runtime/vm/symbols.cc

// Copyright (c) 2012, 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/symbols.h"

#include "platform/unicode.h"
#include "vm/handles.h"
#include "vm/hash_table.h"
#include "vm/heap/safepoint.h"
#include "vm/isolate.h"
#include "vm/object.h"
#include "vm/object_store.h"
#include "vm/raw_object.h"
#include "vm/reusable_handles.h"
#include "vm/snapshot_ids.h"
#include "vm/type_table.h"
#include "vm/visitor.h"

namespace dart {

StringPtr Symbols::predefined_[Symbols::kNumberOfOneCharCodeSymbols];
String* Symbols::symbol_handles_[Symbols::kMaxPredefinedId];

static const char* names[] = {
    // clang-format off
  NULL,
#define DEFINE_SYMBOL_LITERAL(symbol, literal) literal,
  PREDEFINED_SYMBOLS_LIST(DEFINE_SYMBOL_LITERAL)
#undef DEFINE_SYMBOL_LITERAL
  "",  // matches kTokenTableStart.
#define DEFINE_TOKEN_SYMBOL_INDEX(t, s, p, a) s,
  DART_TOKEN_LIST(DEFINE_TOKEN_SYMBOL_INDEX)
  DART_KEYWORD_LIST(DEFINE_TOKEN_SYMBOL_INDEX)
#undef DEFINE_TOKEN_SYMBOL_INDEX
    // clang-format on
};

StringPtr StringFrom(const uint8_t* data, intptr_t len, Heap::Space space) {
  return String::FromLatin1(data, len, space);
}

StringPtr StringFrom(const uint16_t* data, intptr_t len, Heap::Space space) {
  return String::FromUTF16(data, len, space);
}

StringPtr StringFrom(const int32_t* data, intptr_t len, Heap::Space space) {
  return String::FromUTF32(data, len, space);
}

template <typename CharType>
class CharArray {
 public:
  CharArray(const CharType* data, intptr_t len) : data_(data), len_(len) {
    hash_ = String::Hash(data, len);
  }
  StringPtr ToSymbol() const {
    String& result = String::Handle(StringFrom(data_, len_, Heap::kOld));
    result.SetCanonical();
    result.SetHash(hash_);
    return result.raw();
  }
  bool Equals(const String& other) const {
    ASSERT(other.HasHash());
    if (other.Hash() != hash_) {
      return false;
    }
    return other.Equals(data_, len_);
  }
  intptr_t Hash() const { return hash_; }

 private:
  const CharType* data_;
  intptr_t len_;
  intptr_t hash_;
};
typedef CharArray<uint8_t> Latin1Array;
typedef CharArray<uint16_t> UTF16Array;
typedef CharArray<int32_t> UTF32Array;

class StringSlice {
 public:
  StringSlice(const String& str, intptr_t begin_index, intptr_t length)
      : str_(str), begin_index_(begin_index), len_(length) {
    hash_ = is_all() ? str.Hash() : String::Hash(str, begin_index, length);
  }
  StringPtr ToSymbol() const;
  bool Equals(const String& other) const {
    ASSERT(other.HasHash());
    if (other.Hash() != hash_) {
      return false;
    }
    return other.Equals(str_, begin_index_, len_);
  }
  intptr_t Hash() const { return hash_; }

 private:
  bool is_all() const { return begin_index_ == 0 && len_ == str_.Length(); }
  const String& str_;
  intptr_t begin_index_;
  intptr_t len_;
  intptr_t hash_;
};

StringPtr StringSlice::ToSymbol() const {
  if (is_all() && str_.IsOld()) {
    str_.SetCanonical();
    return str_.raw();
  } else {
    String& result =
        String::Handle(String::SubString(str_, begin_index_, len_, Heap::kOld));
    result.SetCanonical();
    result.SetHash(hash_);
    return result.raw();
  }
}

class ConcatString {
 public:
  ConcatString(const String& str1, const String& str2)
      : str1_(str1), str2_(str2), hash_(String::HashConcat(str1, str2)) {}
  StringPtr ToSymbol() const;
  bool Equals(const String& other) const {
    ASSERT(other.HasHash());
    if (other.Hash() != hash_) {
      return false;
    }
    return other.EqualsConcat(str1_, str2_);
  }
  intptr_t Hash() const { return hash_; }

 private:
  const String& str1_;
  const String& str2_;
  intptr_t hash_;
};

