Record async "task backtraces"

base/pending_task_unittest.cc

+// Copyright (c) 2017 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 <vector>
+
+#include "base/bind.h"
+#include "base/message_loop/message_loop.h"
+#include "base/run_loop.h"
+#include "base/strings/stringprintf.h"
+#include "base/threading/thread.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace base {
+
+class PendingTaskTest : public ::testing::Test {
+ public:
+  PendingTaskTest() = default;
+
+  ~PendingTaskTest() override = default;
+
+ protected:
+  using ExpectedTrace = std::vector<const void*>;
+
+  static void VerifyTraceAndPost(
+      const scoped_refptr<TaskRunner>& task_runner,
+      const tracked_objects::Location& posted_from,
+      const tracked_objects::Location& next_from_here,
+      const std::vector<const void*>& expected_trace,
+      Closure task) {
+    SCOPED_TRACE(StringPrintf("Callback Depth: %zu", expected_trace.size()));
+
+    // Beyond depth + 1, the trace is nonsensical because there haven't been
+    // enough nested tasks called.
+    const PendingTask* current_pending_task =
+        MessageLoop::current()->current_pending_task_;
+    size_t window = std::min(current_pending_task->task_backtrace.size(),
+                             expected_trace.size());
+
+    EXPECT_EQ(posted_from,
+              MessageLoop::current()->current_pending_task_->posted_from);
+    for (size_t i = 0; i < window; i++) {
+      SCOPED_TRACE(StringPrintf("Trace frame: %zu", i));
+      EXPECT_EQ(expected_trace[i], current_pending_task->task_backtrace[i]);
+    }
+    task_runner->PostTask(next_from_here, std::move(task));
+  }
+
+  static void RunTwo(Closure c1, Closure c2) {
+    c1.Run();
+    c2.Run();
+  }
+};
+
+// Ensure the task backtrace populates correctly.
+TEST_F(PendingTaskTest, SingleThreadedSimple) {
+  MessageLoop loop;
+  const tracked_objects::Location& location0 = FROM_HERE;
+  const tracked_objects::Location& location1 = FROM_HERE;
+  const tracked_objects::Location& location2 = FROM_HERE;
+  const tracked_objects::Location& location3 = FROM_HERE;
+  const tracked_objects::Location& location4 = FROM_HERE;
+  const tracked_objects::Location& location5 = FROM_HERE;
+
+  Closure task5 = Bind(
+      &PendingTaskTest::VerifyTraceAndPost, loop.task_runner(), location4,
+      location5,
+      ExpectedTrace({location3.program_counter(), location2.program_counter(),
+                     location1.program_counter(), location0.program_counter()}),
+      Bind(&DoNothing));
+  Closure task4 = Bind(
+      &PendingTaskTest::VerifyTraceAndPost, loop.task_runner(), location3,
+      location4,
+      ExpectedTrace({location2.program_counter(), location1.program_counter(),
+                     location0.program_counter(), nullptr}),
+      task5);
+  Closure task3 = Bind(
+      &PendingTaskTest::VerifyTraceAndPost, loop.task_runner(), location2,
+      location3, ExpectedTrace({location1.program_counter(),
+                                location0.program_counter(), nullptr, nullptr}),
+      task4);
+  Closure task2 =
+      Bind(&PendingTaskTest::VerifyTraceAndPost, loop.task_runner(), location1,
+           location2, ExpectedTrace({location0.program_counter()}), task3);
+  Closure task1 = Bind(&PendingTaskTest::VerifyTraceAndPost, loop.task_runner(),
+                       location0, location1, ExpectedTrace({}), task2);
+
+  loop.task_runner()->PostTask(location0, task1);
+
+  RunLoop().RunUntilIdle();
+}
+
+// Post a task onto another thread. Ensure on the other thread, it has the
+// right stack trace.
+TEST_F(PendingTaskTest, MultipleThreads) {
+  MessageLoop loop;  // Implicitly "thread a"
+  Thread thread_b("pt_test_b");
+  Thread thread_c("pt_test_c");
+  thread_b.StartAndWaitForTesting();
+  thread_c.StartAndWaitForTesting();
+
+  const tracked_objects::Location& location_a0 = FROM_HERE;
+  const tracked_objects::Location& location_a1 = FROM_HERE;
+  const tracked_objects::Location& location_a2 = FROM_HERE;
+
+  const tracked_objects::Location& location_b0 = FROM_HERE;
+  const tracked_objects::Location& location_b1 = FROM_HERE;
+
+  const tracked_objects::Location& location_c0 = FROM_HERE;
+
+  // Push one frame onto the stack in thread c and then pass back to thread a.
+  Closure task_a2 =
+      Bind(&PendingTaskTest::VerifyTraceAndPost, loop.task_runner(),
+           location_c0, location_a2,
+           ExpectedTrace(
+               {location_b1.program_counter(), location_b0.program_counter(),
+                location_a1.program_counter(), location_a0.program_counter()}),
+           Bind(&DoNothing));
+  Closure task_c0 = Bind(&PendingTaskTest::VerifyTraceAndPost,
+                         loop.task_runner(), location_b1, location_c0,
+                         ExpectedTrace({location_b0.program_counter(),
+                                        location_a1.program_counter(),
+                                        location_a0.program_counter()}),
+                         task_a2);
+
+  // Push one frame onto the stack in thread b then spawn two tasks, one in
+  // thread b and one in thread c using location_b1.
+  Closure task_b0_fork =
+      Bind(&PendingTaskTest::VerifyTraceAndPost,
+           thread_c.message_loop()->task_runner(), location_b0, location_b1,

