Track thread activities in order to diagnose hangs.

base/debug/activity_tracker.h

Index: base/debug/activity_tracker.h
diff --git a/base/debug/activity_tracker.h b/base/debug/activity_tracker.h
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+// Copyright 2016 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.
+//
+// Activity tracking provides a low-overhead method of collecting information
+// about the state of the application for analysis both while it is running
+// and after it has terminated. Its primary purpose is to help locate reasons
+// the browser becomes unresponsive by providing insight into what all the
+// various threads and processes are (or were) doing.
+
+#ifndef BASE_METRICS_ACTIVITY_TRACKER_H_
+#define BASE_METRICS_ACTIVITY_TRACKER_H_
+
+#include <atomic>
+#include <memory>
+
+#include "base/base_export.h"
+#include "base/location.h"
+#include "base/metrics/persistent_memory_allocator.h"
+#include "base/threading/thread_checker.h"
+#include "base/threading/thread_local_storage.h"
+
+namespace base {
+
+struct PendingTask;
+
+class FilePath;
+class Lock;
+class MemoryMappedFile;
+class PlatformThreadHandle;
+class Process;
+class WaitableEvent;
+
+namespace debug {
+
+#if !defined(OS_NACL)  // NACL doesn't support any kind of file access in build.
+// Enables the global activity tracker according to a field trial setting,
+// using the specified |file| (without extension) for storing information
+// from this run.
+BASE_EXPORT void SetupGlobalActivityTrackerFieldTrial(const FilePath& file);
+#endif  // !defined(OS_NACL)
+
+
+// This class manages tracking a stack of activities for a single thread in
+// a persistent manner. In order to support an operational mode where another

[Sigurður Ásgeirsson, 2016/06/14 15:28:13]

it implements a bounded-size stack in a fixed-size allocation. 

Maybe talk the data format, e.g. header followed stack elements?

[bcwhite, 2016/06/14 19:48:46]

Done.

