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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 <map>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#include "base/base_export.h"
#include "base/gtest_prod_util.h"
#include "base/lazy_instance.h"
#include "base/location.h"
#include "base/profiler/alternate_timer.h"
#include "base/profiler/tracked_time.h"
#include "base/synchronization/lock.h"
#include "base/threading/thread_local_storage.h"
#include "base/tracking_info.h"
// 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 lifecycle 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 created for use ONLY on the thread where this
// instance was created. That Births instance records (in a base class
// BirthOnThread) references to the static data provided in a Location instance,
// as well as a pointer specifying the thread on which the birth takes place.
// Hence there is at most one Births instance for each Location on each thread.
// 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 (i.e., only the statistic needs to
// be handled carefully, and stats are updated exclusively on the birth thread).
// 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 in MessageLoop. 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 thread of birth, 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 amount of memory used in the above data structures depends on how many
// threads there are, and how many Locations of construction there are.
// Fortunately, we don't use memory that is the product of those two counts, but
// rather we only need one Births instance for each thread that constructs an
// instance at a Location. In many cases, instances are only created on one
// thread, so 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 birth place Location that is
// destroyed on a thread, there is a DeathData instance to record the additional
// death count, as well as accumulate the run-time and queue-time durations for
// the instance as it is destroyed (dies). By maintaining a single place to
// aggregate this running sum *only* for the given thread, we avoid the 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 lifecycle description complete, the major remaining detail is
// explaining how each thread maintains a list of DeathData instances, and of
// Births instances, and is able to avoid additional (redundant/unnecessary)
// allocations.
// Each thread maintains a list of data items specific to that thread in a
// ThreadData instance (for that specific thread only). The two critical items
// are lists of DeathData and Births instances. These lists are maintained in
// STL maps, which are indexed by Location. 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.
// To provide a mechanism for iterating over all "known threads," which means
// threads that have recorded a birth or a death, we create a singly linked list
// of ThreadData instances. Each such instance maintains 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 is added to the global list, it is 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
// primarilly 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).
// The ProcessDataSnapshot struct is a serialized representation of the list
// of ThreadData objects for a process. It holds a set of TaskSnapshots
// and tracks parent/child relationships for the executed tasks. 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 constrast, 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 MessageLoops available
// (worker threads don't have message loops generally, 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 message loops being terminated.
// We can *try* to spam the available threads via some message loop proxy to
// achieve this feat, and it *might* be valuable when we are colecting data for
// upload via UMA (where correctness of data may be more significant than for a
// single screen of about:profiler).
// TODO(jar): We should support (optionally) the recording of parent-child
// relationships for tasks. This should be done by detecting what tasks are
// Born during the running of a parent task. The resulting data can be used by
// a smarter profiler to aggregate the cost of a series of child tasks into
// the ancestor task. It can also be used to illuminate what child or parent is
// related to each task.
// 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 slighly 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 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();
// When a birthplace is changed (updated), we need to decrement the counter
// for the old instance.
void ForgetBirth();
// Hack to quickly reset all counts to zero.
void Clear();
// The number of births on this thread for our location_.
int birth_count_;
// Basic info summarizing multiple destructions of a tracked object with a
// single birthplace (fixed Location). Used both on specific threads, and also
// in snapshots when integrating assembled data.
class BASE_EXPORT DeathData {
// Default initializer.
// When deaths have not yet taken place, and we gather data from all the
// threads, we create DeathData stats that tally the number of births without
// a corresponding death.
explicit DeathData(int count);
// Update stats for a task destruction (death) that had a Run() time of
// |duration|, and has had a queueing delay of |queue_duration|.
void RecordDeath(const int32 queue_duration,
const int32 run_duration,
int random_number);
// Metrics accessors, used only for serialization and in tests.
int count() const;
int32 run_duration_sum() const;
int32 run_duration_max() const;
int32 run_duration_sample() const;
int32 queue_duration_sum() const;
int32 queue_duration_max() const;
int32 queue_duration_sample() const;
// Reset the max values to zero.
void ResetMax();
// Reset all tallies to zero. This is used as a hack on realtime data.
void Clear();
// 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).
int count_;
// Basic tallies, used to compute averages.
int32 run_duration_sum_;
int32 queue_duration_sum_;
// Max values, used by local visualization routines. These are often read,
// but rarely updated.
