1 /* Copyright (c) 2009-2015. The SimGrid Team.
2 * All rights reserved. */
4 /* This program is free software; you can redistribute it and/or modify it
5 * under the terms of the license (GNU LGPL) which comes with this package. */
7 /* \file UContext.cpp Context switching with ucontexts from System V */
12 #include <ucontext.h> /* context relative declarations */
14 #include "xbt/parmap.h"
15 #include "src/simix/smx_private.h"
16 #include "src/internal_config.h"
19 /** Many integers are needed to store a pointer
21 * This is a bit paranoid about sizeof(smx_ctx_sysv_t) not being a multiple
22 * of sizeof(int), but it doesn't harm. */
23 #define CTX_ADDR_LEN \
24 (sizeof(void*) / sizeof(int) + \
25 !!(sizeof(void*) % sizeof(int)))
27 /** A better makecontext
29 * Makecontext expects integer arguments, we the context
30 * variable is decomposed into a serie of integers and
31 * each integer is passed as argument to makecontext. */
32 static void simgrid_makecontext(ucontext_t* ucp, void (*func)(int first, ...), void* arg)
34 int ctx_addr[CTX_ADDR_LEN];
35 memcpy(ctx_addr, &arg, sizeof(void*));
36 switch (CTX_ADDR_LEN) {
38 makecontext(ucp, (void (*)())func, 1, ctx_addr[0]);
41 makecontext(ucp, (void (*)()) func, 2, ctx_addr[0], ctx_addr[1]);
44 xbt_die("Ucontexts are not supported on this arch yet (addr len = %zu/%zu = %zu)", sizeof(void*), sizeof(int), CTX_ADDR_LEN);
48 XBT_LOG_EXTERNAL_DEFAULT_CATEGORY(simix_context);
55 class ParallelUContext;
56 class UContextFactory;
59 #if HAVE_THREAD_CONTEXTS
60 static xbt_parmap_t sysv_parmap;
61 static simgrid::kernel::context::ParallelUContext** sysv_workers_context; /* space to save the worker's context in each thread */
62 static uintptr_t sysv_threads_working; /* number of threads that have started their work */
63 static xbt_os_thread_key_t sysv_worker_id_key; /* thread-specific storage for the thread id */
65 static unsigned long sysv_process_index = 0; /* index of the next process to run in the
66 * list of runnable processes */
67 static simgrid::kernel::context::UContext* sysv_maestro_context;
68 static bool sysv_parallel;
70 // The name of this function is currently hardcoded in the code (as string).
71 // Do not change it without fixing those references as well.
72 static void smx_ctx_sysv_wrapper(int first, ...);
78 class UContext : public Context {
80 ucontext_t uc_; /* the ucontext that executes the code */
81 char *stack_ = nullptr; /* the thread stack */
83 friend UContextFactory;
84 UContext(std::function<void()> code,
85 void_pfn_smxprocess_t cleanup_func, smx_actor_t process);
89 class SerialUContext : public UContext {
91 SerialUContext(std::function<void()> code,
92 void_pfn_smxprocess_t cleanup_func, smx_actor_t process)
93 : UContext(std::move(code), cleanup_func, process)
96 void suspend() override;
100 class ParallelUContext : public UContext {
102 ParallelUContext(std::function<void()> code,
103 void_pfn_smxprocess_t cleanup_func, smx_actor_t process)
104 : UContext(std::move(code), cleanup_func, process)
106 void stop() override;
107 void suspend() override;
111 class UContextFactory : public ContextFactory {
114 friend SerialUContext;
115 friend ParallelUContext;
118 ~UContextFactory() override;
119 Context* create_context(std::function<void()> code,
120 void_pfn_smxprocess_t cleanup, smx_actor_t process) override;
121 void run_all() override;
124 XBT_PRIVATE ContextFactory* sysv_factory()
126 XBT_VERB("Activating SYSV context factory");
127 return new UContextFactory();
130 UContextFactory::UContextFactory() : ContextFactory("UContextFactory")
132 if (SIMIX_context_is_parallel()) {
133 sysv_parallel = true;
134 #if HAVE_THREAD_CONTEXTS /* To use parallel ucontexts a thread pool is needed */
135 int nthreads = SIMIX_context_get_nthreads();
136 sysv_parmap = nullptr;
137 sysv_workers_context = xbt_new(ParallelUContext*, nthreads);
138 sysv_maestro_context = nullptr;
139 xbt_os_thread_key_create(&sysv_worker_id_key);
141 THROWF(arg_error, 0, "No thread support for parallel context execution");
144 sysv_parallel = false;
148 UContextFactory::~UContextFactory()
150 #if HAVE_THREAD_CONTEXTS
152 xbt_parmap_destroy(sysv_parmap);
153 xbt_free(sysv_workers_context);
157 /* This function is called by maestro at the beginning of a scheduling round to get all working threads executing some stuff
158 * It is much easier to understand what happens if you see the working threads as bodies that swap their soul for the
159 * ones of the simulated processes that must run.
