text: // Copyright 2009 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_REGEXP_STACK_H_
  #define V8_REGEXP_STACK_H_
  
  namespace v8 {
  namespace internal {
  
  class RegExpStack;
  
  // Maintains a per-v8thread stack area that can be used by irregexp
  // implementation for its backtracking stack.
  // Since there is only one stack area, the Irregexp implementation is not
  // re-entrant. I.e., no regular expressions may be executed in the same thread
  // during a preempted Irregexp execution.
  class RegExpStackScope {
   public:
    // Create and delete an instance to control the life-time of a growing stack.
  
    // Initializes the stack memory area if necessary.
    explicit RegExpStackScope(Isolate* isolate);
    ~RegExpStackScope();  // Releases the stack if it has grown.
  
    RegExpStack* stack() const { return regexp_stack_; }
  
   private:
    RegExpStack* regexp_stack_;
  
    DISALLOW_COPY_AND_ASSIGN(RegExpStackScope);
  };
  
  
  class RegExpStack {
   public:
    // Number of allocated locations on the stack below the limit.
    // No sequence of pushes must be longer that this without doing a stack-limit
    // check.
    static const int kStackLimitSlack = 32;
  
    // Gives the top of the memory used as stack.
    Address stack_base() {
      DCHECK(thread_local_.memory_size_ != 0);
      return thread_local_.memory_ + thread_local_.memory_size_;
    }
  
    // The total size of the memory allocated for the stack.
    size_t stack_capacity() { return thread_local_.memory_size_; }
  
    // If the stack pointer gets below the limit, we should react and
    // either grow the stack or report an out-of-stack exception.
    // There is only a limited number of locations below the stack limit,
    // so users of the stack should check the stack limit during any
    // sequence of pushes longer that this.
    Address* limit_address() { return &(thread_local_.limit_); }
  
    // Ensures that there is a memory area with at least the specified size.
    // If passing zero, the default/minimum size buffer is allocated.
    Address EnsureCapacity(size_t size);
  
    // Thread local archiving.
    static int ArchiveSpacePerThread() {
      return static_cast<int>(sizeof(ThreadLocal));
    }
    char* ArchiveStack(char* to);
    char* RestoreStack(char* from);
    void FreeThreadResources() { thread_local_.Free(); }
  
   private:
    RegExpStack();
    ~RegExpStack();
  
    // Artificial limit used when no memory has been allocated.
    static const uintptr_t kMemoryTop = static_cast<uintptr_t>(-1);
  
    // Minimal size of allocated stack area.
    static const size_t kMinimumStackSize = 1 * KB;
  
    // Maximal size of allocated stack area.
    static const size_t kMaximumStackSize = 64 * MB;
  
    // Structure holding the allocated memory, size and limit.
    struct ThreadLocal {
      ThreadLocal() { Clear(); }
      // If memory_size_ > 0 then memory_ must be non-NULL.
      Address memory_;
      size_t memory_size_;
      Address limit_;
      void Clear() {
        memory_ = NULL;
        memory_size_ = 0;
        limit_ = reinterpret_cast<Address>(kMemoryTop);
      }
      void Free();
    };
  
    // Address of allocated memory.
    Address memory_address() {
      return reinterpret_cast<Address>(&thread_local_.memory_);
    }
  
    // Address of size of allocated memory.
    Address memory_size_address() {
      return reinterpret_cast<Address>(&thread_local_.memory_size_);
    }
  
    // Resets the buffer if it has grown beyond the default/minimum size.
    // After this, the buffer is either the default size, or it is empty, so
    // you have to call EnsureCapacity before using it again.
    void Reset();
  
    ThreadLocal thread_local_;
    Isolate* isolate_;
  
    friend class ExternalReference;
    friend class Isolate;
    friend class RegExpStackScope;
  
    DISALLOW_COPY_AND_ASSIGN(RegExpStack);
  };
  
  }}  // namespace v8::internal
  
  #endif  // V8_REGEXP_STACK_H_
  