Create HangWatchScopeDisabled.

This scope object can be used to disable hang watching when it is known
an operation can run in unbounded time. HangWatchScope is renamed to
HangWatchScopeEnabled as part of this change also for symmetry.

This is done through the introduction of a new persistent flag
kHasActiveHangWatchScopeDisabled that can ensure that new
HangWatchScopeEnabled instances do not count towards hang watching.

Bug: 1034046
Change-Id: I9d8d8b2812a31fe29ba7980d64567798ada3b432
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2288195Reviewed-by: François Doray <fdoray@chromium.org>
Commit-Queue: François Doray <fdoray@chromium.org>
Auto-Submit: Oliver Li <olivierli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796459}

base/task/sequence_manager/thread_controller_with_message_pump_impl.cc

@@ -184,12 +184,13 @@ void ThreadControllerWithMessagePumpImpl::InitializeThreadTaskRunnerHandle() {
   power_monitor_.BindToCurrentThread();
 }
 
-void ThreadControllerWithMessagePumpImpl::MaybeStartHangWatchScope() {
+void ThreadControllerWithMessagePumpImpl::MaybeStartHangWatchScopeEnabled() {
   // Nested runloops are covered by the parent loop hang watch scope.
   // TODO(crbug/1034046): Provide more granular scoping that reuses the parent
   // scope deadline.
   if (main_thread_only().runloop_count == 1 && base::HangWatcher::IsEnabled()) {
-    hang_watch_scope_.emplace(base::HangWatchScope::kDefaultHangWatchTime);
+    hang_watch_scope_.emplace(
+        base::HangWatchScopeEnabled::kDefaultHangWatchTime);
   }
 }
 
@@ -225,7 +226,7 @@ ThreadControllerWithMessagePumpImpl::GetAssociatedThread() const {
 }
 
 void ThreadControllerWithMessagePumpImpl::BeforeDoInternalWork() {
-  MaybeStartHangWatchScope();
+  MaybeStartHangWatchScopeEnabled();
   work_id_provider_->IncrementWorkId();
 }
 
@@ -244,7 +245,7 @@ void ThreadControllerWithMessagePumpImpl::BeforeWait() {
 
 MessagePump::Delegate::NextWorkInfo
 ThreadControllerWithMessagePumpImpl::DoWork() {
-  MaybeStartHangWatchScope();
+  MaybeStartHangWatchScopeEnabled();
 
   work_deduplicator_.OnWorkStarted();
   LazyNow continuation_lazy_now(time_source_);
@@ -367,7 +368,7 @@ TimeDelta ThreadControllerWithMessagePumpImpl::DoWorkImpl(
 
 bool ThreadControllerWithMessagePumpImpl::DoIdleWork() {
   TRACE_EVENT0("sequence_manager", "SequenceManager::DoIdleWork");
-  MaybeStartHangWatchScope();
+  MaybeStartHangWatchScopeEnabled();
 
   work_id_provider_->IncrementWorkId();
 #if defined(OS_WIN)

base/task/sequence_manager/thread_controller_with_message_pump_impl.h

@@ -153,9 +153,9 @@ class BASE_EXPORT ThreadControllerWithMessagePumpImpl
     return main_thread_only_;
   }
 
-  // Instantiate a HangWatchScope to cover the current work if hang
+  // Instantiate a HangWatchScopeEnabled to cover the current work if hang
   // watching is activated via finch and the current loop is not nested.
-  void MaybeStartHangWatchScope();
+  void MaybeStartHangWatchScopeEnabled();
 
   // TODO(altimin): Merge with the one in SequenceManager.
   scoped_refptr<AssociatedThreadId> associated_thread_;
@@ -196,7 +196,7 @@ class BASE_EXPORT ThreadControllerWithMessagePumpImpl
 
   // Reset at the start of each unit of work to cover the work itself and then
   // transition to the next one.
-  base::Optional<HangWatchScope> hang_watch_scope_;
+  base::Optional<HangWatchScopeEnabled> hang_watch_scope_;
 
