| 1 | // workqueue.h -- the work queue for gold -*- C++ -*- |
| 2 | |
| 3 | // After processing the command line, everything the linker does is |
| 4 | // driven from a work queue. This permits us to parallelize the |
| 5 | // linker where possible. |
| 6 | |
| 7 | // Task_token |
| 8 | // A simple locking implementation to ensure proper task ordering. |
| 9 | // Task_read_token, Task_write_token |
| 10 | // Lock a Task_token for read or write. |
| 11 | // Task_locker |
| 12 | // Task locking using RAII. |
| 13 | // Task |
| 14 | // An abstract class for jobs to run. |
| 15 | |
| 16 | #ifndef GOLD_WORKQUEUE_H |
| 17 | #define GOLD_WORKQUEUE_H |
| 18 | |
| 19 | #include "gold-threads.h" |
| 20 | #include "fileread.h" |
| 21 | |
| 22 | namespace gold |
| 23 | { |
| 24 | |
| 25 | class General_options; |
| 26 | class Task; |
| 27 | class Workqueue; |
| 28 | |
| 29 | // Some tasks require access to shared data structures, such as the |
| 30 | // symbol table. Some tasks must be executed in a particular error, |
| 31 | // such as reading input file symbol tables--if we see foo.o -llib, we |
| 32 | // have to read the symbols for foo.o before we read the ones for |
| 33 | // -llib. To implement this safely and efficiently, we use tokens. |
| 34 | // Task_tokens support shared read/exclusive write access to some |
| 35 | // resource. Alternatively, they support blockers: blockers implement |
| 36 | // the requirement that some set of tasks must complete before another |
| 37 | // set of tasks can start. In such a case we increment the block |
| 38 | // count when we create the task, and decrement it when the task |
| 39 | // completes. Task_tokens are only manipulated by the main thread, so |
| 40 | // they do not themselves require any locking. |
| 41 | |
| 42 | class Task_token |
| 43 | { |
| 44 | public: |
| 45 | Task_token(); |
| 46 | |
| 47 | ~Task_token(); |
| 48 | |
| 49 | // A read/write token uses these methods. |
| 50 | |
| 51 | bool |
| 52 | is_readable() const; |
| 53 | |
| 54 | void |
| 55 | add_reader(); |
| 56 | |
| 57 | void |
| 58 | remove_reader(); |
| 59 | |
| 60 | bool |
| 61 | is_writable() const; |
| 62 | |
| 63 | void |
| 64 | add_writer(const Task*); |
| 65 | |
| 66 | void |
| 67 | remove_writer(const Task*); |
| 68 | |
| 69 | bool |
| 70 | has_write_lock(const Task*); |
| 71 | |
| 72 | // A blocker token uses these methods. |
| 73 | |
| 74 | void |
| 75 | add_blocker(); |
| 76 | |
| 77 | // Returns true if block count drops to zero. |
| 78 | bool |
| 79 | remove_blocker(); |
| 80 | |
| 81 | bool |
| 82 | is_blocked() const; |
| 83 | |
| 84 | private: |
| 85 | // It makes no sense to copy these. |
| 86 | Task_token(const Task_token&); |
| 87 | Task_token& operator=(const Task_token&); |
| 88 | |
| 89 | bool is_blocker_; |
| 90 | int readers_; |
| 91 | const Task* writer_; |
| 92 | }; |
| 93 | |
| 94 | // In order to support tokens more reliably, we provide objects which |
| 95 | // handle them using RAII. |
| 96 | |
| 97 | class Task_read_token |
| 98 | { |
| 99 | public: |
| 100 | Task_read_token(Task_token& token) |
| 101 | : token_(token) |
| 102 | { this->token_.add_reader(); } |
| 103 | |
| 104 | ~Task_read_token() |
| 105 | { this->token_.remove_reader(); } |
