text: /*
   * Copyright (C) 2014 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.
   */
  
  #ifndef ART_RUNTIME_GC_ACCOUNTING_READ_BARRIER_TABLE_H_
  #define ART_RUNTIME_GC_ACCOUNTING_READ_BARRIER_TABLE_H_
  
  #include <sys/mman.h>  // For the PROT_* and MAP_* constants.
  
  #include "base/bit_utils.h"
  #include "base/locks.h"
  #include "base/mem_map.h"
  #include "gc/space/space.h"
  #include "runtime_globals.h"
  
  namespace art {
  namespace gc {
  namespace accounting {
  
  // Used to decide whether to take the read barrier fast/slow paths for
  // kUseTableLookupReadBarrier. If an entry is set, take the read
  // barrier slow path. There's an entry per region.
  class ReadBarrierTable {
   public:
    ReadBarrierTable() {
      size_t capacity = static_cast<size_t>(kHeapCapacity / kRegionSize);
      DCHECK_EQ(kHeapCapacity / kRegionSize,
                static_cast<uint64_t>(static_cast<size_t>(kHeapCapacity / kRegionSize)));
      std::string error_msg;
      mem_map_ = MemMap::MapAnonymous("read barrier table",
                                      capacity,
                                      PROT_READ | PROT_WRITE,
                                      /*low_4gb=*/ false,
                                      &error_msg);
      CHECK(mem_map_.IsValid() && mem_map_.Begin() != nullptr)
          << "couldn't allocate read barrier table: " << error_msg;
    }
    void ClearForSpace(space::ContinuousSpace* space) {
      uint8_t* entry_start = EntryFromAddr(space->Begin());
      uint8_t* entry_end = EntryFromAddr(space->Limit());
      memset(reinterpret_cast<void*>(entry_start), 0, entry_end - entry_start);
    }
    void Clear(uint8_t* start_addr, uint8_t* end_addr) {
      DCHECK(IsValidHeapAddr(start_addr)) << start_addr;
      DCHECK(IsValidHeapAddr(end_addr)) << end_addr;
      DCHECK_ALIGNED(start_addr, kRegionSize);
      DCHECK_ALIGNED(end_addr, kRegionSize);
      uint8_t* entry_start = EntryFromAddr(start_addr);
      uint8_t* entry_end = EntryFromAddr(end_addr);
      memset(reinterpret_cast<void*>(entry_start), 0, entry_end - entry_start);
    }
    bool IsSet(const void* heap_addr) const {
      DCHECK(IsValidHeapAddr(heap_addr)) << heap_addr;
      uint8_t entry_value = *EntryFromAddr(heap_addr);
      DCHECK(entry_value == 0 || entry_value == kSetEntryValue);
      return entry_value == kSetEntryValue;
    }
    void ClearAll() {
      mem_map_.MadviseDontNeedAndZero();
    }
    void SetAll() {
      memset(mem_map_.Begin(), kSetEntryValue, mem_map_.Size());
    }
    bool IsAllCleared() const {
      for (uint32_t* p = reinterpret_cast<uint32_t*>(mem_map_.Begin());
           p < reinterpret_cast<uint32_t*>(mem_map_.End()); ++p) {
        if (*p != 0) {
          return false;
        }
      }
      return true;
    }
  
    // This should match RegionSpace::kRegionSize. static_assert'ed in concurrent_copying.h.
    static constexpr size_t kRegionSize = 256 * KB;
  
   private:
    static constexpr uint64_t kHeapCapacity = 4ULL * GB;  // low 4gb.
    static constexpr uint8_t kSetEntryValue = 0x01;
  
    uint8_t* EntryFromAddr(const void* heap_addr) const {
      DCHECK(IsValidHeapAddr(heap_addr)) << heap_addr;
      uint8_t* entry_addr = mem_map_.Begin() + reinterpret_cast<uintptr_t>(heap_addr) / kRegionSize;
      DCHECK(IsValidEntry(entry_addr)) << "heap_addr: " << heap_addr
                                       << " entry_addr: " << reinterpret_cast<void*>(entry_addr);
      return entry_addr;
    }
  
    bool IsValidHeapAddr(const void* heap_addr) const {
  #ifdef __LP64__
      return reinterpret_cast<uint64_t>(heap_addr) < kHeapCapacity;
  #else
      UNUSED(heap_addr);
      return true;
  #endif
    }
  
    bool IsValidEntry(const uint8_t* entry_addr) const {
      uint8_t* begin = mem_map_.Begin();
      uint8_t* end = mem_map_.End();
      return entry_addr >= begin && entry_addr < end;
    }
  
    MemMap mem_map_;
  };
  
  }  // namespace accounting
  }  // namespace gc
  }  // namespace art
  
  #endif  // ART_RUNTIME_GC_ACCOUNTING_READ_BARRIER_TABLE_H_
  