base/task/cancelable_task_tracker.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "base/task/cancelable_task_tracker.h"
   6
   7 #include <utility>
   8
   9 #include "base/bind.h"
  10 #include "base/callback_helpers.h"
  11 #include "base/compiler_specific.h"
  12 #include "base/location.h"
  13 #include "base/memory/ref_counted.h"
  14 #include "base/message_loop/message_loop_proxy.h"
  15 #include "base/synchronization/cancellation_flag.h"
  16 #include "base/task_runner.h"
  17
  18 using base::Bind;
  19 using base::CancellationFlag;
  20 using base::Closure;
  21 using base::hash_map;
  22 using base::TaskRunner;
  23
  24 namespace {
  25
  26 void RunIfNotCanceled(const CancellationFlag* flag, const Closure& task) {
  27   if (!flag->IsSet())
  28     task.Run();
  29 }
  30
  31 void RunIfNotCanceledThenUntrack(const CancellationFlag* flag,
  32                                  const Closure& task,
  33                                  const Closure& untrack) {
  34   RunIfNotCanceled(flag, task);
  35   untrack.Run();
  36 }
  37
  38 bool IsCanceled(const CancellationFlag* flag,
  39                 base::ScopedClosureRunner* cleanup_runner) {
  40   return flag->IsSet();
  41 }
  42
  43 void RunAndDeleteFlag(const Closure& closure, const CancellationFlag* flag) {
  44   closure.Run();
  45   delete flag;
  46 }
  47
  48 void RunOrPostToTaskRunner(TaskRunner* task_runner, const Closure& closure) {
  49   if (task_runner->RunsTasksOnCurrentThread())
  50     closure.Run();
  51   else
  52     task_runner->PostTask(FROM_HERE, closure);
  53 }
  54
  55 }  // namespace
  56
  57 namespace base {
  58
  59 // static
  60 const CancelableTaskTracker::TaskId CancelableTaskTracker::kBadTaskId = 0;
  61
  62 CancelableTaskTracker::CancelableTaskTracker()
  63     : weak_factory_(this), next_id_(1) {}
  64
  65 CancelableTaskTracker::~CancelableTaskTracker() {
  66   DCHECK(thread_checker_.CalledOnValidThread());
  67
  68   TryCancelAll();
  69 }
  70
  71 CancelableTaskTracker::TaskId CancelableTaskTracker::PostTask(
  72     TaskRunner* task_runner,
  73     const tracked_objects::Location& from_here,
  74     const Closure& task) {
  75   DCHECK(thread_checker_.CalledOnValidThread());
  76
  77   return PostTaskAndReply(task_runner, from_here, task, Bind(&base::DoNothing));
  78 }
  79
  80 CancelableTaskTracker::TaskId CancelableTaskTracker::PostTaskAndReply(
  81     TaskRunner* task_runner,
  82     const tracked_objects::Location& from_here,
  83     const Closure& task,
  84     const Closure& reply) {
  85   DCHECK(thread_checker_.CalledOnValidThread());
  86
  87   // We need a MessageLoop to run reply.
  88   DCHECK(base::MessageLoopProxy::current().get());
  89
  90   // Owned by reply callback below.
  91   CancellationFlag* flag = new CancellationFlag();
  92
  93   TaskId id = next_id_;
  94   next_id_++;  // int64 is big enough that we ignore the potential overflow.
  95
  96   const Closure& untrack_closure =
  97       Bind(&CancelableTaskTracker::Untrack, weak_factory_.GetWeakPtr(), id);
  98   bool success =
  99       task_runner->PostTaskAndReply(from_here,
 100                                     Bind(&RunIfNotCanceled, flag, task),
 101                                     Bind(&RunIfNotCanceledThenUntrack,
 102                                          base::Owned(flag),
 103                                          reply,
 104                                          untrack_closure));
 105
 106   if (!success)
 107     return kBadTaskId;
 108
 109   Track(id, flag);
 110   return id;
 111 }
 112
 113 CancelableTaskTracker::TaskId CancelableTaskTracker::NewTrackedTaskId(
 114     IsCanceledCallback* is_canceled_cb) {
 115   DCHECK(thread_checker_.CalledOnValidThread());
 116   DCHECK(base::MessageLoopProxy::current().get());
 117
 118   TaskId id = next_id_;
 119   next_id_++;  // int64 is big enough that we ignore the potential overflow.
 120
 121   // Will be deleted by |untrack_and_delete_flag| after Untrack().
 122   CancellationFlag* flag = new CancellationFlag();
 123
 124   Closure untrack_and_delete_flag = Bind(
 125       &RunAndDeleteFlag,
 126       Bind(&CancelableTaskTracker::Untrack, weak_factory_.GetWeakPtr(), id),
 127       flag);
 128
 129   // Will always run |untrack_and_delete_flag| on current MessageLoop.
 130   base::ScopedClosureRunner* untrack_and_delete_flag_runner =
 131       new base::ScopedClosureRunner(Bind(&RunOrPostToTaskRunner,
 132                                          base::MessageLoopProxy::current(),
 133                                          untrack_and_delete_flag));
 134
 135   *is_canceled_cb =
 136       Bind(&IsCanceled, flag, base::Owned(untrack_and_delete_flag_runner));
 137
 138   Track(id, flag);
 139   return id;
 140 }
 141
 142 void CancelableTaskTracker::TryCancel(TaskId id) {
 143   DCHECK(thread_checker_.CalledOnValidThread());
 144
 145   hash_map<TaskId, CancellationFlag*>::const_iterator it = task_flags_.find(id);
 146   if (it == task_flags_.end()) {
 147     // Two possibilities:
 148     //
 149     //   1. The task has already been untracked.
 150     //   2. The TaskId is bad or unknown.
 151     //
 152     // Since this function is best-effort, it's OK to ignore these.
 153     return;
 154   }
 155   it->second->Set();
 156 }
 157
 158 void CancelableTaskTracker::TryCancelAll() {
 159   DCHECK(thread_checker_.CalledOnValidThread());
 160
 161   for (hash_map<TaskId, CancellationFlag*>::const_iterator it =
 162            task_flags_.begin();
 163        it != task_flags_.end();
 164        ++it) {
 165     it->second->Set();
 166   }
 167 }
 168
 169 bool CancelableTaskTracker::HasTrackedTasks() const {
 170   DCHECK(thread_checker_.CalledOnValidThread());
 171   return !task_flags_.empty();
 172 }
 173
 174 void CancelableTaskTracker::Track(TaskId id, CancellationFlag* flag) {
 175   DCHECK(thread_checker_.CalledOnValidThread());
 176
 177   bool success = task_flags_.insert(std::make_pair(id, flag)).second;
 178   DCHECK(success);
 179 }
 180
 181 void CancelableTaskTracker::Untrack(TaskId id) {
 182   DCHECK(thread_checker_.CalledOnValidThread());
 183   size_t num = task_flags_.erase(id);
 184   DCHECK_EQ(1u, num);
 185 }
 186
 187 }  // namespace base