| 106 | |
| 107 | private: |
| 108 | Task_read_token(const Task_read_token&); |
| 109 | Task_read_token& operator=(const Task_read_token&); |
| 110 | |
| 111 | Task_token& token_; |
| 112 | }; |
| 113 | |
| 114 | class Task_write_token |
| 115 | { |
| 116 | public: |
| 117 | Task_write_token(Task_token& token, const Task* task) |
| 118 | : token_(token), task_(task) |
| 119 | { this->token_.add_writer(this->task_); } |
| 120 | |
| 121 | ~Task_write_token() |
| 122 | { this->token_.remove_writer(this->task_); } |
| 123 | |
| 124 | private: |
| 125 | Task_write_token(const Task_write_token&); |
| 126 | Task_write_token& operator=(const Task_write_token&); |
| 127 | |
| 128 | Task_token& token_; |
| 129 | const Task* task_; |
| 130 | }; |
| 131 | |
| 132 | class Task_block_token |
| 133 | { |
| 134 | public: |
| 135 | // The blocker count must be incremented when the task is created. |
| 136 | // This object is created when the task is run. When we unblock the |
| 137 | // last task, we notify the workqueue. |
| 138 | Task_block_token(Task_token& token, Workqueue* workqueue); |
| 139 | ~Task_block_token(); |
| 140 | |
| 141 | private: |
| 142 | Task_block_token(const Task_block_token&); |
| 143 | Task_block_token& operator=(const Task_block_token&); |
| 144 | |
| 145 | Task_token& token_; |
| 146 | Workqueue* workqueue_; |
| 147 | }; |
| 148 | |
| 149 | // An object which implements an RAII lock for any object which |
| 150 | // supports lock and unlock methods. |
| 151 | |
| 152 | template<typename Obj> |
| 153 | class Task_lock_obj |
| 154 | { |
| 155 | public: |
| 156 | Task_lock_obj(Obj& obj) |
| 157 | : obj_(obj) |
| 158 | { this->obj_.lock(); } |
| 159 | |
| 160 | ~Task_lock_obj() |
| 161 | { this->obj_.unlock(); } |
| 162 | |
| 163 | private: |
| 164 | Task_lock_obj(const Task_lock_obj&); |
| 165 | Task_lock_obj& operator=(const Task_lock_obj&); |
| 166 | |
| 167 | Obj& obj_; |
| 168 | }; |
| 169 | |
| 170 | // An abstract class used to lock Task_tokens using RAII. A typical |
| 171 | // implementation would simply have a set of members of type |
| 172 | // Task_read_token, Task_write_token, and Task_block_token. |
| 173 | |
| 174 | class Task_locker |
| 175 | { |
| 176 | public: |
| 177 | Task_locker() |
| 178 | { } |
| 179 | |
| 180 | virtual ~Task_locker() |
| 181 | { } |
| 182 | }; |
| 183 | |
| 184 | // A version of Task_locker which may be used for a single read lock. |
| 185 | |
| 186 | class Task_locker_read : public Task_locker |
| 187 | { |
| 188 | public: |
| 189 | Task_locker_read(Task_token& token) |
| 190 | : read_token_(token) |
| 191 | { } |
| 192 | |
| 193 | private: |
| 194 | Task_locker_read(const Task_locker_read&); |
| 195 | Task_locker_read& operator=(const Task_locker_read&); |
| 196 | |
| 197 | Task_read_token read_token_; |
| 198 | }; |
| 199 | |
| 200 | // A version of Task_locker which may be used for a single write lock. |
| 201 | |
| 202 | class Task_locker_write : public Task_locker |
| 203 | { |
| 204 | public: |
| 205 | Task_locker_write(Task_token& token, const Task* task) |
| 206 | : write_token_(token, task) |
| 207 | { } |
| 208 | |
| 209 | private: |
| 210 | Task_locker_write(const Task_locker_write&); |
