blob: e1fb7e46139dee5694b00891252a7e2c66d2e153 [file] [log] [blame]
// 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 <stddef.h>
#include <stdint.h>
#include <algorithm>
#include <cstdlib>
#include <memory>
#include <set>
#include <utility>
#include <vector>
#include "base/bind.h"
#include "base/callback.h"
#include "base/compiler_specific.h"
#include "base/files/file_util.h"
#include "base/location.h"
#include "base/macros.h"
#include "base/memory/ptr_util.h"
#include "base/native_library.h"
#include "base/path_service.h"
#include "base/profiler/stack_sampler.h"
#include "base/profiler/stack_sampling_profiler.h"
#include "base/profiler/stack_sampling_profiler_test_util.h"
#include "base/profiler/unwinder.h"
#include "base/run_loop.h"
#include "base/scoped_native_library.h"
#include "base/stl_util.h"
#include "base/strings/utf_string_conversions.h"
#include "base/synchronization/lock.h"
#include "base/synchronization/waitable_event.h"
#include "base/test/bind_test_util.h"
#include "base/threading/simple_thread.h"
#include "base/time/time.h"
#include "build/build_config.h"
#include "testing/gtest/include/gtest/gtest.h"
#if defined(OS_WIN)
#include <intrin.h>
#include <malloc.h>
#include <windows.h>
#else
#include <alloca.h>
#endif
// STACK_SAMPLING_PROFILER_SUPPORTED is used to conditionally enable the tests
// below for supported platforms (currently Win x64 and Mac x64).
#if defined(_WIN64) || (defined(OS_MACOSX) && !defined(OS_IOS))
#define STACK_SAMPLING_PROFILER_SUPPORTED 1
#endif
namespace base {
#if defined(STACK_SAMPLING_PROFILER_SUPPORTED)
#define PROFILER_TEST_F(TestClass, TestName) TEST_F(TestClass, TestName)
#else
#define PROFILER_TEST_F(TestClass, TestName) \
TEST_F(TestClass, DISABLED_##TestName)
#endif
using SamplingParams = StackSamplingProfiler::SamplingParams;
namespace {
// Calls into |wait_for_sample| after using alloca(), to test unwinding with a
// frame pointer.
// Disable inlining for this function so that it gets its own stack frame.
NOINLINE FunctionAddressRange CallWithAlloca(OnceClosure wait_for_sample) {
const void* start_program_counter = GetProgramCounter();
// Volatile to force a dynamic stack allocation.
const volatile size_t alloca_size = 100;
// Use the memory via volatile writes to prevent the allocation from being
// optimized out.
volatile char* const allocation =
const_cast<volatile char*>(static_cast<char*>(alloca(alloca_size)));
for (volatile char* p = allocation; p < allocation + alloca_size; ++p)
*p = '\0';
if (!wait_for_sample.is_null())
std::move(wait_for_sample).Run();
// Volatile to prevent a tail call to GetProgramCounter().
const void* volatile end_program_counter = GetProgramCounter();
return {start_program_counter, end_program_counter};
}
// The function to be executed by the code in the other library.
void OtherLibraryCallback(void* arg) {
OnceClosure* wait_for_sample = static_cast<OnceClosure*>(arg);
std::move(*wait_for_sample).Run();
// Prevent tail call.
volatile int i = 0;
ALLOW_UNUSED_LOCAL(i);
}
// Calls into |wait_for_sample| through a function within another library, to
// test unwinding through multiple modules and scenarios involving unloaded
// modules.
// Disable inlining for this function so that it gets its own stack frame.
NOINLINE FunctionAddressRange
CallThroughOtherLibrary(NativeLibrary library, OnceClosure wait_for_sample) {
const void* start_program_counter = GetProgramCounter();
if (!wait_for_sample.is_null()) {
// A function whose arguments are a function accepting void*, and a void*.
using InvokeCallbackFunction = void (*)(void (*)(void*), void*);
EXPECT_TRUE(library);
InvokeCallbackFunction function = reinterpret_cast<InvokeCallbackFunction>(
GetFunctionPointerFromNativeLibrary(library, "InvokeCallbackFunction"));
EXPECT_TRUE(function);
(*function)(&OtherLibraryCallback, &wait_for_sample);
}
// Volatile to prevent a tail call to GetProgramCounter().
const void* volatile end_program_counter = GetProgramCounter();
return {start_program_counter, end_program_counter};
}
// Profile consists of a set of samples and other sampling information.
struct Profile {
Profile() = default;
Profile(Profile&& other) = default;
Profile(const std::vector<std::vector<Frame>>& samples,
int metadata_count,
TimeDelta profile_duration,
TimeDelta sampling_period);
~Profile() = default;
Profile& operator=(Profile&& other) = default;
// The collected samples.
std::vector<std::vector<Frame>> samples;
// The number of invocations of RecordMetadata().
int metadata_count;
// Duration of this profile.
TimeDelta profile_duration;
// Time between samples.
TimeDelta sampling_period;
};
Profile::Profile(const std::vector<std::vector<Frame>>& samples,
int metadata_count,
TimeDelta profile_duration,
TimeDelta sampling_period)
: samples(samples),
metadata_count(metadata_count),
profile_duration(profile_duration),
sampling_period(sampling_period) {}
// The callback type used to collect a profile. The passed Profile is move-only.
// Other threads, including the UI thread, may block on callback completion so
// this should run as quickly as possible.
using ProfileCompletedCallback = OnceCallback<void(Profile)>;
// TestProfileBuilder collects samples produced by the profiler.
class TestProfileBuilder : public ProfileBuilder {
public:
TestProfileBuilder(ModuleCache* module_cache,
ProfileCompletedCallback callback);
~TestProfileBuilder() override;
// ProfileBuilder:
ModuleCache* GetModuleCache() override;
void RecordMetadata(
base::ProfileBuilder::MetadataProvider* metadata_provider) override;
void OnSampleCompleted(std::vector<Frame> sample) override;
void OnProfileCompleted(TimeDelta profile_duration,
TimeDelta sampling_period) override;
private:
ModuleCache* module_cache_;
// The set of recorded samples.
std::vector<std::vector<Frame>> samples_;
// The number of invocations of RecordMetadata().
int metadata_count_ = 0;
// Callback made when sampling a profile completes.
