text: // Copyright 2012 the V8 project authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  #ifndef V8_ALLOCATION_H_
  #define V8_ALLOCATION_H_
  
  #include "include/v8-platform.h"
  #include "src/base/compiler-specific.h"
  #include "src/base/platform/platform.h"
  #include "src/globals.h"
  #include "src/v8.h"
  
  namespace v8 {
  namespace internal {
  
  // This file defines memory allocation functions. If a first attempt at an
  // allocation fails, these functions call back into the embedder, then attempt
  // the allocation a second time. The embedder callback must not reenter V8.
  
  // Called when allocation routines fail to allocate, even with a possible retry.
  // This function should not return, but should terminate the current processing.
  V8_EXPORT_PRIVATE void FatalProcessOutOfMemory(const char* message);
  
  // Superclass for classes managed with new & delete.
  class V8_EXPORT_PRIVATE Malloced {
      public:
          void* operator new(size_t size) {
              return New(size);
          }
          void  operator delete(void* p) {
              Delete(p);
          }
  
          static void* New(size_t size);
          static void Delete(void* p);
  };
  
  template <typename T>
  T* NewArray(size_t size) {
      T* result = new (std::nothrow) T[size];
      if (result == nullptr) {
          V8::GetCurrentPlatform()->OnCriticalMemoryPressure();
          result = new (std::nothrow) T[size];
          if (result == nullptr) {
              FatalProcessOutOfMemory("NewArray");
          }
      }
      return result;
  }
  
  template <typename T,
            typename = typename std::enable_if<IS_TRIVIALLY_COPYABLE(T)>::type>
  T* NewArray(size_t size, T default_val) {
      T* result = reinterpret_cast<T*>(NewArray<uint8_t>(sizeof(T) * size));
      for (size_t i = 0; i < size; ++i) {
          result[i] = default_val;
      }
      return result;
  }
  
  template <typename T>
  void DeleteArray(T* array) {
      delete[] array;
  }
  
  
  // The normal strdup functions use malloc.  These versions of StrDup
  // and StrNDup uses new and calls the FatalProcessOutOfMemory handler
  // if allocation fails.
  V8_EXPORT_PRIVATE char* StrDup(const char* str);
  char* StrNDup(const char* str, int n);
  
  
  // Allocation policy for allocating in the C free store using malloc
  // and free. Used as the default policy for lists.
  class FreeStoreAllocationPolicy {
      public:
          INLINE(void* New(size_t size)) {
              return Malloced::New(size);
          }
          INLINE(static void Delete(void* p)) {
              Malloced::Delete(p);
          }
  };
  
  // Performs a malloc, with retry logic on failure. Returns nullptr on failure.
  // Call free to release memory allocated with this function.
  void* AllocWithRetry(size_t size);
  
  void* AlignedAlloc(size_t size, size_t alignment);
  void AlignedFree(void* ptr);
  
  // Gets the page granularity for AllocatePages and FreePages. Addresses returned
  // by AllocatePages and AllocatePage are aligned to this size.
  V8_EXPORT_PRIVATE size_t AllocatePageSize();
  
  // Gets the granularity at which the permissions and release calls can be made.
  V8_EXPORT_PRIVATE size_t CommitPageSize();
  
  // Sets the random seed so that GetRandomMmapAddr() will generate repeatable
  // sequences of random mmap addresses.
  V8_EXPORT_PRIVATE void SetRandomMmapSeed(int64_t seed);
  
  // Generate a random address to be used for hinting allocation calls.
  V8_EXPORT_PRIVATE void* GetRandomMmapAddr();
  
  // Allocates memory. Permissions are set according to the access argument.
  // |address| is a hint. |size| and |alignment| must be multiples of
  // AllocatePageSize(). Returns the address of the allocated memory, with the
  // specified size and alignment, or nullptr on failure.
  V8_EXPORT_PRIVATE
  V8_WARN_UNUSED_RESULT void* AllocatePages(void* address, size_t size,
          size_t alignment,
          PageAllocator::Permission access);
  
  // Frees memory allocated by a call to AllocatePages. |address| and |size| must
  // be multiples of AllocatePageSize(). Returns true on success, otherwise false.
  V8_EXPORT_PRIVATE
  V8_WARN_UNUSED_RESULT bool FreePages(void* address, const size_t size);
  
