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// Copyright (c) 2012 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 <stdint.h>
#include <map>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <utility>
#include <vector>
#include "base/allocator/features.h"
#include "base/atomicops.h"
#include "base/base_export.h"
#include "base/containers/hash_tables.h"
#include "base/debug/debugging_flags.h"
#include "base/debug/thread_heap_usage_tracker.h"
#include "base/gtest_prod_util.h"
#include "base/lazy_instance.h"
#include "base/location.h"
#include "base/macros.h"
#include "base/process/process_handle.h"
#include "base/profiler/tracked_time.h"
#include "base/synchronization/lock.h"
#include "base/threading/thread_local_storage.h"
namespace base {
struct TrackingInfo;
// TrackedObjects provides a database of stats about objects (generally Tasks)
// that are tracked. Tracking means their birth, death, duration, birth thread,
// death thread, and birth place are recorded. This data is carefully spread
// across a series of objects so that the counts and times can be rapidly
// updated without (usually) having to lock the data, and hence there is usually
// very little contention caused by the tracking. The data can be viewed via
// the about:profiler URL, with a variety of sorting and filtering choices.
// These classes serve as the basis of a profiler of sorts for the Tasks system.
// As a result, design decisions were made to maximize speed, by minimizing
// recurring allocation/deallocation, lock contention and data copying. In the
// "stable" state, which is reached relatively quickly, there is no separate
// marginal allocation cost associated with construction or destruction of
// tracked objects, no locks are generally employed, and probably the largest
// computational cost is associated with obtaining start and stop times for
// instances as they are created and destroyed.
// The following describes the life cycle of tracking an instance.
// First off, when the instance is created, the FROM_HERE macro is expanded
// to specify the birth place (file, line, function) where the instance was
// created. That data is used to create a transient Location instance
// encapsulating the above triple of information. The strings (like __FILE__)
// are passed around by reference, with the assumption that they are static, and
// will never go away. This ensures that the strings can be dealt with as atoms
// with great efficiency (i.e., copying of strings is never needed, and
// comparisons for equality can be based on pointer comparisons).
// Next, a Births instance is constructed or found. A Births instance records
// (in a base class BirthOnThread) references to the static data provided in a
// Location instance, as well as a pointer to the ThreadData bound to the thread
// on which the birth takes place (see discussion on ThreadData below). There is
// at most one Births instance for each Location / ThreadData pair. The derived
// Births class contains slots for recording statistics about all instances born
// at the same location. Statistics currently include only the count of
// instances constructed.
// Since the base class BirthOnThread contains only constant data, it can be
// freely accessed by any thread at any time. The statistics must be handled
// more carefully; they are updated exclusively by the single thread to which
// the ThreadData is bound at a given time.
// For Tasks, having now either constructed or found the Births instance
// described above, a pointer to the Births instance is then recorded into the
// PendingTask structure. This fact alone is very useful in debugging, when
// there is a question of where an instance came from. In addition, the birth
// time is also recorded and used to later evaluate the lifetime duration of the
// whole Task. As a result of the above embedding, we can find out a Task's
// location of birth, and name of birth thread, without using any locks, as all
// that data is constant across the life of the process.
// The above work *could* also be done for any other object as well by calling
// TallyABirthIfActive() and TallyRunOnNamedThreadIfTracking() as appropriate.
// The upper bound for the amount of memory used in the above data structures is
// the product of the number of ThreadData instances and the number of
// Locations. Fortunately, Locations are often created on a single thread and
// the memory utilization is actually fairly restrained.
// Lastly, when an instance is deleted, the final tallies of statistics are
// carefully accumulated. That tallying writes into slots (members) in a
// collection of DeathData instances. For each Births / death ThreadData pair,
// there is a DeathData instance to record the additional death count, as well
// as to accumulate the run-time and queue-time durations for the instance as it
// is destroyed (dies). Since a ThreadData is bound to at most one thread at a
// time, there is no need to lock such DeathData instances. (i.e., these
// accumulated stats in a DeathData instance are exclusively updated by the
// singular owning thread).
// With the above life cycle description complete, the major remaining detail is
// explaining how existing Births and DeathData instances are found to avoid
// redundant allocations.