+// thread is analyzing this data in real-time, atomic operations are used
+// where necessary to guarantee a consistent view from the outside.
+//
+// This class is not generally used directly but instead managed by the
+// GlobalActivityTracker instance and updated using Scoped*Activity local
+// objects.
+class BASE_EXPORT ThreadActivityTracker {
+ public:
+  // The type of an activity on the stack. Activities are broken into
+  // categories with the category ID taking the top 4 bits and the lower
+  // bits representing an action within that category. This combination
+  // makes it easy to "switch" based on the type during analysis.
+  enum ActivityType : uint8_t {
+    // This "null" constant is used to indicate "do not change" in calls.
+    ACT_NULL = 0,
+
+    // Task activities involve callbacks posted to a thread or thread-pool
+    // using the PostTask() method or any of its friends.
+    ACT_TASK = 1 << 4,
+    ACT_TASK_RUN = ACT_TASK,
+
+    // Lock activities involve the acquisition of "mutex" locks.
+    ACT_LOCK = 2 << 4,
+    ACT_LOCK_ACQUIRE = ACT_LOCK,
+    ACT_LOCK_RELEASE,
+
+    // Event activities involve operations on a WaitableEvent.
+    ACT_EVENT = 3 << 4,
+    ACT_EVENT_WAIT = ACT_EVENT,
+    ACT_EVENT_SIGNAL,
+
+    // Thread activities involve the life management of threads.
+    ACT_THREAD = 4 << 4,
+    ACT_THREAD_START = ACT_THREAD,
+    ACT_THREAD_JOIN,
+
+    // Process activities involve the life management of processes.
+    ACT_PROCESS = 5 << 4,
+    ACT_PROCESS_START = ACT_PROCESS,
+    ACT_PROCESS_WAIT,
+
+    // Generic activities are user defined and can be anything.
+    ACT_GENERIC = 15 << 4,
+
+    // These constants can be used to separate the category and action from
+    // a combined activity type.
+    ACT_CATEGORY_MASK = 0xF << 4,
+    ACT_ACTION_MASK = 0xF
+  };
+
+  // The data associated with an activity is dependent upon the activity type.
+  // This union defines all of the various fields. All fields must be explicitly
+  // sized types to ensure no interoperability problems between 32-bit and
+  // 64-bit systems.
+  union ActivityData {
+    // Generic activities don't have any defined structure.
+    struct {
+      uint32_t id;    // An arbitrary identifier used for association.
+      uint32_t info;  // An arbitrary value used for information purposes.
+    } generic;
+    struct {
+      uint64_t sequence_id;  // The sequience identifier of the posted task.
+    } task;
+    struct {
+      uint64_t lock_address;  // The memory address of the lock object.
+    } lock;
+    struct {
+      uint64_t event_address;  // The memory address of the event object.
+    } event;
+    struct {
+      int64_t thread_id;  // A unique identifier for a thread within a process.
+    } thread;
+    struct {
+      int64_t process_id;  // A unique identifier for a process.
+    } process;
+
+    // These methods create an ActivityData object from the appropriate
+    // parameters. Objects of this type should always be created this way to
+    // ensure that no fields remain unpopulated should the set of recorded
+    // fields change. They're defined inline where practical because they
+    // reduce to loading a small local structure with a few values, roughly
+    // the same as loading all those values into parameters.
+
+    static ActivityData ForGeneric(uint32_t id, uint32_t info) {
+      ActivityData data;
+      data.generic.id = id;
+      data.generic.info = info;
+      return data;
+    }
+
+    static ActivityData ForTask(uint64_t sequence) {
+      ActivityData data;
+      data.task.sequence_id = sequence;
+      return data;
+    }
+
+    static ActivityData ForLock(const void* lock) {
+      ActivityData data;
+      data.lock.lock_address = reinterpret_cast<uintptr_t>(lock);
+      return data;
+    }
+
+    static ActivityData ForEvent(const void* event) {
+      ActivityData data;
+      data.event.event_address = reinterpret_cast<uintptr_t>(event);
+      return data;
+    }
+
+    static ActivityData ForThread(const PlatformThreadHandle& handle);
+    static ActivityData ForThread(const int64_t id) {
+      ActivityData data;
+      data.thread.thread_id = id;
+      return data;
+    }
+
+    static ActivityData ForProcess(const int64_t id) {
+      ActivityData data;
+      data.process.process_id = id;
+      return data;
+    }
+  };
+
+  // This structure is the full contents recorded for every activity pushed