   DISALLOW_COPY_AND_ASSIGN(ThreadControllerWithMessagePumpImpl);
 };

base/task/thread_pool/worker_thread.cc

@@ -325,9 +325,10 @@ void WorkerThread::RunWorker() {
 #if defined(OS_APPLE)
     mac::ScopedNSAutoreleasePool autorelease_pool;
 #endif
-    base::Optional<HangWatchScope> hang_watch_scope;
+    base::Optional<HangWatchScopeEnabled> hang_watch_scope;
     if (watch_for_hangs)
-      hang_watch_scope.emplace(base::HangWatchScope::kDefaultHangWatchTime);
+      hang_watch_scope.emplace(
+          base::HangWatchScopeEnabled::kDefaultHangWatchTime);
 
     UpdateThreadPriority(GetDesiredThreadPriority());
 

base/threading/hang_watcher.h

@@ -27,7 +27,7 @@
 #include "base/time/time.h"
 
 namespace base {
-class HangWatchScope;
+class HangWatchScopeEnabled;
 namespace internal {
 class HangWatchState;
 }  // namespace internal
@@ -35,13 +35,13 @@ class HangWatchState;
 
 namespace base {
 
-// Instantiate a HangWatchScope in a scope to register to be
+// Instantiate a HangWatchScopeEnabled in a code scope to register to be
 // watched for hangs of more than |timeout| by the HangWatcher.
 //
 // Example usage:
 //
 //  void FooBar(){
-//    HangWatchScope scope(base::TimeDelta::FromSeconds(5));
+//    HangWatchScopeEnabled scope(base::TimeDelta::FromSeconds(5));
 //    DoWork();
 //  }
 //
@@ -49,11 +49,12 @@ namespace base {
 // inspects the thread state before Foobar returns a hang will be
 // reported.
 //
-// HangWatchScopes are typically meant to live on the stack. In some cases it's
-// necessary to keep a HangWatchScope instance as a class member but special
-// care is required when doing so as a HangWatchScope that stays alive longer
-// than intended will generate non-actionable hang reports.
-class BASE_EXPORT HangWatchScope {
+// HangWatchScopeEnableds are typically meant to live on the stack. In some
+// cases it's necessary to keep a HangWatchScopeEnabled instance as a class
+// member but special care is required when doing so as a HangWatchScopeEnabled
+// that stays alive longer than intended will generate non-actionable hang
+// reports.
+class BASE_EXPORT HangWatchScopeEnabled {
  public:
   // A good default value needs to be large enough to represent a significant
   // hang and avoid noise while being small enough to not exclude too many
@@ -63,26 +64,69 @@ class BASE_EXPORT HangWatchScope {
   static const base::TimeDelta kDefaultHangWatchTime;
 
   // Constructing/destructing thread must be the same thread.
-  explicit HangWatchScope(TimeDelta timeout);
-  ~HangWatchScope();
+  explicit HangWatchScopeEnabled(TimeDelta timeout);
+  ~HangWatchScopeEnabled();
 
-  HangWatchScope(const HangWatchScope&) = delete;
-  HangWatchScope& operator=(const HangWatchScope&) = delete;
+  HangWatchScopeEnabled(const HangWatchScopeEnabled&) = delete;
+  HangWatchScopeEnabled& operator=(const HangWatchScopeEnabled&) = delete;
 
  private:
   // This object should always be constructed and destructed on the same thread.
   THREAD_CHECKER(thread_checker_);
 
-  // The deadline set by the previous HangWatchScope created on this thread.
-  // Stored so it can be restored when this HangWatchScope is destroyed.
+  // The deadline set by the previous HangWatchScopeEnabled created on this
+  // thread. Stored so it can be restored when this HangWatchScopeEnabled is
+  // destroyed.
   TimeTicks previous_deadline_;
 
+  // Indicates whether the kIgnoreCurrentHang flag must be set upon exiting this
+  // HangWatchScopeEnabled. This is true if the
+  // kIgnoreCurrentHangWatchScopeEnabled flag was set upon entering this scope,
+  // but was cleared for this HangWatchScopeEnabled because there was no active
+  // HangWatchScopeDisabled.
+  bool set_hangs_ignored_on_exit_ = false;
+
 #if DCHECK_IS_ON()
-  // The previous HangWatchScope created on this thread.
-  HangWatchScope* previous_scope_;
+  // The previous HangWatchScopeEnabled created on this thread.
+  HangWatchScopeEnabled* previous_hang_watch_scope_enable_;
 #endif
 };
 