// A ThreadData instance maintains maps of Births and DeathData instances. The
// Births map is indexed by Location and the DeathData map is indexed by
// Births*. As noted earlier, we can compare Locations very efficiently as we
// consider the underlying data (file, function, line) to be atoms, and hence
// pointer comparison is used rather than (slow) string comparisons.
// The first time that a thread calls ThreadData::InitializeThreadContext() or
// ThreadData::Get(), a ThreadData instance is bound to it and stored in TLS. If
// a ThreadData bound to a terminated thread with the same sanitized name (i.e.
// name without trailing digits) as the current thread is available, it is
// reused. Otherwise, a new ThreadData instance is instantiated. Since a
// ThreadData is bound to at most one thread at a time, there is no need to
// acquire a lock to access its maps. Over time, a ThreadData may be bound to
// different threads that share the same sanitized name.
// We maintain a list of all ThreadData instances for the current process. Each
// ThreadData instance has a pointer to the next one. A static member of
// ThreadData provides a pointer to the first item on this global list, and
// access via that all_thread_data_list_head_ item requires the use of the
// list_lock_.
// When new ThreadData instances are added to the global list, they are pre-
// pended, which ensures that any prior acquisition of the list is valid (i.e.,
// the holder can iterate over it without fear of it changing, or the necessity
// of using an additional lock. Iterations are actually pretty rare (used
// primarily for cleanup, or snapshotting data for display), so this lock has
// very little global performance impact.
// The above description tries to define the high performance (run time)
// portions of these classes. After gathering statistics, calls instigated
// by visiting about:profiler will assemble and aggregate data for display. The
// following data structures are used for producing such displays. They are
// not performance critical, and their only major constraint is that they should
// be able to run concurrently with ongoing augmentation of the birth and death
// data.
// This header also exports collection of classes that provide "snapshotted"
// representations of the core tracked_objects:: classes. These snapshotted
// representations are designed for safe transmission of the tracked_objects::
// data across process boundaries. Each consists of:
// (1) a default constructor, to support the IPC serialization macros,
// (2) a constructor that extracts data from the type being snapshotted, and
// (3) the snapshotted data.
// For a given birth location, information about births is spread across data
// structures that are asynchronously changing on various threads. For
// serialization and display purposes, we need to construct TaskSnapshot
// instances for each combination of birth thread, death thread, and location,
// along with the count of such lifetimes. We gather such data into a
// TaskSnapshot instances, so that such instances can be sorted and
// aggregated (and remain frozen during our processing).
// Profiling consists of phases. The concrete phase in the sequence of phases
// is identified by its 0-based index.
// The ProcessDataPhaseSnapshot struct is a serialized representation of the
// list of ThreadData objects for a process for a concrete profiling phase. It
// holds a set of TaskSnapshots. The statistics in a snapshot are gathered
// asynhcronously relative to their ongoing updates.
// It is possible, though highly unlikely, that stats could be incorrectly
// recorded by this process (all data is held in 32 bit ints, but we are not
// atomically collecting all data, so we could have count that does not, for
// example, match with the number of durations we accumulated). The advantage
// to having fast (non-atomic) updates of the data outweighs the minimal risk of
// a singular corrupt statistic snapshot (only the snapshot could be corrupt,
// not the underlying and ongoing statistic). In contrast, pointer data that
// is accessed during snapshotting is completely invariant, and hence is
// perfectly acquired (i.e., no potential corruption, and no risk of a bad
// memory reference).
// TODO(jar): We can implement a Snapshot system that *tries* to grab the
// snapshots on the source threads *when* they have SingleThreadTaskRunners
// available (worker threads don't have SingleThreadTaskRunners, and hence
// gathering from them will continue to be asynchronous). We had an
// implementation of this in the past, but the difficulty is dealing with
// threads being terminated. We can *try* to post a task to threads that have a
// SingleThreadTaskRunner and check if that succeeds (will fail if the thread
// has been terminated). This *might* be valuable when we are collecting data
// for upload via UMA (where correctness of data may be more significant than
// for a single screen of about:profiler).
// TODO(jar): We need to store DataCollections, and provide facilities for
// taking the difference between two gathered DataCollections. For now, we're
// just adding a hack that Reset()s to zero all counts and stats. This is also
// done in a slightly thread-unsafe fashion, as the resetting is done
// asynchronously relative to ongoing updates (but all data is 32 bit in size).
