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 */
10 #include "src/simix/ActorImpl.hpp"
11 #include "src/simix/smx_private.h"
12 #include "xbt/parmap.h"
14 #include "src/mc/mc_ignore.h"
17 /** Many integers are needed to store a pointer
19 * This is a bit paranoid about sizeof(smx_ctx_sysv_t) not being a multiple
20 * of sizeof(int), but it doesn't harm. */
21 #define CTX_ADDR_LEN \
22 (sizeof(void*) / sizeof(int) + \
23 !!(sizeof(void*) % sizeof(int)))
25 /** A better makecontext
27 * Makecontext expects integer arguments, we the context
28 * variable is decomposed into a serie of integers and
29 * each integer is passed as argument to makecontext. */
30 static void simgrid_makecontext(ucontext_t* ucp, void (*func)(int first, ...), void* arg)
32 int ctx_addr[CTX_ADDR_LEN];
33 memcpy(ctx_addr, &arg, sizeof(void*));
34 switch (CTX_ADDR_LEN) {
36 makecontext(ucp, (void (*)())func, 1, ctx_addr[0]);
39 makecontext(ucp, (void (*)()) func, 2, ctx_addr[0], ctx_addr[1]);
42 xbt_die("Ucontexts are not supported on this arch yet (addr len = %zu/%zu = %zu)", sizeof(void*), sizeof(int), CTX_ADDR_LEN);
46 XBT_LOG_EXTERNAL_DEFAULT_CATEGORY(simix_context);
53 class ParallelUContext;
54 class UContextFactory;
57 #if HAVE_THREAD_CONTEXTS
58 static xbt_parmap_t sysv_parmap;
59 static simgrid::kernel::context::ParallelUContext** sysv_workers_context; /* space to save the worker's context in each thread */
60 static uintptr_t sysv_threads_working; /* number of threads that have started their work */
61 static xbt_os_thread_key_t sysv_worker_id_key; /* thread-specific storage for the thread id */
63 static unsigned long sysv_process_index = 0; /* index of the next process to run in the
64 * list of runnable processes */
65 static simgrid::kernel::context::UContext* sysv_maestro_context;
66 static bool sysv_parallel;
68 // The name of this function is currently hardcoded in the code (as string).
69 // Do not change it without fixing those references as well.
70 static void smx_ctx_sysv_wrapper(int first, ...);
76 class UContext : public Context {
78 ucontext_t uc_; /* the ucontext that executes the code */
79 char *stack_ = nullptr; /* the thread stack */
81 friend UContextFactory;
82 UContext(std::function<void()> code,
83 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)
94 void suspend() override;
98 class ParallelUContext : public UContext {
100 ParallelUContext(std::function<void()> code,
101 void_pfn_smxprocess_t cleanup_func, smx_actor_t process)
102 : UContext(std::move(code), cleanup_func, process)
104 void stop() override;
105 void suspend() override;
109 class UContextFactory : public ContextFactory {
112 friend SerialUContext;
113 friend ParallelUContext;
116 ~UContextFactory() override;
117 Context* create_context(std::function<void()> code,
118 void_pfn_smxprocess_t cleanup, smx_actor_t process) override;
119 void run_all() override;
122 XBT_PRIVATE ContextFactory* sysv_factory()
124 XBT_VERB("Activating SYSV context factory");
125 return new UContextFactory();
128 UContextFactory::UContextFactory() : ContextFactory("UContextFactory")
130 if (SIMIX_context_is_parallel()) {
131 sysv_parallel = true;
132 #if HAVE_THREAD_CONTEXTS /* To use parallel ucontexts a thread pool is needed */
133 int nthreads = SIMIX_context_get_nthreads();
134 sysv_parmap = nullptr;
135 sysv_workers_context = xbt_new(ParallelUContext*, nthreads);
136 sysv_maestro_context = nullptr;
137 xbt_os_thread_key_create(&sysv_worker_id_key);
139 THROWF(arg_error, 0, "No thread support for parallel context execution");
142 sysv_parallel = false;
146 UContextFactory::~UContextFactory()
148 #if HAVE_THREAD_CONTEXTS
150 xbt_parmap_destroy(sysv_parmap);
151 xbt_free(sysv_workers_context);
155 /* This function is called by maestro at the beginning of a scheduling round to get all working threads executing some stuff
156 * It is much easier to understand what happens if you see the working threads as bodies that swap their soul for the
157 * ones of the simulated processes that must run.