| 211 | Task_locker_write& operator=(const Task_locker_write&); |
| 212 | |
| 213 | Task_write_token write_token_; |
| 214 | }; |
| 215 | |
| 216 | // A version of Task_locker which may be used for a single blocker |
| 217 | // lock. |
| 218 | |
| 219 | class Task_locker_block : public Task_locker |
| 220 | { |
| 221 | public: |
| 222 | Task_locker_block(Task_token& token, Workqueue* workqueue) |
| 223 | : block_token_(token, workqueue) |
| 224 | { } |
| 225 | |
| 226 | private: |
| 227 | Task_locker_block(const Task_locker_block&); |
| 228 | Task_locker_block& operator=(const Task_locker_block&); |
| 229 | |
| 230 | Task_block_token block_token_; |
| 231 | }; |
| 232 | |
| 233 | // A version of Task_locker which may be used to hold a lock on any |
| 234 | // object which supports lock() and unlock() methods. |
| 235 | |
| 236 | template<typename Obj> |
| 237 | class Task_locker_obj : public Task_locker |
| 238 | { |
| 239 | public: |
| 240 | Task_locker_obj(Obj& obj) |
| 241 | : obj_lock_(obj) |
| 242 | { } |
| 243 | |
| 244 | private: |
| 245 | Task_locker_obj(const Task_locker_obj&); |
| 246 | Task_locker_obj& operator=(const Task_locker_obj&); |
| 247 | |
| 248 | Task_lock_obj<Obj> obj_lock_; |
| 249 | }; |
| 250 | |
| 251 | // The superclass for tasks to be placed on the workqueue. Each |
| 252 | // specific task class will inherit from this one. |
| 253 | |
| 254 | class Task |
| 255 | { |
| 256 | public: |
| 257 | Task() |
| 258 | { } |
| 259 | virtual ~Task() |
| 260 | { } |
| 261 | |
| 262 | // Type returned by Is_runnable. |
| 263 | enum Is_runnable_type |
| 264 | { |
| 265 | // Task is runnable. |
| 266 | IS_RUNNABLE, |
| 267 | // Task is waiting for a block to clear. |
| 268 | IS_BLOCKED, |
| 269 | // Task is not waiting for a block, but is not runnable--i.e., is |
| 270 | // waiting for a lock. |
| 271 | IS_LOCKED |
| 272 | }; |
| 273 | |
| 274 | // Return whether the task can be run now. This method is only |
| 275 | // called from the main thread. |
| 276 | virtual Is_runnable_type |
| 277 | is_runnable(Workqueue*) = 0; |
| 278 | |
| 279 | // Return a pointer to a Task_locker which locks all the resources |
| 280 | // required by the task. We delete the pointer when the task is |
| 281 | // complete. This method can return NULL if no locks are required. |
| 282 | // This method is only called from the main thread. |
| 283 | virtual Task_locker* |
| 284 | locks(Workqueue*) = 0; |
| 285 | |
| 286 | // Run the task. |
| 287 | virtual void |
| 288 | run(Workqueue*) = 0; |
| 289 | |
| 290 | private: |
| 291 | Task(const Task&); |
| 292 | Task& operator=(const Task&); |
| 293 | }; |
| 294 | |
| 295 | // A simple task which waits for a blocker and then runs a function. |
| 296 | |
| 297 | class Task_function_runner |
| 298 | { |
| 299 | public: |
| 300 | virtual ~Task_function_runner() |
| 301 | { } |
| 302 | |
| 303 | virtual void |
| 304 | run(Workqueue*) = 0; |
| 305 | }; |
| 306 | |
| 307 | class Task_function : public Task |
| 308 | { |
| 309 | public: |
| 310 | // Both points should be allocated using new, and will be deleted |
| 311 | // after the task runs. |
| 312 | Task_function(Task_function_runner* runner, Task_token* blocker) |