+  // onto the stack. The |activity_type| indicates what is actually stored in
+  // the |data| field. All fields must be explicitly sized types to ensure no
+  // interoperability problems between 32-bit and 64-bit systems.
+  struct Activity {
+    int64_t time_internal;
+    uint64_t source_address;
+    uint8_t activity_type;
+    ActivityData data;
+  };
+
+  // This structure holds a copy of all the internal data at the moment the
+  // "snapshot" operation is done. It is disconnected from the live tracker
+  // so that continued operation of the thread will not cause changes here.
+  struct BASE_EXPORT ActivitySnapshot {
+    // The name of the thread.
+    std::string thread_name;
+
+    // The process and thread IDs.
+    int64_t process_id = 0;
+    int64_t thread_id = 0;
+
+    // The current set of activities that are underway for this thread. It is
+    // limited in its maximum size with later entries being left off.
+    std::vector<Activity> activity_stack;
+
+    // The current total depth of the activity stack, including those later
+    // entries not recorded in the |activity_stack| vector.
+    uint32_t activity_stack_depth = 0;
+
+    // Explicit constructor/destructor are needed because of complex types
+    // with non-trivial default constructors and destructors.
+    ActivitySnapshot();
+    ~ActivitySnapshot();
+  };
+
+  // This is the base class for having the compiler manage an activity on the
+  // tracker's stack. It does nothing but call methods on the passed |tracker|
+  // if it is not null, making it safe (and cheap) to create these objects
+  // even if activity tracking is not enabled.
+  class BASE_EXPORT ScopedActivity {
+   public:
+    ScopedActivity(ThreadActivityTracker* tracker,
+                   const void* source,
+                   ActivityType type,
+                   const ActivityData& data)
+        : tracker_(tracker), source_(source) {
+      if (tracker_)
+        tracker_->PushActivity(source, type, data);
+    }
+
+    ~ScopedActivity() {
+      if (tracker_)
+        tracker_->PopActivity(source_);
+    }
+
+    void ChangeTypeAndData(ActivityType type, const ActivityData& data) {
+      if (tracker_)
+        tracker_->ChangeActivity(source_, type, data);
+    }
+
+   private:
+    // The thread tracker to which this object reports. It can be null if
+    // activity tracking is not (yet) enabled.
+    ThreadActivityTracker* const tracker_;
+
+    // An identifier for the source at which this object was created. It is
+    // held and passed so the tracker can do run-time checks to ensure that
+    // somehow objects don't get popped in an order different than they
+    // were pushed.
+    const void* const source_;
+  };
+
+  // A ThreadActivityTracker runs on top of memory that is managed externally.
+  // It must be large enough for the internal header and a few Activity
+  // blocks. See SizeForStackDepth().
+  ThreadActivityTracker(void* base, size_t size);
+  virtual ~ThreadActivityTracker();
+
+  // Indicates that an activity has started from a given |source| address in
+  // the code, though it can be null if the creator's address is not known.
+  // The |type| and |data| describe the activity.
+  void PushActivity(const void* source,
+                    ActivityType type,
+                    const ActivityData& data);
+
+  // Changes the activity |type| and |data| of the top-most entry on the stack.
+  // This is useful if the information has changed and it is desireable to
+  // track that change without creating a new stack entry. If the type is
+  // ACT_NULL or the data is kNullActivityData then that value will remain
+  // unchanged. The type, if changed, must remain in the same category.
+  void ChangeActivity(const void* source,
+                      ActivityType type,
+                      const ActivityData& data);
+
+  // Indicates that an activity started from |source| has completed.
+  void PopActivity(const void* source);
+
+  // Returns whether the current data is valid or not. It is not valid if
+  // corruption has been detected in the header or other data structures.
+  bool IsValid() const;
+
+  // Gets a copy of the tracker contents for analysis. Returns false if a
+  // snapshot was not possible, perhaps because the data is not valid; the
+  // contents of |output_snapshot| are undefined in that case.
+  bool Snapshot(ActivitySnapshot* output_snapshot) const;

