| 1 | // workqueue.cc -- the workqueue for gold |
| 2 | |
| 3 | // Copyright 2006, 2007, 2008 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 "workqueue.h" |
| 28 | #include "workqueue-internal.h" |
| 29 | |
| 30 | namespace gold |
| 31 | { |
| 32 | |
| 33 | // Class Task_list. |
| 34 | |
| 35 | // Add T to the end of the list. |
| 36 | |
| 37 | inline void |
| 38 | Task_list::push_back(Task* t) |
| 39 | { |
| 40 | gold_assert(t->list_next() == NULL); |
| 41 | if (this->head_ == NULL) |
| 42 | { |
| 43 | this->head_ = t; |
| 44 | this->tail_ = t; |
| 45 | } |
| 46 | else |
| 47 | { |
| 48 | this->tail_->set_list_next(t); |
| 49 | this->tail_ = t; |
| 50 | } |
| 51 | } |
| 52 | |
| 53 | // Add T to the front of the list. |
| 54 | |
| 55 | inline void |
| 56 | Task_list::push_front(Task* t) |
| 57 | { |
| 58 | gold_assert(t->list_next() == NULL); |
| 59 | if (this->head_ == NULL) |
| 60 | { |
| 61 | this->head_ = t; |
| 62 | this->tail_ = t; |
| 63 | } |
| 64 | else |
| 65 | { |
| 66 | t->set_list_next(this->head_); |
| 67 | this->head_ = t; |
| 68 | } |
| 69 | } |
| 70 | |
| 71 | // Remove and return the first Task waiting for this lock to be |
| 72 | // released. |
| 73 | |
| 74 | inline Task* |
| 75 | Task_list::pop_front() |
| 76 | { |
| 77 | Task* ret = this->head_; |
| 78 | if (ret != NULL) |
| 79 | { |
| 80 | if (ret == this->tail_) |
| 81 | { |
| 82 | gold_assert(ret->list_next() == NULL); |
| 83 | this->head_ = NULL; |
| 84 | this->tail_ = NULL; |
| 85 | } |
| 86 | else |
| 87 | { |
| 88 | this->head_ = ret->list_next(); |
| 89 | gold_assert(this->head_ != NULL); |
| 90 | ret->clear_list_next(); |
| 91 | } |
| 92 | } |
| 93 | return ret; |
| 94 | } |
| 95 | |
| 96 | // The simple single-threaded implementation of Workqueue_threader. |
| 97 | |
| 98 | class Workqueue_threader_single : public Workqueue_threader |
| 99 | { |
| 100 | public: |
| 101 | Workqueue_threader_single(Workqueue* workqueue) |
| 102 | : Workqueue_threader(workqueue) |
| 103 | { } |
| 104 | ~Workqueue_threader_single() |
| 105 | { } |
| 106 | |
| 107 | void |
| 108 | set_thread_count(int thread_count) |
| 109 | { gold_assert(thread_count > 0); } |
| 110 | |
| 111 | bool |
| 112 | should_cancel_thread() |
| 113 | { return false; } |
| 114 | }; |
| 115 | |
| 116 | // Workqueue methods. |
| 117 | |
| 118 | Workqueue::Workqueue(const General_options& options) |
| 119 | : lock_(), |
| 120 | first_tasks_(), |
| 121 | tasks_(), |
| 122 | running_(0), |
| 123 | waiting_(0), |
| 124 | condvar_(this->lock_), |
| 125 | threader_(NULL) |
| 126 | { |
| 127 | bool threads = options.threads(); |
| 128 | #ifndef ENABLE_THREADS |
| 129 | threads = false; |
| 130 | #endif |
| 131 | if (!threads) |
| 132 | this->threader_ = new Workqueue_threader_single(this); |
| 133 | else |
| 134 | { |
| 135 | #ifdef ENABLE_THREADS |
| 136 | this->threader_ = new Workqueue_threader_threadpool(this); |
| 137 | #else |
| 138 | gold_unreachable(); |
| 139 | #endif |
| 140 | } |
| 141 | } |
| 142 | |
| 143 | Workqueue::~Workqueue() |
| 144 | { |
| 145 | } |
| 146 | |
| 147 | // Add a task to the end of a specific queue, or put it on the list |
| 148 | // waiting for a Token. |
| 149 | |
| 150 | void |
| 151 | Workqueue::add_to_queue(Task_list* queue, Task* t, bool front) |
| 152 | { |
| 153 | Hold_lock hl(this->lock_); |
| 154 | |
| 155 | Task_token* token = t->is_runnable(); |
| 156 | if (token != NULL) |
| 157 | { |
| 158 | if (front) |
| 159 | token->add_waiting_front(t); |
| 160 | else |
| 161 | token->add_waiting(t); |