ProfileCompletedCallback callback_;
DISALLOW_COPY_AND_ASSIGN(TestProfileBuilder);
};
TestProfileBuilder::TestProfileBuilder(ModuleCache* module_cache,
ProfileCompletedCallback callback)
: module_cache_(module_cache), callback_(std::move(callback)) {}
TestProfileBuilder::~TestProfileBuilder() = default;
ModuleCache* TestProfileBuilder::GetModuleCache() {
return module_cache_;
}
void TestProfileBuilder::RecordMetadata(
base::ProfileBuilder::MetadataProvider* metadata_provider) {
++metadata_count_;
}
void TestProfileBuilder::OnSampleCompleted(std::vector<Frame> sample) {
samples_.push_back(std::move(sample));
}
void TestProfileBuilder::OnProfileCompleted(TimeDelta profile_duration,
TimeDelta sampling_period) {
std::move(callback_).Run(
Profile(samples_, metadata_count_, profile_duration, sampling_period));
}
// Loads the other library, which defines a function to be called in the
// WITH_OTHER_LIBRARY configuration.
NativeLibrary LoadOtherLibrary() {
// The lambda gymnastics works around the fact that we can't use ASSERT_*
// macros in a function returning non-null.
const auto load = [](NativeLibrary* library) {
FilePath other_library_path;
ASSERT_TRUE(PathService::Get(DIR_EXE, &other_library_path));
other_library_path = other_library_path.AppendASCII(
GetNativeLibraryName("base_profiler_test_support_library"));
NativeLibraryLoadError load_error;
*library = LoadNativeLibrary(other_library_path, &load_error);
ASSERT_TRUE(*library) << "error loading " << other_library_path.value()
<< ": " << load_error.ToString();
};
NativeLibrary library = nullptr;
load(&library);
return library;
}
// Unloads |library| and returns when it has completed unloading. Unloading a
// library is asynchronous on Windows, so simply calling UnloadNativeLibrary()
// is insufficient to ensure it's been unloaded.
void SynchronousUnloadNativeLibrary(NativeLibrary library) {
UnloadNativeLibrary(library);
#if defined(OS_WIN)
// NativeLibrary is a typedef for HMODULE, which is actually the base address
// of the module.
uintptr_t module_base_address = reinterpret_cast<uintptr_t>(library);
HMODULE module_handle;
// Keep trying to get the module handle until the call fails.
while (::GetModuleHandleEx(GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS |
GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT,
reinterpret_cast<LPCTSTR>(module_base_address),
&module_handle) ||
::GetLastError() != ERROR_MOD_NOT_FOUND) {
PlatformThread::Sleep(TimeDelta::FromMilliseconds(1));
}
#elif defined(OS_MACOSX)
// Unloading a library on the Mac is synchronous.
#else
NOTIMPLEMENTED();
#endif
}
void WithTargetThread(ProfileCallback profile_callback) {
UnwindScenario scenario(BindRepeating(&CallWithPlainFunction));
WithTargetThread(&scenario, std::move(profile_callback));
}
struct TestProfilerInfo {
TestProfilerInfo(SamplingProfilerThreadToken thread_token,
const SamplingParams& params,
ModuleCache* module_cache,
StackSamplerTestDelegate* delegate = nullptr)
: completed(WaitableEvent::ResetPolicy::MANUAL,
WaitableEvent::InitialState::NOT_SIGNALED),
profiler(thread_token,
params,
std::make_unique<TestProfileBuilder>(
module_cache,
BindLambdaForTesting([this](Profile result_profile) {
profile = std::move(result_profile);
completed.Signal();
})),
delegate) {}
// The order here is important to ensure objects being referenced don't get
// destructed until after the objects referencing them.
Profile profile;
WaitableEvent completed;
StackSamplingProfiler profiler;
private:
DISALLOW_COPY_AND_ASSIGN(TestProfilerInfo);
};
// Creates multiple profilers based on a vector of parameters.
std::vector<std::unique_ptr<TestProfilerInfo>> CreateProfilers(
SamplingProfilerThreadToken target_thread_token,
const std::vector<SamplingParams>& params,
ModuleCache* module_cache) {
DCHECK(!params.empty());
std::vector<std::unique_ptr<TestProfilerInfo>> profilers;
for (const auto& i : params) {
profilers.push_back(std::make_unique<TestProfilerInfo>(target_thread_token,
i, module_cache));
}
return profilers;
}
// Captures samples as specified by |params| on the TargetThread, and returns
// them. Waits up to |profiler_wait_time| for the profiler to complete.
std::vector<std::vector<Frame>> CaptureSamples(const SamplingParams& params,
TimeDelta profiler_wait_time,
ModuleCache* module_cache) {
std::vector<std::vector<Frame>> samples;
WithTargetThread(BindLambdaForTesting(
[&](SamplingProfilerThreadToken target_thread_token) {
TestProfilerInfo info(target_thread_token, params, module_cache);
info.profiler.Start();
info.completed.TimedWait(profiler_wait_time);
info.profiler.Stop();
info.completed.Wait();
samples = std::move(info.profile.samples);
}));
return samples;
}
// Waits for one of multiple samplings to complete.
size_t WaitForSamplingComplete(
const std::vector<std::unique_ptr<TestProfilerInfo>>& infos) {
// Map unique_ptrs to something that WaitMany can accept.
std::vector<WaitableEvent*> sampling_completed_rawptrs(infos.size());
std::transform(infos.begin(), infos.end(), sampling_completed_rawptrs.begin(),
[](const std::unique_ptr<TestProfilerInfo>& info) {
return &info.get()->completed;
});
// Wait for one profiler to finish.
return WaitableEvent::WaitMany(sampling_completed_rawptrs.data(),
sampling_completed_rawptrs.size());
}
// Returns a duration that is longer than the test timeout. We would use
// TimeDelta::Max() but https://crbug.com/465948.
