1/*
2 *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
3 *
4 *  Use of this source code is governed by a BSD-style license
5 *  that can be found in the LICENSE file in the root of the source
6 *  tree. An additional intellectual property rights grant can be found
7 *  in the file PATENTS.  All contributing project authors may
8 *  be found in the AUTHORS file in the root of the source tree.
9 */
10
11#include <algorithm>
12
13#include "webrtc/base/taskrunner.h"
14
15#include "webrtc/base/common.h"
16#include "webrtc/base/scoped_ptr.h"
17#include "webrtc/base/task.h"
18#include "webrtc/base/logging.h"
19
20namespace rtc {
21
22TaskRunner::TaskRunner()
23  : TaskParent(this),
24    next_timeout_task_(NULL),
25    tasks_running_(false)
26#ifdef _DEBUG
27    , abort_count_(0),
28    deleting_task_(NULL)
29#endif
30{
31}
32
33TaskRunner::~TaskRunner() {
34  // this kills and deletes children silently!
35  AbortAllChildren();
36  InternalRunTasks(true);
37}
38
39void TaskRunner::StartTask(Task * task) {
40  tasks_.push_back(task);
41
42  // the task we just started could be about to timeout --
43  // make sure our "next timeout task" is correct
44  UpdateTaskTimeout(task, 0);
45
46  WakeTasks();
47}
48
49void TaskRunner::RunTasks() {
50  InternalRunTasks(false);
51}
52
53void TaskRunner::InternalRunTasks(bool in_destructor) {
54  // This shouldn't run while an abort is happening.
55  // If that occurs, then tasks may be deleted in this method,
56  // but pointers to them will still be in the
57  // "ChildSet copy" in TaskParent::AbortAllChildren.
58  // Subsequent use of those task may cause data corruption or crashes.
59  ASSERT(!abort_count_);
60  // Running continues until all tasks are Blocked (ok for a small # of tasks)
61  if (tasks_running_) {
62    return;  // don't reenter
63  }
64
65  tasks_running_ = true;
66
67  int64 previous_timeout_time = next_task_timeout();
68
69  int did_run = true;
70  while (did_run) {
71    did_run = false;
72    // use indexing instead of iterators because tasks_ may grow
73    for (size_t i = 0; i < tasks_.size(); ++i) {
74      while (!tasks_[i]->Blocked()) {
75        tasks_[i]->Step();
76        did_run = true;
77      }
78    }
79  }
80  // Tasks are deleted when running has paused
81  bool need_timeout_recalc = false;
82  for (size_t i = 0; i < tasks_.size(); ++i) {
83    if (tasks_[i]->IsDone()) {
84      Task* task = tasks_[i];
85      if (next_timeout_task_ &&
86          task->unique_id() == next_timeout_task_->unique_id()) {
87        next_timeout_task_ = NULL;
88        need_timeout_recalc = true;
89      }
90
91#ifdef _DEBUG
92      deleting_task_ = task;
93#endif
94      delete task;
95#ifdef _DEBUG
96      deleting_task_ = NULL;
97#endif
98      tasks_[i] = NULL;
99    }
100  }
101  // Finally, remove nulls
102  std::vector<Task *>::iterator it;
103  it = std::remove(tasks_.begin(),
104                   tasks_.end(),
105                   reinterpret_cast<Task *>(NULL));
106
107  tasks_.erase(it, tasks_.end());
108
109  if (need_timeout_recalc)
110    RecalcNextTimeout(NULL);
111
112  // Make sure that adjustments are done to account
113  // for any timeout changes (but don't call this
114  // while being destroyed since it calls a pure virtual function).
115  if (!in_destructor)
116    CheckForTimeoutChange(previous_timeout_time);
117
118  tasks_running_ = false;
119}
120
121void TaskRunner::PollTasks() {
122  // see if our "next potentially timed-out task" has indeed timed out.
123  // If it has, wake it up, then queue up the next task in line
124  // Repeat while we have new timed-out tasks.
