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// 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 <memory>
#include <vector>
#include "base/base_export.h"
#include "base/macros.h"
#include "base/optional.h"
#include "base/profiler/profile_builder.h"
#include "base/profiler/sampling_profiler_thread_token.h"
#include "base/synchronization/waitable_event.h"
#include "base/threading/platform_thread.h"
#include "base/time/time.h"
namespace base {
class Unwinder;
class StackSampler;
class StackSamplerTestDelegate;
// StackSamplingProfiler periodically stops a thread to sample its stack, for
// the purpose of collecting information about which code paths are
// executing. This information is used in aggregate by UMA to identify hot
// and/or janky code paths.
// Sample StackSamplingProfiler usage:
// // Create and customize params as desired.
// base::StackStackSamplingProfiler::SamplingParams params;
// // To process the profiles, use a custom ProfileBuilder subclass:
// class SubProfileBuilder : public base::ProfileBuilder {...}
// // Then create the profiler:
// base::StackSamplingProfiler profiler(base::PlatformThread::CurrentId(),
// params, std::make_unique<SubProfileBuilder>(...));
// // On Android the |sampler| is not implemented in base. So, client can pass
// // in |sampler| to use while profiling.
// base::StackSamplingProfiler profiler(base::PlatformThread::CurrentId(),
// params, std::make_unique<SubProfileBuilder>(...), <optional> sampler);
// // Then start the profiling.
// profiler.Start();
// // ... work being done on the target thread here ...
// // Optionally stop collection before complete per params.
// profiler.Stop();
// The default SamplingParams causes stacks to be recorded in a single profile
// at a 10Hz interval for a total of 30 seconds. All of these parameters may be
// altered as desired.
// When a call stack profile is complete, or the profiler is stopped,
// ProfileBuilder's OnProfileCompleted function is called from a thread created
// by the profiler.
class BASE_EXPORT StackSamplingProfiler {
// Represents parameters that configure the sampling.
struct BASE_EXPORT SamplingParams {
// Time to delay before first samples are taken.
TimeDelta initial_delay = TimeDelta::FromMilliseconds(0);
// Number of samples to record per profile.
int samples_per_profile = 300;
// Interval between samples during a sampling profile. This is the desired
// duration from the start of one sample to the start of the next sample.
TimeDelta sampling_interval = TimeDelta::FromMilliseconds(100);
// When true, keeps the average sampling interval = |sampling_interval|,
// irrespective of how long each sample takes. If a sample takes too long,
// keeping the interval constant will lock out the sampled thread. When
// false, sample is created with an interval of |sampling_interval|,
// excluding the time taken by a sample. The metrics collected will not be
// accurate, since sampling could take arbitrary amount of time, but makes
// sure that the sampled thread gets at least the interval amount of time to
// run between samples.
bool keep_consistent_sampling_interval = true;
// Creates a profiler for the specified thread. An optional |test_delegate|
// can be supplied by tests.
// The caller must ensure that this object gets destroyed before the thread
// exits.
StackSamplingProfiler(SamplingProfilerThreadToken thread_token,
const SamplingParams& params,
std::unique_ptr<ProfileBuilder> profile_builder,
StackSamplerTestDelegate* test_delegate = nullptr);
// Same as above function, with custom |sampler| implementation. The sampler
// on Android is not implemented in base.
StackSamplingProfiler(SamplingProfilerThreadToken thread_token,
const SamplingParams& params,
std::unique_ptr<ProfileBuilder> profile_builder,
std::unique_ptr<StackSampler> sampler,
StackSamplerTestDelegate* test_delegate = nullptr);
// Stops any profiling currently taking place before destroying the profiler.
// This will block until profile_builder_'s OnProfileCompleted function has
// executed if profiling has started but not already finished.
// Initializes the profiler and starts sampling. Might block on a
// WaitableEvent if this StackSamplingProfiler was previously started and
// recently stopped, while the previous profiling phase winds down.
void Start();
// Stops the profiler and any ongoing sampling. This method will return
// immediately with the profile_builder_'s OnProfileCompleted function being
// run asynchronously. At most one more stack sample will be taken after this
// method returns. Calling this function is optional; if not invoked profiling
// terminates when all the profiling samples specified in the SamplingParams
// are completed or the profiler object is destroyed, whichever occurs first.
void Stop();
// Adds an auxiliary unwinder to handle additional, non-native-code unwind
// scenarios.
void AddAuxUnwinder(std::unique_ptr<Unwinder> unwinder);
// Test peer class. These functions are purely for internal testing of
// StackSamplingProfiler; DO NOT USE within tests outside of this directory.
// The functions are static because they interact with the sampling thread, a
// singleton used by all StackSamplingProfiler objects. The functions can
// only be called by the same thread that started the sampling.
class BASE_EXPORT TestPeer {
// Resets the internal state to that of a fresh start. This is necessary
// so that tests don't inherit state from previous tests.
static void Reset();
// Returns whether the sampling thread is currently running or not.
static bool IsSamplingThreadRunning();
// Disables inherent idle-shutdown behavior.
static void DisableIdleShutdown();
// Initiates an idle shutdown task, as though the idle timer had expired,
// causing the thread to exit. There is no "idle" check so this must be
// called only when all sampling tasks have completed. This blocks until
// the task has been executed, though the actual stopping of the thread
// still happens asynchronously. Watch IsSamplingThreadRunning() to know
// when the thread has exited. If |simulate_intervening_start| is true then
// this method will make it appear to the shutdown task that a new profiler
// was started between when the idle-shutdown was initiated and when it
// runs.
static void PerformSamplingThreadIdleShutdown(
bool simulate_intervening_start);
// SamplingThread is a separate thread used to suspend and sample stacks from
// the target thread.
class SamplingThread;
// Friend the global function from so that it can call into
// the function below.
friend void ApplyMetadataToPastSamplesImpl(TimeTicks period_start,
TimeTicks period_end,
int64_t name_hash,
Optional<int64_t> key,
int64_t value);
// Apply metadata to already recorded samples. See the
// ApplyMetadataToPastSamples() docs in sample_metadata.h.
static void ApplyMetadataToPastSamples(TimeTicks period_start,
TimeTicks period_end,
int64_t name_hash,
Optional<int64_t> key,
int64_t value);
// The thread whose stack will be sampled.
SamplingProfilerThreadToken thread_token_;
const SamplingParams params_;
// Receives the sampling data and builds a profile. The ownership of this
// object will be transferred to the sampling thread when thread sampling
// starts.
std::unique_ptr<ProfileBuilder> profile_builder_;
// Stack sampler which stops the thread and collects stack frames. The
// ownership of this object will be transferred to the sampling thread when
// thread sampling starts.
std::unique_ptr<StackSampler> sampler_;
// If an AuxUnwinder is added before Start() it will be saved here until it
// can be passed to the sampling thread when thread sampling starts.
std::unique_ptr<Unwinder> pending_aux_unwinder_;
// This starts "signaled", is reset when sampling begins, and is signaled
// when that sampling is complete and the profile_builder_'s
// OnProfileCompleted function has executed.
WaitableEvent profiling_inactive_;
// An ID uniquely identifying this profiler to the sampling thread. This
// will be an internal "null" value when no collection has been started.
int profiler_id_;
// Stored until it can be passed to the StackSampler created in Start().
StackSamplerTestDelegate* const test_delegate_;
} // namespace base