TimeDelta AVeryLongTimeDelta() {
return TimeDelta::FromDays(1);
}
// Tests the scenario where the library is unloaded after copying the stack, but
// before walking it. If |wait_until_unloaded| is true, ensures that the
// asynchronous library loading has completed before walking the stack. If
// false, the unloading may still be occurring during the stack walk.
void TestLibraryUnload(bool wait_until_unloaded, ModuleCache* module_cache) {
// Test delegate that supports intervening between the copying of the stack
// and the walking of the stack.
class StackCopiedSignaler : public StackSamplerTestDelegate {
public:
StackCopiedSignaler(WaitableEvent* stack_copied,
WaitableEvent* start_stack_walk,
bool wait_to_walk_stack)
: stack_copied_(stack_copied),
start_stack_walk_(start_stack_walk),
wait_to_walk_stack_(wait_to_walk_stack) {}
void OnPreStackWalk() override {
stack_copied_->Signal();
if (wait_to_walk_stack_)
start_stack_walk_->Wait();
}
private:
WaitableEvent* const stack_copied_;
WaitableEvent* const start_stack_walk_;
const bool wait_to_walk_stack_;
};
SamplingParams params;
params.sampling_interval = TimeDelta::FromMilliseconds(0);
params.samples_per_profile = 1;
NativeLibrary other_library = LoadOtherLibrary();
UnwindScenario scenario(
BindRepeating(&CallThroughOtherLibrary, Unretained(other_library)));
UnwindScenario::SampleEvents events;
TargetThread target_thread(
BindLambdaForTesting([&]() { scenario.Execute(&events); }));
PlatformThreadHandle target_thread_handle;
EXPECT_TRUE(PlatformThread::Create(0, &target_thread, &target_thread_handle));
events.ready_for_sample.Wait();
WaitableEvent sampling_thread_completed(
WaitableEvent::ResetPolicy::MANUAL,
WaitableEvent::InitialState::NOT_SIGNALED);
Profile profile;
WaitableEvent stack_copied(WaitableEvent::ResetPolicy::MANUAL,
WaitableEvent::InitialState::NOT_SIGNALED);
WaitableEvent start_stack_walk(WaitableEvent::ResetPolicy::MANUAL,
WaitableEvent::InitialState::NOT_SIGNALED);
StackCopiedSignaler test_delegate(&stack_copied, &start_stack_walk,
wait_until_unloaded);
StackSamplingProfiler profiler(
target_thread.thread_token(), params,
std::make_unique<TestProfileBuilder>(
module_cache,
BindLambdaForTesting(
[&profile, &sampling_thread_completed](Profile result_profile) {
profile = std::move(result_profile);
sampling_thread_completed.Signal();
})),
&test_delegate);
profiler.Start();
// Wait for the stack to be copied and the target thread to be resumed.
stack_copied.Wait();
// Cause the target thread to finish, so that it's no longer executing code in
// the library we're about to unload.
events.sample_finished.Signal();
PlatformThread::Join(target_thread_handle);
// Unload the library now that it's not being used.
if (wait_until_unloaded)
SynchronousUnloadNativeLibrary(other_library);
else
UnloadNativeLibrary(other_library);
// Let the stack walk commence after unloading the library, if we're waiting
// on that event.
start_stack_walk.Signal();
// Wait for the sampling thread to complete and fill out |profile|.
sampling_thread_completed.Wait();
// Look up the sample.
ASSERT_EQ(1u, profile.samples.size());
const std::vector<Frame>& sample = profile.samples[0];
if (wait_until_unloaded) {
// We expect the stack to look something like this, with the frame in the
// now-unloaded library having a null module.
//
// ... WaitableEvent and system frames ...
// WaitForSample()
// TargetThread::OtherLibraryCallback
// <frame in unloaded library>
EXPECT_EQ(nullptr, sample.back().module)
<< "Stack:\n"
<< FormatSampleForDiagnosticOutput(sample);
ExpectStackContains(sample, {scenario.GetWaitForSampleAddressRange()});
ExpectStackDoesNotContain(sample,
{scenario.GetSetupFunctionAddressRange(),
scenario.GetOuterFunctionAddressRange()});
} else {
// We didn't wait for the asynchronous unloading to complete, so the results
// are non-deterministic: if the library finished unloading we should have
// the same stack as |wait_until_unloaded|, if not we should have the full
// stack. The important thing is that we should not crash.
if (!sample.back().module) {
// This is the same case as |wait_until_unloaded|.
ExpectStackContains(sample, {scenario.GetWaitForSampleAddressRange()});
ExpectStackDoesNotContain(sample,
{scenario.GetSetupFunctionAddressRange(),
scenario.GetOuterFunctionAddressRange()});
return;
}
ExpectStackContains(sample, {scenario.GetWaitForSampleAddressRange(),
scenario.GetSetupFunctionAddressRange(),
scenario.GetOuterFunctionAddressRange()});
}
}
// Provide a suitable (and clean) environment for the tests below. All tests
// must use this class to ensure that proper clean-up is done and thus be
// usable in a later test.
class StackSamplingProfilerTest : public testing::Test {
public:
void SetUp() override {
// The idle-shutdown time is too long for convenient (and accurate) testing.
// That behavior is checked instead by artificially triggering it through
// the TestPeer.
StackSamplingProfiler::TestPeer::DisableIdleShutdown();
}
void TearDown() override {
// Be a good citizen and clean up after ourselves. This also re-enables the
// idle-shutdown behavior.
StackSamplingProfiler::TestPeer::Reset();
}
protected:
ModuleCache* module_cache() { return &module_cache_; }
private:
ModuleCache module_cache_;
};
} // namespace
// Checks that the basic expected information is present in sampled frames.
//
// macOS ASAN is not yet supported - crbug.com/718628.
#if !(defined(ADDRESS_SANITIZER) && defined(OS_MACOSX))
#define MAYBE_Basic Basic
#else
#define MAYBE_Basic DISABLED_Basic
#endif
PROFILER_TEST_F(StackSamplingProfilerTest, MAYBE_Basic) {
UnwindScenario scenario(BindRepeating(&CallWithPlainFunction));
const std::vector<Frame>& sample = SampleScenario(&scenario, module_cache());
// Check that all the modules are valid.
for (const auto& frame : sample)
EXPECT_NE(nullptr, frame.module);
// The stack should contain a full unwind.
ExpectStackContains(sample, {scenario.GetWaitForSampleAddressRange(),
scenario.GetSetupFunctionAddressRange(),
scenario.GetOuterFunctionAddressRange()});
}
// A simple unwinder that always generates one frame then aborts the stack walk.
class TestAuxUnwinder : public Unwinder {
public:
TestAuxUnwinder(const Frame& frame_to_report)
: frame_to_report_(frame_to_report) {}
TestAuxUnwinder(const TestAuxUnwinder&) = delete;
TestAuxUnwinder& operator=(const TestAuxUnwinder&) = delete;
bool CanUnwindFrom(const Frame* current_frame) const override { return true; }
UnwindResult TryUnwind(RegisterContext* thread_context,
uintptr_t stack_top,
ModuleCache* module_cache,
std::vector<Frame>* stack) const override {
stack->push_back(frame_to_report_);
return UnwindResult::ABORTED;
}
private:
const Frame frame_to_report_;
};
// Checks that the profiler handles stacks containing dynamically-allocated
// stack memory.