| 162 | ++this->waiting_; |
| 163 | } |
| 164 | else |
| 165 | { |
| 166 | if (front) |
| 167 | queue->push_front(t); |
| 168 | else |
| 169 | queue->push_back(t); |
| 170 | // Tell any waiting thread that there is work to do. |
| 171 | this->condvar_.signal(); |
| 172 | } |
| 173 | } |
| 174 | |
| 175 | // Add a task to the queue. |
| 176 | |
| 177 | void |
| 178 | Workqueue::queue(Task* t) |
| 179 | { |
| 180 | this->add_to_queue(&this->tasks_, t, false); |
| 181 | } |
| 182 | |
| 183 | // Queue a task which should run soon. |
| 184 | |
| 185 | void |
| 186 | Workqueue::queue_soon(Task* t) |
| 187 | { |
| 188 | t->set_should_run_soon(); |
| 189 | this->add_to_queue(&this->first_tasks_, t, false); |
| 190 | } |
| 191 | |
| 192 | // Queue a task which should run next. |
| 193 | |
| 194 | void |
| 195 | Workqueue::queue_next(Task* t) |
| 196 | { |
| 197 | t->set_should_run_soon(); |
| 198 | this->add_to_queue(&this->first_tasks_, t, true); |
| 199 | } |
| 200 | |
| 201 | // Return whether to cancel the current thread. |
| 202 | |
| 203 | inline bool |
| 204 | Workqueue::should_cancel_thread() |
| 205 | { |
| 206 | return this->threader_->should_cancel_thread(); |
| 207 | } |
| 208 | |
| 209 | // Find a runnable task in TASKS. Return NULL if none could be found. |
| 210 | // If we find a Task waiting for a Token, add it to the list for that |
| 211 | // Token. The workqueue lock must be held when this is called. |
| 212 | |
| 213 | Task* |
| 214 | Workqueue::find_runnable_in_list(Task_list* tasks) |
| 215 | { |
| 216 | Task* t; |
| 217 | while ((t = tasks->pop_front()) != NULL) |
| 218 | { |
| 219 | Task_token* token = t->is_runnable(); |
| 220 | |
| 221 | if (token == NULL) |
| 222 | return t; |
| 223 | |
| 224 | token->add_waiting(t); |
| 225 | ++this->waiting_; |
| 226 | } |
| 227 | |
| 228 | // We couldn't find any runnable task. |
| 229 | return NULL; |
| 230 | } |
| 231 | |
| 232 | // Find a runnable task. Return NULL if none could be found. The |
| 233 | // workqueue lock must be held when this is called. |
| 234 | |
| 235 | Task* |
| 236 | Workqueue::find_runnable() |
| 237 | { |
| 238 | Task* t = this->find_runnable_in_list(&this->first_tasks_); |
| 239 | if (t == NULL) |
| 240 | t = this->find_runnable_in_list(&this->tasks_); |
| 241 | return t; |
| 242 | } |
| 243 | |
| 244 | // Find a runnable a task, and wait until we find one. Return NULL if |
| 245 | // we should exit. The workqueue lock must be held when this is |
| 246 | // called. |
| 247 | |
| 248 | Task* |
| 249 | Workqueue::find_runnable_or_wait(int thread_number) |
| 250 | { |
| 251 | Task* t = this->find_runnable(); |
| 252 | |
| 253 | while (t == NULL) |
| 254 | { |
| 255 | if (this->running_ == 0 |
| 256 | && this->first_tasks_.empty() |
| 257 | && this->tasks_.empty()) |
| 258 | { |
| 259 | // Kick all the threads to make them exit. |
| 260 | this->condvar_.broadcast(); |
| 261 | |
| 262 | gold_assert(this->waiting_ == 0); |
| 263 | return NULL; |
| 264 | } |
| 265 | |
| 266 | if (this->should_cancel_thread()) |
| 267 | return NULL; |
| 268 | |
| 269 | gold_debug(DEBUG_TASK, "%3d sleeping", thread_number); |
| 270 | |
| 271 | this->condvar_.wait(); |
| 272 | |
| 273 | gold_debug(DEBUG_TASK, "%3d awake", thread_number); |
| 274 | |
| 275 | t = this->find_runnable(); |
| 276 | } |
| 277 | |
| 278 | return t; |
| 279 | } |
| 280 | |
| 281 | // Find and run tasks. If we can't find a runnable task, wait for one |
| 282 | // to become available. If we run a task, and it frees up another |
