| 1 | // workqueue.cc -- the workqueue for gold |
| 2 | |
| 3 | // Copyright (C) 2006-2019 Free Software Foundation, Inc. |
| 4 | // Written by Ian Lance Taylor <iant@google.com>. |
| 5 | |
| 6 | // This file is part of gold. |
| 7 | |
| 8 | // This program is free software; you can redistribute it and/or modify |
| 9 | // it under the terms of the GNU General Public License as published by |
| 10 | // the Free Software Foundation; either version 3 of the License, or |
| 11 | // (at your option) any later version. |
| 12 | |
| 13 | // This program is distributed in the hope that it will be useful, |
| 14 | // but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 15 | // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 16 | // GNU General Public License for more details. |
| 17 | |
| 18 | // You should have received a copy of the GNU General Public License |
| 19 | // along with this program; if not, write to the Free Software |
| 20 | // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, |
| 21 | // MA 02110-1301, USA. |
| 22 | |
| 23 | #include "gold.h" |
| 24 | |
| 25 | #include "debug.h" |
| 26 | #include "options.h" |
| 27 | #include "timer.h" |
| 28 | #include "workqueue.h" |
| 29 | #include "workqueue-internal.h" |
| 30 | |
| 31 | namespace gold |
| 32 | { |
| 33 | |
| 34 | // Class Task_list. |
| 35 | |
| 36 | // Add T to the end of the list. |
| 37 | |
| 38 | inline void |
| 39 | Task_list::push_back(Task* t) |
| 40 | { |
| 41 | gold_assert(t->list_next() == NULL); |
| 42 | if (this->head_ == NULL) |
| 43 | { |
| 44 | this->head_ = t; |
| 45 | this->tail_ = t; |
| 46 | } |
| 47 | else |
| 48 | { |
| 49 | this->tail_->set_list_next(t); |
| 50 | this->tail_ = t; |
| 51 | } |
| 52 | } |
| 53 | |
| 54 | // Add T to the front of the list. |
| 55 | |
| 56 | inline void |
| 57 | Task_list::push_front(Task* t) |
| 58 | { |
| 59 | gold_assert(t->list_next() == NULL); |
| 60 | if (this->head_ == NULL) |
| 61 | { |
| 62 | this->head_ = t; |
| 63 | this->tail_ = t; |
| 64 | } |
| 65 | else |
| 66 | { |
| 67 | t->set_list_next(this->head_); |
| 68 | this->head_ = t; |
| 69 | } |
| 70 | } |
| 71 | |
| 72 | // Remove and return the first Task waiting for this lock to be |
| 73 | // released. |
| 74 | |
| 75 | inline Task* |
| 76 | Task_list::pop_front() |
| 77 | { |
| 78 | Task* ret = this->head_; |
| 79 | if (ret != NULL) |
| 80 | { |
| 81 | if (ret == this->tail_) |
| 82 | { |
| 83 | gold_assert(ret->list_next() == NULL); |
| 84 | this->head_ = NULL; |
| 85 | this->tail_ = NULL; |
| 86 | } |
| 87 | else |
| 88 | { |
| 89 | this->head_ = ret->list_next(); |
| 90 | gold_assert(this->head_ != NULL); |
| 91 | ret->clear_list_next(); |
| 92 | } |
| 93 | } |
| 94 | return ret; |
| 95 | } |
| 96 | |
| 97 | // The simple single-threaded implementation of Workqueue_threader. |
| 98 | |
| 99 | class Workqueue_threader_single : public Workqueue_threader |
| 100 | { |
| 101 | public: |
| 102 | Workqueue_threader_single(Workqueue* workqueue) |
| 103 | : Workqueue_threader(workqueue) |
| 104 | { } |
| 105 | ~Workqueue_threader_single() |
| 106 | { } |
| 107 | |
| 108 | void |