// For basic profiling, this will work "most of the time," and should be
// sufficient... but storing away DataCollections is the "right way" to do this.
// We'll accomplish this via JavaScript storage of snapshots, and then we'll
// remove the Reset() methods. We may also need a short-term-max value in
// DeathData that is reset (as synchronously as possible) during each snapshot.
// This will facilitate displaying a max value for each snapshot period.
namespace tracked_objects {
// For a specific thread, and a specific birth place, the collection of all
// death info (with tallies for each death thread, to prevent access conflicts).
class ThreadData;
class BASE_EXPORT BirthOnThread {
BirthOnThread(const Location& location, const ThreadData& current);
const Location& location() const { return location_; }
const ThreadData* birth_thread() const { return birth_thread_; }
// File/lineno of birth. This defines the essence of the task, as the context
// of the birth (construction) often tell what the item is for. This field
// is const, and hence safe to access from any thread.
const Location location_;
// The thread that records births into this object. Only this thread is
// allowed to update birth_count_ (which changes over time).
const ThreadData* const birth_thread_;
// A "snapshotted" representation of the BirthOnThread class.
struct BASE_EXPORT BirthOnThreadSnapshot {
explicit BirthOnThreadSnapshot(const BirthOnThread& birth);
LocationSnapshot location;
std::string sanitized_thread_name;
// A class for accumulating counts of births (without bothering with a map<>).
class BASE_EXPORT Births: public BirthOnThread {
Births(const Location& location, const ThreadData& current);
int birth_count() const;
// When we have a birth we update the count for this birthplace.
void RecordBirth();
// The number of births on this thread for our location_.
int birth_count_;
class DeathData;
// A "snapshotted" representation of the DeathData class.
struct BASE_EXPORT DeathDataSnapshot {
// Constructs the snapshot from individual values.
// The alternative would be taking a DeathData parameter, but this would
// create a loop since DeathData indirectly refers DeathDataSnapshot. Passing
// a wrapper structure as a param or using an empty constructor for
// snapshotting DeathData would be less efficient.
DeathDataSnapshot(int count,
int32_t run_duration_sum,
int32_t run_duration_max,
int32_t run_duration_sample,
int32_t queue_duration_sum,
int32_t queue_duration_max,
int32_t queue_duration_sample,
int32_t alloc_ops,
int32_t free_ops,
int64_t allocated_bytes,
int64_t freed_bytes,
int64_t alloc_overhead_bytes,
int32_t max_allocated_bytes);
DeathDataSnapshot(const DeathData& death_data);
DeathDataSnapshot(const DeathDataSnapshot& other);
// Calculates and returns the delta between this snapshot and an earlier
// snapshot of the same task |older|.
DeathDataSnapshot Delta(const DeathDataSnapshot& older) const;
int count;
int32_t run_duration_sum;
int32_t run_duration_max;
int32_t run_duration_sample;
int32_t queue_duration_sum;
int32_t queue_duration_max;
int32_t queue_duration_sample;
int32_t alloc_ops;
int32_t free_ops;
int64_t allocated_bytes;
int64_t freed_bytes;
int64_t alloc_overhead_bytes;
int32_t max_allocated_bytes;
// A "snapshotted" representation of the DeathData for a particular profiling
// phase. Used as an element of the list of phase snapshots owned by DeathData.
struct DeathDataPhaseSnapshot {
DeathDataPhaseSnapshot(int profiling_phase,
const DeathData& death_data,
const DeathDataPhaseSnapshot* prev);
// Profiling phase at which completion this snapshot was taken.
int profiling_phase;
// Death data snapshot.
DeathDataSnapshot death_data;
// Pointer to a snapshot from the previous phase.
const DeathDataPhaseSnapshot* prev;
// Information about deaths of a task on a given thread, called "death thread".
// Access to members of this class is never protected by a lock. The fields
// are accessed in such a way that corruptions resulting from race conditions
// are not significant, and don't accumulate as a result of multiple accesses.
