runtime/gc/allocation_record.cc

/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "allocation_record.h"

#include "art_method-inl.h"
#include "base/logging.h"  // For VLOG
#include "base/pointer_size.h"
#include "base/stl_util.h"
#include "instrumentation.h"
#include "obj_ptr-inl.h"
#include "object_callbacks.h"
#include "stack.h"
#include "thread-inl.h"  // For GetWeakRefAccessEnabled().

#include <android-base/properties.h>

namespace art HIDDEN {
namespace gc {

int32_t AllocRecordStackTraceElement::ComputeLineNumber() const {
  DCHECK(method_ != nullptr);
  int32_t line_number = method_->GetLineNumFromDexPC(dex_pc_);
  if (line_number == -1 && !method_->IsProxyMethod()) {
    // If we failed to map the dex pc to a line number, then most probably there is no debug info.
    // Make the line_number same as the dex pc - it can be decoded later using a map file.
    // See b/30183883 and b/228000954.
    line_number = static_cast<int32_t>(dex_pc_);
  }
  return line_number;
}

const char* AllocRecord::GetClassDescriptor(std::string* storage) const {
  // klass_ could contain null only if we implement class unloading.
  return klass_.IsNull() ? "null" : klass_.Read()->GetDescriptor(storage);
}

void AllocRecordObjectMap::SetMaxStackDepth(size_t max_stack_depth) {
  // Log fatal since this should already be checked when calling VMDebug.setAllocTrackerStackDepth.
  CHECK_LE(max_stack_depth, kMaxSupportedStackDepth)
      << "Allocation record max stack depth is too large";
  max_stack_depth_ = max_stack_depth;
}

AllocRecordObjectMap::~AllocRecordObjectMap() {
  Clear();
}

void AllocRecordObjectMap::VisitRoots(RootVisitor* visitor) {
  // When we are compacting in userfaultfd GC, the class GC-roots are already
  // updated in SweepAllocationRecords()->SweepClassObject().
  if (Runtime::Current()->GetHeap()->IsPerformingUffdCompaction()) {
    return;
  }
  CHECK_LE(recent_record_max_, alloc_record_max_);
  BufferedRootVisitor<kDefaultBufferedRootCount> buffered_visitor(visitor, RootInfo(kRootDebugger));
  size_t count = recent_record_max_;
  // Only visit the last recent_record_max_ number of allocation records in entries_ and mark the
  // klass_ fields as strong roots.
  for (auto it = entries_.rbegin(), end = entries_.rend(); it != end; ++it) {
    AllocRecord& record = it->second;
    if (count > 0) {
      buffered_visitor.VisitRootIfNonNull(record.GetClassGcRoot());
      --count;
    }
    // Visit all of the stack frames to make sure no methods in the stack traces get unloaded by
    // class unloading.
    for (size_t i = 0, depth = record.GetDepth(); i < depth; ++i) {
      const AllocRecordStackTraceElement& element = record.StackElement(i);
      DCHECK(element.GetMethod() != nullptr);
      element.GetMethod()->VisitRoots(buffered_visitor, kRuntimePointerSize);
    }
  }
}

static inline void SweepClassObject(AllocRecord* record, IsMarkedVisitor* visitor)
    REQUIRES_SHARED(Locks::mutator_lock_)
    REQUIRES(Locks::alloc_tracker_lock_) {
  GcRoot<mirror::Class>& klass = record->GetClassGcRoot();
  // This does not need a read barrier because this is called by GC.
  mirror::Object* old_object = klass.Read<kWithoutReadBarrier>();
  if (old_object != nullptr) {
    // The class object can become null if we implement class unloading.
    // In that case we might still want to keep the class name string (not implemented).
    mirror::Object* new_object = visitor->IsMarked(old_object);
    DCHECK(new_object != nullptr);
    if (UNLIKELY(old_object != new_object)) {
      // We can't use AsClass() as it uses IsClass in a DCHECK, which expects
      // the class' contents to be there. This is not the case in userfaultfd
      // GC.
      klass = GcRoot<mirror::Class>(ObjPtr<mirror::Class>::DownCast(new_object));
    }
  }
}

void AllocRecordObjectMap::SweepAllocationRecords(IsMarkedVisitor* visitor) {
  VLOG(heap) << "Start SweepAllocationRecords()";
  size_t count_deleted = 0, count_moved = 0, count = 0;
  // Only the first (size - recent_record_max_) number of records can be deleted.
  const size_t delete_bound = std::max(entries_.size(), recent_record_max_) - recent_record_max_;
  for (auto it = entries_.begin(), end = entries_.end(); it != end;) {
    ++count;
    // This does not need a read barrier because this is called by GC.
    mirror::Object* old_object = it->first.Read<kWithoutReadBarrier>();
    AllocRecord& record = it->second;
    mirror::Object* new_object = old_object == nullptr ? nullptr : visitor->IsMarked(old_object);
    if (new_object == nullptr) {
      if (count > delete_bound) {
        it->first = GcRoot<mirror::Object>(nullptr);
        SweepClassObject(&record, visitor);
        ++it;
      } else {
        it = entries_.erase(it);
        ++count_deleted;
      }
    } else {
      if (old_object != new_object) {
        it->first = GcRoot<mirror::Object>(new_object);
        ++count_moved;
      }
      SweepClassObject(&record, visitor);
      ++it;
    }
  }
  VLOG(heap) << "Deleted " << count_deleted << " allocation records";
  VLOG(heap) << "Updated " << count_moved << " allocation records";
}

