Rewrite workqueue. This version eliminates the master thread, and

reduces the amount of locking required to find a new thread to run.

1 files changed, 50 insertions, 119 deletions

diff --git a/gold/workqueue-threads.cc b/gold/workqueue-threads.cc
index 3c30b32..ae09e29 100644
--- a/gold/workqueue-threads.cc
+++ b/gold/workqueue-threads.cc
@@ -44,7 +44,7 @@ namespace gold
 class Workqueue_thread
 {
  public:
-  Workqueue_thread(Workqueue_runner_threadpool*);
+  Workqueue_thread(Workqueue_threader_threadpool*, int thread_number);
 
   ~Workqueue_thread();
 
@@ -62,20 +62,19 @@ class Workqueue_thread
   static void*
   thread_body(void*);
 
-  // The main loop of the thread.
-  void
-  run();
-
   // A pointer to the threadpool that this thread is part of.
-  Workqueue_runner_threadpool* threadpool_;
+  Workqueue_threader_threadpool* threadpool_;
+  // The thread number.
+  int thread_number_;
   // The thread ID.
   pthread_t tid_;
 };
 
 // Create the thread in the constructor.
 
-Workqueue_thread::Workqueue_thread(Workqueue_runner_threadpool* threadpool)
-  : threadpool_(threadpool)
+Workqueue_thread::Workqueue_thread(Workqueue_threader_threadpool* threadpool,
+				   int thread_number)
+  : threadpool_(threadpool), thread_number_(thread_number)
 {
   pthread_attr_t attr;
   int err = pthread_attr_init(&attr);
@@ -114,7 +113,8 @@ void*
 Workqueue_thread::thread_body(void* arg)
 {
   Workqueue_thread* pwt = reinterpret_cast<Workqueue_thread*>(arg);
-  pwt->run();
+
+  pwt->threadpool_->process(pwt->thread_number_);
 
   // Delete the thread object as we exit.
   delete pwt;
@@ -122,144 +122,75 @@ Workqueue_thread::thread_body(void* arg)
   return NULL;
 }
 
-// This is the main loop of a worker thread.  It picks up a new Task
-// and runs it.
-
-void
-Workqueue_thread::run()
-{
-  Workqueue_runner_threadpool* threadpool = this->threadpool_;
-  Workqueue* workqueue = threadpool->get_workqueue();
-
-  while (true)
-    {
-      Task* t;
-      Task_locker* tl;
-      if (!threadpool->get_next(&t, &tl))
-	return;
-
-      gold_debug(DEBUG_TASK, "running   task %s", t->name().c_str());
-
-      t->run(workqueue);
-      threadpool->thread_completed(t, tl);
-    }
-}
-
-// Class Workqueue_runner_threadpool.
+// Class Workqueue_threader_threadpool.
 
 // Constructor.
 
-Workqueue_runner_threadpool::Workqueue_runner_threadpool(Workqueue* workqueue)
-  : Workqueue_runner(workqueue),
-    desired_thread_count_(0),
+Workqueue_threader_threadpool::Workqueue_threader_threadpool(
+    Workqueue* workqueue)
+  : Workqueue_threader(workqueue),
+    check_thread_count_(0),
     lock_(),
-    actual_thread_count_(0),
-    running_thread_count_(0),
-    task_queue_(),
-    task_queue_condvar_(this->lock_)
+    desired_thread_count_(1),
+    threads_(1)
 {
 }
 
 // Destructor.
 