// All invocations of DeathData::OnProfilingPhaseCompleted and
// ThreadData::SnapshotMaps (which takes DeathData snapshot) in a given process
// must be called from the same thread. It doesn't matter what thread it is, but
// it's important the same thread is used as a snapshot thread during the whole
// process lifetime. All fields except sample_probability_count_ can be
// snapshotted.
class BASE_EXPORT DeathData {
DeathData(const DeathData& other);
// Update stats for a task destruction (death) that had a Run() time of
// |duration|, and has had a queueing delay of |queue_duration|.
void RecordDurations(const int32_t queue_duration,
const int32_t run_duration,
const uint32_t random_number);
// Update stats for a task destruction that performed |alloc_ops|
// allocations, |free_ops| frees, allocated |allocated_bytes| bytes, freed
// |freed_bytes|, where an estimated |alloc_overhead_bytes| went to heap
// overhead, and where at most |max_allocated_bytes| were outstanding at any
// one time.
// Note that |alloc_overhead_bytes|/|alloc_ops| yields the average estimated
// heap overhead of allocations in the task, and |allocated_bytes|/|alloc_ops|
// yields the average size of allocation.
// Note also that |allocated_bytes|-|freed_bytes| yields the net heap memory
// usage of the task, which can be negative.
void RecordAllocations(const uint32_t alloc_ops,
const uint32_t free_ops,
const uint32_t allocated_bytes,
const uint32_t freed_bytes,
const uint32_t alloc_overhead_bytes,
const uint32_t max_allocated_bytes);
// Metrics and past snapshots accessors, used only for serialization and in
// tests.
int count() const { return base::subtle::NoBarrier_Load(&count_); }
int32_t run_duration_sum() const {
return base::subtle::NoBarrier_Load(&run_duration_sum_);
int32_t run_duration_max() const {
return base::subtle::NoBarrier_Load(&run_duration_max_);
int32_t run_duration_sample() const {
return base::subtle::NoBarrier_Load(&run_duration_sample_);
int32_t queue_duration_sum() const {
return base::subtle::NoBarrier_Load(&queue_duration_sum_);
int32_t queue_duration_max() const {
return base::subtle::NoBarrier_Load(&queue_duration_max_);
int32_t queue_duration_sample() const {
return base::subtle::NoBarrier_Load(&queue_duration_sample_);
int32_t alloc_ops() const {
return base::subtle::NoBarrier_Load(&alloc_ops_);
int32_t free_ops() const { return base::subtle::NoBarrier_Load(&free_ops_); }
int64_t allocated_bytes() const {
return ConsistentCumulativeByteCountRead(&allocated_bytes_);
int64_t freed_bytes() const {
return ConsistentCumulativeByteCountRead(&freed_bytes_);
int64_t alloc_overhead_bytes() const {
return ConsistentCumulativeByteCountRead(&alloc_overhead_bytes_);
int64_t max_allocated_bytes() const {
return base::subtle::NoBarrier_Load(&max_allocated_bytes_);
const DeathDataPhaseSnapshot* last_phase_snapshot() const {
return last_phase_snapshot_;
// Called when the current profiling phase, identified by |profiling_phase|,
// ends.
// Must be called only on the snapshot thread.
void OnProfilingPhaseCompleted(int profiling_phase);
#if defined(ARCH_CPU_64_BITS)
using CumulativeByteCount = base::subtle::Atomic64;
struct CumulativeByteCount {
base::subtle::Atomic32 hi_word;
base::subtle::Atomic32 lo_word;
// Reads a cumulative byte counter consistently.
int64_t ConsistentCumulativeByteCountRead(
const CumulativeByteCount* count) const;
// Reads the value of a cumulative byte count, only returns consistent
// results on the owning thread.
static int64_t UnsafeCumulativeByteCountRead(
const CumulativeByteCount* count);
// A saturating addition operation for member variables. This elides the
// use of atomic-primitive reads for members that are only written on the
// owning thread.
static void SaturatingMemberAdd(const uint32_t addend,
base::subtle::Atomic32* sum);
// A saturating addition operation for byte count variables.
// On 32 bit machines, this may only be called while |byte_update_counter_|
// is odd - e.g. locked.
void SaturatingByteCountMemberAdd(const uint32_t addend,
CumulativeByteCount* sum);
// Members are ordered from most regularly read and updated, to least
// frequently used. This might help a bit with cache lines.
// Number of runs seen (divisor for calculating averages).
// Can be incremented only on the death thread.
base::subtle::Atomic32 count_;
// Count used in determining probability of selecting exec/queue times from a
// recorded death as samples.
