Record async "task backtraces"

base/pending_task.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/pending_task.h"
 
 #include "base/tracked_objects.h"
 
 namespace base {
 
 PendingTask::PendingTask(const tracked_objects::Location& posted_from,
+                         const PendingTask* parent_task,
                          const base::Closure& task)
     : base::TrackingInfo(posted_from, TimeTicks()),
       task(task),
       posted_from(posted_from),
       sequence_num(0),
       nestable(true),
       is_high_res(false) {
+  task_backtrace[0] = posted_from.program_counter();
+  if (parent_task) {
+    memcpy(&task_backtrace[1], &parent_task->task_backtrace[0],
+           sizeof(task_backtrace[0]) * ARRAYSIZE_UNSAFE(task_backtrace) - 1);
+  }
 }
 
 PendingTask::PendingTask(const tracked_objects::Location& posted_from,
+                         const PendingTask* parent_task,
                          const base::Closure& task,
                          TimeTicks delayed_run_time,
                          bool nestable)
     : base::TrackingInfo(posted_from, delayed_run_time),
       task(task),
       posted_from(posted_from),
       sequence_num(0),
       nestable(nestable),
       is_high_res(false) {
+  task_backtrace[0] = posted_from.program_counter();
+  if (parent_task) {
+    memcpy(&task_backtrace[1], &parent_task->task_backtrace[0],
+           sizeof(task_backtrace[0]) * ARRAYSIZE_UNSAFE(task_backtrace) - 1);
+  }
 }
 
 PendingTask::~PendingTask() {
 }
 
 bool PendingTask::operator<(const PendingTask& other) const {
   // Since the top of a priority queue is defined as the "greatest" element, we
   // need to invert the comparison here.  We want the smaller time to be at the
   // top of the heap.
 
   if (delayed_run_time < other.delayed_run_time)
     return false;
 
   if (delayed_run_time > other.delayed_run_time)
     return true;
 
   // If the times happen to match, then we use the sequence number to decide.
   // Compare the difference to support integer roll-over.
   return (sequence_num - other.sequence_num) > 0;
 }
 
 void TaskQueue::Swap(TaskQueue* queue) {
   c.swap(queue->c);  // Calls std::deque::swap.
 }
 
 }  // namespace base