runtime/intern_table.cc

/*
 * Copyright (C) 2011 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 "intern_table.h"

#include "mirror/string.h"
#include "thread.h"
#include "UniquePtr.h"
#include "utf.h"

namespace art {

InternTable::InternTable() : intern_table_lock_("InternTable lock"), is_dirty_(false) {
}

size_t InternTable::Size() const {
  MutexLock mu(Thread::Current(), intern_table_lock_);
  return strong_interns_.size() + weak_interns_.size();
}

void InternTable::DumpForSigQuit(std::ostream& os) const {
  MutexLock mu(Thread::Current(), intern_table_lock_);
  os << "Intern table: " << strong_interns_.size() << " strong; "
     << weak_interns_.size() << " weak; "
     << image_strong_interns_.size() << " image strong\n";
}

void InternTable::VisitRoots(RootVisitor* visitor, void* arg, bool clean_dirty) {
  MutexLock mu(Thread::Current(), intern_table_lock_);
  for (const auto& strong_intern : strong_interns_) {
    visitor(strong_intern.second, arg);
  }
  if (clean_dirty) {
    is_dirty_ = false;
  }
  // Note: we deliberately don't visit the weak_interns_ table and the immutable image roots.
}

mirror::String* InternTable::Lookup(Table& table, mirror::String* s, uint32_t hash_code) {
  intern_table_lock_.AssertHeld(Thread::Current());
  for (auto it = table.find(hash_code), end = table.end(); it != end; ++it) {
    mirror::String* existing_string = it->second;
    if (existing_string->Equals(s)) {
      return existing_string;
    }
  }
  return NULL;
}

mirror::String* InternTable::Insert(Table& table, mirror::String* s, uint32_t hash_code) {
  intern_table_lock_.AssertHeld(Thread::Current());
  table.insert(std::make_pair(hash_code, s));
  return s;
}

void InternTable::RegisterStrong(mirror::String* s) {
  MutexLock mu(Thread::Current(), intern_table_lock_);
  Insert(image_strong_interns_, s, s->GetHashCode());
}

void InternTable::Remove(Table& table, const mirror::String* s, uint32_t hash_code) {
  intern_table_lock_.AssertHeld(Thread::Current());
  for (auto it = table.find(hash_code), end = table.end(); it != end; ++it) {
    if (it->second == s) {
      table.erase(it);
      return;
    }
  }
}

mirror::String* InternTable::Insert(mirror::String* s, bool is_strong) {
  MutexLock mu(Thread::Current(), intern_table_lock_);

  DCHECK(s != NULL);
  uint32_t hash_code = s->GetHashCode();

  if (is_strong) {
    // Check the strong table for a match.
    mirror::String* strong = Lookup(strong_interns_, s, hash_code);
    if (strong != NULL) {
      return strong;
    }
    // Check the image table for a match.
    mirror::String* image = Lookup(image_strong_interns_, s, hash_code);
    if (image != NULL) {
      return image;
    }

    // Mark as dirty so that we rescan the roots.
    Dirty();

    // There is no match in the strong table, check the weak table.
    mirror::String* weak = Lookup(weak_interns_, s, hash_code);
    if (weak != NULL) {
      // A match was found in the weak table. Promote to the strong table.
      Remove(weak_interns_, weak, hash_code);
      return Insert(strong_interns_, weak, hash_code);
    }

    // No match in the strong table or the weak table. Insert into the strong table.
    return Insert(strong_interns_, s, hash_code);
  }

  // Check the strong table for a match.
  mirror::String* strong = Lookup(strong_interns_, s, hash_code);
  if (strong != NULL) {
    return strong;
  }
  // Check the image table for a match.
  mirror::String* image = Lookup(image_strong_interns_, s, hash_code);
  if (image != NULL) {
    return image;
  }
  // Check the weak table for a match.
  mirror::String* weak = Lookup(weak_interns_, s, hash_code);
  if (weak != NULL) {
    return weak;
  }
  // Insert into the weak table.
  return Insert(weak_interns_, s, hash_code);
}

mirror::String* InternTable::InternStrong(int32_t utf16_length, const char* utf8_data) {
  return InternStrong(mirror::String::AllocFromModifiedUtf8(Thread::Current(), utf16_length, utf8_data));
}

mirror::String* InternTable::InternStrong(const char* utf8_data) {
  return InternStrong(mirror::String::AllocFromModifiedUtf8(Thread::Current(), utf8_data));
}

mirror::String* InternTable::InternStrong(mirror::String* s) {
  if (s == NULL) {
    return NULL;
  }
  return Insert(s, true);
}

mirror::String* InternTable::InternWeak(mirror::String* s) {
  if (s == NULL) {
    return NULL;
  }
  return Insert(s, false);
}

bool InternTable::ContainsWeak(mirror::String* s) {
  MutexLock mu(Thread::Current(), intern_table_lock_);
  const mirror::String* found = Lookup(weak_interns_, s, s->GetHashCode());
  return found == s;
}

void InternTable::SweepInternTableWeaks(IsMarkedTester is_marked, void* arg) {
  MutexLock mu(Thread::Current(), intern_table_lock_);
  // TODO: std::remove_if + lambda.
  for (auto it = weak_interns_.begin(), end = weak_interns_.end(); it != end;) {
    mirror::Object* object = it->second;
    if (!is_marked(object, arg)) {
      weak_interns_.erase(it++);
    } else {
      ++it;
    }
  }
}

}  // namespace art