// Gets incremented only on the death thread, but can be set to 0 by
// OnProfilingPhaseCompleted() on the snapshot thread.
base::subtle::Atomic32 sample_probability_count_;
// Basic tallies, used to compute averages. Can be incremented only on the
// death thread.
base::subtle::Atomic32 run_duration_sum_;
base::subtle::Atomic32 queue_duration_sum_;
// Max values, used by local visualization routines. These are often read,
// but rarely updated. The max values get assigned only on the death thread,
// but these fields can be set to 0 by OnProfilingPhaseCompleted() on the
// snapshot thread.
base::subtle::Atomic32 run_duration_max_;
base::subtle::Atomic32 queue_duration_max_;
// The cumulative number of allocation and free operations.
base::subtle::Atomic32 alloc_ops_;
base::subtle::Atomic32 free_ops_;
#if !defined(ARCH_CPU_64_BITS)
// On 32 bit systems this is used to achieve consistent reads for cumulative
// byte counts. This is odd while updates are in progress, and even while
// quiescent. If this has the same value before and after reading the
// cumulative counts, the read is consistent.
base::subtle::Atomic32 byte_update_counter_;
// The number of bytes allocated by the task.
CumulativeByteCount allocated_bytes_;
// The number of bytes freed by the task.
CumulativeByteCount freed_bytes_;
// The cumulative number of overhead bytes. Where available this yields an
// estimate of the heap overhead for allocations.
CumulativeByteCount alloc_overhead_bytes_;
// The high-watermark for the number of outstanding heap allocated bytes.
base::subtle::Atomic32 max_allocated_bytes_;
// Samples, used by crowd sourcing gatherers. These are almost never read,
// and rarely updated. They can be modified only on the death thread.
base::subtle::Atomic32 run_duration_sample_;
base::subtle::Atomic32 queue_duration_sample_;
// Snapshot of this death data made at the last profiling phase completion, if
// any. DeathData owns the whole list starting with this pointer.
// Can be accessed only on the snapshot thread.
const DeathDataPhaseSnapshot* last_phase_snapshot_;
// A temporary collection of data that can be sorted and summarized. It is
// gathered (carefully) from many threads. Instances are held in arrays and
// processed, filtered, and rendered.
// The source of this data was collected on many threads, and is asynchronously
// changing. The data in this instance is not asynchronously changing.
struct BASE_EXPORT TaskSnapshot {
TaskSnapshot(const BirthOnThreadSnapshot& birth,
const DeathDataSnapshot& death_data,
const std::string& death_sanitized_thread_name);
BirthOnThreadSnapshot birth;
// Delta between death data for a thread for a certain profiling phase and the
// snapshot for the pervious phase, if any. Otherwise, just a snapshot.
DeathDataSnapshot death_data;
std::string death_sanitized_thread_name;
// For each thread, we have a ThreadData that stores all tracking info generated
// on this thread. This prevents the need for locking as data accumulates.
// We use ThreadLocalStorage to quickly identfy the current ThreadData context.
// We also have a linked list of ThreadData instances, and that list is used to
// harvest data from all existing instances.
struct ProcessDataPhaseSnapshot;
struct ProcessDataSnapshot;
class BASE_EXPORT TaskStopwatch;
// Map from profiling phase number to the process-wide snapshotted
// representation of the list of ThreadData objects that died during the given
// phase.
typedef std::map<int, ProcessDataPhaseSnapshot> PhasedProcessDataSnapshotMap;
class BASE_EXPORT ThreadData {
// Current allowable states of the tracking system. The states can vary
// between ACTIVE and DEACTIVATED, but can never go back to UNINITIALIZED.
enum Status {
UNINITIALIZED, // Pristine, link-time state before running.
DORMANT_DURING_TESTS, // Only used during testing.
DEACTIVATED, // No longer recording profiling.
PROFILING_ACTIVE, // Recording profiles.
typedef std::unordered_map<Location, Births*, Location::Hash> BirthMap;
typedef std::map<const Births*, DeathData> DeathMap;
// Initialize the current thread context with a new instance of ThreadData.
// This is used by all threads that have names, and should be explicitly
// set *before* any births on the threads have taken place.
static void InitializeThreadContext(const std::string& thread_name);
// Using Thread Local Store, find the current instance for collecting data.