int32 run_duration_max_;
int32 queue_duration_max_;
// Samples, used by crowd sourcing gatherers. These are almost never read,
// and rarely updated.
int32 run_duration_sample_;
int32 queue_duration_sample_;
// A "snapshotted" representation of the DeathData class.
struct BASE_EXPORT DeathDataSnapshot {
explicit DeathDataSnapshot(const DeathData& death_data);
int count;
int32 run_duration_sum;
int32 run_duration_max;
int32 run_duration_sample;
int32 queue_duration_sum;
int32 queue_duration_max;
int32 queue_duration_sample;
// 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 BirthOnThread& birth,
const DeathData& death_data,
const std::string& death_thread_name);
BirthOnThreadSnapshot birth;
DeathDataSnapshot death_data;
std::string death_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 ProcessDataSnapshot;
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 profling.
PROFILING_ACTIVE, // Recording profiles (no parent-child links).
PROFILING_CHILDREN_ACTIVE, // Fully active, recording parent-child links.
typedef std::map<Location, Births*> BirthMap;
typedef std::map<const Births*, DeathData> DeathMap;
typedef std::pair<const Births*, const Births*> ParentChildPair;
typedef std::set<ParentChildPair> ParentChildSet;
typedef std::stack<const Births*> ParentStack;
// 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. It is generally
// only used by the message loop, which has a well defined thread name.
static void InitializeThreadContext(const std::string& suggested_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| with all the recursive results in our process.
// During the scavenging, if |reset_max| is true, then the DeathData instances
// max-values are reset to zero during this scan.
static void Snapshot(bool reset_max, ProcessDataSnapshot* process_data);
// 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 TrackedTime& start_of_run,
const TrackedTime& end_of_run);
// 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* birth,
const TrackedTime& time_posted,
const TrackedTime& start_of_run,
const TrackedTime& end_of_run);
// Record the end of execution in region, generally corresponding to a scope
// being exited.
static void TallyRunInAScopedRegionIfTracking(
const Births* birth,
const TrackedTime& start_of_run,
const TrackedTime& end_of_run);
const std::string& thread_name() const { return thread_name_; }
// Hack: asynchronously clear all birth counts and death tallies data values
// in all ThreadData instances. The numerical (zeroing) part is done without
// use of a locks or atomics exchanges, and may (for int64 values) produce
// bogus counts VERY rarely.
static void ResetAllThreadData();
// Initializes all statics if needed (this initialization call should be made
// while we are single threaded). Returns false if unable to initialize.
static bool Initialize();
// Sets internal status_.
// If |status| is false, then status_ is set to DEACTIVATED.
// If |status| is true, then status_ is set to, PROFILING_ACTIVE, or
// If tracking is not compiled in, this function will return false.
// If parent-child tracking is not compiled in, then an attempt to set the
// status to PROFILING_CHILDREN_ACTIVE will only result in a status of
// PROFILING_ACTIVE (i.e., it can't be set to a higher level than what is
// compiled into the binary, and parent-child tracking at the
// PROFILING_CHILDREN_ACTIVE level might not be compiled in).
static bool InitializeAndSetTrackingStatus(Status status);
static Status status();
// Indicate if any sort of profiling is being done (i.e., we are more than
static bool TrackingStatus();
// For testing only, indicate if the status of parent-child tracking is turned
// on. This is currently a compiled option, atop TrackingStatus().
static bool TrackingParentChildStatus();
// Special versions of Now() for getting times at start and end of a tracked
// run. They are super fast when tracking is disabled, and have some internal
// side effects when we are tracking, so that we can deduce the amount of time
// accumulated outside of execution of tracked runs.
