regexp-stack.h

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// 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_