StringPtr ConcatString::ToSymbol() const {
  String& result = String::Handle(String::Concat(str1_, str2_, Heap::kOld));
  result.SetCanonical();
  result.SetHash(hash_);
  return result.raw();
}

class SymbolTraits {
 public:
  static const char* Name() { return "SymbolTraits"; }
  static bool ReportStats() { return false; }

  static bool IsMatch(const Object& a, const Object& b) {
    const String& a_str = String::Cast(a);
    const String& b_str = String::Cast(b);
    ASSERT(a_str.HasHash());
    ASSERT(b_str.HasHash());
    if (a_str.Hash() != b_str.Hash()) {
      return false;
    }
    intptr_t a_len = a_str.Length();
    if (a_len != b_str.Length()) {
      return false;
    }
    // Use a comparison which does not consider the state of the canonical bit.
    return a_str.Equals(b_str, 0, a_len);
  }
  template <typename CharType>
  static bool IsMatch(const CharArray<CharType>& array, const Object& obj) {
    return array.Equals(String::Cast(obj));
  }
  static bool IsMatch(const StringSlice& slice, const Object& obj) {
    return slice.Equals(String::Cast(obj));
  }
  static bool IsMatch(const ConcatString& concat, const Object& obj) {
    return concat.Equals(String::Cast(obj));
  }
  static uword Hash(const Object& key) { return String::Cast(key).Hash(); }
  template <typename CharType>
  static uword Hash(const CharArray<CharType>& array) {
    return array.Hash();
  }
  static uword Hash(const StringSlice& slice) { return slice.Hash(); }
  static uword Hash(const ConcatString& concat) { return concat.Hash(); }
  template <typename CharType>
  static ObjectPtr NewKey(const CharArray<CharType>& array) {
    return array.ToSymbol();
  }
  static ObjectPtr NewKey(const StringSlice& slice) { return slice.ToSymbol(); }
  static ObjectPtr NewKey(const ConcatString& concat) {
    return concat.ToSymbol();
  }
};
typedef UnorderedHashSet<SymbolTraits> SymbolTable;

const char* Symbols::Name(SymbolId symbol) {
  ASSERT((symbol > kIllegal) && (symbol < kNullCharId));
  return names[symbol];
}

const String& Symbols::Token(Token::Kind token) {
  const int tok_index = token;
  ASSERT((0 <= tok_index) && (tok_index < Token::kNumTokens));
  // First keyword symbol is in symbol_handles_[kTokenTableStart + 1].
  const intptr_t token_id = Symbols::kTokenTableStart + 1 + tok_index;
  ASSERT(symbol_handles_[token_id] != NULL);
  return *symbol_handles_[token_id];
}

void Symbols::Init(Isolate* vm_isolate) {
  // Should only be run by the vm isolate.
  ASSERT(Isolate::Current() == Dart::vm_isolate());
  ASSERT(vm_isolate == Dart::vm_isolate());
  Zone* zone = Thread::Current()->zone();

  // Create and setup a symbol table in the vm isolate.
  SetupSymbolTable(vm_isolate);

  // Create all predefined symbols.
  ASSERT((sizeof(names) / sizeof(const char*)) == Symbols::kNullCharId);

  SymbolTable table(zone, vm_isolate->object_store()->symbol_table());

  // First set up all the predefined string symbols.
  // Create symbols for language keywords. Some keywords are equal to
  // symbols we already created, so use New() instead of Add() to ensure
  // that the symbols are canonicalized.
  for (intptr_t i = 1; i < Symbols::kNullCharId; i++) {
    String* str = String::ReadOnlyHandle();
    *str = OneByteString::New(names[i], Heap::kOld);
    str->Hash();
    *str ^= table.InsertOrGet(*str);
    str->SetCanonical();  // Make canonical once entered.
    symbol_handles_[i] = str;
  }

