smx_ctx_sysv_wrapper(int first, ...)
237 // Rebuild the Context* pointer from the integers:
238 int ctx_addr[CTX_ADDR_LEN];
239 simgrid::kernel::context::UContext* context;
241 if (CTX_ADDR_LEN > 1) {
244 for (unsigned i = 1; i < CTX_ADDR_LEN; i++)
245 ctx_addr[i] = va_arg(ap, int);
248 memcpy(&context, ctx_addr, sizeof(simgrid::kernel::context::UContext*));
258 void SerialUContext::stop()
264 void SerialUContext::suspend()
266 /* determine the next context */
267 SerialUContext* next_context = nullptr;
268 unsigned long int i = sysv_process_index++;
270 if (i < simix_global->process_to_run.size()) {
271 /* execute the next process */
272 XBT_DEBUG("Run next process");
273 next_context = static_cast<SerialUContext*>(simix_global->process_to_run[i]->context);
275 /* all processes were run, return to maestro */
276 XBT_DEBUG("No more process to run");
277 next_context = static_cast<SerialUContext*>(sysv_maestro_context);
279 SIMIX_context_set_current(next_context);
280 swapcontext(&this->uc_, &next_context->uc_);
285 void SerialUContext::resume()
287 SIMIX_context_set_current(this);
288 swapcontext(&static_cast<SerialUContext*>(sysv_maestro_context)->uc_, &this->uc_);
291 void ParallelUContext::stop()
297 /** Run one particular simulated process on the current thread. */
298 void ParallelUContext::resume()
300 #if HAVE_THREAD_CONTEXTS
301 // What is my containing body?
302 uintptr_t worker_id = __sync_fetch_and_add(&sysv_threads_working, 1);
303 // Store the number of my containing body in os-thread-specific area :
304 xbt_os_thread_set_specific(sysv_worker_id_key, (void*) worker_id);
305 // Get my current soul:
306 ParallelUContext* worker_context = static_cast<ParallelUContext*>(SIMIX_context_self());
307 // Write down that this soul is hosted in that body (for now)
308 sysv_workers_context[worker_id] = worker_context;
309 // Retrieve the system-level info that fuels this soul:
310 ucontext_t* worker_stack = &worker_context->uc_;
311 // Write in simix that I switched my soul
312 SIMIX_context_set_current(this);
313 // Actually do that using the relevant library call:
314 swapcontext(worker_stack, &this->uc_);
315 // No body runs that soul anymore at this point.
316 // Instead the current body took the soul of simulated process
317 // The simulated process wakes back after the call to
318 // "SIMIX_context_suspend(self->context);" within
319 // smx_process.c::SIMIX_process_yield()
321 // From now on, the simulated processes will change their
322 // soul with the next soul to execute (in suspend_parallel, below).
323 // When nobody is to be executed in this scheduling round,
324 // the last simulated process will take back the initial
325 // soul of the current working thread
331 * This function is called when a simulated process wants to yield back
332 * to the maestro in a blocking simcall. This naturally occurs within
333 * SIMIX_context_suspend(self->context), called from SIMIX_process_yield()
334 * Actually, it does not really yield back to maestro, but into the next
335 * process that must be executed. If no one is to be executed, then it
336 * yields to the initial soul that was in this working thread (that was
337 * saved in resume_parallel).
339 void ParallelUContext::suspend()
341 #if HAVE_THREAD_CONTEXTS
342 /* determine the next context */
343 // Get the next soul to embody now:
344 boost::optional<smx_actor_t> next_work = sysv_parmap->next();
345 ParallelUContext* next_context;
347 // There is a next soul to embody (ie, a next process to resume)
348 XBT_DEBUG("Run next process");
349 next_context = static_cast<ParallelUContext*>(next_work.get()->context);
351 // All processes were run, go to the barrier
352 XBT_DEBUG("No more processes to run");
353 // Get back the identity of my body that was stored when starting
354 // the scheduling round
355 uintptr_t worker_id =
356 (uintptr_t) xbt_os_thread_get_specific(sysv_worker_id_key);
357 // Deduce the initial soul of that body
358 next_context = sysv_workers_context[worker_id];
359 // When given that soul, the body will wait for the next scheduling round
362 // Will contain the next soul to run, either simulated or initial minion's one
363 ucontext_t* next_stack = &next_context->uc_;
365 SIMIX_context_set_current(next_context);
366 // Get that next soul:
367 swapcontext(&this->uc_, next_stack);
371 }}} // namespace simgrid::kernel::context