// macOS ASAN is not yet supported - crbug.com/718628.
#if !(defined(ADDRESS_SANITIZER) && defined(OS_MACOSX))
#define MAYBE_Alloca Alloca
#else
#define MAYBE_Alloca DISABLED_Alloca
#endif
PROFILER_TEST_F(StackSamplingProfilerTest, MAYBE_Alloca) {
UnwindScenario scenario(BindRepeating(&CallWithAlloca));
const std::vector<Frame>& sample = SampleScenario(&scenario, module_cache());
// The stack should contain a full unwind.
ExpectStackContains(sample, {scenario.GetWaitForSampleAddressRange(),
scenario.GetSetupFunctionAddressRange(),
scenario.GetOuterFunctionAddressRange()});
}
// Checks that a stack that runs through another library produces a stack with
// the expected functions.
// macOS ASAN is not yet supported - crbug.com/718628.
#if !(defined(ADDRESS_SANITIZER) && defined(OS_MACOSX))
#define MAYBE_OtherLibrary OtherLibrary
#else
#define MAYBE_OtherLibrary DISABLED_OtherLibrary
#endif
PROFILER_TEST_F(StackSamplingProfilerTest, MAYBE_OtherLibrary) {
ScopedNativeLibrary other_library(LoadOtherLibrary());
UnwindScenario scenario(
BindRepeating(&CallThroughOtherLibrary, Unretained(other_library.get())));
const std::vector<Frame>& sample = SampleScenario(&scenario, module_cache());
// The stack should contain a full unwind.
ExpectStackContains(sample, {scenario.GetWaitForSampleAddressRange(),
scenario.GetSetupFunctionAddressRange(),
scenario.GetOuterFunctionAddressRange()});
}
// Checks that a stack that runs through a library that is unloading produces a
// stack, and doesn't crash.
// Unloading is synchronous on the Mac, so this test is inapplicable.
#if !defined(OS_MACOSX)
#define MAYBE_UnloadingLibrary UnloadingLibrary
#else
#define MAYBE_UnloadingLibrary DISABLED_UnloadingLibrary
#endif
PROFILER_TEST_F(StackSamplingProfilerTest, MAYBE_UnloadingLibrary) {
TestLibraryUnload(false, module_cache());
}
// Checks that a stack that runs through a library that has been unloaded
// produces a stack, and doesn't crash.
// macOS ASAN is not yet supported - crbug.com/718628.
#if !(defined(ADDRESS_SANITIZER) && defined(OS_MACOSX))
#define MAYBE_UnloadedLibrary UnloadedLibrary
#else
#define MAYBE_UnloadedLibrary DISABLED_UnloadedLibrary
#endif
PROFILER_TEST_F(StackSamplingProfilerTest, MAYBE_UnloadedLibrary) {
TestLibraryUnload(true, module_cache());
}
// Checks that a profiler can stop/destruct without ever having started.
PROFILER_TEST_F(StackSamplingProfilerTest, StopWithoutStarting) {
WithTargetThread(BindLambdaForTesting(
[this](SamplingProfilerThreadToken target_thread_token) {
SamplingParams params;
params.sampling_interval = TimeDelta::FromMilliseconds(0);
params.samples_per_profile = 1;
Profile profile;
WaitableEvent sampling_completed(
WaitableEvent::ResetPolicy::MANUAL,
WaitableEvent::InitialState::NOT_SIGNALED);
StackSamplingProfiler profiler(
target_thread_token, params,
std::make_unique<TestProfileBuilder>(
module_cache(),
BindLambdaForTesting(
[&profile, &sampling_completed](Profile result_profile) {
profile = std::move(result_profile);
sampling_completed.Signal();
})));
profiler.Stop(); // Constructed but never started.
EXPECT_FALSE(sampling_completed.IsSignaled());
}));
}
// Checks that its okay to stop a profiler before it finishes even when the
// sampling thread continues to run.
PROFILER_TEST_F(StackSamplingProfilerTest, StopSafely) {
// Test delegate that counts samples.
class SampleRecordedCounter : public StackSamplerTestDelegate {
public:
SampleRecordedCounter() = default;
void OnPreStackWalk() override {
AutoLock lock(lock_);
++count_;
}
size_t Get() {
AutoLock lock(lock_);
return count_;
}
private:
Lock lock_;
size_t count_ = 0;
};
WithTargetThread(BindLambdaForTesting(
[this](SamplingProfilerThreadToken target_thread_token) {
SamplingParams params[2];
// Providing an initial delay makes it more likely that both will be
// scheduled before either starts to run. Once started, samples will
// run ordered by their scheduled, interleaved times regardless of
// whatever interval the thread wakes up.
params[0].initial_delay = TimeDelta::FromMilliseconds(10);
params[0].sampling_interval = TimeDelta::FromMilliseconds(1);
params[0].samples_per_profile = 100000;
params[1].initial_delay = TimeDelta::FromMilliseconds(10);
params[1].sampling_interval = TimeDelta::FromMilliseconds(1);
params[1].samples_per_profile = 100000;
SampleRecordedCounter samples_recorded[size(params)];
TestProfilerInfo profiler_info0(target_thread_token, params[0],
module_cache(), &samples_recorded[0]);
TestProfilerInfo profiler_info1(target_thread_token, params[1],
module_cache(), &samples_recorded[1]);
profiler_info0.profiler.Start();
profiler_info1.profiler.Start();
// Wait for both to start accumulating samples. Using a WaitableEvent is
// possible but gets complicated later on because there's no way of
// knowing if 0 or 1 additional sample will be taken after Stop() and
// thus no way of knowing how many Wait() calls to make on it.
while (samples_recorded[0].Get() == 0 || samples_recorded[1].Get() == 0)
PlatformThread::Sleep(TimeDelta::FromMilliseconds(1));
// Ensure that the first sampler can be safely stopped while the second
// continues to run. The stopped first profiler will still have a
// RecordSampleTask pending that will do nothing when executed because
// the collection will have been removed by Stop().
profiler_info0.profiler.Stop();
profiler_info0.completed.Wait();
size_t count0 = samples_recorded[0].Get();
size_t count1 = samples_recorded[1].Get();
// Waiting for the second sampler to collect a couple samples ensures
// that the pending RecordSampleTask for the first has executed because
// tasks are always ordered by their next scheduled time.
while (samples_recorded[1].Get() < count1 + 2)
PlatformThread::Sleep(TimeDelta::FromMilliseconds(1));
// Ensure that the first profiler didn't do anything since it was
// stopped.
