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);
87 class SerialUContext : public UContext {
89 SerialUContext(std::function<void()> code,
90 void_pfn_smxprocess_t cleanup_func, smx_actor_t process)
91 : 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 suspend() override;
107 class UContextFactory : public ContextFactory {
110 friend SerialUContext;
111 friend ParallelUContext;
114 ~UContextFactory() override;
115 Context* create_context(std::function<void()> code,
116 void_pfn_smxprocess_t cleanup, smx_actor_t process) override;
117 void run_all() override;
120 XBT_PRIVATE ContextFactory* sysv_factory()
122 XBT_VERB("Activating SYSV context factory");
123 return new UContextFactory();
126 UContextFactory::UContextFactory() : ContextFactory("UContextFactory")
128 if (SIMIX_context_is_parallel()) {
129 sysv_parallel = true;
130 #if HAVE_THREAD_CONTEXTS /* To use parallel ucontexts a thread pool is needed */
131 int nthreads = SIMIX_context_get_nthreads();
132 sysv_parmap = nullptr;
133 sysv_workers_context = xbt_new(ParallelUContext*, nthreads);
134 sysv_maestro_context = nullptr;
135 xbt_os_thread_key_create(&sysv_worker_id_key);
137 THROWF(arg_error, 0, "No thread support for parallel context execution");
140 sysv_parallel = false;
144 UContextFactory::~UContextFactory()
146 #if HAVE_THREAD_CONTEXTS
148 xbt_free(sysv_workers_context);
152 /* This function is called by maestro at the beginning of a scheduling round to get all working threads executing some stuff
153 * It is much easier to understand what happens if you see the working threads as bodies that swap their soul for the
154 * ones of the simulated processes that must run.
156 void UContextFactory::run_all()
159 #if HAVE_THREAD_CONTEXTS
160 sysv_threads_working = 0;
161 // Parmap_apply ensures that every working thread get an index in the
162 // process_to_run array (through an atomic fetch_and_add),
163 // and runs the smx_ctx_sysv_resume_parallel function on that index
165 // We lazily create the parmap because the parmap creates context
166 // with simix_global->context_factory (which might not be initialized
167 // when bootstrapping):
168 if (sysv_parmap == nullptr)
170 new simgrid::xbt::Parmap<smx_actor_t>(SIMIX_context_get_nthreads(), SIMIX_context_get_parallel_mode());
173 [](smx_actor_t process) {
174 ParallelUContext* context = static_cast<ParallelUContext*>(process->context);
177 simix_global->process_to_run);
179 xbt_die("You asked for a parallel execution, but you don't have any threads.");
183 if (simix_global->process_to_run.empty())
186 smx_actor_t first_process = simix_global->process_to_run.front();
187 sysv_process_index = 1;
188 SerialUContext* context = static_cast<SerialUContext*>(first_process->context);
193 Context* UContextFactory::create_context(std::function<void()> code,
194 void_pfn_smxprocess_t cleanup, smx_actor_t process)
197 return new_context<ParallelUContext>(std::move(code), cleanup, process);
199 return new_context<SerialUContext>(std::move(code), cleanup, process);
202 UContext::UContext(std::function<void()> code,
203 void_pfn_smxprocess_t cleanup_func, smx_actor_t process)
204 : Context(std::move(code), cleanup_func, process)
206 /* if the user provided a function for the process then use it, otherwise it is the context for maestro */
208 this->stack_ = (char*) SIMIX_context_stack_new();
209 getcontext(&this->uc_);
210 this->uc_.uc_link = nullptr;
211 this->uc_.uc_stack.ss_sp = sg_makecontext_stack_addr(this->stack_);
212 this->uc_.uc_stack.ss_size = sg_makecontext_stack_size(smx_context_usable_stack_size);
213 simgrid_makecontext(&this->uc_, smx_ctx_sysv_wrapper, this);
215 if (process != nullptr && sysv_maestro_context == nullptr)
216 sysv_maestro_context = this;
220 if (MC_is_active() && has_code()) {
221 MC_register_stack_area(this->stack_, process,
222 &(this->uc_), smx_context_usable_stack_size);
227 UContext::~UContext()
229 SIMIX_context_stack_delete(this->stack_);
232 void UContext::stop()
237 }}} // namespace simgrid::kernel::context
239 static void smx_ctx_sysv_wrapper(int first, ...)
