gold/workqueue-threads.cc

   1 // workqueue-threads.cc -- the threaded workqueue for gold
   2
   3 // Copyright 2007 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 // This file holds the workqueue implementation which may be used when
  24 // using threads.
  25
  26 #include "gold.h"
  27
  28 #ifdef ENABLE_THREADS
  29
  30 #include <cstring>
  31 #include <pthread.h>
  32
  33 #include "debug.h"
  34 #include "gold-threads.h"
  35 #include "workqueue.h"
  36 #include "workqueue-internal.h"
  37
  38 namespace gold
  39 {
  40
  41 // Class Workqueue_thread represents a single thread.  Creating an
  42 // instance of this spawns a new thread.
  43
  44 class Workqueue_thread
  45 {
  46  public:
  47   Workqueue_thread(Workqueue_runner_threadpool*);
  48
  49   ~Workqueue_thread();
  50
  51  private:
  52   // This class can not be copied.
  53   Workqueue_thread(const Workqueue_thread&);
  54   Workqueue_thread& operator=(const Workqueue_thread&);
  55
  56   // Check for error from a pthread function.
  57   void
  58   check(const char* function, int err) const;
  59
  60   // A function to pass to pthread_create.  This is called with a
  61   // pointer to an instance of this object.
  62   static void*
  63   thread_body(void*);
  64
  65   // The main loop of the thread.
  66   void
  67   run();
  68
  69   // A pointer to the threadpool that this thread is part of.
  70   Workqueue_runner_threadpool* threadpool_;
  71   // The thread ID.
  72   pthread_t tid_;
  73 };
  74
  75 // Create the thread in the constructor.
  76
  77 Workqueue_thread::Workqueue_thread(Workqueue_runner_threadpool* threadpool)
  78   : threadpool_(threadpool)
  79 {
  80   pthread_attr_t attr;
  81   int err = pthread_attr_init(&attr);
  82   this->check("pthread_attr_init", err);
  83
  84   err = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
  85   this->check("pthread_attr_setdetachstate", err);
  86
  87   err = pthread_create(&this->tid_, &attr, &Workqueue_thread::thread_body,
  88                        reinterpret_cast<void*>(this));
  89   this->check("pthread_create", err);
  90
  91   err = pthread_attr_destroy(&attr);
  92   this->check("pthread_attr_destroy", err);
  93 }
  94
  95 // The destructor will be called when the thread is exiting.
  96
  97 Workqueue_thread::~Workqueue_thread()
  98 {
  99 }
 100
 101 // Check for an error.
 102
 103 void
 104 Workqueue_thread::check(const char* function, int err) const
 105 {
 106   if (err != 0)
 107     gold_fatal(_("%s failed: %s"), function, strerror(err));
 108 }
 109
 110 // Passed to pthread_create.
 111
 112 extern "C"
 113 void*
 114 Workqueue_thread::thread_body(void* arg)
 115 {
 116   Workqueue_thread* pwt = reinterpret_cast<Workqueue_thread*>(arg);
 117   pwt->run();
 118
 119   // Delete the thread object as we exit.
 120   delete pwt;
 121
 122   return NULL;
 123 }
 124
 125 // This is the main loop of a worker thread.  It picks up a new Task
 126 // and runs it.
 127
 128 void
 129 Workqueue_thread::run()
 130 {
 131   Workqueue_runner_threadpool* threadpool = this->threadpool_;
 132   Workqueue* workqueue = threadpool->get_workqueue();
 133
 134   while (true)
 135     {
 136       Task* t;
 137       Task_locker* tl;
 138       if (!threadpool->get_next(&t, &tl))
 139         return;
 140
 141       gold_debug(DEBUG_TASK, "running   task %s", t->name().c_str());
 142
 143       t->run(workqueue);
 144       threadpool->thread_completed(t, tl);
 145     }
 146 }
 147
 148 // Class Workqueue_runner_threadpool.
 149
 150 // Constructor.