  // Add Latin1 characters as Symbols, so that Symbols::FromCharCode is fast.
  for (intptr_t c = 0; c < kNumberOfOneCharCodeSymbols; c++) {
    intptr_t idx = (kNullCharId + c);
    ASSERT(idx < kMaxPredefinedId);
    ASSERT(Utf::IsLatin1(c));
    uint8_t ch = static_cast<uint8_t>(c);
    String* str = String::ReadOnlyHandle();
    *str = OneByteString::New(&ch, 1, Heap::kOld);
    str->Hash();
    *str ^= table.InsertOrGet(*str);
    ASSERT(predefined_[c] == nullptr);
    str->SetCanonical();  // Make canonical once entered.
    predefined_[c] = str->raw();
    symbol_handles_[idx] = str;
  }

  vm_isolate->object_store()->set_symbol_table(table.Release());
}

void Symbols::InitFromSnapshot(Isolate* vm_isolate) {
  // Should only be run by the vm isolate.
  ASSERT(Isolate::Current() == Dart::vm_isolate());
  ASSERT(vm_isolate == Dart::vm_isolate());
  Zone* zone = Thread::Current()->zone();

  SymbolTable table(zone, vm_isolate->object_store()->symbol_table());

  // Lookup all the predefined string symbols and language keyword symbols
  // and cache them in the read only handles for fast access.
  for (intptr_t i = 1; i < Symbols::kNullCharId; i++) {
    String* str = String::ReadOnlyHandle();
    const unsigned char* name =
        reinterpret_cast<const unsigned char*>(names[i]);
    *str ^= table.GetOrNull(Latin1Array(name, strlen(names[i])));
    ASSERT(!str->IsNull());
    ASSERT(str->HasHash());
    ASSERT(str->IsCanonical());
    symbol_handles_[i] = str;
  }

  // Lookup Latin1 character Symbols and cache them in read only handles,
  // so that Symbols::FromCharCode is fast.
  for (intptr_t c = 0; c < kNumberOfOneCharCodeSymbols; c++) {
    intptr_t idx = (kNullCharId + c);
    ASSERT(idx < kMaxPredefinedId);
    ASSERT(Utf::IsLatin1(c));
    uint8_t ch = static_cast<uint8_t>(c);
    String* str = String::ReadOnlyHandle();
    *str ^= table.GetOrNull(Latin1Array(&ch, 1));
    ASSERT(!str->IsNull());
    ASSERT(str->HasHash());
    ASSERT(str->IsCanonical());
    predefined_[c] = str->raw();
    symbol_handles_[idx] = str;
  }

  vm_isolate->object_store()->set_symbol_table(table.Release());
}

void Symbols::SetupSymbolTable(Isolate* isolate) {
  ASSERT(isolate != NULL);

  // Setup the symbol table used within the String class.
  const intptr_t initial_size = (isolate == Dart::vm_isolate())
                                    ? kInitialVMIsolateSymtabSize
                                    : kInitialSymtabSize;
  Array& array =
      Array::Handle(HashTables::New<SymbolTable>(initial_size, Heap::kOld));
  isolate->object_store()->set_symbol_table(array);
}

void Symbols::Compact() {
  Thread* thread = Thread::Current();
  ASSERT(thread->isolate() != Dart::vm_isolate());
  HANDLESCOPE(thread);
  Zone* zone = thread->zone();
  ObjectStore* object_store = thread->isolate()->object_store();

  // 1. Drop the tables and do a full garbage collection.
  object_store->set_symbol_table(Object::empty_array());
  object_store->set_canonical_types(Object::empty_array());
  object_store->set_canonical_type_parameters(Object::empty_array());
  object_store->set_canonical_type_arguments(Object::empty_array());
  thread->heap()->CollectAllGarbage();

