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.
+
+#ifndef BASE_METRICS_ACTIVITY_TRACKER_H_
+#define BASE_METRICS_ACTIVITY_TRACKER_H_
+
+#include <atomic>
+#include <memory>
+
+#include "base/base_export.h"
+#include "base/feature_list.h"
+#include "base/files/file_path.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 Lock;
+class MemoryMappedFile;
+class WaitableEvent;
+
+namespace debug {
+
+class ThreadActivityAnalyzer;
+
+#if !defined(OS_NACL)  // NACL doesn't support any kind of file access in build.

[manzagop (departed), 2016/06/01 21:59:41]

Do you need this #if at the callsite in  chrome_browser_field_trials_desktop.cc?

[bcwhite, 2016/06/02 16:18:16]

No because that file is under chrome/ which isn't compiled for NaCL while all of
base/ is.

+// 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. However, in order to support an operational mode where
+// another thread is analyzing this data in real-time, atomic operations are
+// used where necessary to guarantee a consistent view from the outside.
+class BASE_EXPORT ThreadActivityTracker {
+ public:
+  enum ActivityType : uint8_t {
+    ACT_TASK,
+    ACT_LOCK,
+    ACT_EVENT,
+  };
+
+  union StackEntryData {
+    struct {
+      uint64_t sequence_id;
+    } task;
+    struct {
+      uint64_t lock_address;
+    } lock;
+    struct {
+      uint64_t event_address;
+    } event;
+
+    static StackEntryData ForTask(uint64_t sequence) {
+      StackEntryData data;
+      data.task.sequence_id = sequence;
+      return data;
+    }
+
+    static StackEntryData ForLock(const void* lock) {

[manzagop (departed), 2016/06/01 21:59:41]

Add a comment to specificy this is "ForLockAcquisistion"?

I wonder how we could handle the lock in addition to the lock acquisition.
Doesn't seem to fit in a stack...

[bcwhite, 2016/06/02 16:18:16]

Yeah, lots of comments required everywhere.

The stack can only track those activities which block in some way or take a
potentially significant amount of time to run.

However, it would be useful to know where a lock/event was unblocked in the past
as an indication of a "failure by omission" because it's not happening now.

This would be a separate set of information collected aside from the stack. 
Something to discuss in a group.