[Sigurður Ásgeirsson, 2016/06/14 15:53:26]

this is IMHO out of place in the public interface of this class, as this way the
same interface contains both mutation and snapshotting. It's IMHO kind of weird
to instantiate the mutator on some other process/thread's data for snapshotting?
If it were up to me, I'd push the data management to a *Base class, then use two
subclasses to provide the Mutation and Snapshot functionality.

[bcwhite, 2016/06/14 19:48:46]

You can request a snapshot from the same instance object that is doing the
tracking.  That seems normal enough.

Creating a second tracker on the same memory in order to request a snapshot from
within a different process is a bit odd but I don't think it's worth any added
complexity to separate it out.

+
+  // Calculates the memory size required for a given stack depth, including
+  // the internal header structure for the stack.
+  static size_t SizeForStackDepth(int stack_depth);
+
+  // A "null" activity-data that can be passed to indicate "do not change".
+  static const ActivityData kNullActivityData;
+
+ private:
+  friend class ActivityTrackerTest;
+
+  // This structure contains all the common information about the thread so
+  // it doesn't have to be repeated in every entry on the stack. It is defined
+  // and used completely within the .cc file.
+  struct Header;
+
+  Header* const header_;        // Pointer to the Header structure.
+  Activity* const stack_;       // The stack of activities.
+  const uint32_t stack_slots_;  // The total number of stack slots.
+
+  bool valid_ = false;          // Tracks whether the data is valid or not.
+
+  base::ThreadChecker thread_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(ThreadActivityTracker);
+};
+
+
+// The global tracker manages all the individual thread trackers. Memory for
+// the thread trackers is taken from a PersistentMemoryAllocator which allows
+// for the data to be analyzed by a parallel process or even post-mortem.
+class BASE_EXPORT GlobalActivityTracker {
+ public:
+  // Type identifiers used when storing in persistent memory so they can be
+  // identified during extraction; the first 4 bytes of the SHA1 of the name
+  // is used as a unique integer. A "version number" is added to the base
+  // so that, if the structure of that object changes, stored older versions
+  // will be safely ignored. These are public so that an external process
+  // can recognize records of this type within an allocator.
+  enum : uint32_t {
+    kTypeIdActivityTracker     = 0x5D7381AF + 1,  // SHA1(ActivityTracker) v1
+    kTypeIdActivityTrackerFree = 0x3F0272FB,      // SHA1(ActivityTrackerFree)
+  };
+
+  // This is a thin wrapper around the thread-tracker's ScopedActivity that
+  // accesses the global tracker to provide some of the information, notably
+  // which thread-tracker to use. It is safe to create even if activity
+  // tracking is not enabled.
+  class BASE_EXPORT ScopedThreadActivity
+      : public ThreadActivityTracker::ScopedActivity {
+   public:
+    ScopedThreadActivity(const void* source,
+                         ThreadActivityTracker::ActivityType type,
+                         const ThreadActivityTracker::ActivityData& data,
+                         bool lock_allowed)
+        : ThreadActivityTracker::ScopedActivity(
+              GetOrCreateTracker(lock_allowed),
+              source,
+              type,
+              data) {}
+
+   private:
+    // Gets (or creates) a tracker for the current thread. If locking is not
+    // allowed (because a lock is being tracked which would cause recursion)
+    // then the attempt to create one if none found will be skipped. Once
+    // the tracker for this thread has been created for other reasons, locks
+    // will be tracked.
+    static ThreadActivityTracker* GetOrCreateTracker(bool lock_allowed) {
+      GlobalActivityTracker* global_tracker = Get();
+      if (!global_tracker)
+        return nullptr;
+      if (lock_allowed)
+        return global_tracker->GetOrCreateTrackerForCurrentThread();
+      else
+        return global_tracker->GetTrackerForCurrentThread();
+    }
+  };
+
+  ~GlobalActivityTracker();
+
+  // Creates a global tracker using a given persistent-memory |allocator| and
+  // providing the given |stack_depth| to each thread tracker it manages. The
+  // created object is activated so tracking will begin immediately upon return.
+  static void CreateWithAllocator(
+      std::unique_ptr<PersistentMemoryAllocator> allocator,
+      int stack_depth);
+
+#if !defined(OS_NACL)
+  // Like above but internally creates an allocator around a disk file with
+  // the specified |size| at the given |file_path|. Any existing file will be
+  // overwritten. The |id| and |name| are arbitrary and stored in the allocator
+  // for referece by whatever process reads it.
+  static void CreateWithFile(const FilePath& file_path,
+                             size_t size,
+                             uint64_t id,
+                             StringPiece name,
+                             int stack_depth);
+#endif  // !defined(OS_NACL)
+
+  // Like above but internally creates an allocator using local heap memory of
+  // the specified size. This is used primarily for unit tests.
+  static void CreateWithLocalMemory(size_t size,
+                                    uint64_t id,
+                                    StringPiece name,
+                                    int stack_depth);
+
+  // Gets the global activity-tracker or null if none exists.
+  static GlobalActivityTracker* Get() { return g_tracker_; }
+
+  // Gets the persistent-memory-allocator in which data is stored. Callers
+  // can store additional records here to pass more information to the
+  // analysis process.
+  PersistentMemoryAllocator* allocator() { return allocator_.get(); }
+
+  // Gets the thread's activity-tracker if it exists. This is inline for
+  // performance reasons and it uses thread-local-storage (TLS) so that there
+  // is no significant lookup time required to find the one for the calling
+  // thread. Ownership remains with the global tracker.
+  ThreadActivityTracker* GetTrackerForCurrentThread() {
+    return reinterpret_cast<ThreadActivityTracker*>(this_thread_tracker_.Get());
+  }
+
+  // Gets the thread's activity-tracker or creates one if none exists. This
+  // is inline for performance reasons. Ownership remains with the global
+  // tracker.
+  ThreadActivityTracker* GetOrCreateTrackerForCurrentThread() {
+    ThreadActivityTracker* tracker = GetTrackerForCurrentThread();
+    if (!tracker)
+      tracker = CreateTrackerForCurrentThread();
+    return tracker;
+  }
+
+  // Creates an activity-tracker for the current thread.
+  ThreadActivityTracker* CreateTrackerForCurrentThread();
+
+  // Releases the activity-tracker for the current thread (for testing only).
+  void ReleaseTrackerForCurrentThreadForTesting();
+
+ private:
+  friend class ActivityTrackerTest;
+
+  enum : int {
+    // The maximum number of threads that can be tracked within a process.
+    // If more than this number gets created, tracking of them may cease.
+    kMaxThreadCount = 100,
+  };
+
+  // A thin wrapper around the main thread-tracker that keeps additional
+  // information that the global tracker needs to handle joined threads.
+  class ManagedActivityTracker : public ThreadActivityTracker {
+   public:
+    ManagedActivityTracker(PersistentMemoryAllocator::Reference mem_reference,
+                           void* base,
+                           size_t size);
+    ~ManagedActivityTracker() override;
+
+    // The reference into persistent memory from which this the tread-tracker's
+    // memory was created.
+    const PersistentMemoryAllocator::Reference mem_reference_;
+
+    // The physical address used for the thread-tracker's memory.
+    void* const mem_base_;
+  };
+
+  // Creates a global tracker using a given persistent-memory |allocator| and
+  // providing the given |stack_depth| to each thread tracker it manages. The
+  // created object is activated so tracking will begin immediately upon return.
+  GlobalActivityTracker(std::unique_ptr<PersistentMemoryAllocator> allocator,
+                        int stack_depth);
+
+  // Returns the memory used by an activity-tracker managed by this class.
+  void ReturnTrackerMemory(ManagedActivityTracker* tracker);
+
+  // Releases the activity-tracker associcated with thread. It is called
+  // automatically when a thread is joined and thus there is nothing more to
+  // be tracked. |value| is a pointer to a ManagedActivityTracker.
+  static void OnTLSDestroy(void* value);
+
+  // The persistent-memory allocator from which the memory for all trackers
+  // is taken.
+  std::unique_ptr<PersistentMemoryAllocator> allocator_;
+
+  // The size (in bytes) of memory required by a ThreadActivityTracker to
+  // provide stack-depth requsted during construction.