  // 2. Walk the heap to find surviving canonical objects.
  GrowableArray<String*> symbols;
  GrowableArray<class Type*> types;
  GrowableArray<class TypeParameter*> type_params;
  GrowableArray<class TypeArguments*> type_args;
  class SymbolCollector : public ObjectVisitor {
   public:
    SymbolCollector(Thread* thread,
                    GrowableArray<String*>* symbols,
                    GrowableArray<class Type*>* types,
                    GrowableArray<class TypeParameter*>* type_params,
                    GrowableArray<class TypeArguments*>* type_args)
        : symbols_(symbols),
          types_(types),
          type_params_(type_params),
          type_args_(type_args),
          zone_(thread->zone()) {}

    void VisitObject(ObjectPtr obj) {
      if (obj->ptr()->IsCanonical()) {
        if (obj->IsStringInstance()) {
          symbols_->Add(&String::Handle(zone_, String::RawCast(obj)));
        } else if (obj->IsType()) {
          types_->Add(&Type::Handle(zone_, Type::RawCast(obj)));
        } else if (obj->IsTypeParameter()) {
          type_params_->Add(
              &TypeParameter::Handle(zone_, TypeParameter::RawCast(obj)));
        } else if (obj->IsTypeArguments()) {
          type_args_->Add(
              &TypeArguments::Handle(zone_, TypeArguments::RawCast(obj)));
        }
      }
    }

   private:
    GrowableArray<String*>* symbols_;
    GrowableArray<class Type*>* types_;
    GrowableArray<class TypeParameter*>* type_params_;
    GrowableArray<class TypeArguments*>* type_args_;
    Zone* zone_;
  };

  {
    HeapIterationScope iteration(thread);
    SymbolCollector visitor(thread, &symbols, &types, &type_params, &type_args);
    iteration.IterateObjects(&visitor);
  }

  // 3. Build new tables from the surviving canonical objects.
  {
    Array& array = Array::Handle(
        zone,
        HashTables::New<SymbolTable>(symbols.length() * 4 / 3, Heap::kOld));
    SymbolTable table(zone, array.raw());
    for (intptr_t i = 0; i < symbols.length(); i++) {
      String& symbol = *symbols[i];
      ASSERT(symbol.IsString());
      ASSERT(symbol.IsCanonical());
      bool present = table.Insert(symbol);
      ASSERT(!present);
    }
    object_store->set_symbol_table(table.Release());
  }

  {
    Array& array = Array::Handle(zone, HashTables::New<CanonicalTypeSet>(
                                           types.length() * 4 / 3, Heap::kOld));
    CanonicalTypeSet table(zone, array.raw());
    for (intptr_t i = 0; i < types.length(); i++) {
      class Type& type = *types[i];
      ASSERT(type.IsType());
      ASSERT(type.IsCanonical());
      bool present = table.Insert(type);
      // Two recursive types with different topology (and hashes) may be equal.
      ASSERT(!present || type.IsRecursive());
    }
    object_store->set_canonical_types(table.Release());
  }

  {
    Array& array =
        Array::Handle(zone, HashTables::New<CanonicalTypeParameterSet>(
                                type_params.length() * 4 / 3, Heap::kOld));
    CanonicalTypeParameterSet table(zone, array.raw());
    for (intptr_t i = 0; i < type_params.length(); i++) {
      class TypeParameter& type_param = *type_params[i];
      ASSERT(type_param.IsTypeParameter());
      ASSERT(type_param.IsCanonical());
      if (type_param.IsDeclaration()) continue;
      bool present = table.Insert(type_param);
      ASSERT(!present);
    }
    object_store->set_canonical_type_parameters(table.Release());
  }

  {
    Array& array =
        Array::Handle(zone, HashTables::New<CanonicalTypeArgumentsSet>(
                                type_args.length() * 4 / 3, Heap::kOld));
    CanonicalTypeArgumentsSet table(zone, array.raw());
    for (intptr_t i = 0; i < type_args.length(); i++) {
      class TypeArguments& type_arg = *type_args[i];
      ASSERT(type_arg.IsTypeArguments());
      ASSERT(type_arg.IsCanonical());
      bool present = table.Insert(type_arg);
      // Two recursive types with different topology (and hashes) may be equal.
      ASSERT(!present || type_arg.IsRecursive());
    }
    object_store->set_canonical_type_arguments(table.Release());
  }
}

void Symbols::GetStats(Isolate* isolate, intptr_t* size, intptr_t* capacity) {
  ASSERT(isolate != NULL);
  SymbolTable table(isolate->object_store()->symbol_table());
  *size = table.NumOccupied();
  *capacity = table.NumEntries();
  table.Release();
}