159 void UContextFactory::run_all()
162 #if HAVE_THREAD_CONTEXTS
163 sysv_threads_working = 0;
164 // Parmap_apply ensures that every working thread get an index in the
165 // process_to_run array (through an atomic fetch_and_add),
166 // and runs the smx_ctx_sysv_resume_parallel function on that index
168 // We lazily create the parmap because the parmap creates context
169 // with simix_global->context_factory (which might not be initialized
170 // when bootstrapping):
171 if (sysv_parmap == nullptr)
172 sysv_parmap = xbt_parmap_new(
173 SIMIX_context_get_nthreads(), SIMIX_context_get_parallel_mode());
175 xbt_parmap_apply(sysv_parmap,
177 smx_actor_t process = (smx_actor_t) arg;
178 ParallelUContext* context = static_cast<ParallelUContext*>(process->context);
181 simix_global->process_to_run);
183 xbt_die("You asked for a parallel execution, but you don't have any threads.");
187 if (xbt_dynar_is_empty(simix_global->process_to_run))
190 smx_actor_t first_process = xbt_dynar_get_as(simix_global->process_to_run, 0, smx_actor_t);
191 sysv_process_index = 1;
192 SerialUContext* context = static_cast<SerialUContext*>(first_process->context);
197 Context* UContextFactory::create_context(std::function<void()> code,
198 void_pfn_smxprocess_t cleanup, smx_actor_t process)
201 return new_context<ParallelUContext>(std::move(code), cleanup, process);
203 return new_context<SerialUContext>(std::move(code), cleanup, process);
206 UContext::UContext(std::function<void()> code,
207 void_pfn_smxprocess_t cleanup_func, smx_actor_t process)
208 : Context(std::move(code), cleanup_func, process)
210 /* if the user provided a function for the process then use it, otherwise it is the context for maestro */
212 this->stack_ = (char*) SIMIX_context_stack_new();
213 getcontext(&this->uc_);
214 this->uc_.uc_link = nullptr;
215 this->uc_.uc_stack.ss_sp = sg_makecontext_stack_addr(this->stack_);
216 this->uc_.uc_stack.ss_size = sg_makecontext_stack_size(smx_context_usable_stack_size);
217 simgrid_makecontext(&this->uc_, smx_ctx_sysv_wrapper, this);
219 if (process != nullptr && sysv_maestro_context == nullptr)
220 sysv_maestro_context = this;
224 if (MC_is_active() && has_code()) {
225 MC_register_stack_area(this->stack_, process,
226 &(this->uc_), smx_context_usable_stack_size);
231 UContext::~UContext()
233 SIMIX_context_stack_delete(this->stack_);
236 }}} // namespace simgrid::kernel::context
238 static void smx_ctx_sysv_wrapper(int first, ...)