EXPECT_EQ(count0, samples_recorded[0].Get());
}));
}
// Checks that no sample are captured if the profiling is stopped during the
// initial delay.
PROFILER_TEST_F(StackSamplingProfilerTest, StopDuringInitialDelay) {
SamplingParams params;
params.initial_delay = TimeDelta::FromSeconds(60);
std::vector<std::vector<Frame>> samples =
CaptureSamples(params, TimeDelta::FromMilliseconds(0), module_cache());
EXPECT_TRUE(samples.empty());
}
// Checks that tasks can be stopped before completion and incomplete samples are
// captured.
PROFILER_TEST_F(StackSamplingProfilerTest, StopDuringInterSampleInterval) {
// Test delegate that counts samples.
class SampleRecordedEvent : public StackSamplerTestDelegate {
public:
SampleRecordedEvent()
: sample_recorded_(WaitableEvent::ResetPolicy::MANUAL,
WaitableEvent::InitialState::NOT_SIGNALED) {}
void OnPreStackWalk() override { sample_recorded_.Signal(); }
void WaitForSample() { sample_recorded_.Wait(); }
private:
WaitableEvent sample_recorded_;
};
WithTargetThread(BindLambdaForTesting(
[this](SamplingProfilerThreadToken target_thread_token) {
SamplingParams params;
params.sampling_interval = AVeryLongTimeDelta();
params.samples_per_profile = 2;
SampleRecordedEvent samples_recorded;
TestProfilerInfo profiler_info(target_thread_token, params,
module_cache(), &samples_recorded);
profiler_info.profiler.Start();
// Wait for profiler to start accumulating samples.
samples_recorded.WaitForSample();
// Ensure that it can stop safely.
profiler_info.profiler.Stop();
profiler_info.completed.Wait();
EXPECT_EQ(1u, profiler_info.profile.samples.size());
}));
}
// Checks that we can destroy the profiler while profiling.
PROFILER_TEST_F(StackSamplingProfilerTest, DestroyProfilerWhileProfiling) {
SamplingParams params;
params.sampling_interval = TimeDelta::FromMilliseconds(10);
Profile profile;
WithTargetThread(BindLambdaForTesting([&, this](SamplingProfilerThreadToken
target_thread_token) {
std::unique_ptr<StackSamplingProfiler> profiler;
auto profile_builder = std::make_unique<TestProfileBuilder>(
module_cache(),
BindLambdaForTesting([&profile](Profile result_profile) {
profile = std::move(result_profile);
}));
profiler.reset(new StackSamplingProfiler(target_thread_token, params,
std::move(profile_builder)));
profiler->Start();
profiler.reset();
// Wait longer than a sample interval to catch any use-after-free actions by
// the profiler thread.
PlatformThread::Sleep(TimeDelta::FromMilliseconds(50));
}));
}
// Checks that the different profilers may be run.
PROFILER_TEST_F(StackSamplingProfilerTest, CanRunMultipleProfilers) {
SamplingParams params;
params.sampling_interval = TimeDelta::FromMilliseconds(0);
params.samples_per_profile = 1;
std::vector<std::vector<Frame>> samples =
CaptureSamples(params, AVeryLongTimeDelta(), module_cache());
ASSERT_EQ(1u, samples.size());
samples = CaptureSamples(params, AVeryLongTimeDelta(), module_cache());
ASSERT_EQ(1u, samples.size());
}
// Checks that a sampler can be started while another is running.
PROFILER_TEST_F(StackSamplingProfilerTest, MultipleStart) {
WithTargetThread(BindLambdaForTesting(
[this](SamplingProfilerThreadToken target_thread_token) {
std::vector<SamplingParams> params(2);
params[0].initial_delay = AVeryLongTimeDelta();
params[0].samples_per_profile = 1;
params[1].sampling_interval = TimeDelta::FromMilliseconds(1);
params[1].samples_per_profile = 1;
std::vector<std::unique_ptr<TestProfilerInfo>> profiler_infos =
CreateProfilers(target_thread_token, params, module_cache());
profiler_infos[0]->profiler.Start();
profiler_infos[1]->profiler.Start();
profiler_infos[1]->completed.Wait();
EXPECT_EQ(1u, profiler_infos[1]->profile.samples.size());
}));
}
// Checks that the profile duration and the sampling interval are calculated
// correctly. Also checks that RecordMetadata() is invoked each time a sample
// is recorded.
PROFILER_TEST_F(StackSamplingProfilerTest, ProfileGeneralInfo) {
WithTargetThread(BindLambdaForTesting(
[this](SamplingProfilerThreadToken target_thread_token) {
SamplingParams params;
params.sampling_interval = TimeDelta::FromMilliseconds(1);
params.samples_per_profile = 3;
TestProfilerInfo profiler_info(target_thread_token, params,
module_cache());
profiler_info.profiler.Start();
profiler_info.completed.Wait();
EXPECT_EQ(3u, profiler_info.profile.samples.size());
// The profile duration should be greater than the total sampling
// intervals.
EXPECT_GT(profiler_info.profile.profile_duration,
profiler_info.profile.sampling_period * 3);
EXPECT_EQ(TimeDelta::FromMilliseconds(1),
profiler_info.profile.sampling_period);
// The number of invocations of RecordMetadata() should be equal to the
// number of samples recorded.
EXPECT_EQ(3, profiler_info.profile.metadata_count);
}));
}
// Checks that the sampling thread can shut down.
PROFILER_TEST_F(StackSamplingProfilerTest, SamplerIdleShutdown) {
SamplingParams params;
params.sampling_interval = TimeDelta::FromMilliseconds(0);
params.samples_per_profile = 1;
std::vector<std::vector<Frame>> samples =
CaptureSamples(params, AVeryLongTimeDelta(), module_cache());
ASSERT_EQ(1u, samples.size());
// Capture thread should still be running at this point.
