1 /* Copyright (c) 2009-2015. 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/simix/ActorImpl.hpp"
12 #include "src/simix/smx_private.h"
13 #include "xbt/parmap.h"
15 /** Many integers are needed to store a pointer
17 * This is a bit paranoid about sizeof(smx_ctx_sysv_t) not being a multiple
18 * of sizeof(int), but it doesn't harm. */
19 #define CTX_ADDR_LEN \
20 (sizeof(void*) / sizeof(int) + \
21 !!(sizeof(void*) % sizeof(int)))
23 /** A better makecontext
25 * Makecontext expects integer arguments, we the context
26 * variable is decomposed into a serie of integers and
27 * each integer is passed as argument to makecontext. */
28 static void simgrid_makecontext(ucontext_t* ucp, void (*func)(int first, ...), void* arg)
30 int ctx_addr[CTX_ADDR_LEN];
31 memcpy(ctx_addr, &arg, sizeof(void*));
32 switch (CTX_ADDR_LEN) {
34 makecontext(ucp, (void (*)())func, 1, ctx_addr[0]);
37 makecontext(ucp, (void (*)()) func, 2, ctx_addr[0], ctx_addr[1]);
40 xbt_die("Ucontexts are not supported on this arch yet (addr len = %zu/%zu = %zu)", sizeof(void*), sizeof(int), CTX_ADDR_LEN);
44 XBT_LOG_EXTERNAL_DEFAULT_CATEGORY(simix_context);
51 class ParallelUContext;
52 class UContextFactory;
55 #if HAVE_THREAD_CONTEXTS
56 static xbt_parmap_t sysv_parmap;
57 static simgrid::kernel::context::ParallelUContext** sysv_workers_context; /* space to save the worker's context in each thread */
58 static uintptr_t sysv_threads_working; /* number of threads that have started their work */
59 static xbt_os_thread_key_t sysv_worker_id_key; /* thread-specific storage for the thread id */
61 static unsigned long sysv_process_index = 0; /* index of the next process to run in the
62 * list of runnable processes */
63 static simgrid::kernel::context::UContext* sysv_maestro_context;
64 static bool sysv_parallel;
66 // The name of this function is currently hardcoded in the code (as string).
67 // Do not change it without fixing those references as well.
68 static void smx_ctx_sysv_wrapper(int first, ...);
74 class UContext : public Context {
76 ucontext_t uc_; /* the ucontext that executes the code */
77 char *stack_ = nullptr; /* the thread stack */
79 friend UContextFactory;
80 UContext(std::function<void()> code,
81 void_pfn_smxprocess_t cleanup_func, smx_actor_t process);
85 class SerialUContext : public UContext {
87 SerialUContext(std::function<void()> code,
88 void_pfn_smxprocess_t cleanup_func, smx_actor_t process)
89 : UContext(std::move(code), cleanup_func, process)
92 void suspend() override;
96 class ParallelUContext : public UContext {
98 ParallelUContext(std::function<void()> code,
99 void_pfn_smxprocess_t cleanup_func, smx_actor_t process)
100 : UContext(std::move(code), cleanup_func, process)
102 void stop() override;
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_parmap_destroy(sysv_parmap);
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)
170 sysv_parmap = xbt_parmap_new(
171 SIMIX_context_get_nthreads(), SIMIX_context_get_parallel_mode());
173 xbt_parmap_apply(sysv_parmap,
175 smx_actor_t process = (smx_actor_t) arg;
176 ParallelUContext* context = static_cast<ParallelUContext*>(process->context);
179 simix_global->process_to_run);
181 xbt_die("You asked for a parallel execution, but you don't have any threads.");
185 if (xbt_dynar_is_empty(simix_global->process_to_run))
188 smx_actor_t first_process =
189 xbt_dynar_get_as(simix_global->process_to_run, 0, smx_actor_t);
190 sysv_process_index = 1;
191 SerialUContext* context =
192 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;
280 /* all processes were run, return to maestro */
281 XBT_DEBUG("No more process to run");
282 next_context = (SerialUContext*) sysv_maestro_context;
284 SIMIX_context_set_current(next_context);
285 swapcontext(&this->uc_, &next_context->uc_);
290 void SerialUContext::resume()
292 SIMIX_context_set_current(this);
293 swapcontext(&((SerialUContext*)sysv_maestro_context)->uc_, &this->uc_);
296 void ParallelUContext::stop()
302 /** Run one particular simulated process on the current thread. */
303 void ParallelUContext::resume()
305 #if HAVE_THREAD_CONTEXTS
306 // What is my containing body?
307 uintptr_t worker_id = __sync_fetch_and_add(&sysv_threads_working, 1);
308 // Store the number of my containing body in os-thread-specific area :
309 xbt_os_thread_set_specific(sysv_worker_id_key, (void*) worker_id);
310 // Get my current soul:
311 ParallelUContext* worker_context = (ParallelUContext*) SIMIX_context_self();
312 // Write down that this soul is hosted in that body (for now)
313 sysv_workers_context[worker_id] = worker_context;
314 // Retrieve the system-level info that fuels this soul:
315 ucontext_t* worker_stack = &((ParallelUContext*) worker_context)->uc_;
316 // Write in simix that I switched my soul
317 SIMIX_context_set_current(this);
318 // Actually do that using the relevant library call:
319 swapcontext(worker_stack, &this->uc_);
320 // No body runs that soul anymore at this point.
321 // Instead the current body took the soul of simulated process
322 // The simulated process wakes back after the call to
323 // "SIMIX_context_suspend(self->context);" within
324 // smx_process.c::SIMIX_process_yield()
326 // From now on, the simulated processes will change their
327 // soul with the next soul to execute (in suspend_parallel, below).
328 // When nobody is to be executed in this scheduling round,
329 // the last simulated process will take back the initial
330 // soul of the current working thread
336 * This function is called when a simulated process wants to yield back
337 * to the maestro in a blocking simcall. This naturally occurs within
338 * SIMIX_context_suspend(self->context), called from SIMIX_process_yield()
339 * Actually, it does not really yield back to maestro, but into the next
340 * process that must be executed. If no one is to be executed, then it
341 * yields to the initial soul that was in this working thread (that was
342 * saved in resume_parallel).
344 void ParallelUContext::suspend()
346 #if HAVE_THREAD_CONTEXTS
347 /* determine the next context */
348 // Get the next soul to embody now:
349 smx_actor_t next_work = (smx_actor_t) xbt_parmap_next(sysv_parmap);
350 ParallelUContext* next_context = nullptr;
351 // Will contain the next soul to run, either simulated or initial minion's one
352 ucontext_t* next_stack;
354 if (next_work != nullptr) {
355 // There is a next soul to embody (ie, a next process to resume)
356 XBT_DEBUG("Run next process");
357 next_context = (ParallelUContext*) next_work->context;
360 // All processes were run, go to the barrier
361 XBT_DEBUG("No more processes to run");
362 // Get back the identity of my body that was stored when starting
363 // the scheduling round
364 uintptr_t worker_id =
365 (uintptr_t) xbt_os_thread_get_specific(sysv_worker_id_key);
366 // Deduce the initial soul of that body
367 next_context = (ParallelUContext*) sysv_workers_context[worker_id];
368 // When given that soul, the body will wait for the next scheduling round
371 next_stack = &next_context->uc_;
373 SIMIX_context_set_current(next_context);
374 // Get that next soul:
375 swapcontext(&this->uc_, next_stack);
379 }}} // namespace simgrid::kernel::context