// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

#include "vm/message.h"

namespace dart {

MessageQueue::MessageQueue() {
  head_ = NULL;
  tail_ = NULL;
}


MessageQueue::~MessageQueue() {
  // Ensure that all pending messages have been released.
  Clear();
  ASSERT(head_ == NULL);
}


void MessageQueue::Enqueue(Message* msg) {
  // Make sure messages are not reused.
  ASSERT(msg->next_ == NULL);
  if (head_ == NULL) {
    // Only element in the queue.
    ASSERT(tail_ == NULL);
    head_ = msg;
    tail_ = msg;
  } else {
    ASSERT(tail_ != NULL);
    // Append at the tail.
    tail_->next_ = msg;
    tail_ = msg;
  }
}


Message* MessageQueue::Dequeue() {
  Message* result = head_;
  if (result != NULL) {
    head_ = result->next_;
    // The following update to tail_ is not strictly needed.
    if (head_ == NULL) {
      tail_ = NULL;
    }
#if defined(DEBUG)
    result->next_ = result;  // Make sure to trigger ASSERT in Enqueue.
#endif  // DEBUG
    return result;
  }
  return NULL;
}


void MessageQueue::Clear() {
  Message* cur = head_;
  head_ = NULL;
  tail_ = NULL;
  while (cur != NULL) {
    Message* next = cur->next_;
    delete cur;
    cur = next;
  }
}


}  // namespace dart