ASSERT_TRUE(StackSamplingProfiler::TestPeer::IsSamplingThreadRunning());
// Initiate an "idle" shutdown and ensure it happens. Idle-shutdown was
// disabled by the test fixture so the test will fail due to a timeout if
// it does not exit.
StackSamplingProfiler::TestPeer::PerformSamplingThreadIdleShutdown(false);
// While the shutdown has been initiated, the actual exit of the thread still
// happens asynchronously. Watch until the thread actually exits. This test
// will time-out in the case of failure.
while (StackSamplingProfiler::TestPeer::IsSamplingThreadRunning())
PlatformThread::Sleep(TimeDelta::FromMilliseconds(1));
}
// Checks that additional requests will restart a stopped profiler.
PROFILER_TEST_F(StackSamplingProfilerTest,
WillRestartSamplerAfterIdleShutdown) {
SamplingParams params;
params.sampling_interval = TimeDelta::FromMilliseconds(0);
params.samples_per_profile = 1;
std::vector<std::vector<Frame>> samples =
CaptureSamples(params, AVeryLongTimeDelta(), module_cache());
ASSERT_EQ(1u, samples.size());
// Capture thread should still be running at this point.
ASSERT_TRUE(StackSamplingProfiler::TestPeer::IsSamplingThreadRunning());
// Post a ShutdownTask on the sampling thread which, when executed, will
// mark the thread as EXITING and begin shut down of the thread.
StackSamplingProfiler::TestPeer::PerformSamplingThreadIdleShutdown(false);
// Ensure another capture will start the sampling thread and run.
samples = CaptureSamples(params, AVeryLongTimeDelta(), module_cache());
ASSERT_EQ(1u, samples.size());
EXPECT_TRUE(StackSamplingProfiler::TestPeer::IsSamplingThreadRunning());
}
// Checks that it's safe to stop a task after it's completed and the sampling
// thread has shut-down for being idle.
PROFILER_TEST_F(StackSamplingProfilerTest, StopAfterIdleShutdown) {
WithTargetThread(BindLambdaForTesting(
[this](SamplingProfilerThreadToken target_thread_token) {
SamplingParams params;
params.sampling_interval = TimeDelta::FromMilliseconds(1);
params.samples_per_profile = 1;
TestProfilerInfo profiler_info(target_thread_token, params,
module_cache());
profiler_info.profiler.Start();
profiler_info.completed.Wait();
// Capture thread should still be running at this point.
ASSERT_TRUE(StackSamplingProfiler::TestPeer::IsSamplingThreadRunning());
// Perform an idle shutdown.
StackSamplingProfiler::TestPeer::PerformSamplingThreadIdleShutdown(
false);
// Stop should be safe though its impossible to know at this moment if
// the sampling thread has completely exited or will just "stop soon".
profiler_info.profiler.Stop();
}));
}
// Checks that profilers can run both before and after the sampling thread has
// started.
PROFILER_TEST_F(StackSamplingProfilerTest,
ProfileBeforeAndAfterSamplingThreadRunning) {
WithTargetThread(BindLambdaForTesting(
[this](SamplingProfilerThreadToken target_thread_token) {
std::vector<SamplingParams> params(2);
params[0].initial_delay = AVeryLongTimeDelta();
params[0].sampling_interval = TimeDelta::FromMilliseconds(1);
params[0].samples_per_profile = 1;
params[1].initial_delay = TimeDelta::FromMilliseconds(0);
params[1].sampling_interval = TimeDelta::FromMilliseconds(1);
params[1].samples_per_profile = 1;
std::vector<std::unique_ptr<TestProfilerInfo>> profiler_infos =
CreateProfilers(target_thread_token, params, module_cache());
// First profiler is started when there has never been a sampling
// thread.
EXPECT_FALSE(
StackSamplingProfiler::TestPeer::IsSamplingThreadRunning());
profiler_infos[0]->profiler.Start();
// Second profiler is started when sampling thread is already running.
EXPECT_TRUE(StackSamplingProfiler::TestPeer::IsSamplingThreadRunning());
profiler_infos[1]->profiler.Start();
// Only the second profiler should finish before test times out.
size_t completed_profiler = WaitForSamplingComplete(profiler_infos);
EXPECT_EQ(1U, completed_profiler);
}));
}
// Checks that an idle-shutdown task will abort if a new profiler starts
// between when it was posted and when it runs.
PROFILER_TEST_F(StackSamplingProfilerTest, IdleShutdownAbort) {
WithTargetThread(BindLambdaForTesting(
[this](SamplingProfilerThreadToken target_thread_token) {
SamplingParams params;
params.sampling_interval = TimeDelta::FromMilliseconds(1);
params.samples_per_profile = 1;
TestProfilerInfo profiler_info(target_thread_token, params,
module_cache());
profiler_info.profiler.Start();
profiler_info.completed.Wait();
EXPECT_EQ(1u, profiler_info.profile.samples.size());
// Perform an idle shutdown but simulate that a new capture is started
// before it can actually run.
StackSamplingProfiler::TestPeer::PerformSamplingThreadIdleShutdown(
true);
// Though the shutdown-task has been executed, any actual exit of the
// thread is asynchronous so there is no way to detect that *didn't*
// exit except to wait a reasonable amount of time and then check. Since
// the thread was just running ("perform" blocked until it was), it
// should finish almost immediately and without any waiting for tasks or
// events.
PlatformThread::Sleep(TimeDelta::FromMilliseconds(200));
EXPECT_TRUE(StackSamplingProfiler::TestPeer::IsSamplingThreadRunning());
// Ensure that it's still possible to run another sampler.
TestProfilerInfo another_info(target_thread_token, params,
module_cache());
another_info.profiler.Start();
another_info.completed.Wait();
EXPECT_EQ(1u, another_info.profile.samples.size());
}));
}
// Checks that synchronized multiple sampling requests execute in parallel.
