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/simix/smx_private.hpp"
17 #include "src/internal_config.h"
18 #include "src/context_sysv_config.h" /* loads context system definitions */
21 /** Many integers are needed to store a pointer
23 * This is a bit paranoid about sizeof(smx_ctx_sysv_t) not being a multiple
24 * of sizeof(int), but it doesn't harm. */
25 #define CTX_ADDR_LEN \
26 (sizeof(void*) / sizeof(int) + \
27 !!(sizeof(void*) % sizeof(int)))
29 /** A better makecontext
31 * Makecontext expects integer arguments, we the context
32 * variable is decomposed into a serie of integers and
33 * each integer is passed as argument to makecontext. */
35 void simgrid_makecontext(ucontext_t* ucp, void (*func)(int first, ...), void* arg)
37 int ctx_addr[CTX_ADDR_LEN];
38 memcpy(ctx_addr, &arg, sizeof(void*));
39 switch (CTX_ADDR_LEN) {
41 makecontext(ucp, (void (*)())func, 1, ctx_addr[0]);
44 makecontext(ucp, (void (*)()) func, 2, ctx_addr[0], ctx_addr[1]);
47 xbt_die("Ucontexts are not supported on this arch yet (addr len = %zu/%zu = %zu)",
48 sizeof(void*), sizeof(int), CTX_ADDR_LEN);
52 XBT_LOG_EXTERNAL_DEFAULT_CATEGORY(simix_context);
58 class ParallelUContext;
59 class UContextFactory;
63 #ifdef HAVE_THREAD_CONTEXTS
64 static xbt_parmap_t sysv_parmap;
65 static simgrid::simix::ParallelUContext** sysv_workers_context; /* space to save the worker's context in each thread */
66 static uintptr_t sysv_threads_working; /* number of threads that have started their work */
67 static xbt_os_thread_key_t sysv_worker_id_key; /* thread-specific storage for the thread id */
69 static unsigned long sysv_process_index = 0; /* index of the next process to run in the
70 * list of runnable processes */
71 static simgrid::simix::UContext* sysv_maestro_context;
72 static bool sysv_parallel;
74 // The name of this function is currently hardcoded in the code (as string).
75 // Do not change it without fixing those references as well.
76 static void smx_ctx_sysv_wrapper(int first, ...);
81 class UContext : public Context {
83 ucontext_t uc_; /* the ucontext that executes the code */
84 char *stack_ = nullptr; /* the thread stack */
86 friend UContextFactory;
87 UContext(std::function<void()> code,
88 void_pfn_smxprocess_t cleanup_func, smx_process_t process);
92 class SerialUContext : public UContext {
94 SerialUContext(std::function<void()> code,
95 void_pfn_smxprocess_t cleanup_func, smx_process_t process)
96 : UContext(std::move(code), cleanup_func, process)
99 void suspend() override;
103 class ParallelUContext : public UContext {
105 ParallelUContext(std::function<void()> code,
106 void_pfn_smxprocess_t cleanup_func, smx_process_t process)
107 : UContext(std::move(code), cleanup_func, process)
109 void stop() override;
110 void suspend() override;
114 class UContextFactory : public ContextFactory {
117 friend SerialUContext;
118 friend ParallelUContext;
121 virtual ~UContextFactory();
122 virtual Context* create_context(std::function<void()> code,
123 void_pfn_smxprocess_t, smx_process_t process) override;
124 void run_all() override;
127 XBT_PRIVATE ContextFactory* sysv_factory()
129 XBT_VERB("Activating SYSV context factory");
130 return new UContextFactory();
133 UContextFactory::UContextFactory() : ContextFactory("UContextFactory")
135 if (SIMIX_context_is_parallel()) {
136 sysv_parallel = true;
137 #ifdef HAVE_THREAD_CONTEXTS /* To use parallel ucontexts a thread pool is needed */
138 int nthreads = SIMIX_context_get_nthreads();
139 sysv_parmap = nullptr;
140 sysv_workers_context = xbt_new(ParallelUContext*, nthreads);
141 sysv_maestro_context = nullptr;
142 xbt_os_thread_key_create(&sysv_worker_id_key);
144 THROWF(arg_error, 0, "No thread support for parallel context execution");
147 sysv_parallel = false;
151 UContextFactory::~UContextFactory()
153 #ifdef HAVE_THREAD_CONTEXTS
155 xbt_parmap_destroy(sysv_parmap);
156 xbt_free(sysv_workers_context);
160 /* This function is called by maestro at the beginning of a scheduling round to get all working threads executing some stuff
161 * It is much easier to understand what happens if you see the working threads as bodies that swap their soul for the
162 * ones of the simulated processes that must run.