StringPtr Symbols::New(Thread* thread, const char* cstr, intptr_t len) {
  ASSERT((cstr != NULL) && (len >= 0));
  const uint8_t* utf8_array = reinterpret_cast<const uint8_t*>(cstr);
  return Symbols::FromUTF8(thread, utf8_array, len);
}

StringPtr Symbols::FromUTF8(Thread* thread,
                            const uint8_t* utf8_array,
                            intptr_t array_len) {
  if (array_len == 0 || utf8_array == NULL) {
    return FromLatin1(thread, reinterpret_cast<uint8_t*>(NULL), 0);
  }
  Utf8::Type type;
  intptr_t len = Utf8::CodeUnitCount(utf8_array, array_len, &type);
  ASSERT(len != 0);
  Zone* zone = thread->zone();
  if (type == Utf8::kLatin1) {
    uint8_t* characters = zone->Alloc<uint8_t>(len);
    if (!Utf8::DecodeToLatin1(utf8_array, array_len, characters, len)) {
      Utf8::ReportInvalidByte(utf8_array, array_len, len);
      return String::null();
    }
    return FromLatin1(thread, characters, len);
  }
  ASSERT((type == Utf8::kBMP) || (type == Utf8::kSupplementary));
  uint16_t* characters = zone->Alloc<uint16_t>(len);
  if (!Utf8::DecodeToUTF16(utf8_array, array_len, characters, len)) {
    Utf8::ReportInvalidByte(utf8_array, array_len, len);
    return String::null();
  }
  return FromUTF16(thread, characters, len);
}

StringPtr Symbols::FromLatin1(Thread* thread,
                              const uint8_t* latin1_array,
                              intptr_t len) {
  return NewSymbol(thread, Latin1Array(latin1_array, len));
}

StringPtr Symbols::FromUTF16(Thread* thread,
                             const uint16_t* utf16_array,
                             intptr_t len) {
  return NewSymbol(thread, UTF16Array(utf16_array, len));
}

StringPtr Symbols::FromUTF32(Thread* thread,
                             const int32_t* utf32_array,
                             intptr_t len) {
  return NewSymbol(thread, UTF32Array(utf32_array, len));
}

StringPtr Symbols::FromConcat(Thread* thread,
                              const String& str1,
                              const String& str2) {
  if (str1.Length() == 0) {
    return New(thread, str2);
  } else if (str2.Length() == 0) {
    return New(thread, str1);
  } else {
    return NewSymbol(thread, ConcatString(str1, str2));
  }
}

StringPtr Symbols::FromGet(Thread* thread, const String& str) {
  return FromConcat(thread, GetterPrefix(), str);
}

StringPtr Symbols::FromSet(Thread* thread, const String& str) {
  return FromConcat(thread, SetterPrefix(), str);
}

StringPtr Symbols::FromDot(Thread* thread, const String& str) {
  return FromConcat(thread, str, Dot());
}

// TODO(srdjan): If this becomes performance critical code, consider looking
// up symbol from hash of pieces instead of concatenating them first into
// a string.
StringPtr Symbols::FromConcatAll(
    Thread* thread,
    const GrowableHandlePtrArray<const String>& strs) {
  const intptr_t strs_length = strs.length();
  GrowableArray<intptr_t> lengths(strs_length);

  intptr_t len_sum = 0;
  const intptr_t kOneByteChar = 1;
  intptr_t char_size = kOneByteChar;

  for (intptr_t i = 0; i < strs_length; i++) {
    const String& str = strs[i];
    const intptr_t str_len = str.Length();
    if ((String::kMaxElements - len_sum) < str_len) {
      Exceptions::ThrowOOM();
      UNREACHABLE();
    }
    len_sum += str_len;
    lengths.Add(str_len);
    char_size = Utils::Maximum(char_size, str.CharSize());
  }
  const bool is_one_byte_string = char_size == kOneByteChar;

