weak_code.cc

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// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
 
#include "vm/heap/weak_code.h"
 
#include "platform/assert.h"
 
#include "vm/code_patcher.h"
#include "vm/hash_table.h"
#include "vm/object.h"
#include "vm/runtime_entry.h"
#include "vm/stack_frame.h"
 
namespace dart {
 
class CodeTraits {
 public:
  static const char* Name() { return "CodeTraits"; }
  static bool ReportStats() { return false; }
  static bool IsMatch(const Object& a, const Object& b) {
    return a.ptr() == b.ptr();
  }
  static uword Hash(const Object& key) { return Code::Cast(key).Hash(); }
};
 
typedef UnorderedHashSet<CodeTraits, WeakArrayStorageTraits> WeakCodeSet;
 
bool WeakCodeReferences::HasCodes() const {
  return !array_.IsNull() && (array_.Length() > 0);
}
 
void WeakCodeReferences::Register(const Code& value) {
  WeakCodeSet set(array_.IsNull() ? HashTables::New<WeakCodeSet>(4, Heap::kOld)
                                  : array_.ptr());
  set.Insert(value);
  UpdateArrayTo(set.Release());
}
 
void WeakCodeReferences::DisableCode(bool are_mutators_stopped) {
#if defined(DART_PRECOMPILED_RUNTIME)
  ASSERT(array_.IsNull());
  return;
#else
  // Ensure mutators see empty code_objects only after code was deoptimized.
  DEBUG_ASSERT(
      IsolateGroup::Current()->program_lock()->IsCurrentThreadWriter());
 
  if (array_.IsNull()) {
    return;
  }
 
  WeakCodeSet set(array_.ptr());
 
  auto isolate_group = IsolateGroup::Current();
  auto disable_code_fun = [&]() {
    Code& code = Code::Handle();
    isolate_group->ForEachIsolate(
        [&](Isolate* isolate) {
          auto mutator_thread = isolate->mutator_thread();
          if (mutator_thread == nullptr) {
            return;
          }
          DartFrameIterator iterator(
              mutator_thread, StackFrameIterator::kAllowCrossThreadIteration);
          StackFrame* frame = iterator.NextFrame();
          while (frame != nullptr) {
            code = frame->LookupDartCode();
 
            if (set.ContainsKey(code)) {
              ReportDeoptimization(code);
              DeoptimizeAt(mutator_thread, code, frame);
            }
            frame = iterator.NextFrame();
          }
        },
        /*at_safepoint=*/true);
 
    // Switch functions that use dependent code to unoptimized code.
    Object& owner = Object::Handle();
    Function& function = Function::Handle();
    WeakCodeSet::Iterator it(&set);
    while (it.MoveNext()) {
      code ^= set.GetKey(it.Current());
      if (code.IsNull()) {
        // Code was garbage collected already.
        continue;
      }
      owner = code.owner();
      if (owner.IsFunction()) {
        function ^= owner.ptr();
      } else if (owner.IsClass()) {
        Class& cls = Class::Handle();
        cls ^= owner.ptr();
        cls.DisableAllocationStub();
        continue;
      } else if (owner.IsNull()) {
        code.Print();
        continue;
      }
 
      // Only optimized code can make dependencies (assumptions) about CHA /
      // field guards and might need to be deoptimized if those assumptions no
      // longer hold.
      // See similar assertions when code gets registered in
      // `Field::RegisterDependentCode` and `Class::RegisterCHACode`.
      ASSERT(code.is_optimized());
      ASSERT(function.unoptimized_code() != code.ptr());
 
      // If function uses dependent code switch it to unoptimized.
      if (function.CurrentCode() == code.ptr()) {
        ReportSwitchingCode(code);
        function.SwitchToUnoptimizedCode();
      } else {
        // Make non-OSR code non-entrant.
        if (!code.IsDisabled()) {
          ReportSwitchingCode(code);
          code.DisableDartCode();
        }
      }
    }
 
    UpdateArrayTo(WeakArray::Handle());
  };
 
  // Deoptimize stacks and disable code (with mutators stopped if they are not
  // stopped yet).
  if (are_mutators_stopped) {
    disable_code_fun();
  } else {
    isolate_group->RunWithStoppedMutators(disable_code_fun);
  }
 
  set.Release();
 
#endif  // defined(DART_PRECOMPILED_RUNTIME)
}
 
}  // namespace dart