161 void UContextFactory::run_all()
164 #if HAVE_THREAD_CONTEXTS
165 sysv_threads_working = 0;
166 // Parmap_apply ensures that every working thread get an index in the
167 // process_to_run array (through an atomic fetch_and_add),
168 // and runs the smx_ctx_sysv_resume_parallel function on that index
170 // We lazily create the parmap because the parmap creates context
171 // with simix_global->context_factory (which might not be initialized
172 // when bootstrapping):
173 if (sysv_parmap == nullptr)
174 sysv_parmap = xbt_parmap_new(
175 SIMIX_context_get_nthreads(), SIMIX_context_get_parallel_mode());
177 xbt_parmap_apply(sysv_parmap,
179 smx_actor_t process = (smx_actor_t) arg;
180 ParallelUContext* context = static_cast<ParallelUContext*>(process->context);
183 simix_global->process_to_run);
185 xbt_die("You asked for a parallel execution, but you don't have any threads.");
189 if (xbt_dynar_is_empty(simix_global->process_to_run))
192 smx_actor_t first_process =
193 xbt_dynar_get_as(simix_global->process_to_run, 0, smx_actor_t);
194 sysv_process_index = 1;
195 SerialUContext* context =
196 static_cast<SerialUContext*>(first_process->context);
201 Context* UContextFactory::create_context(std::function<void()> code,
202 void_pfn_smxprocess_t cleanup, smx_actor_t process)
205 return new_context<ParallelUContext>(std::move(code), cleanup, process);
207 return new_context<SerialUContext>(std::move(code), cleanup, process);
210 UContext::UContext(std::function<void()> code,
211 void_pfn_smxprocess_t cleanup_func, smx_actor_t process)
212 : Context(std::move(code), cleanup_func, process)
214 /* if the user provided a function for the process then use it, otherwise it is the context for maestro */
216 this->stack_ = (char*) SIMIX_context_stack_new();
217 getcontext(&this->uc_);
218 this->uc_.uc_link = nullptr;
219 this->uc_.uc_stack.ss_sp = sg_makecontext_stack_addr(this->stack_);
220 this->uc_.uc_stack.ss_size = sg_makecontext_stack_size(smx_context_usable_stack_size);
221 simgrid_makecontext(&this->uc_, smx_ctx_sysv_wrapper, this);
223 if (process != nullptr && sysv_maestro_context == nullptr)
224 sysv_maestro_context = this;
228 if (MC_is_active() && has_code()) {
229 MC_register_stack_area(this->stack_, process,
230 &(this->uc_), smx_context_usable_stack_size);
235 UContext::~UContext()
237 SIMIX_context_stack_delete(this->stack_);
240 }}} // namespace simgrid::kernel::context
242 static void smx_ctx_sysv_wrapper(int first, ...)