  Zone* zone = thread->zone();
  if (is_one_byte_string) {
    uint8_t* buffer = zone->Alloc<uint8_t>(len_sum);
    const uint8_t* const orig_buffer = buffer;
    for (intptr_t i = 0; i < strs_length; i++) {
      NoSafepointScope no_safepoint;
      intptr_t str_len = lengths[i];
      if (str_len > 0) {
        const String& str = strs[i];
        ASSERT(str.IsOneByteString() || str.IsExternalOneByteString());
        const uint8_t* src_p = str.IsOneByteString()
                                   ? OneByteString::DataStart(str)
                                   : ExternalOneByteString::DataStart(str);
        memmove(buffer, src_p, str_len);
        buffer += str_len;
      }
    }
    ASSERT(len_sum == buffer - orig_buffer);
    return Symbols::FromLatin1(thread, orig_buffer, len_sum);
  } else {
    uint16_t* buffer = zone->Alloc<uint16_t>(len_sum);
    const uint16_t* const orig_buffer = buffer;
    for (intptr_t i = 0; i < strs_length; i++) {
      NoSafepointScope no_safepoint;
      intptr_t str_len = lengths[i];
      if (str_len > 0) {
        const String& str = strs[i];
        if (str.IsTwoByteString()) {
          memmove(buffer, TwoByteString::DataStart(str), str_len * 2);
        } else if (str.IsExternalTwoByteString()) {
          memmove(buffer, ExternalTwoByteString::DataStart(str), str_len * 2);
        } else {
          // One-byte to two-byte string copy.
          ASSERT(str.IsOneByteString() || str.IsExternalOneByteString());
          const uint8_t* src_p = str.IsOneByteString()
                                     ? OneByteString::DataStart(str)
                                     : ExternalOneByteString::DataStart(str);
          for (int n = 0; n < str_len; n++) {
            buffer[n] = src_p[n];
          }
        }
        buffer += str_len;
      }
    }
    ASSERT(len_sum == buffer - orig_buffer);
    return Symbols::FromUTF16(thread, orig_buffer, len_sum);
  }
}

// StringType can be StringSlice, ConcatString, or {Latin1,UTF16,UTF32}Array.
template <typename StringType>
StringPtr Symbols::NewSymbol(Thread* thread, const StringType& str) {
  REUSABLE_OBJECT_HANDLESCOPE(thread);
  REUSABLE_SMI_HANDLESCOPE(thread);
  REUSABLE_ARRAY_HANDLESCOPE(thread);
  String& symbol = String::Handle(thread->zone());
  dart::Object& key = thread->ObjectHandle();
  Smi& value = thread->SmiHandle();
  Array& data = thread->ArrayHandle();
  {
    Isolate* vm_isolate = Dart::vm_isolate();
    data = vm_isolate->object_store()->symbol_table();
    SymbolTable table(&key, &value, &data);
    symbol ^= table.GetOrNull(str);
    table.Release();
  }
  if (symbol.IsNull()) {
    IsolateGroup* group = thread->isolate_group();
    Isolate* isolate = thread->isolate();
    // In JIT object_store lives on isolate, not on isolate group.
    ObjectStore* object_store = group->object_store() == nullptr
                                    ? isolate->object_store()
                                    : group->object_store();
    if (thread->IsAtSafepoint()) {
      // There are two cases where we can cause symbol allocation while holding
      // a safepoint:
      //    - FLAG_enable_isolate_groups in AOT due to the usage of
      //      `RunWithStoppedMutators` in SwitchableCall runtime entry.
      //    - non-PRODUCT mode where the vm-service uses a HeapIterationScope
      //      while building instances
      // Ideally we should get rid of both cases to avoid this unsafe usage of
      // the symbol table (we are assuming here that no other thread holds the
      // symbols_lock).
      // TODO(https://dartbug.com/41943): Get rid of the symbol table accesses
      // within safepoint operation scope.
      RELEASE_ASSERT(group->safepoint_handler()->IsOwnedByTheThread(thread));
      RELEASE_ASSERT(FLAG_enable_isolate_groups || !USING_PRODUCT);