[danakj, 2017/02/09 21:16:27]

The names of the locations are a bit inconsistent. Like here it's going to
thread_c but the next location is location_b1 (named for where its coming from).

for task_a1 its going to thread_b, and the next location is location_b0 (named
for where its going)

[awong, 2017/02/09 21:25:36]

That's actually me doing the backtrace wrong. :-/

Fixed to set the "next_from_here" to c0 since it's the first frame on thread c.

+           ExpectedTrace({location_a1.program_counter(),
+                          location_a0.program_counter(), nullptr}),
+           task_c0);
+  Closure task_b0_local =
+      Bind(&PendingTaskTest::VerifyTraceAndPost,
+           thread_b.message_loop()->task_runner(), location_b0, location_b1,
+           ExpectedTrace({location_a1.program_counter(),
+                          location_a0.program_counter(), nullptr}),
+           Bind(&DoNothing));
+
+  // Push one frame onto the stack in thread a then pass to thread b.

[danakj, 2017/02/09 21:16:27]

The comment explanations are helpful but also a bit inconsistent.

Here it says:
- push a stack in thread a => posts a task on thread_a.
- pass to thread b => posts a task on thread_b

For the block above it says:
- push a frame on the stack => i don't see this in the code
- then spawn two tasks one in thread b => posts to thread_b
- and one in thread c => posts to thread_c

For the topmost block it says:
- push one frame on the stack in thread c => I don't see this it posts to
thread_a?
- then pass to thread a => it posts a 2nd task onto thread a

We should make the code and comments consistent here at least.

[awong, 2017/02/09 21:25:37]

I think the comments were actually right and the code was wrong. I matched up
the code to the comments.

+  Closure task_a1 =
+      Bind(&PendingTaskTest::VerifyTraceAndPost,
+           thread_b.message_loop()->task_runner(), location_a1, location_b0,
+           ExpectedTrace({location_a0.program_counter(), nullptr}),
+           Bind(&PendingTaskTest::RunTwo, task_b0_local, task_b0_fork));
+  Closure task_a0 =
+      Bind(&PendingTaskTest::VerifyTraceAndPost, loop.task_runner(),
+           location_a0, location_a1, ExpectedTrace({nullptr}), task_a1);
+
+  loop.task_runner()->PostTask(location_a0, task_a0);
+
+  RunLoop().RunUntilIdle();
+
+  thread_b.FlushForTesting();
+  thread_b.Stop();
+
+  thread_c.FlushForTesting();
+  thread_c.Stop();
+}
+
+}  // namespace base