+      StackEntryData data;
+      data.lock.lock_address = reinterpret_cast<uintptr_t>(lock);
+      return data;
+    }
+
+    static StackEntryData ForEvent(const void* event) {
+      StackEntryData data;
+      data.event.event_address = reinterpret_cast<uintptr_t>(event);
+      return data;
+    }
+  };
+
+  struct StackEntry {
+    int64_t time_ticks;
+    uintptr_t source_address;
+    uint8_t activity_type;
+    StackEntryData data;
+  };
+
+  class BASE_EXPORT ScopedActivity {
+   public:
+    ScopedActivity(ThreadActivityTracker* tracker,
+                   const void* source,
+                   ActivityType activity,
+                   const StackEntryData& data)
+        : tracker_(tracker), source_(source) {
+      if (tracker_)
+        tracker_->PushActivity(source, activity, data);
+    }
+    ~ScopedActivity() {
+      if (tracker_)
+        tracker_->PopActivity(source_);
+    }
+
+   private:
+    ThreadActivityTracker* const tracker_;
+    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 StackEntry
+  // blocks. See SizeForStackDepth().
+  ThreadActivityTracker(void* base, size_t size);
+  virtual ~ThreadActivityTracker();
+
+  // Indicate that a method of the given (arbitrary) identifier has started.
+  void PushActivity(const void* source,
+                    ActivityType activity,
+                    const StackEntryData& data);
+
+  // Indicate that a method of the given (arbitrary) identifier has finished.
+  void PopActivity(const void* source);
+
+  // Returns whether the current data is valid or not. It is not valid if
+  // corruption is detected in the header or other data structures. Fetching
+  // a copy of the stack will return nothing if the data is not valid.
+  bool is_valid() { return valid_; }
+
+  // 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);
+
+ private:
+  friend class ThreadActivityAnalyzer;
+  friend class ActivityTrackerTest;
+
+  struct Header;
+
+  Header* const header_;
+  StackEntry* const stack_;
+  const uint32_t stack_slots_;
+
+  bool valid_ = false;
+
+  base::ThreadChecker thread_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(ThreadActivityTracker);
+};
+
+
+// Be sure not to create multiple Analyzers for given tracker data as parallel
+// operation could lead to inconsistencies from concurrent synchronization with
+// an active tracker.
+class BASE_EXPORT ThreadActivityAnalyzer {
+ public:
+  using StackEntry = ThreadActivityTracker::StackEntry;
+
+  // Creates an analyzer for an existing activity-tracker. The passed tracker
+  // must live at least as long as the created object. The tracker may continue
+  // to be active even with an attached analyzer.
+  explicit ThreadActivityAnalyzer(ThreadActivityTracker* tracker);
+
+  // Creates an anaylzer for a block of memory held within a persistent-memory
+  // |allocator| at the given |reference|. The memory must live at least as
+  // long as the created object. It's permissable for a tracker to remain active
+  // on the memory from this thread, other threads, or even other processes.
+  // The reference must be to an object of type kTypeIdActivityTracker, above.
+  ThreadActivityAnalyzer(PersistentMemoryAllocator* allocator,
+                         PersistentMemoryAllocator::Reference reference);
+
+  // Creates an anaylzer for a block of memory currently or previously in-use
+  // by an activity-tracker. The memory must live at least as long as the
+  // created object. It's permissable for a tracker to remain active on the
+  // memory from this thread, other threads, or even other processes.
+  ThreadActivityAnalyzer(void* base, size_t size);
+
+  ~ThreadActivityAnalyzer();
+
+  // Gets a copy of the current stack contents. The return value is the current
+  // depth of the stack which may be greater than the number of StackEntry
+  // records returned. If so, the returned stack has the "base" of the stack
+  // with later entries omitted.
+  uint32_t SnapshotStack(std::vector<StackEntry>* snapshot);
+
+ private:
+  ThreadActivityTracker tracker_;
+
+  DISALLOW_COPY_AND_ASSIGN(ThreadActivityAnalyzer);
+};
+
+
+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 and use them to
+  // create ThreadActivityAnalyzer objects.
+  enum : uint32_t {
+    kTypeIdActivityTracker     = 0x5D7381AF + 1,  // SHA1(ActivityTracker) v1
+    kTypeIdActivityTrackerFree = 0x3F0272FB,      // SHA1(ActivityTrackerFree)
+  };
+
+  class BASE_EXPORT ScopedThreadActivity
+      : public ThreadActivityTracker::ScopedActivity {
+   public:
+    ScopedThreadActivity(const void* source,
+                         ThreadActivityTracker::ActivityType activity,
+                         const ThreadActivityTracker::StackEntryData& data,
+                         bool lock_allowed)
+        : ThreadActivityTracker::ScopedActivity(
+              GetOrCreateTracker(lock_allowed),
+              source,
+              activity,
+              data) {}
+
+   private:
+    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();
+
+  static void CreateWithAllocator(
+      std::unique_ptr<PersistentMemoryAllocator> allocator,
+      int stack_depth);
+
+  static void CreateWithLocalMemory(size_t size,
+                                    uint64_t id,
+                                    StringPiece name,
+                                    int stack_depth);
+
+#if !defined(OS_NACL)
+  static void CreateWithFile(const FilePath& file_path,
+                             size_t size,
+                             uint64_t id,
+                             StringPiece name,
+                             int stack_depth);
+#endif  // !defined(OS_NACL)
+
+  // 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 additional 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. Ownership remains with the global tracker.
+  ThreadActivityTracker* GetTrackerForCurrentThread() {
+    void* tracker = this_thread_tracker_.Get();
+    return reinterpret_cast<ThreadActivityTracker*>(tracker);
+  }
+
+  // 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 {
+    kMaxThreadCount = 100,
+  };
+
+  class ManagedActivityTracker : public ThreadActivityTracker {
+   public:
+    ManagedActivityTracker(PersistentMemoryAllocator::Reference mem_reference,
+                           void* base,
+                           size_t size);
+    ~ManagedActivityTracker() override;
+
+   private:
+    const PersistentMemoryAllocator::Reference mem_reference_;
+    void* const mem_base_;
+  };
+
+  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,
+                           PersistentMemoryAllocator::Reference mem_reference,
+                           void* mem_base);
+
+  static void OnTLSDestroy(void* value);
+
+  std::unique_ptr<PersistentMemoryAllocator> allocator_;
+  const size_t stack_memory_size_;
+
+  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];
+
+  static GlobalActivityTracker* g_tracker_;
+};
+
+
+class BASE_EXPORT ScopedTaskActivity
+    : public GlobalActivityTracker::ScopedThreadActivity {
+ public:
+  ScopedTaskActivity(const base::PendingTask& task);
+};
+
+class BASE_EXPORT ScopedLockActivity
+    : public GlobalActivityTracker::ScopedThreadActivity {
+ public:
+  ScopedLockActivity(const base::internal::LockImpl* lock);
+};
+
+class BASE_EXPORT ScopedEventActivity
+    : public GlobalActivityTracker::ScopedThreadActivity {
+ public:
+  ScopedEventActivity(const base::WaitableEvent* event);
+};
+
+}  // namespace debug
+}  // namespace base
+
+#endif  // BASE_METRICS_ACTIVITY_TRACKER_H_