      // Uncommon case: We are at a safepoint, all mutators are stopped and we
      // have therefore exclusive access to the symbol table.
      data = object_store->symbol_table();
      SymbolTable table(&key, &value, &data);
      symbol ^= table.InsertNewOrGet(str);
      object_store->set_symbol_table(table.Release());
    } else {
      // Most common case: We are not at a safepoint and the symbol is available
      // in the symbol table: We require only read access.
      {
        SafepointReadRwLocker sl(thread, group->symbols_lock());
        data = object_store->symbol_table();
        SymbolTable table(&key, &value, &data);
        symbol ^= table.GetOrNull(str);
        table.Release();
      }
      // Second common case: We are not at a safepoint and the symbol is not
      // available in the symbol table: We require only exclusive access.
      if (symbol.IsNull()) {
        auto insert_or_get = [&]() {
          data = object_store->symbol_table();
          SymbolTable table(&key, &value, &data);
          symbol ^= table.InsertNewOrGet(str);
          object_store->set_symbol_table(table.Release());
        };

        SafepointWriteRwLocker sl(thread, group->symbols_lock());
        if (FLAG_enable_isolate_groups || !USING_PRODUCT) {
          // NOTE: Strictly speaking we should use a safepoint operation scope
          // here to ensure the lock-free usage inside safepoint operations (see
          // above) is safe. Though this would really kill the performance.
          // TODO(https://dartbug.com/41943): Get rid of the symbol table
          // accesses within safepoint operation scope.
          group->RunWithStoppedMutators(insert_or_get,
                                        /*force_heap_growth=*/true);
        } else {
          insert_or_get();
        }
      }
    }
  }
  ASSERT(symbol.IsSymbol());
  ASSERT(symbol.HasHash());
  return symbol.raw();
}

template <typename StringType>
StringPtr Symbols::Lookup(Thread* thread, const StringType& str) {
  REUSABLE_OBJECT_HANDLESCOPE(thread);
  REUSABLE_SMI_HANDLESCOPE(thread);
  REUSABLE_ARRAY_HANDLESCOPE(thread);
  String& symbol = String::Handle(thread->zone());
  dart::Object& key = thread->ObjectHandle();
  Smi& value = thread->SmiHandle();
  Array& data = thread->ArrayHandle();
  {
    Isolate* vm_isolate = Dart::vm_isolate();
    data = vm_isolate->object_store()->symbol_table();
    SymbolTable table(&key, &value, &data);
    symbol ^= table.GetOrNull(str);
    table.Release();
  }
  if (symbol.IsNull()) {
    IsolateGroup* group = thread->isolate_group();
    Isolate* isolate = thread->isolate();
    // In JIT object_store lives on isolate, not on isolate group.
    ObjectStore* object_store = group->object_store() == nullptr
                                    ? isolate->object_store()
                                    : group->object_store();
    // See `Symbols::NewSymbol` for more information why we separate the two
    // cases.
    if (thread->IsAtSafepoint()) {
      RELEASE_ASSERT(group->safepoint_handler()->IsOwnedByTheThread(thread));
      // In DEBUG mode the snapshot writer also calls this method inside a
      // safepoint.
#if !defined(DEBUG)
      RELEASE_ASSERT(FLAG_enable_isolate_groups || !USING_PRODUCT);
#endif
      data = object_store->symbol_table();
      SymbolTable table(&key, &value, &data);
      symbol ^= table.GetOrNull(str);
      table.Release();
    } else {
      SafepointReadRwLocker sl(thread, group->symbols_lock());
      data = object_store->symbol_table();
      SymbolTable table(&key, &value, &data);
      symbol ^= table.GetOrNull(str);
      table.Release();
    }
  }
  ASSERT(symbol.IsNull() || symbol.IsSymbol());
  ASSERT(symbol.IsNull() || symbol.HasHash());
  return symbol.raw();
}

