regexp-stack.h

// Copyright 2009 the V8 project authors. All rights reserved.
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#ifndef V8_REGEXP_STACK_H_
#define V8_REGEXP_STACK_H_

namespace v8 {
namespace internal {

// 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 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;

  // Create and delete an instance to control the life-time of a growing stack.
  RegExpStack();  // Initializes the stack memory area if necessary.
  ~RegExpStack();  // Releases the stack if it has grown.

  // Gives the top of the memory used as stack.
  static Address stack_base() {
    ASSERT(thread_local_.memory_size_ != 0);
    return thread_local_.memory_ + thread_local_.memory_size_;
  }

  // The total size of the memory allocated for the stack.
  static 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.
  static 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.
  static Address EnsureCapacity(size_t size);

  // Thread local archiving.
  static int ArchiveSpacePerThread() {
    return static_cast<int>(sizeof(thread_local_));
  }
  static char* ArchiveStack(char* to);
  static char* RestoreStack(char* from);
  static void FreeThreadResources() { thread_local_.Free(); }

 private:
  // 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()
        : memory_(NULL),
          memory_size_(0),
          limit_(reinterpret_cast<Address>(kMemoryTop)) {}
    // If memory_size_ > 0 then memory_ must be non-NULL.
    Address memory_;
    size_t memory_size_;
    Address limit_;
    void Free();
  };

  // Address of allocated memory.
  static Address memory_address() {
    return reinterpret_cast<Address>(&thread_local_.memory_);
  }

  // Address of size of allocated memory.
  static 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.
  static void Reset();

  static ThreadLocal thread_local_;

  friend class ExternalReference;
};

}}  // namespace v8::internal

#endif  // V8_REGEXP_STACK_H_