241 // Rebuild the Context* pointer from the integers:
242 int ctx_addr[CTX_ADDR_LEN];
243 simgrid::kernel::context::UContext* context;
245 if (CTX_ADDR_LEN > 1) {
248 for (unsigned i = 1; i < CTX_ADDR_LEN; i++)
249 ctx_addr[i] = va_arg(ap, int);
252 memcpy(&context, ctx_addr, sizeof(simgrid::kernel::context::UContext*));
256 context->Context::stop();
257 } catch (simgrid::kernel::context::Context::StopRequest const&) {
258 XBT_DEBUG("Caught a StopRequest");
267 void SerialUContext::suspend()
269 /* determine the next context */
270 SerialUContext* next_context = nullptr;
271 unsigned long int i = sysv_process_index++;
273 if (i < simix_global->process_to_run.size()) {
274 /* execute the next process */
275 XBT_DEBUG("Run next process");
276 next_context = static_cast<SerialUContext*>(simix_global->process_to_run[i]->context);
278 /* all processes were run, return to maestro */
279 XBT_DEBUG("No more process to run");
280 next_context = static_cast<SerialUContext*>(sysv_maestro_context);
282 SIMIX_context_set_current(next_context);
283 swapcontext(&this->uc_, &next_context->uc_);
288 void SerialUContext::resume()
290 SIMIX_context_set_current(this);
291 swapcontext(&static_cast<SerialUContext*>(sysv_maestro_context)->uc_, &this->uc_);
294 /** Run one particular simulated process on the current thread. */
295 void ParallelUContext::resume()
297 #if HAVE_THREAD_CONTEXTS
298 // What is my containing body?
299 uintptr_t worker_id = __sync_fetch_and_add(&sysv_threads_working, 1);
300 // Store the number of my containing body in os-thread-specific area :
301 xbt_os_thread_set_specific(sysv_worker_id_key, (void*) worker_id);
302 // Get my current soul:
303 ParallelUContext* worker_context = static_cast<ParallelUContext*>(SIMIX_context_self());
304 // Write down that this soul is hosted in that body (for now)
305 sysv_workers_context[worker_id] = worker_context;
306 // Retrieve the system-level info that fuels this soul:
307 ucontext_t* worker_stack = &worker_context->uc_;
308 // Write in simix that I switched my soul
309 SIMIX_context_set_current(this);
310 // Actually do that using the relevant library call:
311 swapcontext(worker_stack, &this->uc_);
312 // No body runs that soul anymore at this point.
313 // Instead the current body took the soul of simulated process
314 // The simulated process wakes back after the call to
315 // "SIMIX_context_suspend(self->context);" within
316 // smx_process.c::SIMIX_process_yield()
318 // From now on, the simulated processes will change their
319 // soul with the next soul to execute (in suspend_parallel, below).
320 // When nobody is to be executed in this scheduling round,
321 // the last simulated process will take back the initial
322 // soul of the current working thread
328 * This function is called when a simulated process wants to yield back
329 * to the maestro in a blocking simcall. This naturally occurs within
330 * SIMIX_context_suspend(self->context), called from SIMIX_process_yield()
331 * Actually, it does not really yield back to maestro, but into the next
332 * process that must be executed. If no one is to be executed, then it
333 * yields to the initial soul that was in this working thread (that was
334 * saved in resume_parallel).
336 void ParallelUContext::suspend()
338 #if HAVE_THREAD_CONTEXTS
339 /* determine the next context */
340 // Get the next soul to embody now:
341 boost::optional<smx_actor_t> next_work = sysv_parmap->next();
342 ParallelUContext* next_context;
344 // There is a next soul to embody (ie, a next process to resume)
345 XBT_DEBUG("Run next process");
346 next_context = static_cast<ParallelUContext*>(next_work.get()->context);
348 // All processes were run, go to the barrier
349 XBT_DEBUG("No more processes to run");
350 // Get back the identity of my body that was stored when starting
351 // the scheduling round
352 uintptr_t worker_id =
353 (uintptr_t) xbt_os_thread_get_specific(sysv_worker_id_key);
354 // Deduce the initial soul of that body
355 next_context = sysv_workers_context[worker_id];
356 // When given that soul, the body will wait for the next scheduling round
359 // Will contain the next soul to run, either simulated or initial minion's one
360 ucontext_t* next_stack = &next_context->uc_;
362 SIMIX_context_set_current(next_context);
363 // Get that next soul:
364 swapcontext(&this->uc_, next_stack);
368 }}} // namespace simgrid::kernel::context