StringPtr Symbols::LookupFromConcat(Thread* thread,
                                    const String& str1,
                                    const String& str2) {
  if (str1.Length() == 0) {
    return Lookup(thread, str2);
  } else if (str2.Length() == 0) {
    return Lookup(thread, str1);
  } else {
    return Lookup(thread, ConcatString(str1, str2));
  }
}

StringPtr Symbols::LookupFromGet(Thread* thread, const String& str) {
  return LookupFromConcat(thread, GetterPrefix(), str);
}

StringPtr Symbols::LookupFromSet(Thread* thread, const String& str) {
  return LookupFromConcat(thread, SetterPrefix(), str);
}

StringPtr Symbols::LookupFromDot(Thread* thread, const String& str) {
  return LookupFromConcat(thread, str, Dot());
}

StringPtr Symbols::New(Thread* thread, const String& str) {
  if (str.IsSymbol()) {
    return str.raw();
  }
  return New(thread, str, 0, str.Length());
}

StringPtr Symbols::New(Thread* thread,
                       const String& str,
                       intptr_t begin_index,
                       intptr_t len) {
  return NewSymbol(thread, StringSlice(str, begin_index, len));
}

StringPtr Symbols::NewFormatted(Thread* thread, const char* format, ...) {
  va_list args;
  va_start(args, format);
  StringPtr result = NewFormattedV(thread, format, args);
  NoSafepointScope no_safepoint;
  va_end(args);
  return result;
}

StringPtr Symbols::NewFormattedV(Thread* thread,
                                 const char* format,
                                 va_list args) {
  va_list args_copy;
  va_copy(args_copy, args);
  intptr_t len = Utils::VSNPrint(NULL, 0, format, args_copy);
  va_end(args_copy);

  Zone* zone = Thread::Current()->zone();
  char* buffer = zone->Alloc<char>(len + 1);
  Utils::VSNPrint(buffer, (len + 1), format, args);

  return Symbols::New(thread, buffer);
}

StringPtr Symbols::FromCharCode(Thread* thread, int32_t char_code) {
  if (char_code > kMaxOneCharCodeSymbol) {
    return FromUTF32(thread, &char_code, 1);
  }
  return predefined_[char_code];
}

void Symbols::DumpStats(Isolate* isolate) {
  intptr_t size = -1;
  intptr_t capacity = -1;
  // First dump VM symbol table stats.
  GetStats(Dart::vm_isolate(), &size, &capacity);
  OS::PrintErr("VM Isolate: Number of symbols : %" Pd "\n", size);
  OS::PrintErr("VM Isolate: Symbol table capacity : %" Pd "\n", capacity);
  // Now dump regular isolate symbol table stats.
  GetStats(isolate, &size, &capacity);
  OS::PrintErr("Isolate: Number of symbols : %" Pd "\n", size);
  OS::PrintErr("Isolate: Symbol table capacity : %" Pd "\n", capacity);
  // TODO(koda): Consider recording growth and collision stats in HashTable,
  // in DEBUG mode.
}

void Symbols::DumpTable(Isolate* isolate) {
  OS::PrintErr("symbols:\n");
  SymbolTable table(isolate->object_store()->symbol_table());
  table.Dump();
  table.Release();
}

intptr_t Symbols::LookupPredefinedSymbol(ObjectPtr obj) {
  for (intptr_t i = 1; i < Symbols::kMaxPredefinedId; i++) {
    if (symbol_handles_[i]->raw() == obj) {
      return (i + kMaxPredefinedObjectIds);
    }
  }
  return kInvalidIndex;
}

ObjectPtr Symbols::GetPredefinedSymbol(intptr_t object_id) {
  ASSERT(IsPredefinedSymbolId(object_id));
  intptr_t i = (object_id - kMaxPredefinedObjectIds);
  if ((i > kIllegal) && (i < Symbols::kMaxPredefinedId)) {
    return symbol_handles_[i]->raw();
  }
  return Object::null();
}

}  // namespace dart