| 109 | set_thread_count(int thread_count) |
| 110 | { gold_assert(thread_count > 0); } |
| 111 | |
| 112 | bool |
| 113 | should_cancel_thread(int) |
| 114 | { return false; } |
| 115 | }; |
| 116 | |
| 117 | // Workqueue methods. |
| 118 | |
| 119 | Workqueue::Workqueue(const General_options& options) |
| 120 | : lock_(), |
| 121 | first_tasks_(), |
| 122 | tasks_(), |
| 123 | running_(0), |
| 124 | waiting_(0), |
| 125 | condvar_(this->lock_), |
| 126 | threader_(NULL) |
| 127 | { |
| 128 | bool threads = options.threads(); |
| 129 | #ifndef ENABLE_THREADS |
| 130 | threads = false; |
| 131 | #endif |
| 132 | if (!threads) |
| 133 | this->threader_ = new Workqueue_threader_single(this); |
| 134 | else |
| 135 | { |
| 136 | #ifdef ENABLE_THREADS |
| 137 | this->threader_ = new Workqueue_threader_threadpool(this); |
| 138 | #else |
| 139 | gold_unreachable(); |
| 140 | #endif |
| 141 | } |
| 142 | } |
| 143 | |
| 144 | Workqueue::~Workqueue() |
| 145 | { |
| 146 | } |
| 147 | |
| 148 | // Add a task to the end of a specific queue, or put it on the list |
| 149 | // waiting for a Token. |
| 150 | |
| 151 | void |
| 152 | Workqueue::add_to_queue(Task_list* queue, Task* t, bool front) |
| 153 | { |
| 154 | Hold_lock hl(this->lock_); |
| 155 | |
| 156 | Task_token* token = t->is_runnable(); |
| 157 | if (token != NULL) |
| 158 | { |
| 159 | if (front) |
| 160 | token->add_waiting_front(t); |
| 161 | else |
| 162 | token->add_waiting(t); |
| 163 | ++this->waiting_; |
| 164 | } |
| 165 | else |
| 166 | { |
| 167 | if (front) |
| 168 | queue->push_front(t); |
| 169 | else |
| 170 | queue->push_back(t); |
| 171 | // Tell any waiting thread that there is work to do. |
| 172 | this->condvar_.signal(); |
| 173 | } |
| 174 | } |
| 175 | |
| 176 | // Add a task to the queue. |
| 177 | |
| 178 | void |
| 179 | Workqueue::queue(Task* t) |
| 180 | { |
| 181 | this->add_to_queue(&this->tasks_, t, false); |
| 182 | } |
| 183 | |
| 184 | // Queue a task which should run soon. |
| 185 | |
| 186 | void |
| 187 | Workqueue::queue_soon(Task* t) |
| 188 | { |
| 189 | t->set_should_run_soon(); |
| 190 | this->add_to_queue(&this->first_tasks_, t, false); |
| 191 | } |
| 192 | |
| 193 | // Queue a task which should run next. |
| 194 | |
| 195 | void |
| 196 | Workqueue::queue_next(Task* t) |
| 197 | { |
| 198 | t->set_should_run_soon(); |
| 199 | this->add_to_queue(&this->first_tasks_, t, true); |
| 200 | } |
| 201 | |
| 202 | // Return whether to cancel the current thread. |
| 203 | |
| 204 | inline bool |
| 205 | Workqueue::should_cancel_thread(int thread_number) |
| 206 | { |
| 207 | return this->threader_->should_cancel_thread(thread_number); |
| 208 | } |
| 209 | |
| 210 | // Find a runnable task in TASKS. Return NULL if none could be found. |
| 211 | // If we find a Task waiting for a Token, add it to the list for that |
| 212 | // Token. The workqueue lock must be held when this is called. |
| 213 | |
| 214 | Task* |
| 215 | Workqueue::find_runnable_in_list(Task_list* tasks) |
| 216 | { |
| 217 | Task* t; |
| 218 | while ((t = tasks->pop_front()) != NULL) |
| 219 | { |
| 220 | Task_token* token = t->is_runnable(); |
| 221 | |