PROFILER_TEST_F(StackSamplingProfilerTest, ConcurrentProfiling_InSync) {
WithTargetThread(BindLambdaForTesting(
[this](SamplingProfilerThreadToken target_thread_token) {
std::vector<SamplingParams> params(2);
// Providing an initial delay makes it more likely that both will be
// scheduled before either starts to run. Once started, samples will
// run ordered by their scheduled, interleaved times regardless of
// whatever interval the thread wakes up. Thus, total execution time
// will be 10ms (delay) + 10x1ms (sampling) + 1/2 timer minimum
// interval.
params[0].initial_delay = TimeDelta::FromMilliseconds(10);
params[0].sampling_interval = TimeDelta::FromMilliseconds(1);
params[0].samples_per_profile = 9;
params[1].initial_delay = TimeDelta::FromMilliseconds(11);
params[1].sampling_interval = TimeDelta::FromMilliseconds(1);
params[1].samples_per_profile = 8;
std::vector<std::unique_ptr<TestProfilerInfo>> profiler_infos =
CreateProfilers(target_thread_token, params, module_cache());
profiler_infos[0]->profiler.Start();
profiler_infos[1]->profiler.Start();
// Wait for one profiler to finish.
size_t completed_profiler = WaitForSamplingComplete(profiler_infos);
size_t other_profiler = 1 - completed_profiler;
// Wait for the other profiler to finish.
profiler_infos[other_profiler]->completed.Wait();
// Ensure each got the correct number of samples.
EXPECT_EQ(9u, profiler_infos[0]->profile.samples.size());
EXPECT_EQ(8u, profiler_infos[1]->profile.samples.size());
}));
}
// Checks that several mixed sampling requests execute in parallel.
PROFILER_TEST_F(StackSamplingProfilerTest, ConcurrentProfiling_Mixed) {
WithTargetThread(BindLambdaForTesting(
[this](SamplingProfilerThreadToken target_thread_token) {
std::vector<SamplingParams> params(3);
params[0].initial_delay = TimeDelta::FromMilliseconds(8);
params[0].sampling_interval = TimeDelta::FromMilliseconds(4);
params[0].samples_per_profile = 10;
params[1].initial_delay = TimeDelta::FromMilliseconds(9);
params[1].sampling_interval = TimeDelta::FromMilliseconds(3);
params[1].samples_per_profile = 10;
params[2].initial_delay = TimeDelta::FromMilliseconds(10);
params[2].sampling_interval = TimeDelta::FromMilliseconds(2);
params[2].samples_per_profile = 10;
std::vector<std::unique_ptr<TestProfilerInfo>> profiler_infos =
CreateProfilers(target_thread_token, params, module_cache());
for (auto& i : profiler_infos)
i->profiler.Start();
// Wait for one profiler to finish.
size_t completed_profiler = WaitForSamplingComplete(profiler_infos);
EXPECT_EQ(10u,
profiler_infos[completed_profiler]->profile.samples.size());
// Stop and destroy all profilers, always in the same order. Don't
// crash.
for (auto& i : profiler_infos)
i->profiler.Stop();
for (auto& i : profiler_infos)
i.reset();
}));
}
// Checks that different threads can be sampled in parallel.
PROFILER_TEST_F(StackSamplingProfilerTest, MultipleSampledThreads) {
UnwindScenario scenario1(BindRepeating(&CallWithPlainFunction));
UnwindScenario::SampleEvents events1;
TargetThread target_thread1(
BindLambdaForTesting([&]() { scenario1.Execute(&events1); }));
PlatformThreadHandle target_thread_handle1;
EXPECT_TRUE(
PlatformThread::Create(0, &target_thread1, &target_thread_handle1));
events1.ready_for_sample.Wait();
UnwindScenario scenario2(BindRepeating(&CallWithPlainFunction));
UnwindScenario::SampleEvents events2;
TargetThread target_thread2(
BindLambdaForTesting([&]() { scenario2.Execute(&events2); }));
PlatformThreadHandle target_thread_handle2;
EXPECT_TRUE(
PlatformThread::Create(0, &target_thread2, &target_thread_handle2));
events2.ready_for_sample.Wait();
// Providing an initial delay makes it more likely that both will be
// scheduled before either starts to run. Once started, samples will
// run ordered by their scheduled, interleaved times regardless of
// whatever interval the thread wakes up.
SamplingParams params1, params2;
params1.initial_delay = TimeDelta::FromMilliseconds(10);
params1.sampling_interval = TimeDelta::FromMilliseconds(1);
params1.samples_per_profile = 9;
params2.initial_delay = TimeDelta::FromMilliseconds(10);
params2.sampling_interval = TimeDelta::FromMilliseconds(1);
params2.samples_per_profile = 8;
Profile profile1, profile2;
WaitableEvent sampling_thread_completed1(
WaitableEvent::ResetPolicy::MANUAL,
WaitableEvent::InitialState::NOT_SIGNALED);
StackSamplingProfiler profiler1(
target_thread1.thread_token(), params1,
std::make_unique<TestProfileBuilder>(
module_cache(),
BindLambdaForTesting(
[&profile1, &sampling_thread_completed1](Profile result_profile) {
profile1 = std::move(result_profile);
sampling_thread_completed1.Signal();
})));
WaitableEvent sampling_thread_completed2(
WaitableEvent::ResetPolicy::MANUAL,
WaitableEvent::InitialState::NOT_SIGNALED);
StackSamplingProfiler profiler2(
target_thread2.thread_token(), params2,
std::make_unique<TestProfileBuilder>(
module_cache(),
BindLambdaForTesting(
[&profile2, &sampling_thread_completed2](Profile result_profile) {
profile2 = std::move(result_profile);
sampling_thread_completed2.Signal();
})));
// Finally the real work.
profiler1.Start();
profiler2.Start();
sampling_thread_completed1.Wait();
sampling_thread_completed2.Wait();
EXPECT_EQ(9u, profile1.samples.size());
EXPECT_EQ(8u, profile2.samples.size());
events1.sample_finished.Signal();
events2.sample_finished.Signal();
PlatformThread::Join(target_thread_handle1);
PlatformThread::Join(target_thread_handle2);
}
// A simple thread that runs a profiler on another thread.
class ProfilerThread : public SimpleThread {
public:
ProfilerThread(const std::string& name,
SamplingProfilerThreadToken thread_token,
const SamplingParams& params,
ModuleCache* module_cache)
: SimpleThread(name, Options()),
run_(WaitableEvent::ResetPolicy::MANUAL,
WaitableEvent::InitialState::NOT_SIGNALED),
completed_(WaitableEvent::ResetPolicy::MANUAL,
WaitableEvent::InitialState::NOT_SIGNALED),
profiler_(thread_token,
params,
std::make_unique<TestProfileBuilder>(
module_cache,
BindLambdaForTesting([this](Profile result_profile) {
profile_ = std::move(result_profile);
completed_.Signal();
}))) {}
void Run() override {
run_.Wait();
profiler_.Start();
}
void Go() { run_.Signal(); }
void Wait() { completed_.Wait(); }
Profile& profile() { return profile_; }
private:
WaitableEvent run_;
Profile profile_;
WaitableEvent completed_;
StackSamplingProfiler profiler_;
};
// Checks that different threads can run samplers in parallel.
