Add threading support.

gold/workqueue-threads.cc

@@ -0,0 +1,266 @@
+// workqueue-threads.cc -- the threaded workqueue for gold
+
+// Copyright 2007 Free Software Foundation, Inc.
+// Written by Ian Lance Taylor <iant@google.com>.
+
+// This file is part of gold.
+
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program; if not, write to the Free Software
+// Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
+// MA 02110-1301, USA.
+
+// This file holds the workqueue implementation which may be used when
+// using threads.
+
+#include "gold.h"
+
+#ifdef ENABLE_THREADS
+
+#include <cstring>
+#include <pthread.h>
+
+#include "debug.h"
+#include "gold-threads.h"
+#include "workqueue.h"
+#include "workqueue-internal.h"
+
+namespace gold
+{
+
+// Class Workqueue_thread represents a single thread.  Creating an
+// instance of this spawns a new thread.
+
+class Workqueue_thread
+{
+ public:
+  Workqueue_thread(Workqueue_runner_threadpool*);
+
+  ~Workqueue_thread();
+
+ private:
+  // This class can not be copied.
+  Workqueue_thread(const Workqueue_thread&);
+  Workqueue_thread& operator=(const Workqueue_thread&);
+
+  // Check for error from a pthread function.
+  void
+  check(const char* function, int err) const;
+
+  // A function to pass to pthread_create.  This is called with a
+  // pointer to an instance of this object.
+  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_;
+  // The thread ID.
+  pthread_t tid_;
+};
+
+// Create the thread in the constructor.
+
+Workqueue_thread::Workqueue_thread(Workqueue_runner_threadpool* threadpool)
+  : threadpool_(threadpool)
+{
+  pthread_attr_t attr;
+  int err = pthread_attr_init(&attr);
+  this->check("pthread_attr_init", err);
+
+  err = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
+  this->check("pthread_attr_setdetachstate", err);
+
+  err = pthread_create(&this->tid_, &attr, &Workqueue_thread::thread_body,
+		       reinterpret_cast<void*>(this));
+  this->check("pthread_create", err);
+
+  err = pthread_attr_destroy(&attr);
+  this->check("pthread_attr_destroy", err);
+}
+
+// The destructor will be called when the thread is exiting.
+
+Workqueue_thread::~Workqueue_thread()
+{
+}
+
+// Check for an error.
+
+void
+Workqueue_thread::check(const char* function, int err) const
+{
+  if (err != 0)
+    gold_fatal(_("%s failed: %s"), function, strerror(err));
+}
+
+// Passed to pthread_create.
+
+extern "C"
+void*
+Workqueue_thread::thread_body(void* arg)
+{
+  Workqueue_thread* pwt = reinterpret_cast<Workqueue_thread*>(arg);
+  pwt->run();
+
+  // Delete the thread object as we exit.
+  delete pwt;
+
+  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.
+
+// Constructor.
+
+Workqueue_runner_threadpool::Workqueue_runner_threadpool(Workqueue* workqueue)
+  : Workqueue_runner(workqueue),
+    desired_thread_count_(0),
+    lock_(),
+    actual_thread_count_(0),
+    running_thread_count_(0),
+    task_queue_(),
+    task_queue_condvar_(this->lock_)
+{
+}
+
+// Destructor.
+
+Workqueue_runner_threadpool::~Workqueue_runner_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 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();
+}
+
+// Set the thread count.  This is only called in the main thread, and
+// is only called when there are no threads running.
+
+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)
+{
+  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;
+    }
+
+  while (this->task_queue_.empty() && this->desired_thread_count_ > 0)
+    {
+      // Wait for a new task to become available.
+      this->task_queue_condvar_.wait();
+    }
+
+  // Check whether we are exiting.
+  if (this->desired_thread_count_ == 0)
+    {
+      gold_assert(this->actual_thread_count_ > 0);
+      --this->actual_thread_count_;
+      return false;
+    }
+
+  *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.
+
+void
+Workqueue_runner_threadpool::thread_completed(Task* t, Task_locker* tl)
+{
+  {
+    Hold_lock hl(this->lock_);
+    gold_assert(this->actual_thread_count_ > 0);
+    gold_assert(this->running_thread_count_ > 0);
+    --this->running_thread_count_;
+  }
+
+  this->completed(t, tl);
+}
+
+} // End namespace gold.
+
+#endif // defined(ENABLE_THREADS)