  // Releases memory that is no longer needed. The range specified by |address|
  // and |size| must be an allocated memory region. |size| and |new_size| must be
  // multiples of CommitPageSize(). Memory from |new_size| to |size| is released.
  // Released memory is left in an undefined state, so it should not be accessed.
  // Returns true on success, otherwise false.
  V8_EXPORT_PRIVATE
  V8_WARN_UNUSED_RESULT bool ReleasePages(void* address, size_t size,
                                          size_t new_size);
  
  // Sets permissions according to |access|. |address| and |size| must be
  // multiples of CommitPageSize(). Setting permission to kNoAccess may
  // cause the memory contents to be lost. Returns true on success, otherwise
  // false.
  V8_EXPORT_PRIVATE
  V8_WARN_UNUSED_RESULT bool SetPermissions(void* address, size_t size,
          PageAllocator::Permission access);
  
  // Convenience function that allocates a single system page with read and write
  // permissions. |address| is a hint. Returns the base address of the memory and
  // the page size via |allocated| on success. Returns nullptr on failure.
  V8_EXPORT_PRIVATE
  V8_WARN_UNUSED_RESULT byte* AllocatePage(void* address, size_t* allocated);
  
  // Function that may release reserved memory regions to allow failed allocations
  // to succeed. |length| is the amount of memory needed. Returns |true| if memory
  // could be released, false otherwise.
  V8_EXPORT_PRIVATE bool OnCriticalMemoryPressure(size_t length);
  
  // Represents and controls an area of reserved memory.
  class V8_EXPORT_PRIVATE VirtualMemory {
      public:
          // Empty VirtualMemory object, controlling no reserved memory.
          VirtualMemory();
  
          // Reserves virtual memory containing an area of the given size that is
          // aligned per alignment. This may not be at the position returned by
          // address().
          VirtualMemory(size_t size, void* hint, size_t alignment = AllocatePageSize());
  
          // Construct a virtual memory by assigning it some already mapped address
          // and size.
          VirtualMemory(void* address, size_t size) : address_(address), size_(size) {}
  
          // Releases the reserved memory, if any, controlled by this VirtualMemory
          // object.
          ~VirtualMemory();
  
          // Returns whether the memory has been reserved.
          bool IsReserved() const {
              return address_ != nullptr;
          }
  
          // Initialize or resets an embedded VirtualMemory object.
          void Reset();
  
          // Returns the start address of the reserved memory.
          // If the memory was reserved with an alignment, this address is not
          // necessarily aligned. The user might need to round it up to a multiple of
          // the alignment to get the start of the aligned block.
          void* address() const {
              DCHECK(IsReserved());
              return address_;
          }
  
          void* end() const {
              DCHECK(IsReserved());
              return reinterpret_cast<void*>(reinterpret_cast<uintptr_t>(address_) +
                                             size_);
          }
  
          // Returns the size of the reserved memory. The returned value is only
          // meaningful when IsReserved() returns true.
          // If the memory was reserved with an alignment, this size may be larger
          // than the requested size.
          size_t size() const {
              return size_;
          }
  
          // Sets permissions according to the access argument. address and size must be
          // multiples of CommitPageSize(). Returns true on success, otherwise false.
          bool SetPermissions(void* address, size_t size,
                              PageAllocator::Permission access);
  
          // Releases memory after |free_start|. Returns the number of bytes released.
          size_t Release(void* free_start);
  
          // Frees all memory.
          void Free();
  
          // Assign control of the reserved region to a different VirtualMemory object.
          // The old object is no longer functional (IsReserved() returns false).
          void TakeControl(VirtualMemory* from);
  
          bool InVM(void* address, size_t size) {
              return (reinterpret_cast<uintptr_t>(address_) <=
                      reinterpret_cast<uintptr_t>(address)) &&
                     ((reinterpret_cast<uintptr_t>(address_) + size_) >=
                      (reinterpret_cast<uintptr_t>(address) + size));
          }
  
      private:
          void* address_;  // Start address of the virtual memory.
          size_t size_;    // Size of the virtual memory.
  };
  
  bool AllocVirtualMemory(size_t size, void* hint, VirtualMemory* result);
  bool AlignedAllocVirtualMemory(size_t size, size_t alignment, void* hint,
                                 VirtualMemory* result);
  
  }  // namespace internal
  }  // namespace v8
  
  #endif  // V8_ALLOCATION_H_
  