| 222 | if (token == NULL) |
| 223 | return t; |
| 224 | |
| 225 | token->add_waiting(t); |
| 226 | ++this->waiting_; |
| 227 | } |
| 228 | |
| 229 | // We couldn't find any runnable task. |
| 230 | return NULL; |
| 231 | } |
| 232 | |
| 233 | // Find a runnable task. Return NULL if none could be found. The |
| 234 | // workqueue lock must be held when this is called. |
| 235 | |
| 236 | Task* |
| 237 | Workqueue::find_runnable() |
| 238 | { |
| 239 | Task* t = this->find_runnable_in_list(&this->first_tasks_); |
| 240 | if (t == NULL) |
| 241 | t = this->find_runnable_in_list(&this->tasks_); |
| 242 | return t; |
| 243 | } |
| 244 | |
| 245 | // Find a runnable a task, and wait until we find one. Return NULL if |
| 246 | // we should exit. The workqueue lock must be held when this is |
| 247 | // called. |
| 248 | |
| 249 | Task* |
| 250 | Workqueue::find_runnable_or_wait(int thread_number) |
| 251 | { |
| 252 | Task* t = this->find_runnable(); |
| 253 | |
| 254 | while (t == NULL) |
| 255 | { |
| 256 | if (this->running_ == 0 |
| 257 | && this->first_tasks_.empty() |
| 258 | && this->tasks_.empty()) |
| 259 | { |
| 260 | // Kick all the threads to make them exit. |
| 261 | this->condvar_.broadcast(); |
| 262 | |
| 263 | gold_assert(this->waiting_ == 0); |
| 264 | return NULL; |
| 265 | } |
| 266 | |
| 267 | if (this->should_cancel_thread(thread_number)) |
| 268 | return NULL; |
| 269 | |
| 270 | gold_debug(DEBUG_TASK, "%3d sleeping", thread_number); |
| 271 | |
| 272 | this->condvar_.wait(); |
| 273 | |
| 274 | gold_debug(DEBUG_TASK, "%3d awake", thread_number); |
| 275 | |
| 276 | t = this->find_runnable(); |
| 277 | } |
| 278 | |
| 279 | return t; |
| 280 | } |
| 281 | |
| 282 | // Find and run tasks. If we can't find a runnable task, wait for one |
| 283 | // to become available. If we run a task, and it frees up another |
| 284 | // runnable task, then run that one too. This returns true if we |
| 285 | // should look for another task, false if we are cancelling this |
| 286 | // thread. |
| 287 | |
| 288 | bool |
| 289 | Workqueue::find_and_run_task(int thread_number) |
| 290 | { |
| 291 | Task* t; |
| 292 | Task_locker tl; |
| 293 | |
| 294 | { |
| 295 | Hold_lock hl(this->lock_); |
| 296 | |
| 297 | // Find a runnable task. |
| 298 | t = this->find_runnable_or_wait(thread_number); |
| 299 | |
| 300 | if (t == NULL) |
| 301 | return false; |
| 302 | |
| 303 | // Get the locks for the task. This must be called while we are |
| 304 | // still holding the Workqueue lock. |
| 305 | t->locks(&tl); |
| 306 | |
| 307 | ++this->running_; |
| 308 | } |
| 309 | |
| 310 | while (t != NULL) |
| 311 | { |
| 312 | gold_debug(DEBUG_TASK, "%3d running task %s", thread_number, |
| 313 | t->name().c_str()); |
| 314 | |
| 315 | Timer timer; |
| 316 | if (is_debugging_enabled(DEBUG_TASK)) |
| 317 | timer.start(); |
| 318 | |
| 319 | t->run(this); |
| 320 | |
| 321 | if (is_debugging_enabled(DEBUG_TASK)) |
| 322 | { |
| 323 | Timer::TimeStats elapsed = timer.get_elapsed_time(); |
| 324 | |
| 325 | gold_debug(DEBUG_TASK, |
| 326 | "%3d completed task %s " |
| 327 | "(user: %ld.%06ld sys: %ld.%06ld wall: %ld.%06ld)", |
