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/debug/task_annotator.h"
6
7 #include <array>
8
9 #include "base/debug/activity_tracker.h"
10 #include "base/debug/alias.h"
11 #include "base/no_destructor.h"
12 #include "base/pending_task.h"
13 #include "base/threading/thread_local.h"
14 #include "base/trace_event/trace_event.h"
15
16 namespace base {
17 namespace debug {
18
19 namespace {
20
21 TaskAnnotator::ObserverForTesting* g_task_annotator_observer = nullptr;
22
23 // Returns the TLS slot that stores the PendingTask currently in progress on
24 // each thread. Used to allow creating a breadcrumb of program counters on the
25 // stack to help identify a task's origin in crashes.
GetTLSForCurrentPendingTask()26 ThreadLocalPointer<const PendingTask>* GetTLSForCurrentPendingTask() {
27 static NoDestructor<ThreadLocalPointer<const PendingTask>>
28 tls_for_current_pending_task;
29 return tls_for_current_pending_task.get();
30 }
31
32 } // namespace
33
34 TaskAnnotator::TaskAnnotator() = default;
35
36 TaskAnnotator::~TaskAnnotator() = default;
37
WillQueueTask(const char * queue_function,PendingTask * pending_task)38 void TaskAnnotator::WillQueueTask(const char* queue_function,
39 PendingTask* pending_task) {
40 if (queue_function) {
41 TRACE_EVENT_WITH_FLOW0(TRACE_DISABLED_BY_DEFAULT("toplevel.flow"),
42 queue_function,
43 TRACE_ID_MANGLE(GetTaskTraceID(*pending_task)),
44 TRACE_EVENT_FLAG_FLOW_OUT);
45 }
46
47 // TODO(https://crbug.com/826902): Fix callers that invoke WillQueueTask()
48 // twice for the same PendingTask.
49 // DCHECK(!pending_task.task_backtrace[0])
50 // << "Task backtrace was already set, task posted twice??";
51 if (!pending_task->task_backtrace[0]) {
52 const PendingTask* parent_task = GetTLSForCurrentPendingTask()->Get();
53 if (parent_task) {
54 pending_task->task_backtrace[0] =
55 parent_task->posted_from.program_counter();
56 std::copy(parent_task->task_backtrace.begin(),
57 parent_task->task_backtrace.end() - 1,
58 pending_task->task_backtrace.begin() + 1);
59 }
60 }
61 }
62
RunTask(const char * queue_function,PendingTask * pending_task)63 void TaskAnnotator::RunTask(const char* queue_function,
64 PendingTask* pending_task) {
65 ScopedTaskRunActivity task_activity(*pending_task);
66
67 if (queue_function) {
68 TRACE_EVENT_WITH_FLOW0(TRACE_DISABLED_BY_DEFAULT("toplevel.flow"),
69 queue_function,
70 TRACE_ID_MANGLE(GetTaskTraceID(*pending_task)),
71 TRACE_EVENT_FLAG_FLOW_IN);
72 }
73
74 // Before running the task, store the task backtrace with the chain of
75 // PostTasks that resulted in this call and deliberately alias it to ensure
76 // it is on the stack if the task crashes. Be careful not to assume that the
77 // variable itself will have the expected value when displayed by the
78 // optimizer in an optimized build. Look at a memory dump of the stack.
79 static constexpr int kStackTaskTraceSnapshotSize =
80 std::tuple_size<decltype(pending_task->task_backtrace)>::value + 3;
81 std::array<const void*, kStackTaskTraceSnapshotSize> task_backtrace;
82
83 // Store a marker to locate |task_backtrace| content easily on a memory
84 // dump.
85 task_backtrace.front() = reinterpret_cast<void*>(0xefefefefefefefef);
86 task_backtrace.back() = reinterpret_cast<void*>(0xfefefefefefefefe);
87
88 task_backtrace[1] = pending_task->posted_from.program_counter();
89 std::copy(pending_task->task_backtrace.begin(),
90 pending_task->task_backtrace.end(), task_backtrace.begin() + 2);
91 debug::Alias(&task_backtrace);
92
93 ThreadLocalPointer<const PendingTask>* tls_for_current_pending_task =
94 GetTLSForCurrentPendingTask();
95 const PendingTask* previous_pending_task =
96 tls_for_current_pending_task->Get();
97 tls_for_current_pending_task->Set(pending_task);
98
99 if (g_task_annotator_observer)
100 g_task_annotator_observer->BeforeRunTask(pending_task);
101 std::move(pending_task->task).Run();
102
103 tls_for_current_pending_task->Set(previous_pending_task);
104 }
105
GetTaskTraceID(const PendingTask & task) const106 uint64_t TaskAnnotator::GetTaskTraceID(const PendingTask& task) const {
107 return (static_cast<uint64_t>(task.sequence_num) << 32) |
108 ((static_cast<uint64_t>(reinterpret_cast<intptr_t>(this)) << 32) >>
109 32);
110 }
111
112 // static
RegisterObserverForTesting(ObserverForTesting * observer)113 void TaskAnnotator::RegisterObserverForTesting(ObserverForTesting* observer) {
114 DCHECK(!g_task_annotator_observer);
115 g_task_annotator_observer = observer;
116 }
117
118 // static
ClearObserverForTesting()119 void TaskAnnotator::ClearObserverForTesting() {
120 g_task_annotator_observer = nullptr;
121 }
122
123 } // namespace debug
124 } // namespace base
125