164 void UContextFactory::run_all()
167 #ifdef HAVE_THREAD_CONTEXTS
168 sysv_threads_working = 0;
169 // Parmap_apply ensures that every working thread get an index in the
170 // process_to_run array (through an atomic fetch_and_add),
171 // and runs the smx_ctx_sysv_resume_parallel function on that index
173 // We lazily create the parmap because the parmap creates context
174 // with simix_global->context_factory (which might not be initialized
175 // when bootstrapping):
176 if (sysv_parmap == nullptr)
177 sysv_parmap = xbt_parmap_new(
178 SIMIX_context_get_nthreads(), SIMIX_context_get_parallel_mode());
180 xbt_parmap_apply(sysv_parmap,
182 smx_process_t process = (smx_process_t) arg;
183 ParallelUContext* context = static_cast<ParallelUContext*>(process->context);
186 simix_global->process_to_run);
188 xbt_die("You asked for a parallel execution, but you don't have any threads.");
192 smx_process_t first_process =
193 xbt_dynar_get_as(simix_global->process_to_run, 0, smx_process_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_process_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_process_t process)
212 : Context(std::move(code), cleanup_func, process)
214 /* if the user provided a function for the process then use it,
215 otherwise it is the context for maestro */
217 this->stack_ = (char*) SIMIX_context_stack_new();
218 getcontext(&this->uc_);
219 this->uc_.uc_link = nullptr;
220 this->uc_.uc_stack.ss_sp = pth_skaddr_makecontext(
221 this->stack_, smx_context_usable_stack_size);
222 this->uc_.uc_stack.ss_size = pth_sksize_makecontext(
223 this->stack_, smx_context_usable_stack_size);
224 simgrid_makecontext(&this->uc_, smx_ctx_sysv_wrapper, this);
226 if (process != NULL && sysv_maestro_context == NULL)
227 sysv_maestro_context = this;
231 if (MC_is_active() && has_code()) {
232 MC_register_stack_area(this->stack_, process,
233 &(this->uc_), smx_context_usable_stack_size);
238 UContext::~UContext()
240 SIMIX_context_stack_delete(this->stack_);
246 static void smx_ctx_sysv_wrapper(int first, ...)
248 // Rebuild the Context* pointer from the integers:
249 int ctx_addr[CTX_ADDR_LEN];
250 simgrid::simix::UContext* context;
252 if (CTX_ADDR_LEN > 1) {
255 for (unsigned i = 1; i < CTX_ADDR_LEN; i++)
256 ctx_addr[i] = va_arg(ap, int);
259 memcpy(&context, ctx_addr, sizeof(simgrid::simix::UContext*));
268 void SerialUContext::stop()
274 void SerialUContext::suspend()
276 /* determine the next context */
277 SerialUContext* next_context = nullptr;
278 unsigned long int i = sysv_process_index++;
280 if (i < xbt_dynar_length(simix_global->process_to_run)) {
281 /* execute the next process */
282 XBT_DEBUG("Run next process");
283 next_context = (SerialUContext*) xbt_dynar_get_as(
284 simix_global->process_to_run,i, smx_process_t)->context;
287 /* all processes were run, return to maestro */
288 XBT_DEBUG("No more process to run");
289 next_context = (SerialUContext*) sysv_maestro_context;
291 SIMIX_context_set_current(next_context);
292 swapcontext(&this->uc_, &next_context->uc_);
297 void SerialUContext::resume()
299 SIMIX_context_set_current(this);
300 swapcontext(&((SerialUContext*)sysv_maestro_context)->uc_, &this->uc_);
303 void ParallelUContext::stop()
309 /** Run one particular simulated process on the current thread. */
310 void ParallelUContext::resume()
312 #ifdef HAVE_THREAD_CONTEXTS
313 // What is my containing body?
314 uintptr_t worker_id = __sync_fetch_and_add(&sysv_threads_working, 1);
315 // Store the number of my containing body in os-thread-specific area :
316 xbt_os_thread_set_specific(sysv_worker_id_key, (void*) worker_id);
317 // Get my current soul:
318 ParallelUContext* worker_context = (ParallelUContext*) SIMIX_context_self();
319 // Write down that this soul is hosted in that body (for now)
320 sysv_workers_context[worker_id] = worker_context;
321 // Retrieve the system-level info that fuels this soul:
322 ucontext_t* worker_stack = &((ParallelUContext*) worker_context)->uc_;
323 // Write in simix that I switched my soul
324 SIMIX_context_set_current(this);
325 // Actually do that using the relevant library call:
326 swapcontext(worker_stack, &this->uc_);
327 // No body runs that soul anymore at this point.
328 // Instead the current body took the soul of simulated process
329 // The simulated process wakes back after the call to
330 // "SIMIX_context_suspend(self->context);" within
331 // smx_process.c::SIMIX_process_yield()
333 // From now on, the simulated processes will change their
334 // soul with the next soul to execute (in suspend_parallel, below).
335 // When nobody is to be executed in this scheduling round,
336 // the last simulated process will take back the initial
337 // soul of the current working thread
343 * This function is called when a simulated process wants to yield back
344 * to the maestro in a blocking simcall. This naturally occurs within
345 * SIMIX_context_suspend(self->context), called from SIMIX_process_yield()
346 * Actually, it does not really yield back to maestro, but into the next
347 * process that must be executed. If no one is to be executed, then it
348 * yields to the initial soul that was in this working thread (that was
349 * saved in resume_parallel).
351 void ParallelUContext::suspend()
353 #ifdef HAVE_THREAD_CONTEXTS
354 /* determine the next context */
355 // Get the next soul to embody now:
356 smx_process_t next_work = (smx_process_t) xbt_parmap_next(sysv_parmap);
357 ParallelUContext* next_context = nullptr;
358 // Will contain the next soul to run, either simulated or initial minion's one
359 ucontext_t* next_stack;
361 if (next_work != NULL) {
362 // There is a next soul to embody (ie, a next process to resume)
363 XBT_DEBUG("Run next process");
364 next_context = (ParallelUContext*) next_work->context;
367 // All processes were run, go to the barrier
368 XBT_DEBUG("No more processes to run");
369 // Get back the identity of my body that was stored when starting
370 // the scheduling round
371 uintptr_t worker_id =
372 (uintptr_t) xbt_os_thread_get_specific(sysv_worker_id_key);
373 // Deduce the initial soul of that body
374 next_context = (ParallelUContext*) sysv_workers_context[worker_id];
375 // When given that soul, the body will wait for the next scheduling round
378 next_stack = &next_context->uc_;
380 SIMIX_context_set_current(next_context);
381 // Get that next soul:
382 swapcontext(&this->uc_, next_stack);