| 283 | // runnable task, then run that one too. This returns true if we |
| 284 | // should look for another task, false if we are cancelling this |
| 285 | // thread. |
| 286 | |
| 287 | bool |
| 288 | Workqueue::find_and_run_task(int thread_number) |
| 289 | { |
| 290 | Task* t; |
| 291 | Task_locker tl; |
| 292 | |
| 293 | { |
| 294 | Hold_lock hl(this->lock_); |
| 295 | |
| 296 | // Find a runnable task. |
| 297 | t = this->find_runnable_or_wait(thread_number); |
| 298 | |
| 299 | if (t == NULL) |
| 300 | return false; |
| 301 | |
| 302 | // Get the locks for the task. This must be called while we are |
| 303 | // still holding the Workqueue lock. |
| 304 | t->locks(&tl); |
| 305 | |
| 306 | ++this->running_; |
| 307 | } |
| 308 | |
| 309 | while (t != NULL) |
| 310 | { |
| 311 | gold_debug(DEBUG_TASK, "%3d running task %s", thread_number, |
| 312 | t->name().c_str()); |
| 313 | |
| 314 | t->run(this); |
| 315 | |
| 316 | gold_debug(DEBUG_TASK, "%3d completed task %s", thread_number, |
| 317 | t->name().c_str()); |
| 318 | |
| 319 | Task* next; |
| 320 | { |
| 321 | Hold_lock hl(this->lock_); |
| 322 | |
| 323 | --this->running_; |
| 324 | |
| 325 | // Release the locks for the task. This must be done with the |
| 326 | // workqueue lock held. Get the next Task to run if any. |
| 327 | next = this->release_locks(t, &tl); |
| 328 | |
| 329 | if (next == NULL) |
| 330 | next = this->find_runnable(); |
| 331 | |
| 332 | // If we have another Task to run, get the Locks. This must |
| 333 | // be called while we are still holding the Workqueue lock. |
| 334 | if (next != NULL) |
| 335 | { |
| 336 | tl.clear(); |
| 337 | next->locks(&tl); |
| 338 | |
| 339 | ++this->running_; |
| 340 | } |
| 341 | } |
| 342 | |
| 343 | // We are done with this task. |
| 344 | delete t; |
| 345 | |
| 346 | t = next; |
| 347 | } |
| 348 | |
| 349 | return true; |
| 350 | } |
| 351 | |
| 352 | // Handle the return value of release_locks, and get tasks ready to |
| 353 | // run. |
| 354 | |
| 355 | // 1) If T is not runnable, queue it on the appropriate token. |
| 356 | |
| 357 | // 2) Otherwise, T is runnable. If *PRET is not NULL, then we have |
| 358 | // already decided which Task to run next. Add T to the list of |
| 359 | // runnable tasks, and signal another thread. |
| 360 | |
| 361 | // 3) Otherwise, *PRET is NULL. If IS_BLOCKER is false, then T was |
| 362 | // waiting on a write lock. We can grab that lock now, so we run T |
| 363 | // now. |
| 364 | |
| 365 | // 4) Otherwise, IS_BLOCKER is true. If we should run T soon, then |
| 366 | // run it now. |
| 367 | |
| 368 | // 5) Otherwise, check whether there are other tasks to run. If there |
| 369 | // are, then we generally get a better ordering if we run those tasks |
| 370 | // now, before T. A typical example is tasks waiting on the Dirsearch |
| 371 | // blocker. We don't want to run those tasks right away just because |
| 372 | // the Dirsearch was unblocked. |
| 373 | |
| 374 | // 6) Otherwise, there are no other tasks to run, so we might as well |
| 375 | // run this one now. |
| 376 | |
| 377 | // This function must be called with the Workqueue lock held. |
| 378 | |
| 379 | // Return true if we set *PRET to T, false otherwise. |
| 380 | |
| 381 | bool |
| 382 | Workqueue::return_or_queue(Task* t, bool is_blocker, Task** pret) |
| 383 | { |
| 384 | Task_token* token = t->is_runnable(); |
| 385 | |
| 386 | if (token != NULL) |
| 387 | { |
| 388 | token->add_waiting(t); |
| 389 | ++this->waiting_; |
| 390 | return false; |
| 391 | } |