125  // TODO: We need to guard against WakeTasks not updating
126  // next_timeout_task_. Maybe also add documentation in the header file once
127  // we understand this code better.
128  Task* old_timeout_task = NULL;
129  while (next_timeout_task_ &&
130      old_timeout_task != next_timeout_task_ &&
131      next_timeout_task_->TimedOut()) {
132    old_timeout_task = next_timeout_task_;
133    next_timeout_task_->Wake();
134    WakeTasks();
135  }
136}
137
138int64 TaskRunner::next_task_timeout() const {
139  if (next_timeout_task_) {
140    return next_timeout_task_->timeout_time();
141  }
142  return 0;
143}
144
145// this function gets called frequently -- when each task changes
146// state to something other than DONE, ERROR or BLOCKED, it calls
147// ResetTimeout(), which will call this function to make sure that
148// the next timeout-able task hasn't changed.  The logic in this function
149// prevents RecalcNextTimeout() from getting called in most cases,
150// effectively making the task scheduler O-1 instead of O-N
151
152void TaskRunner::UpdateTaskTimeout(Task* task,
153                                   int64 previous_task_timeout_time) {
154  ASSERT(task != NULL);
155  int64 previous_timeout_time = next_task_timeout();
156  bool task_is_timeout_task = next_timeout_task_ != NULL &&
157      task->unique_id() == next_timeout_task_->unique_id();
158  if (task_is_timeout_task) {
159    previous_timeout_time = previous_task_timeout_time;
160  }
161
162  // if the relevant task has a timeout, then
163  // check to see if it's closer than the current
164  // "about to timeout" task
165  if (task->timeout_time()) {
166    if (next_timeout_task_ == NULL ||
167        (task->timeout_time() <= next_timeout_task_->timeout_time())) {
168      next_timeout_task_ = task;
169    }
170  } else if (task_is_timeout_task) {
171    // otherwise, if the task doesn't have a timeout,
172    // and it used to be our "about to timeout" task,
173    // walk through all the tasks looking for the real
174    // "about to timeout" task
175    RecalcNextTimeout(task);
176  }
177
178  // Note when task_running_, then the running routine
179  // (TaskRunner::InternalRunTasks) is responsible for calling
180  // CheckForTimeoutChange.
181  if (!tasks_running_) {
182    CheckForTimeoutChange(previous_timeout_time);
183  }
184}
185
186void TaskRunner::RecalcNextTimeout(Task *exclude_task) {
187  // walk through all the tasks looking for the one
188  // which satisfies the following:
189  //   it's not finished already
190  //   we're not excluding it
191  //   it has the closest timeout time
192
193  int64 next_timeout_time = 0;
194  next_timeout_task_ = NULL;
195
196  for (size_t i = 0; i < tasks_.size(); ++i) {
197    Task *task = tasks_[i];
198    // if the task isn't complete, and it actually has a timeout time
199    if (!task->IsDone() && (task->timeout_time() > 0))
200      // if it doesn't match our "exclude" task
201      if (exclude_task == NULL ||
202          exclude_task->unique_id() != task->unique_id())
203        // if its timeout time is sooner than our current timeout time
204        if (next_timeout_time == 0 ||
205            task->timeout_time() <= next_timeout_time) {
206          // set this task as our next-to-timeout
207          next_timeout_time = task->timeout_time();
208          next_timeout_task_ = task;
209        }
210  }
211}
212
213void TaskRunner::CheckForTimeoutChange(int64 previous_timeout_time) {
214  int64 next_timeout = next_task_timeout();
215  bool timeout_change = (previous_timeout_time == 0 && next_timeout != 0) ||
216      next_timeout < previous_timeout_time ||
217      (previous_timeout_time <= CurrentTime() &&
218       previous_timeout_time != next_timeout);
219  if (timeout_change) {
220    OnTimeoutChange();
221  }
222}
223
224} // namespace rtc
225