-Workqueue_runner_threadpool::~Workqueue_runner_threadpool()
+Workqueue_threader_threadpool::~Workqueue_threader_threadpool()
 {
   // Tell the threads to exit.
-  Hold_lock hl(this->lock_);
-  this->desired_thread_count_ = 0;
-  this->task_queue_condvar_.broadcast();
-}
-
-// Run a task.  This doesn't actually run the task: it pushes it on
-// the queue of tasks to run.  This is always called in the main
-// thread.
-
-void
-Workqueue_runner_threadpool::run(Task* t, Task_locker* tl)
-{
-  Hold_lock hl(this->lock_);
-
-  // This is where we create threads as needed, subject to the limit
-  // of the desired thread count.
-  gold_assert(this->desired_thread_count_ > 0);
-  gold_assert(this->actual_thread_count_ >= this->running_thread_count_);
-  if (this->actual_thread_count_ == this->running_thread_count_
-      && this->actual_thread_count_ < this->desired_thread_count_)
-    {
-      // Note that threads delete themselves when they exit, so we
-      // don't keep pointers to them.
-      new Workqueue_thread(this);
-      ++this->actual_thread_count_;
-    }
-
-  this->task_queue_.push(std::make_pair(t, tl));
-  this->task_queue_condvar_.signal();
+  this->get_workqueue()->set_thread_count(0);
 }
 
-// Set the thread count.  This is only called in the main thread, and
-// is only called when there are no threads running.
+// Set the thread count.
 
 void
-Workqueue_runner_threadpool::set_thread_count(int thread_count)
-{
-  gold_assert(this->running_thread_count_ <= 1);
-  gold_assert(thread_count > 0);
-  this->desired_thread_count_ = thread_count;
-}
-
-// Get the next task to run.  This is always called by an instance of
-// Workqueue_thread, and is never called in the main thread.  It
-// returns false if the calling thread should exit.
-
-bool
-Workqueue_runner_threadpool::get_next(Task** pt, Task_locker** ptl)
+Workqueue_threader_threadpool::set_thread_count(int thread_count)
 {
-  Hold_lock hl(this->lock_);
-
-  // This is where we destroy threads, by telling them to exit.
-  gold_assert(this->actual_thread_count_ > this->running_thread_count_);
-  if (this->actual_thread_count_ > this->desired_thread_count_)
-    {
-      --this->actual_thread_count_;
-      return false;
-    }
+  int create;
+  {
+    Hold_lock hl(this->lock_);
 
-  while (this->task_queue_.empty() && this->desired_thread_count_ > 0)
-    {
-      // Wait for a new task to become available.
-      this->task_queue_condvar_.wait();
-    }
+    this->desired_thread_count_ = thread_count;
+    create = this->desired_thread_count_ - this->threads_;
+    if (create < 0)
+      this->check_thread_count_ = 1;
+  }
 
-  // Check whether we are exiting.
-  if (this->desired_thread_count_ == 0)
+  if (create > 0)
     {
-      gold_assert(this->actual_thread_count_ > 0);
-      --this->actual_thread_count_;
-      return false;
+      for (int i = 0; i < create; ++i)
+	{
+	  // Note that threads delete themselves when they exit, so we
+	  // don't keep pointers to them.
+	  new Workqueue_thread(this, this->threads_);
+	  ++this->threads_;
+	}
     }
-
-  *pt = this->task_queue_.front().first;
-  *ptl = this->task_queue_.front().second;
-  this->task_queue_.pop();
-
-  ++this->running_thread_count_;
-
-  return true;
 }
 
-// This is called when a thread completes its task.
+// Return whether the current thread should be cancelled.
 
-void
-Workqueue_runner_threadpool::thread_completed(Task* t, Task_locker* tl)
+bool
+Workqueue_threader_threadpool::should_cancel_thread()
 {
+  // Fast exit without taking a lock.
+  if (!this->check_thread_count_)
+    return false;
+
   {
     Hold_lock hl(this->lock_);
-    gold_assert(this->actual_thread_count_ > 0);
-    gold_assert(this->running_thread_count_ > 0);
-    --this->running_thread_count_;
+    if (this->threads_ > this->desired_thread_count_)
+      {
+	--this->threads_;
+	return true;
+      }
+    this->check_thread_count_ = 0;
   }
 
-  this->completed(t, tl);
+  return false;
 }
 
 } // End namespace gold.