244 // Rebuild the Context* pointer from the integers:
245 int ctx_addr[CTX_ADDR_LEN];
246 simgrid::kernel::context::UContext* context;
248 if (CTX_ADDR_LEN > 1) {
251 for (unsigned i = 1; i < CTX_ADDR_LEN; i++)
252 ctx_addr[i] = va_arg(ap, int);
255 memcpy(&context, ctx_addr, sizeof(simgrid::kernel::context::UContext*));
265 void SerialUContext::stop()
271 void SerialUContext::suspend()
273 /* determine the next context */
274 SerialUContext* next_context = nullptr;
275 unsigned long int i = sysv_process_index++;
277 if (i < xbt_dynar_length(simix_global->process_to_run)) {
278 /* execute the next process */
279 XBT_DEBUG("Run next process");
280 next_context = (SerialUContext*) xbt_dynar_get_as(
281 simix_global->process_to_run,i, smx_actor_t)->context;
284 /* all processes were run, return to maestro */
285 XBT_DEBUG("No more process to run");
286 next_context = (SerialUContext*) sysv_maestro_context;
288 SIMIX_context_set_current(next_context);
289 swapcontext(&this->uc_, &next_context->uc_);
294 void SerialUContext::resume()
296 SIMIX_context_set_current(this);
297 swapcontext(&((SerialUContext*)sysv_maestro_context)->uc_, &this->uc_);
300 void ParallelUContext::stop()
306 /** Run one particular simulated process on the current thread. */
307 void ParallelUContext::resume()
309 #if HAVE_THREAD_CONTEXTS
310 // What is my containing body?
311 uintptr_t worker_id = __sync_fetch_and_add(&sysv_threads_working, 1);
312 // Store the number of my containing body in os-thread-specific area :
313 xbt_os_thread_set_specific(sysv_worker_id_key, (void*) worker_id);
314 // Get my current soul:
315 ParallelUContext* worker_context = (ParallelUContext*) SIMIX_context_self();
316 // Write down that this soul is hosted in that body (for now)
317 sysv_workers_context[worker_id] = worker_context;
318 // Retrieve the system-level info that fuels this soul:
319 ucontext_t* worker_stack = &((ParallelUContext*) worker_context)->uc_;
320 // Write in simix that I switched my soul
321 SIMIX_context_set_current(this);
322 // Actually do that using the relevant library call:
323 swapcontext(worker_stack, &this->uc_);
324 // No body runs that soul anymore at this point.
325 // Instead the current body took the soul of simulated process
326 // The simulated process wakes back after the call to
327 // "SIMIX_context_suspend(self->context);" within
328 // smx_process.c::SIMIX_process_yield()
330 // From now on, the simulated processes will change their
331 // soul with the next soul to execute (in suspend_parallel, below).
332 // When nobody is to be executed in this scheduling round,
333 // the last simulated process will take back the initial
334 // soul of the current working thread
340 * This function is called when a simulated process wants to yield back
341 * to the maestro in a blocking simcall. This naturally occurs within
342 * SIMIX_context_suspend(self->context), called from SIMIX_process_yield()
343 * Actually, it does not really yield back to maestro, but into the next
344 * process that must be executed. If no one is to be executed, then it
345 * yields to the initial soul that was in this working thread (that was
346 * saved in resume_parallel).
348 void ParallelUContext::suspend()
350 #if HAVE_THREAD_CONTEXTS
351 /* determine the next context */
352 // Get the next soul to embody now:
353 smx_actor_t next_work = (smx_actor_t) xbt_parmap_next(sysv_parmap);
354 ParallelUContext* next_context = nullptr;
355 // Will contain the next soul to run, either simulated or initial minion's one
356 ucontext_t* next_stack;
358 if (next_work != nullptr) {
359 // There is a next soul to embody (ie, a next process to resume)
360 XBT_DEBUG("Run next process");
361 next_context = (ParallelUContext*) next_work->context;
364 // All processes were run, go to the barrier
365 XBT_DEBUG("No more processes to run");
366 // Get back the identity of my body that was stored when starting
367 // the scheduling round
368 uintptr_t worker_id =
369 (uintptr_t) xbt_os_thread_get_specific(sysv_worker_id_key);
370 // Deduce the initial soul of that body
371 next_context = (ParallelUContext*) sysv_workers_context[worker_id];
372 // When given that soul, the body will wait for the next scheduling round
375 next_stack = &next_context->uc_;
377 SIMIX_context_set_current(next_context);
378 // Get that next soul:
379 swapcontext(&this->uc_, next_stack);
383 }}} // namespace simgrid::kernel::context