| 328 | thread_number, t->name().c_str(), |
| 329 | elapsed.user / 1000, (elapsed.user % 1000) * 1000, |
| 330 | elapsed.sys / 1000, (elapsed.sys % 1000) * 1000, |
| 331 | elapsed.wall / 1000, (elapsed.wall % 1000) * 1000); |
| 332 | } |
| 333 | |
| 334 | Task* next; |
| 335 | { |
| 336 | Hold_lock hl(this->lock_); |
| 337 | |
| 338 | --this->running_; |
| 339 | |
| 340 | // Release the locks for the task. This must be done with the |
| 341 | // workqueue lock held. Get the next Task to run if any. |
| 342 | next = this->release_locks(t, &tl); |
| 343 | |
| 344 | if (next == NULL) |
| 345 | next = this->find_runnable(); |
| 346 | |
| 347 | // If we have another Task to run, get the Locks. This must |
| 348 | // be called while we are still holding the Workqueue lock. |
| 349 | if (next != NULL) |
| 350 | { |
| 351 | tl.clear(); |
| 352 | next->locks(&tl); |
| 353 | |
| 354 | ++this->running_; |
| 355 | } |
| 356 | } |
| 357 | |
| 358 | // We are done with this task. |
| 359 | delete t; |
| 360 | |
| 361 | t = next; |
| 362 | } |
| 363 | |
| 364 | return true; |
| 365 | } |
| 366 | |
| 367 | // Handle the return value of release_locks, and get tasks ready to |
| 368 | // run. |
| 369 | |
| 370 | // 1) If T is not runnable, queue it on the appropriate token. |
| 371 | |
| 372 | // 2) Otherwise, T is runnable. If *PRET is not NULL, then we have |
| 373 | // already decided which Task to run next. Add T to the list of |
| 374 | // runnable tasks, and signal another thread. |
| 375 | |
| 376 | // 3) Otherwise, *PRET is NULL. If IS_BLOCKER is false, then T was |
| 377 | // waiting on a write lock. We can grab that lock now, so we run T |
| 378 | // now. |
| 379 | |
| 380 | // 4) Otherwise, IS_BLOCKER is true. If we should run T soon, then |
| 381 | // run it now. |
| 382 | |
| 383 | // 5) Otherwise, check whether there are other tasks to run. If there |
| 384 | // are, then we generally get a better ordering if we run those tasks |
| 385 | // now, before T. A typical example is tasks waiting on the Dirsearch |
| 386 | // blocker. We don't want to run those tasks right away just because |
| 387 | // the Dirsearch was unblocked. |
| 388 | |
| 389 | // 6) Otherwise, there are no other tasks to run, so we might as well |
| 390 | // run this one now. |
| 391 | |
| 392 | // This function must be called with the Workqueue lock held. |
| 393 | |
| 394 | // Return true if we set *PRET to T, false otherwise. |
| 395 | |
| 396 | bool |
| 397 | Workqueue::return_or_queue(Task* t, bool is_blocker, Task** pret) |
| 398 | { |
| 399 | Task_token* token = t->is_runnable(); |
| 400 | |
| 401 | if (token != NULL) |
| 402 | { |
| 403 | token->add_waiting(t); |
| 404 | ++this->waiting_; |
| 405 | return false; |
| 406 | } |
| 407 | |
| 408 | bool should_queue = false; |
| 409 | bool should_return = false; |
| 410 | |
| 411 | if (*pret != NULL) |
| 412 | should_queue = true; |
| 413 | else if (!is_blocker) |
| 414 | should_return = true; |
| 415 | else if (t->should_run_soon()) |
| 416 | should_return = true; |
| 417 | else if (!this->first_tasks_.empty() || !this->tasks_.empty()) |
| 418 | should_queue = true; |