// If an instance does not exist, construct one (and remember it for use on
// this thread.
// This may return NULL if the system is disabled for any reason.
static ThreadData* Get();
// Fills |process_data_snapshot| with phased snapshots of all profiling
// phases, including the current one, identified by |current_profiling_phase|.
// |current_profiling_phase| is necessary because a child process can start
// after several phase-changing events, so it needs to receive the current
// phase number from the browser process to fill the correct entry for the
// current phase in the |process_data_snapshot| map.
static void Snapshot(int current_profiling_phase,
ProcessDataSnapshot* process_data_snapshot);
// Called when the current profiling phase, identified by |profiling_phase|,
// ends.
// |profiling_phase| is necessary because a child process can start after
// several phase-changing events, so it needs to receive the phase number from
// the browser process to fill the correct entry in the
// completed_phases_snapshots_ map.
static void OnProfilingPhaseCompleted(int profiling_phase);
// Finds (or creates) a place to count births from the given location in this
// thread, and increment that tally.
// TallyABirthIfActive will returns NULL if the birth cannot be tallied.
static Births* TallyABirthIfActive(const Location& location);
// Records the end of a timed run of an object. The |completed_task| contains
// a pointer to a Births, the time_posted, and a delayed_start_time if any.
// The |start_of_run| indicates when we started to perform the run of the
// task. The delayed_start_time is non-null for tasks that were posted as
// delayed tasks, and it indicates when the task should have run (i.e., when
// it should have posted out of the timer queue, and into the work queue.
// The |end_of_run| was just obtained by a call to Now() (just after the task
// finished). It is provided as an argument to help with testing.
static void TallyRunOnNamedThreadIfTracking(
const base::TrackingInfo& completed_task,
const TaskStopwatch& stopwatch);
// Record the end of a timed run of an object. The |birth| is the record for
// the instance, the |time_posted| records that instant, which is presumed to
// be when the task was posted into a queue to run on a worker thread.
// The |start_of_run| is when the worker thread started to perform the run of
// the task.
// The |end_of_run| was just obtained by a call to Now() (just after the task
// finished).
static void TallyRunOnWorkerThreadIfTracking(const Births* births,
const TrackedTime& time_posted,
const TaskStopwatch& stopwatch);
// Record the end of execution in region, generally corresponding to a scope
// being exited.
static void TallyRunInAScopedRegionIfTracking(const Births* births,
const TaskStopwatch& stopwatch);
const std::string& sanitized_thread_name() const {
return sanitized_thread_name_;
// Initializes all statics if needed (this initialization call should be made
// while we are single threaded).
static void EnsureTlsInitialization();
// Sets internal status_.
// If |status| is false, then status_ is set to DEACTIVATED.
// If |status| is true, then status_ is set to PROFILING_ACTIVE.
static void InitializeAndSetTrackingStatus(Status status);
static Status status();
// Indicate if any sort of profiling is being done (i.e., we are more than
static bool TrackingStatus();
// Enables profiler timing.
static void EnableProfilerTiming();
// Provide a time function that does nothing (runs fast) when we don't have
// the profiler enabled. It will generally be optimized away when it is
// ifdef'ed to be small enough (allowing the profiler to be "compiled out" of
// the code).
static TrackedTime Now();
// This function can be called at process termination to validate that thread
// cleanup routines have been called for at least some number of named
// threads.
static void EnsureCleanupWasCalled(int major_threads_shutdown_count);
friend class TaskStopwatch;
// Allow only tests to call ShutdownSingleThreadedCleanup. We NEVER call it
// in production code.
// TODO(jar): Make this a friend in DEBUG only, so that the optimizer has a
// better change of optimizing (inlining? etc.) private methods (knowing that
// there will be no need for an external entry point).
friend class TrackedObjectsTest;
FRIEND_TEST_ALL_PREFIXES(TrackedObjectsTest, MinimalStartupShutdown);
FRIEND_TEST_ALL_PREFIXES(TrackedObjectsTest, TinyStartupShutdown);
// Type for an alternate timer function (testing only).
typedef unsigned int NowFunction();
typedef std::map<const BirthOnThread*, int> BirthCountMap;
typedef std::vector<std::pair<const Births*, DeathDataPhaseSnapshot>>
explicit ThreadData(const std::string& sanitized_thread_name);
// Push this instance to the head of all_thread_data_list_head_, linking it to
// the previous head. This is performed after each construction, and leaves
// the instance permanently on that list.
void PushToHeadOfList();
// (Thread safe) Get start of list of all ThreadData instances using the lock.
static ThreadData* first();
// Iterate through the null terminated list of ThreadData instances.
