[TaskManager] Allow a Task to mutate its PID after creation

chrome/browser/task_manager/sampling/task_group.cc

 // Copyright 2015 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 "chrome/browser/task_manager/sampling/task_group.h"
 
 #include <algorithm>
 #include <limits>
 
 #include "base/bind.h"
@@ skipping 90 matching lines @@
 #if !defined(DISABLE_NACL)
       nacl_debug_stub_port_(nacl::kGdbDebugStubPortUnknown),
 #endif  // !defined(DISABLE_NACL)
       idle_wakeups_per_second_(-1),
 #if defined(OS_LINUX)
       open_fd_count_(-1),
 #endif  // defined(OS_LINUX)
       gpu_memory_has_duplicates_(false),
       is_backgrounded_(false),
       weak_ptr_factory_(this) {
-  scoped_refptr<TaskGroupSampler> sampler(
-      new TaskGroupSampler(base::Process::Open(proc_id),
-                           blocking_pool_runner,
-                           base::Bind(&TaskGroup::OnCpuRefreshDone,
-                                      weak_ptr_factory_.GetWeakPtr()),
-                           base::Bind(&TaskGroup::OnMemoryUsageRefreshDone,
-                                      weak_ptr_factory_.GetWeakPtr()),
-                           base::Bind(&TaskGroup::OnIdleWakeupsRefreshDone,
-                                      weak_ptr_factory_.GetWeakPtr()),
+  if (process_id_ != base::kNullProcessId) {
+    worker_thread_sampler_ = base::MakeRefCounted<TaskGroupSampler>(
+        base::Process::Open(process_id_), blocking_pool_runner,
+        base::Bind(&TaskGroup::OnCpuRefreshDone,
+                   weak_ptr_factory_.GetWeakPtr()),
+        base::Bind(&TaskGroup::OnMemoryUsageRefreshDone,
+                   weak_ptr_factory_.GetWeakPtr()),
+        base::Bind(&TaskGroup::OnIdleWakeupsRefreshDone,
+                   weak_ptr_factory_.GetWeakPtr()),
 #if defined(OS_LINUX)
-                           base::Bind(&TaskGroup::OnOpenFdCountRefreshDone,
-                                      weak_ptr_factory_.GetWeakPtr()),
+        base::Bind(&TaskGroup::OnOpenFdCountRefreshDone,
+                   weak_ptr_factory_.GetWeakPtr()),
 #endif  // defined(OS_LINUX)
-                           base::Bind(&TaskGroup::OnProcessPriorityDone,
-                                      weak_ptr_factory_.GetWeakPtr())));
-  worker_thread_sampler_.swap(sampler);
-
+        base::Bind(&TaskGroup::OnProcessPriorityDone,
+                   weak_ptr_factory_.GetWeakPtr()));
+  }
   shared_sampler_->RegisterCallbacks(
-      process_id_, base::Bind(&TaskGroup::OnIdleWakeupsRefreshDone,
-                              weak_ptr_factory_.GetWeakPtr()),
+      process_id_,
+      base::Bind(&TaskGroup::OnIdleWakeupsRefreshDone,
+                 weak_ptr_factory_.GetWeakPtr()),
       base::Bind(&TaskGroup::OnPhysicalMemoryUsageRefreshDone,
                  weak_ptr_factory_.GetWeakPtr()),
       base::Bind(&TaskGroup::OnStartTimeRefreshDone,
                  weak_ptr_factory_.GetWeakPtr()),
       base::Bind(&TaskGroup::OnCpuTimeRefreshDone,
                  weak_ptr_factory_.GetWeakPtr()));

[afakhry, 2017/07/10 17:27:54]

It seems we can also exclude the shared_sampler_ callback registeration too?

We just return if it's the null process:
https://cs.chromium.org/chromium/src/chrome/browser/task_manager/sampling/sha...

[ncarter (slow), 2017/07/31 22:30:29]

Done.

 }
 
 TaskGroup::~TaskGroup() {
   shared_sampler_->UnregisterCallbacks(process_id_);
 }
 
 void TaskGroup::AddTask(Task* task) {
   DCHECK(task);
   tasks_.push_back(task);
 }
@@ skipping 69 matching lines @@
             process_handle_);
   }
 
   // The remaining resource refreshes are time consuming and cannot be done on
   // the UI thread. Do them all on the worker thread using the TaskGroupSampler.
   // 7-  CPU usage.
   // 8-  Memory usage.
   // 9-  Idle Wakeups per second.
   // 10-  (Linux and ChromeOS only) The number of file descriptors current open.
   // 11- Process priority (foreground vs. background).
-  worker_thread_sampler_->Refresh(refresh_flags);
+  if (worker_thread_sampler_)
+    worker_thread_sampler_->Refresh(refresh_flags);
 }
 
 Task* TaskGroup::GetTaskById(TaskId task_id) const {
   for (Task* task : tasks_) {
     if (task->task_id() == task_id)
       return task;
   }
   NOTREACHED();
   return nullptr;
 }
@@ skipping 114 matching lines @@
 
 void TaskGroup::OnBackgroundRefreshTypeFinished(int64_t finished_refresh_type) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
 
   current_on_bg_done_flags_ |= finished_refresh_type;
   if (AreBackgroundCalculationsDone())
     on_background_calculations_done_.Run();
 }
 
 }  // namespace task_manager