+// Scoped object that disables hang watching on the thread. The object nullifies
+// the effect of all live HangWatchScopeEnabled instances and also that of new
+// HangWatchScopeEnabled instances created during its lifetime. Use to avoid
+// capturing hangs for operations known to take unbounded time like waiting for
+// user input. This does not unregister the thread so when this object is
+// destroyed hang watching resumes for new HangWatchScopeEnableds.
+//
+// Example usage:
+//  {
+//    HangWatchScopeEnabled scope_1;
+//    {
+//      HangWatchScopeEnabled scope_2;
+//      HangWatchScopeDisabled disabler;
+//      WaitForUserInput();
+//      HangWatchScopeEnabled scope_3;
+//    }
+//
+//    HangWatchScopeEnabled scope_4;
+//  }
+//
+// HangWatchScopeEnabled scope_5;
+//
+// In this example hang watching is disabled for HangWatchScopeEnableds 1, 2 and
+// 3 since they were either active at the time of the |disabler|'s creation or
+// created while the disabler was still active. HangWatchScopeEnableds 4 and 5
+// are unaffected since they were created after the disabler was destroyed.
+//
+class BASE_EXPORT HangWatchScopeDisabled {
+ public:
+  HangWatchScopeDisabled();
+  ~HangWatchScopeDisabled();
+  HangWatchScopeDisabled(const HangWatchScopeDisabled&) = delete;
+  HangWatchScopeDisabled& operator=(const HangWatchScopeDisabled&) = delete;
+};
+
 // Monitors registered threads for hangs by inspecting their associated
 // HangWatchStates for deadline overruns. This happens at a regular interval on
 // a separate thread. Only one instance of HangWatcher can exist at a time
@@ -298,10 +342,13 @@ class BASE_EXPORT HangWatchDeadline {
   enum class Flag : uint64_t {
     // Minimum value for validation purposes. Not currently used.
     kMinValue = bits::LeftmostBit<uint64_t>() >> 7,
+    // Persistent because control by the lifetime of HangWatchScopeDisabled.
+    kHasActiveHangWatchScopeDisabled = bits::LeftmostBit<uint64_t>() >> 2,
     // Persistent because if hang detection is disabled on a thread it should
     // be re-enabled manually.
-    kIgnoreHangs = bits::LeftmostBit<uint64_t>() >> 1,
-    // Non-persistent because a new value means a new hang watch scope started
+    kIgnoreCurrentHangWatchScopeEnabled = bits::LeftmostBit<uint64_t>() >> 1,
+    // Non-persistent because a new value means a new HangWatchScopeEnabled
+    // started
     // after the beginning of capture. It can't be implicated in the hang so we
     // don't want it to block.
     kShouldBlockOnHang = bits::LeftmostBit<uint64_t>() >> 0,
@@ -346,11 +393,17 @@ class BASE_EXPORT HangWatchDeadline {
   // not set the flag and returns false.
   bool SetShouldBlockOnHang(uint64_t old_flags, TimeTicks old_deadline);
 
-  // Sets the kIgnoreHangs flag.
-  void SetIgnoreHangs();
+  // Sets the kHasActiveHangWatchScopeDisabled flag.
+  void SetHasActiveHangWatchScopeDisabled();
 
-  // Clears the kIgnoreHangs flag.
-  void UnsetIgnoreHangs();
+  // Clears the kHasActiveHangWatchScopeDisabled flag.
+  void UnsetHasActiveHangWatchScopeDisabled();
+
+  // Sets the kIgnoreCurrentHangWatchScopeEnabled flag.
+  void SetIgnoreCurrentHangWatchScopeEnabled();
+
+  // Clears the kIgnoreCurrentHangWatchScopeEnabled flag.
+  void UnsetIgnoreCurrentHangWatchScopeEnabled();
 
   // Use to simulate the value of |bits_| changing between the calling a
   // Set* function and the moment of atomically switching the values. The
@@ -466,6 +519,22 @@ class BASE_EXPORT HangWatchState {
   // Sets the deadline to a new value.
   void SetDeadline(TimeTicks deadline);
 