void AllocRecordObjectMap::AllowNewAllocationRecords() {
  CHECK(!gUseReadBarrier);
  allow_new_record_ = true;
  new_record_condition_.Broadcast(Thread::Current());
}

void AllocRecordObjectMap::DisallowNewAllocationRecords() {
  CHECK(!gUseReadBarrier);
  allow_new_record_ = false;
}

void AllocRecordObjectMap::BroadcastForNewAllocationRecords() {
  new_record_condition_.Broadcast(Thread::Current());
}

void AllocRecordObjectMap::SetAllocTrackingEnabled(bool enable) {
  Thread* self = Thread::Current();
  Heap* heap = Runtime::Current()->GetHeap();
  if (enable) {
    {
      MutexLock mu(self, *Locks::alloc_tracker_lock_);
      if (heap->IsAllocTrackingEnabled()) {
        return;  // Already enabled, bail.
      }
      AllocRecordObjectMap* records = heap->GetAllocationRecords();
      if (records == nullptr) {
        records = new AllocRecordObjectMap;
        heap->SetAllocationRecords(records);
      }
      CHECK(records != nullptr);
      records->SetMaxStackDepth(heap->GetAllocTrackerStackDepth());
      size_t sz = sizeof(AllocRecordStackTraceElement) * records->max_stack_depth_ +
                  sizeof(AllocRecord) + sizeof(AllocRecordStackTrace);
      LOG(INFO) << "Enabling alloc tracker (" << records->alloc_record_max_ << " entries of "
                << records->max_stack_depth_ << " frames, taking up to "
                << PrettySize(sz * records->alloc_record_max_) << ")";
    }
    Runtime::Current()->GetInstrumentation()->InstrumentQuickAllocEntryPoints();
    {
      MutexLock mu(self, *Locks::alloc_tracker_lock_);
      heap->SetAllocTrackingEnabled(true);
    }
  } else {
    // Delete outside of the critical section to avoid possible lock violations like the runtime
    // shutdown lock.
    {
      MutexLock mu(self, *Locks::alloc_tracker_lock_);
      if (!heap->IsAllocTrackingEnabled()) {
        return;  // Already disabled, bail.
      }
      heap->SetAllocTrackingEnabled(false);
      LOG(INFO) << "Disabling alloc tracker";
      AllocRecordObjectMap* records = heap->GetAllocationRecords();
      records->Clear();
    }
    // If an allocation comes in before we uninstrument, we will safely drop it on the floor.
    Runtime::Current()->GetInstrumentation()->UninstrumentQuickAllocEntryPoints();
  }
}

void AllocRecordObjectMap::RecordAllocation(Thread* self,
                                            ObjPtr<mirror::Object>* obj,
                                            size_t byte_count) {
  // Get stack trace outside of lock in case there are allocations during the stack walk.
  // b/27858645.
  AllocRecordStackTrace trace;
  {
    StackHandleScope<1> hs(self);
    auto obj_wrapper = hs.NewHandleWrapper(obj);

    StackVisitor::WalkStack(
        [&](const art::StackVisitor* stack_visitor) REQUIRES_SHARED(Locks::mutator_lock_) {
          if (trace.GetDepth() >= max_stack_depth_) {
            return false;
          }
          ArtMethod* m = stack_visitor->GetMethod();
          // m may be null if we have inlined methods of unresolved classes. b/27858645
          if (m != nullptr && !m->IsRuntimeMethod()) {
            m = m->GetInterfaceMethodIfProxy(kRuntimePointerSize);
            trace.AddStackElement(AllocRecordStackTraceElement(m, stack_visitor->GetDexPc()));
          }
          return true;
        },
        self,
        /* context= */ nullptr,
        art::StackVisitor::StackWalkKind::kIncludeInlinedFrames);
  }

  MutexLock mu(self, *Locks::alloc_tracker_lock_);
  Heap* const heap = Runtime::Current()->GetHeap();
  if (!heap->IsAllocTrackingEnabled()) {
    // In the process of shutting down recording, bail.
    return;
  }

  // TODO Skip recording allocations associated with DDMS. This was a feature of the old debugger
  // but when we switched to the JVMTI based debugger the feature was (unintentionally) broken.
  // Since nobody seemed to really notice or care it might not be worth the trouble.

  // Wait for GC's sweeping to complete and allow new records.
  while (UNLIKELY((!gUseReadBarrier && !allow_new_record_) ||
                  (gUseReadBarrier && !self->GetWeakRefAccessEnabled()))) {
    // Check and run the empty checkpoint before blocking so the empty checkpoint will work in the
    // presence of threads blocking for weak ref access.
    self->CheckEmptyCheckpointFromWeakRefAccess(Locks::alloc_tracker_lock_);
    new_record_condition_.WaitHoldingLocks(self);
  }

  if (!heap->IsAllocTrackingEnabled()) {
    // Return if the allocation tracking has been disabled while waiting for system weak access
    // above.
    return;
  }

  DCHECK_LE(Size(), alloc_record_max_);

  // Erase extra unfilled elements.
  trace.SetTid(self->GetTid());

  // Add the record.
  Put(obj->Ptr(), AllocRecord(byte_count, (*obj)->GetClass(), std::move(trace)));
  DCHECK_LE(Size(), alloc_record_max_);
}

void AllocRecordObjectMap::Clear() {
  entries_.clear();
}

AllocRecordObjectMap::AllocRecordObjectMap()
    : new_record_condition_("New allocation record condition", *Locks::alloc_tracker_lock_) {}

}  // namespace gc
}  // namespace art