 151
 152 Workqueue_runner_threadpool::Workqueue_runner_threadpool(Workqueue* workqueue)
 153   : Workqueue_runner(workqueue),
 154     desired_thread_count_(0),
 155     lock_(),
 156     actual_thread_count_(0),
 157     running_thread_count_(0),
 158     task_queue_(),
 159     task_queue_condvar_(this->lock_)
 160 {
 161 }
 162
 163 // Destructor.
 164
 165 Workqueue_runner_threadpool::~Workqueue_runner_threadpool()
 166 {
 167   // Tell the threads to exit.
 168   Hold_lock hl(this->lock_);
 169   this->desired_thread_count_ = 0;
 170   this->task_queue_condvar_.broadcast();
 171 }
 172
 173 // Run a task.  This doesn't actually run the task: it pushes on the
 174 // queue of tasks to run.  This is always called in the main thread.
 175
 176 void
 177 Workqueue_runner_threadpool::run(Task* t, Task_locker* tl)
 178 {
 179   Hold_lock hl(this->lock_);
 180
 181   // This is where we create threads as needed, subject to the limit
 182   // of the desired thread count.
 183   gold_assert(this->desired_thread_count_ > 0);
 184   gold_assert(this->actual_thread_count_ >= this->running_thread_count_);
 185   if (this->actual_thread_count_ == this->running_thread_count_
 186       && this->actual_thread_count_ < this->desired_thread_count_)
 187     {
 188       // Note that threads delete themselves when they exit, so we
 189       // don't keep pointers to them.
 190       new Workqueue_thread(this);
 191       ++this->actual_thread_count_;
 192     }
 193
 194   this->task_queue_.push(std::make_pair(t, tl));
 195   this->task_queue_condvar_.signal();
 196 }
 197
 198 // Set the thread count.  This is only called in the main thread, and
 199 // is only called when there are no threads running.
 200
 201 void
 202 Workqueue_runner_threadpool::set_thread_count(int thread_count)
 203 {
 204   gold_assert(this->running_thread_count_ <= 1);
 205   gold_assert(thread_count > 0);
 206   this->desired_thread_count_ = thread_count;
 207 }
 208
 209 // Get the next task to run.  This is always called by an instance of
 210 // Workqueue_thread, and is never called in the main thread.  It
 211 // returns false if the calling thread should exit.
 212
 213 bool
 214 Workqueue_runner_threadpool::get_next(Task** pt, Task_locker** ptl)
 215 {
 216   Hold_lock hl(this->lock_);
 217
 218   // This is where we destroy threads, by telling them to exit.
 219   gold_assert(this->actual_thread_count_ > this->running_thread_count_);
 220   if (this->actual_thread_count_ > this->desired_thread_count_)
 221     {
 222       --this->actual_thread_count_;
 223       return false;
 224     }
 225
 226   while (this->task_queue_.empty() && this->desired_thread_count_ > 0)
 227     {
 228       // Wait for a new task to become available.
 229       this->task_queue_condvar_.wait();
 230     }
 231
 232   // Check whether we are exiting.
 233   if (this->desired_thread_count_ == 0)
 234     {
 235       gold_assert(this->actual_thread_count_ > 0);
 236       --this->actual_thread_count_;
 237       return false;
 238     }
 239
 240   *pt = this->task_queue_.front().first;
 241   *ptl = this->task_queue_.front().second;
 242   this->task_queue_.pop();
 243
 244   ++this->running_thread_count_;
 245
 246   return true;
 247 }
 248
 249 // This is called when a thread completes its task.
 250
 251 void
 252 Workqueue_runner_threadpool::thread_completed(Task* t, Task_locker* tl)
 253 {
 254   {
 255     Hold_lock hl(this->lock_);
 256     gold_assert(this->actual_thread_count_ > 0);
 257     gold_assert(this->running_thread_count_ > 0);
 258     --this->running_thread_count_;
 259   }
 260
 261   this->completed(t, tl);
 262 }
 263
 264 } // End namespace gold.
 265
 266 #endif // defined(ENABLE_THREADS)