| 392 | |
| 393 | bool should_queue = false; |
| 394 | bool should_return = false; |
| 395 | |
| 396 | if (*pret != NULL) |
| 397 | should_queue = true; |
| 398 | else if (!is_blocker) |
| 399 | should_return = true; |
| 400 | else if (t->should_run_soon()) |
| 401 | should_return = true; |
| 402 | else if (!this->first_tasks_.empty() || !this->tasks_.empty()) |
| 403 | should_queue = true; |
| 404 | else |
| 405 | should_return = true; |
| 406 | |
| 407 | if (should_return) |
| 408 | { |
| 409 | gold_assert(*pret == NULL); |
| 410 | *pret = t; |
| 411 | return true; |
| 412 | } |
| 413 | else if (should_queue) |
| 414 | { |
| 415 | if (t->should_run_soon()) |
| 416 | this->first_tasks_.push_back(t); |
| 417 | else |
| 418 | this->tasks_.push_back(t); |
| 419 | this->condvar_.signal(); |
| 420 | return false; |
| 421 | } |
| 422 | |
| 423 | gold_unreachable(); |
| 424 | } |
| 425 | |
| 426 | // Release the locks associated with a Task. Return the first |
| 427 | // runnable Task that we find. If we find more runnable tasks, add |
| 428 | // them to the run queue and signal any other threads. This must be |
| 429 | // called with the Workqueue lock held. |
| 430 | |
| 431 | Task* |
| 432 | Workqueue::release_locks(Task* t, Task_locker* tl) |
| 433 | { |
| 434 | Task* ret = NULL; |
| 435 | for (Task_locker::iterator p = tl->begin(); p != tl->end(); ++p) |
| 436 | { |
| 437 | Task_token* token = *p; |
| 438 | if (token->is_blocker()) |
| 439 | { |
| 440 | if (token->remove_blocker()) |
| 441 | { |
| 442 | // The token has been unblocked. Every waiting Task may |
| 443 | // now be runnable. |
| 444 | Task* t; |
| 445 | while ((t = token->remove_first_waiting()) != NULL) |
| 446 | { |
| 447 | --this->waiting_; |
| 448 | this->return_or_queue(t, true, &ret); |
| 449 | } |
| 450 | } |
| 451 | } |
| 452 | else |
| 453 | { |
| 454 | token->remove_writer(t); |
| 455 | |
| 456 | // One more waiting Task may now be runnable. If we are |
| 457 | // going to run it next, we can stop. Otherwise we need to |
| 458 | // move all the Tasks to the runnable queue, to avoid a |
| 459 | // potential deadlock if the locking status changes before |
| 460 | // we run the next thread. |
| 461 | Task* t; |
| 462 | while ((t = token->remove_first_waiting()) != NULL) |
| 463 | { |
| 464 | --this->waiting_; |
| 465 | if (this->return_or_queue(t, false, &ret)) |
| 466 | break; |
| 467 | } |
| 468 | } |
| 469 | } |
| 470 | return ret; |
| 471 | } |
| 472 | |
| 473 | // Process all the tasks on the workqueue. Keep going until the |
| 474 | // workqueue is empty, or until we have been told to exit. This |
| 475 | // function is called by all threads. |
| 476 | |
| 477 | void |
| 478 | Workqueue::process(int thread_number) |
| 479 | { |
| 480 | while (this->find_and_run_task(thread_number)) |
| 481 | ; |
| 482 | } |
| 483 | |
| 484 | // Set the number of threads to use for the workqueue, if we are using |
| 485 | // threads. |
| 486 | |
| 487 | void |
| 488 | Workqueue::set_thread_count(int threads) |
| 489 | { |
| 490 | Hold_lock hl(this->lock_); |
| 491 | |
| 492 | this->threader_->set_thread_count(threads); |
| 493 | // Wake up all the threads, since something has changed. |
| 494 | this->condvar_.broadcast(); |
| 495 | } |
| 496 | |
| 497 | // Add a new blocker to an existing Task_token. |
| 498 | |
| 499 | void |
| 500 | Workqueue::add_blocker(Task_token* token) |
| 501 | { |
| 502 | Hold_lock hl(this->lock_); |
| 503 | token->add_blocker(); |
| 504 | } |
| 505 | |
| 506 | } // End namespace gold. |