240 // Rebuild the Context* pointer from the integers:
241 int ctx_addr[CTX_ADDR_LEN];
242 simgrid::kernel::context::UContext* context;
244 if (CTX_ADDR_LEN > 1) {
247 for (unsigned i = 1; i < CTX_ADDR_LEN; i++)
248 ctx_addr[i] = va_arg(ap, int);
251 memcpy(&context, ctx_addr, sizeof(simgrid::kernel::context::UContext*));
261 void SerialUContext::stop()
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 < xbt_dynar_length(simix_global->process_to_run)) {
274 /* execute the next process */
275 XBT_DEBUG("Run next process");
276 next_context = (SerialUContext*) xbt_dynar_get_as(
277 simix_global->process_to_run,i, smx_actor_t)->context;
279 /* all processes were run, return to maestro */
280 XBT_DEBUG("No more process to run");
281 next_context = (SerialUContext*) sysv_maestro_context;
283 SIMIX_context_set_current(next_context);
284 swapcontext(&this->uc_, &next_context->uc_);
289 void SerialUContext::resume()
291 SIMIX_context_set_current(this);
292 swapcontext(&((SerialUContext*)sysv_maestro_context)->uc_, &this->uc_);
295 void ParallelUContext::stop()
301 /** Run one particular simulated process on the current thread. */
302 void ParallelUContext::resume()
304 #if HAVE_THREAD_CONTEXTS
305 // What is my containing body?
306 uintptr_t worker_id = __sync_fetch_and_add(&sysv_threads_working, 1);
307 // Store the number of my containing body in os-thread-specific area :
308 xbt_os_thread_set_specific(sysv_worker_id_key, (void*) worker_id);
309 // Get my current soul:
310 ParallelUContext* worker_context = (ParallelUContext*) SIMIX_context_self();
311 // Write down that this soul is hosted in that body (for now)
312 sysv_workers_context[worker_id] = worker_context;
313 // Retrieve the system-level info that fuels this soul:
314 ucontext_t* worker_stack = &((ParallelUContext*) worker_context)->uc_;
315 // Write in simix that I switched my soul
316 SIMIX_context_set_current(this);
317 // Actually do that using the relevant library call:
318 swapcontext(worker_stack, &this->uc_);
319 // No body runs that soul anymore at this point.
320 // Instead the current body took the soul of simulated process
321 // The simulated process wakes back after the call to
322 // "SIMIX_context_suspend(self->context);" within
323 // smx_process.c::SIMIX_process_yield()
325 // From now on, the simulated processes will change their
326 // soul with the next soul to execute (in suspend_parallel, below).
327 // When nobody is to be executed in this scheduling round,
328 // the last simulated process will take back the initial
329 // soul of the current working thread
335 * This function is called when a simulated process wants to yield back
336 * to the maestro in a blocking simcall. This naturally occurs within
337 * SIMIX_context_suspend(self->context), called from SIMIX_process_yield()
338 * Actually, it does not really yield back to maestro, but into the next
339 * process that must be executed. If no one is to be executed, then it
340 * yields to the initial soul that was in this working thread (that was
341 * saved in resume_parallel).
343 void ParallelUContext::suspend()
345 #if HAVE_THREAD_CONTEXTS
346 /* determine the next context */
347 // Get the next soul to embody now:
348 smx_actor_t next_work = (smx_actor_t) xbt_parmap_next(sysv_parmap);
349 ParallelUContext* next_context = nullptr;
350 // Will contain the next soul to run, either simulated or initial minion's one
351 ucontext_t* next_stack;
353 if (next_work != nullptr) {
354 // There is a next soul to embody (ie, a next process to resume)
355 XBT_DEBUG("Run next process");
356 next_context = (ParallelUContext*) next_work->context;
358 // All processes were run, go to the barrier
359 XBT_DEBUG("No more processes to run");
360 // Get back the identity of my body that was stored when starting
361 // the scheduling round
362 uintptr_t worker_id =
363 (uintptr_t) xbt_os_thread_get_specific(sysv_worker_id_key);
364 // Deduce the initial soul of that body
365 next_context = (ParallelUContext*) sysv_workers_context[worker_id];
366 // When given that soul, the body will wait for the next scheduling round
369 next_stack = &next_context->uc_;
371 SIMIX_context_set_current(next_context);
372 // Get that next soul:
373 swapcontext(&this->uc_, next_stack);
377 }}} // namespace simgrid::kernel::context