PROFILER_TEST_F(StackSamplingProfilerTest, MultipleProfilerThreads) {
WithTargetThread(
BindLambdaForTesting([](SamplingProfilerThreadToken target_thread_token) {
// Providing an initial delay makes it more likely that both will be
// scheduled before either starts to run. Once started, samples will
// run ordered by their scheduled, interleaved times regardless of
// whatever interval the thread wakes up.
SamplingParams params1, params2;
params1.initial_delay = TimeDelta::FromMilliseconds(10);
params1.sampling_interval = TimeDelta::FromMilliseconds(1);
params1.samples_per_profile = 9;
params2.initial_delay = TimeDelta::FromMilliseconds(10);
params2.sampling_interval = TimeDelta::FromMilliseconds(1);
params2.samples_per_profile = 8;
// Start the profiler threads and give them a moment to get going.
ModuleCache module_cache1;
ProfilerThread profiler_thread1("profiler1", target_thread_token,
params1, &module_cache1);
ModuleCache module_cache2;
ProfilerThread profiler_thread2("profiler2", target_thread_token,
params2, &module_cache2);
profiler_thread1.Start();
profiler_thread2.Start();
PlatformThread::Sleep(TimeDelta::FromMilliseconds(10));
// This will (approximately) synchronize the two threads.
profiler_thread1.Go();
profiler_thread2.Go();
// Wait for them both to finish and validate collection.
profiler_thread1.Wait();
profiler_thread2.Wait();
EXPECT_EQ(9u, profiler_thread1.profile().samples.size());
EXPECT_EQ(8u, profiler_thread2.profile().samples.size());
profiler_thread1.Join();
profiler_thread2.Join();
}));
}
PROFILER_TEST_F(StackSamplingProfilerTest, AddAuxUnwinder_BeforeStart) {
SamplingParams params;
params.sampling_interval = TimeDelta::FromMilliseconds(0);
params.samples_per_profile = 1;
UnwindScenario scenario(BindRepeating(&CallWithPlainFunction));
Profile profile;
WithTargetThread(
&scenario,
BindLambdaForTesting(
[&](SamplingProfilerThreadToken target_thread_token) {
WaitableEvent sampling_thread_completed(
WaitableEvent::ResetPolicy::MANUAL,
WaitableEvent::InitialState::NOT_SIGNALED);
StackSamplingProfiler profiler(
target_thread_token, params,
std::make_unique<TestProfileBuilder>(
module_cache(),
BindLambdaForTesting([&profile, &sampling_thread_completed](
Profile result_profile) {
profile = std::move(result_profile);
sampling_thread_completed.Signal();
})));
profiler.AddAuxUnwinder(
std::make_unique<TestAuxUnwinder>(Frame(23, nullptr)));
profiler.Start();
sampling_thread_completed.Wait();
}));
// The sample should have one frame from the context values and one from the
// TestAuxUnwinder.
ASSERT_EQ(1u, profile.samples.size());
const std::vector<Frame>& frames = profile.samples[0];
ASSERT_EQ(2u, frames.size());
EXPECT_EQ(23u, frames[1].instruction_pointer);
EXPECT_EQ(nullptr, frames[1].module);
}
PROFILER_TEST_F(StackSamplingProfilerTest, AddAuxUnwinder_AfterStart) {
SamplingParams params;
params.sampling_interval = TimeDelta::FromMilliseconds(0);
params.samples_per_profile = 1;
UnwindScenario scenario(BindRepeating(&CallWithPlainFunction));
Profile profile;
WithTargetThread(
&scenario,
BindLambdaForTesting(
[&](SamplingProfilerThreadToken target_thread_token) {
WaitableEvent sampling_thread_completed(
WaitableEvent::ResetPolicy::MANUAL,
WaitableEvent::InitialState::NOT_SIGNALED);
StackSamplingProfiler profiler(
target_thread_token, params,
std::make_unique<TestProfileBuilder>(
module_cache(),
BindLambdaForTesting([&profile, &sampling_thread_completed](
Profile result_profile) {
profile = std::move(result_profile);
sampling_thread_completed.Signal();
})));
profiler.Start();
profiler.AddAuxUnwinder(
std::make_unique<TestAuxUnwinder>(Frame(23, nullptr)));
sampling_thread_completed.Wait();
}));
// The sample should have one frame from the context values and one from the
// TestAuxUnwinder.
ASSERT_EQ(1u, profile.samples.size());
const std::vector<Frame>& frames = profile.samples[0];
ASSERT_EQ(2u, frames.size());
EXPECT_EQ(23u, frames[1].instruction_pointer);
EXPECT_EQ(nullptr, frames[1].module);
}
PROFILER_TEST_F(StackSamplingProfilerTest, AddAuxUnwinder_AfterStop) {
SamplingParams params;
params.sampling_interval = TimeDelta::FromMilliseconds(0);
params.samples_per_profile = 1;
UnwindScenario scenario(BindRepeating(&CallWithPlainFunction));
Profile profile;
WithTargetThread(
&scenario,
BindLambdaForTesting(
[&](SamplingProfilerThreadToken target_thread_token) {
WaitableEvent sampling_thread_completed(
WaitableEvent::ResetPolicy::MANUAL,
WaitableEvent::InitialState::NOT_SIGNALED);
StackSamplingProfiler profiler(
target_thread_token, params,
std::make_unique<TestProfileBuilder>(
module_cache(),
BindLambdaForTesting([&profile, &sampling_thread_completed](
Profile result_profile) {
profile = std::move(result_profile);
sampling_thread_completed.Signal();
})));
profiler.Start();
profiler.Stop();
profiler.AddAuxUnwinder(
std::make_unique<TestAuxUnwinder>(Frame(23, nullptr)));
sampling_thread_completed.Wait();
}));
// The AuxUnwinder should be accepted without error. It will have no effect
// since the collection has stopped.
}
} // namespace base