[Sigurður Ásgeirsson, 2016/06/14 15:28:13]

nit: the ... requested

[bcwhite, 2016/06/14 19:48:46]

Done.

+  const size_t stack_memory_size_;
+
+  // The activity tracker for the currently executing thread.
+  base::ThreadLocalStorage::Slot this_thread_tracker_;
+
+  // These have to be lock-free because lock activity is tracked and causes
+  // re-entry problems.
+  std::atomic<int> thread_tracker_count_;
+  std::atomic<int> available_memories_count_;
+  std::atomic<PersistentMemoryAllocator::Reference>
+      available_memories_[kMaxThreadCount];
+
+  // The active global activity tracker.
+  static GlobalActivityTracker* g_tracker_;
+};
+
+
+// Record entry in to and out of an arbitrary block of code.
+class BASE_EXPORT ScopedActivity
+    : public GlobalActivityTracker::ScopedThreadActivity {
+ public:
+  // Track activity at the specified FROM_HERE location for an arbitrary
+  // 4-bit |action|, an arbitrary 32-bit |id|, and 32-bits of arbitrary
+  // |info|. None of these values affect operation; they're all purely
+  // for association and analysis. To have unique identifiers across a
+  // diverse code-base, create the number by taking the first 8 characters
+  // of the hash of the activity being tracked.
+  //
+  // For example:
+  //   Tracking method: void MayNeverExit(uint32_t foo) {...}
+  //   echo -n "MayNeverExit" | sha1sum   =>   e44873ccab21e2b71270da24aa1...
+  //
+  //   void MayNeverExit(uint32_t foo) {
+  //     base::debug::ScopedActivity track_me(FROM_HERE, 0, 0xE44873CC, foo);
+  //     ...
+  //   }
+  ScopedActivity(const tracked_objects::Location& location,
+                 uint8_t action,
+                 uint32_t id,
+                 uint32_t info);
+
+  // Because this is inline, the FROM_HERE macro will resolve the current
+  // program-counter as the location in the calling code.
+  ScopedActivity() : ScopedActivity(FROM_HERE, 0, 0, 0) {}
+
+  // Changes the |action| and/or |info| of this activity on the stack. This
+  // is useful for tracking progress through a function, updating the action
+  // to indicate "milestones" in the block (max 16 milestones: 0-15) or the
+  // info to reflect other changes.
+  void ChangeAction(uint8_t action);
+  void ChangeInfo(uint32_t info);
+  void ChangeActionAndInfo(uint8_t action, uint32_t info);
+
+ private:
+  // A copy of the ID code so it doesn't have to be passed by the caller when
+  // changing the |info| field.
+  uint32_t id_;
+};
+
+
+// These "scoped" classes provide easy tracking of various blocking actions.
+
+class BASE_EXPORT ScopedTaskRunActivity
+    : public GlobalActivityTracker::ScopedThreadActivity {
+ public:
+  ScopedTaskRunActivity(const base::PendingTask& task);
+};
+
+class BASE_EXPORT ScopedLockAcquireActivity
+    : public GlobalActivityTracker::ScopedThreadActivity {
+ public:
+  ScopedLockAcquireActivity(const base::internal::LockImpl* lock);
+};
+
+class BASE_EXPORT ScopedEventWaitActivity
+    : public GlobalActivityTracker::ScopedThreadActivity {
+ public:
+  ScopedEventWaitActivity(const base::WaitableEvent* event);
+};
+
+class BASE_EXPORT ScopedThreadJoinActivity
+    : public GlobalActivityTracker::ScopedThreadActivity {
+ public:
+  ScopedThreadJoinActivity(const base::PlatformThreadHandle* thread);
+};
+
+// Some systems don't have base::Process
+#if !defined(OS_NACL) && !defined(OS_IOS)
+class BASE_EXPORT ScopedProcessWaitActivity
+    : public GlobalActivityTracker::ScopedThreadActivity {
+ public:
+  ScopedProcessWaitActivity(const base::Process* process);
+};
+#endif
+
+}  // namespace debug
+}  // namespace base
+
+#endif  // BASE_METRICS_ACTIVITY_TRACKER_H_