// The task that will be tracked is passed in as |parent| so that parent-child
// relationships can be (optionally) calculated.
static TrackedTime NowForStartOfRun(const Births* parent);
static TrackedTime NowForEndOfRun();
// 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();
// Use the function |now| to provide current times, instead of calling the
// TrackedTime::Now() function. Since this alternate function is being used,
// the other time arguments (used for calculating queueing delay) will be
// ignored.
static void SetAlternateTimeSource(NowFunction* 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);
// 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);
FRIEND_TEST_ALL_PREFIXES(TrackedObjectsTest, ParentChildTest);
friend class TrackedTimeTest;
typedef std::map<const BirthOnThread*, int> BirthCountMap;
// Worker thread construction creates a name since there is none.
explicit ThreadData(int thread_number);
// Message loop based construction should provide a name.
explicit ThreadData(const std::string& suggested_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& birth, int32 queue_duration, int32 duration);
// Snapshot (under a lock) the profiled data for the tasks in each ThreadData
// instance. Also updates the |birth_counts| tally for each task to keep
// track of the number of living instances of the task. If |reset_max| is
// true, then the max values in each DeathData instance are reset during the
// scan.
static void SnapshotAllExecutedTasks(bool reset_max,
ProcessDataSnapshot* process_data,
BirthCountMap* birth_counts);
// 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 the tasks
// with with entries in the death_map_ -- into |process_data|. 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. If
// |reset_max| is true, then the max values in each DeathData instance are
// reset during the scan.
void SnapshotExecutedTasks(bool reset_max,
ProcessDataSnapshot* process_data,
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 reallocaed while they are copied. If |reset_max| is
// true, then, just after we copy the DeathMap, we will set the max values to
// zero in the active DeathMap (not the snapshot).
void SnapshotMaps(bool reset_max,
BirthMap* birth_map,
DeathMap* death_map,
ParentChildSet* parent_child_set);
// Using our lock to protect the iteration, Clear all birth and death data.
void Reset();
// 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);
// When non-null, this specifies an external function that supplies monotone
// increasing time functcion.
static NowFunction* now_function_;
// We use thread local store to identify which ThreadData to interact with.
static base::ThreadLocalStorage::StaticSlot tls_index_;
// List of ThreadData instances for use with worker threads. When a worker
// thread is done (terminated), we push it onto this llist. When a new worker
// thread is created, we first try to re-use a ThreadData instance from the
// list, and if none are available, construct a new one.
// This is only accessed while list_lock_ is held.
static ThreadData* first_retired_worker_;
// 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 next available worker thread number. This should only be accessed when
// the list_lock_ is held.
static int worker_thread_data_creation_count_;
// 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 Status status_;
// Link to next instance (null terminated list). Used to globally track all
// registered instances (corresponds to all registered threads where we keep
// data).
ThreadData* next_;
// Pointer to another ThreadData instance for a Worker-Thread that has been
// retired (its thread was terminated). This value is non-NULL only for a
// retired ThreadData associated with a Worker-Thread.
ThreadData* next_retired_worker_;
// The name of the thread that is being recorded. If this thread has no
// message_loop, then this is a worker thread, with a sequence number postfix.
std::string thread_name_;
// Indicate if this is a worker thread, and the ThreadData contexts should be
// stored in the unregistered_thread_data_pool_ when not in use.
// Value is zero when it is not a worker thread. Value is a positive integer
// corresponding to the created thread name if it is a worker thread.
int worker_thread_number_;
// 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_;
// A set of parents that created children tasks on this thread. Each pair
// corresponds to potentially non-local Births (location and thread), and a
// local Births (that took place on this thread).
ParentChildSet parent_child_set_;
// 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_;
// The stack of parents that are currently being profiled. This includes only
// tasks that have started a timer recently via NowForStartOfRun(), but not
// yet concluded with a NowForEndOfRun(). Usually this stack is one deep, but
// if a scoped region is profiled, or <sigh> a task runs a nested-message
// loop, then the stack can grow larger. Note that we don't try to deduct
// time in nested porfiles, as our current timer is based on wall-clock time,
// and not CPU time (and we're hopeful that nested timing won't be a
// significant additional cost).
ParentStack parent_stack_;
// 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.
int32 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_;
// A snapshotted representation of a (parent, child) task pair, for tracking
// hierarchical profiles.
struct BASE_EXPORT ParentChildPairSnapshot {
explicit ParentChildPairSnapshot(
const ThreadData::ParentChildPair& parent_child);
BirthOnThreadSnapshot parent;
BirthOnThreadSnapshot child;
// A snapshotted representation of the list of ThreadData objects for a process.
struct BASE_EXPORT ProcessDataSnapshot {
std::vector<TaskSnapshot> tasks;
std::vector<ParentChildPairSnapshot> descendants;
int process_id;
} // namespace tracked_objects