| 313 | : runner_(runner), blocker_(blocker) |
| 314 | { } |
| 315 | |
| 316 | ~Task_function() |
| 317 | { |
| 318 | delete this->runner_; |
| 319 | delete this->blocker_; |
| 320 | } |
| 321 | |
| 322 | // The standard task methods. |
| 323 | |
| 324 | // Wait until the task is unblocked. |
| 325 | Is_runnable_type |
| 326 | is_runnable(Workqueue*) |
| 327 | { return this->blocker_->is_blocked() ? IS_BLOCKED : IS_RUNNABLE; } |
| 328 | |
| 329 | // This type of task does not normally hold any locks. |
| 330 | virtual Task_locker* |
| 331 | locks(Workqueue*) |
| 332 | { return NULL; } |
| 333 | |
| 334 | // Run the action. |
| 335 | void |
| 336 | run(Workqueue* workqueue) |
| 337 | { this->runner_->run(workqueue); } |
| 338 | |
| 339 | private: |
| 340 | Task_function(const Task_function&); |
| 341 | Task_function& operator=(const Task_function&); |
| 342 | |
| 343 | Task_function_runner* runner_; |
| 344 | Task_token* blocker_; |
| 345 | }; |
| 346 | |
| 347 | // The workqueue |
| 348 | |
| 349 | class Workqueue_runner; |
| 350 | |
| 351 | class Workqueue |
| 352 | { |
| 353 | public: |
| 354 | Workqueue(const General_options&); |
| 355 | ~Workqueue(); |
| 356 | |
| 357 | // Add a new task to the work queue. |
| 358 | void |
| 359 | queue(Task*); |
| 360 | |
| 361 | // Add a new task to the front of the work queue. It will be the |
| 362 | // next task to run if it is ready. |
| 363 | void |
| 364 | queue_front(Task*); |
| 365 | |
| 366 | // Process all the tasks on the work queue. |
| 367 | void |
| 368 | process(); |
| 369 | |
| 370 | // A complete set of blocking tasks has completed. |
| 371 | void |
| 372 | cleared_blocker(); |
| 373 | |
| 374 | private: |
| 375 | // This class can not be copied. |
| 376 | Workqueue(const Workqueue&); |
| 377 | Workqueue& operator=(const Workqueue&); |
| 378 | |
| 379 | typedef std::list<Task*> Task_list; |
| 380 | |
| 381 | // Run a task. |
| 382 | void run(Task*); |
| 383 | |
| 384 | friend class Workqueue_runner; |
| 385 | |
| 386 | // Find a runnable task. |
| 387 | Task* find_runnable(Task_list&, bool*); |
| 388 | |
| 389 | // Add a lock to the completed queue. |
| 390 | void completed(Task*, Task_locker*); |
| 391 | |
| 392 | // Clear the completed queue. |
| 393 | bool clear_completed(); |
| 394 | |
| 395 | // How to run a task. Only accessed from main thread. |
| 396 | Workqueue_runner* runner_; |
| 397 | |
| 398 | // Lock for access to tasks_ members. |
| 399 | Lock tasks_lock_; |
| 400 | // List of tasks to execute at each link level. |
| 401 | Task_list tasks_; |
| 402 | |
| 403 | // Lock for access to completed_ and running_ members. |
| 404 | Lock completed_lock_; |
| 405 | // List of Task_locker objects for main thread to free. |
| 406 | std::list<Task_locker*> completed_; |
| 407 | // Number of tasks currently running. |
| 408 | int running_; |
| 409 | // Condition variable signalled when a new entry is added to completed_. |
| 410 | Condvar completed_condvar_; |
| 411 | |
| 412 | // Number of blocker tokens which were fully cleared. Only accessed |
| 413 | // from main thread. |
| 414 | int cleared_blockers_; |
| 415 | }; |
| 416 | |
| 417 | } // End namespace gold. |
| 418 | |
| 419 | #endif // !defined(GOLD_WORKQUEUE_H) |