ThreadData* next() const;
// In this thread's data, record a new birth.
Births* TallyABirth(const Location& location);
// Find a place to record a death on this thread.
void TallyADeath(const Births& births,
int32_t queue_duration,
const TaskStopwatch& stopwatch);
// Snapshots (under a lock) the profiled data for the tasks for this thread
// and writes all of the executed tasks' data -- i.e. the data for all
// profiling phases (including the current one: |current_profiling_phase|) for
// the tasks with with entries in the death_map_ -- into |phased_snapshots|.
// Also updates the |birth_counts| tally for each task to keep track of the
// number of living instances of the task -- that is, each task maps to the
// number of births for the task that have not yet been balanced by a death.
void SnapshotExecutedTasks(int current_profiling_phase,
PhasedProcessDataSnapshotMap* phased_snapshots,
BirthCountMap* birth_counts);
// Using our lock, make a copy of the specified maps. This call may be made
// on non-local threads, which necessitate the use of the lock to prevent
// the map(s) from being reallocated while they are copied.
void SnapshotMaps(int profiling_phase,
BirthMap* birth_map,
DeathsSnapshot* deaths);
// Called for this thread when the current profiling phase, identified by
// |profiling_phase|, ends.
void OnProfilingPhaseCompletedOnThread(int profiling_phase);
// This method is called by the TLS system when a thread terminates.
// The argument may be NULL if this thread has never tracked a birth or death.
static void OnThreadTermination(void* thread_data);
// This method should be called when a worker thread terminates, so that we
// can save all the thread data into a cache of reusable ThreadData instances.
void OnThreadTerminationCleanup();
// Cleans up data structures, and returns statics to near pristine (mostly
// uninitialized) state. If there is any chance that other threads are still
// using the data structures, then the |leak| argument should be passed in as
// true, and the data structures (birth maps, death maps, ThreadData
// insntances, etc.) will be leaked and not deleted. If you have joined all
// threads since the time that InitializeAndSetTrackingStatus() was called,
// then you can pass in a |leak| value of false, and this function will
// delete recursively all data structures, starting with the list of
// ThreadData instances.
static void ShutdownSingleThreadedCleanup(bool leak);
// Returns a ThreadData instance for a thread whose sanitized name is
// |sanitized_thread_name|. The returned instance may have been extracted from
// the list of retired ThreadData instances or newly allocated.
static ThreadData* GetRetiredOrCreateThreadData(
const std::string& sanitized_thread_name);
// When non-null, this specifies an external function that supplies monotone
// increasing time functcion.
static NowFunction* now_function_for_testing_;
// We use thread local store to identify which ThreadData to interact with.
static base::ThreadLocalStorage::StaticSlot tls_index_;
// Linked list of ThreadData instances that were associated with threads that
// have been terminated and that have not been associated with a new thread
// since then. This is only accessed while |list_lock_| is held.
static ThreadData* first_retired_thread_data_;
// Link to the most recently created instance (starts a null terminated list).
// The list is traversed by about:profiler when it needs to snapshot data.
// This is only accessed while list_lock_ is held.
static ThreadData* all_thread_data_list_head_;
// The number of times TLS has called us back to cleanup a ThreadData
// instance. This is only accessed while list_lock_ is held.
static int cleanup_count_;
// Incarnation sequence number, indicating how many times (during unittests)
// we've either transitioned out of UNINITIALIZED, or into that state. This
// value is only accessed while the list_lock_ is held.
static int incarnation_counter_;
// Protection for access to all_thread_data_list_head_, and to
// unregistered_thread_data_pool_. This lock is leaked at shutdown.
// The lock is very infrequently used, so we can afford to just make a lazy
// instance and be safe.
static base::LazyInstance<base::Lock>::Leaky list_lock_;
// We set status_ to SHUTDOWN when we shut down the tracking service.
static base::subtle::Atomic32 status_;
// Link to next instance (null terminated list). Used to globally track all
// registered instances (corresponds to all registered threads where we keep
// data). Only modified in the constructor.