+  // Mark this thread as ignored for hang watching. This means existing hang
+  // watch will not trigger hangs.
+  void SetIgnoreCurrentHangWatchScopeEnabled();
+
+  // Reactivate hang watching on this thread. Should be called when all
+  // HangWatchScopeEnabled instances that were ignored have completed.
+  void UnsetIgnoreCurrentHangWatchScopeEnabled();
+
+  // Mark hang watching as disabled on this thread. This means new
+  // HangWatchScopeEnabled instances will not trigger hangs.
+  void SetHasActiveHangWatchScopeDisabled();
+
+  // Reactivate hang watching on this thread. New HangWatchScopeEnabled
+  // instances will trigger hangs.
+  void UnsetHasActiveHangWatchScopeDisabled();
+
   // Mark the current state as having to block in its destruction until hang
   // capture completes.
   bool SetShouldBlockOnHang(uint64_t old_flags, TimeTicks old_deadline);
@@ -479,11 +548,12 @@ class BASE_EXPORT HangWatchState {
   bool IsOverDeadline() const;
 
 #if DCHECK_IS_ON()
-  // Saves the supplied HangWatchScope as the currently active scope.
-  void SetCurrentHangWatchScope(HangWatchScope* scope);
+  // Saves the supplied HangWatchScopeEnabled as the currently active
+  // HangWatchScopeEnabled.
+  void SetCurrentHangWatchScopeEnabled(HangWatchScopeEnabled* scope);
 
   // Retrieve the currently active scope.
-  HangWatchScope* GetCurrentHangWatchScope();
+  HangWatchScopeEnabled* GetCurrentHangWatchScopeEnabled();
 #endif
 
   PlatformThreadId GetThreadID() const;
@@ -491,6 +561,15 @@ class BASE_EXPORT HangWatchState {
   // Retrieve the current hang watch deadline directly. For testing only.
   HangWatchDeadline* GetHangWatchDeadlineForTesting();
 
+  // Returns the current nesting level.
+  int nesting_level() { return nesting_level_; }
+
+  // Increase the nesting level by 1;
+  void IncrementNestingLevel();
+
+  // Reduce the nesting level by 1;
+  void DecrementNestingLevel();
+
  private:
   // The thread that creates the instance should be the class that updates
   // the deadline.
@@ -502,10 +581,13 @@ class BASE_EXPORT HangWatchState {
 
   const PlatformThreadId thread_id_;
 
+  // Number of active HangWatchScopeEnables on this thread.
+  int nesting_level_ = 0;
+
 #if DCHECK_IS_ON()
-  // Used to keep track of the current HangWatchScope and detect improper usage.
-  // Scopes should always be destructed in reverse order from the one they were
-  // constructed in. Example of improper use:
+  // Used to keep track of the current HangWatchScopeEnabled and detect improper
+  // usage. Scopes should always be destructed in reverse order from the one
+  // they were constructed in. Example of improper use:
   //
   // {
   //   std::unique_ptr<Scope> scope = std::make_unique<Scope>(...);
@@ -513,7 +595,7 @@ class BASE_EXPORT HangWatchState {
   //   |scope| gets deallocated first, violating reverse destruction order.
   //   scope.reset();
   // }
-  HangWatchScope* current_hang_watch_scope_{nullptr};
+  HangWatchScopeEnabled* current_hang_watch_scope_enable_{nullptr};
 #endif
 };
 

base/threading/thread_restrictions.h

@@ -10,6 +10,7 @@
 #include "base/gtest_prod_util.h"
 #include "base/location.h"
 #include "base/macros.h"
+#include "base/threading/hang_watcher.h"
 
 // -----------------------------------------------------------------------------
 // Usage documentation
@@ -570,6 +571,11 @@ class BASE_EXPORT ScopedAllowBaseSyncPrimitivesOutsideBlockingScope {
   const bool was_disallowed_;
 #endif
 
+  // Since this object is used to indicate that sync primitives will be used to
+  // wait for an event ignore the current operation for hang watching purposes
+  // since the wait time duration is unknown.
+  base::HangWatchScopeDisabled hang_watch_scope_disabled_;
+
   DISALLOW_COPY_AND_ASSIGN(ScopedAllowBaseSyncPrimitivesOutsideBlockingScope);
 };