| 419 | else |
| 420 | should_return = true; |
| 421 | |
| 422 | if (should_return) |
| 423 | { |
| 424 | gold_assert(*pret == NULL); |
| 425 | *pret = t; |
| 426 | return true; |
| 427 | } |
| 428 | else if (should_queue) |
| 429 | { |
| 430 | if (t->should_run_soon()) |
| 431 | this->first_tasks_.push_back(t); |
| 432 | else |
| 433 | this->tasks_.push_back(t); |
| 434 | this->condvar_.signal(); |
| 435 | return false; |
| 436 | } |
| 437 | |
| 438 | gold_unreachable(); |
| 439 | } |
| 440 | |
| 441 | // Release the locks associated with a Task. Return the first |
| 442 | // runnable Task that we find. If we find more runnable tasks, add |
| 443 | // them to the run queue and signal any other threads. This must be |
| 444 | // called with the Workqueue lock held. |
| 445 | |
| 446 | Task* |
| 447 | Workqueue::release_locks(Task* t, Task_locker* tl) |
| 448 | { |
| 449 | Task* ret = NULL; |
| 450 | for (Task_locker::iterator p = tl->begin(); p != tl->end(); ++p) |
| 451 | { |
| 452 | Task_token* token = *p; |
| 453 | if (token->is_blocker()) |
| 454 | { |
| 455 | if (token->remove_blocker()) |
| 456 | { |
| 457 | // The token has been unblocked. Every waiting Task may |
| 458 | // now be runnable. |
| 459 | Task* t; |
| 460 | while ((t = token->remove_first_waiting()) != NULL) |
| 461 | { |
| 462 | --this->waiting_; |
| 463 | this->return_or_queue(t, true, &ret); |
| 464 | } |
| 465 | } |
| 466 | } |
| 467 | else |
| 468 | { |
| 469 | token->remove_writer(t); |
| 470 | |
| 471 | // One more waiting Task may now be runnable. If we are |
| 472 | // going to run it next, we can stop. Otherwise we need to |
| 473 | // move all the Tasks to the runnable queue, to avoid a |
| 474 | // potential deadlock if the locking status changes before |
| 475 | // we run the next thread. |
| 476 | Task* t; |
| 477 | while ((t = token->remove_first_waiting()) != NULL) |
| 478 | { |
| 479 | --this->waiting_; |
| 480 | if (this->return_or_queue(t, false, &ret)) |
| 481 | break; |
| 482 | } |
| 483 | } |
| 484 | } |
| 485 | return ret; |
| 486 | } |
| 487 | |
| 488 | // Process all the tasks on the workqueue. Keep going until the |
| 489 | // workqueue is empty, or until we have been told to exit. This |
| 490 | // function is called by all threads. |
| 491 | |
| 492 | void |
| 493 | Workqueue::process(int thread_number) |
| 494 | { |
| 495 | while (this->find_and_run_task(thread_number)) |
| 496 | ; |
| 497 | } |
| 498 | |
| 499 | // Set the number of threads to use for the workqueue, if we are using |
| 500 | // threads. |
| 501 | |
| 502 | void |
| 503 | Workqueue::set_thread_count(int threads) |
| 504 | { |
| 505 | Hold_lock hl(this->lock_); |
| 506 | |
| 507 | this->threader_->set_thread_count(threads); |
| 508 | // Wake up all the threads, since something has changed. |
| 509 | this->condvar_.broadcast(); |
| 510 | } |
| 511 | |
| 512 | // Add a new blocker to an existing Task_token. |
| 513 | |
| 514 | void |
| 515 | Workqueue::add_blocker(Task_token* token) |
| 516 | { |
| 517 | Hold_lock hl(this->lock_); |
| 518 | token->add_blocker(); |
| 519 | } |
| 520 | |
| 521 | } // End namespace gold. |