ThreadData* next_;
// Pointer to another retired ThreadData instance. This value is nullptr if
// this is associated with an active thread.
ThreadData* next_retired_thread_data_;
// The name of the thread that is being recorded, with all trailing digits
// replaced with a single "*" character.
const std::string sanitized_thread_name_;
// A map used on each thread to keep track of Births on this thread.
// This map should only be accessed on the thread it was constructed on.
// When a snapshot is needed, this structure can be locked in place for the
// duration of the snapshotting activity.
BirthMap birth_map_;
// Similar to birth_map_, this records informations about death of tracked
// instances (i.e., when a tracked instance was destroyed on this thread).
// It is locked before changing, and hence other threads may access it by
// locking before reading it.
DeathMap death_map_;
// Lock to protect *some* access to BirthMap and DeathMap. The maps are
// regularly read and written on this thread, but may only be read from other
// threads. To support this, we acquire this lock if we are writing from this
// thread, or reading from another thread. For reading from this thread we
// don't need a lock, as there is no potential for a conflict since the
// writing is only done from this thread.
mutable base::Lock map_lock_;
// A random number that we used to select decide which sample to keep as a
// representative sample in each DeathData instance. We can't start off with
// much randomness (because we can't call RandInt() on all our threads), so
// we stir in more and more as we go.
uint32_t random_number_;
// Record of what the incarnation_counter_ was when this instance was created.
// If the incarnation_counter_ has changed, then we avoid pushing into the
// pool (this is only critical in tests which go through multiple
// incarnations).
int incarnation_count_for_pool_;
// Most recently started (i.e. most nested) stopwatch on the current thread,
// if it exists; NULL otherwise.
TaskStopwatch* current_stopwatch_;
// Stopwatch to measure task run time or simply create a time interval that will
// be subtracted from the current most nested task's run time. Stopwatches
// coordinate with the stopwatches in which they are nested to avoid
// double-counting nested tasks run times.
class BASE_EXPORT TaskStopwatch {
// Starts the stopwatch.
// Starts stopwatch.
void Start();
// Stops stopwatch.
void Stop();
// Returns the start time.
TrackedTime StartTime() const;
// Task's duration is calculated as the wallclock duration between starting
// and stopping this stopwatch, minus the wallclock durations of any other
// instances that are immediately nested in this one, started and stopped on
// this thread during that period.
int32_t RunDurationMs() const;
const base::debug::ThreadHeapUsageTracker& heap_usage() const {
return heap_usage_;
bool heap_tracking_enabled() const { return heap_tracking_enabled_; }
// Returns tracking info for the current thread.
ThreadData* GetThreadData() const;
// Time when the stopwatch was started.
TrackedTime start_time_;
base::debug::ThreadHeapUsageTracker heap_usage_;
bool heap_tracking_enabled_;
// Wallclock duration of the task.
int32_t wallclock_duration_ms_;
// Tracking info for the current thread.
ThreadData* current_thread_data_;
// Sum of wallclock durations of all stopwatches that were directly nested in
// this one.
int32_t excluded_duration_ms_;
// Stopwatch which was running on our thread when this stopwatch was started.
// That preexisting stopwatch must be adjusted to the exclude the wallclock
// duration of this stopwatch.
TaskStopwatch* parent_;
// State of the stopwatch. Stopwatch is first constructed in a created state
// state, then is optionally started/stopped, then destructed.
enum { CREATED, RUNNING, STOPPED } state_;
// Currently running stopwatch that is directly nested in this one, if such
// stopwatch exists. NULL otherwise.
TaskStopwatch* child_;
// A snapshotted representation of the list of ThreadData objects for a process,
// for a single profiling phase.
struct BASE_EXPORT ProcessDataPhaseSnapshot {
ProcessDataPhaseSnapshot(const ProcessDataPhaseSnapshot& other);
std::vector<TaskSnapshot> tasks;
// A snapshotted representation of the list of ThreadData objects for a process,
// for all profiling phases, including the current one.
struct BASE_EXPORT ProcessDataSnapshot {
ProcessDataSnapshot(const ProcessDataSnapshot& other);
PhasedProcessDataSnapshotMap phased_snapshots;
base::ProcessId process_id;
} // namespace tracked_objects