src/liveedit.h

// Copyright 2012 the V8 project authors. All rights reserved.
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// modification, are permitted provided that the following conditions are
// met:
//
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#ifndef V8_LIVEEDIT_H_
#define V8_LIVEEDIT_H_



// Live Edit feature implementation.
// User should be able to change script on already running VM. This feature
// matches hot swap features in other frameworks.
//
// The basic use-case is when user spots some mistake in function body
// from debugger and wishes to change the algorithm without restart.
//
// A single change always has a form of a simple replacement (in pseudo-code):
//   script.source[positions, positions+length] = new_string;
// Implementation first determines, which function's body includes this
// change area. Then both old and new versions of script are fully compiled
// in order to analyze, whether the function changed its outer scope
// expectations (or number of parameters). If it didn't, function's code is
// patched with a newly compiled code. If it did change, enclosing function
// gets patched. All inner functions are left untouched, whatever happened
// to them in a new script version. However, new version of code will
// instantiate newly compiled functions.


#include "allocation.h"
#include "compiler.h"

namespace v8 {
namespace internal {

// This class collects some specific information on structure of functions
// in a particular script. It gets called from compiler all the time, but
// actually records any data only when liveedit operation is in process;
// in any other time this class is very cheap.
//
// The primary interest of the Tracker is to record function scope structures
// in order to analyze whether function code maybe safely patched (with new
// code successfully reading existing data from function scopes). The Tracker
// also collects compiled function codes.
class LiveEditFunctionTracker {
 public:
  explicit LiveEditFunctionTracker(Isolate* isolate, FunctionLiteral* fun);
  ~LiveEditFunctionTracker();
  void RecordFunctionInfo(Handle<SharedFunctionInfo> info,
                          FunctionLiteral* lit, Zone* zone);
  void RecordRootFunctionInfo(Handle<Code> code);

  static bool IsActive(Isolate* isolate);

 private:
#ifdef ENABLE_DEBUGGER_SUPPORT
  Isolate* isolate_;
#endif
};

#ifdef ENABLE_DEBUGGER_SUPPORT

class LiveEdit : AllStatic {
 public:
  static JSArray* GatherCompileInfo(Handle<Script> script,
                                    Handle<String> source);

  static void WrapSharedFunctionInfos(Handle<JSArray> array);

  MUST_USE_RESULT static MaybeObject* ReplaceFunctionCode(
      Handle<JSArray> new_compile_info_array,
      Handle<JSArray> shared_info_array);

  static MaybeObject* FunctionSourceUpdated(Handle<JSArray> shared_info_array);

  // Updates script field in FunctionSharedInfo.
  static void SetFunctionScript(Handle<JSValue> function_wrapper,
                                Handle<Object> script_handle);

  MUST_USE_RESULT static MaybeObject* PatchFunctionPositions(
      Handle<JSArray> shared_info_array, Handle<JSArray> position_change_array);

  // For a script updates its source field. If old_script_name is provided
  // (i.e. is a String), also creates a copy of the script with its original
  // source and sends notification to debugger.
  static Object* ChangeScriptSource(Handle<Script> original_script,
                                    Handle<String> new_source,
                                    Handle<Object> old_script_name);

  // In a code of a parent function replaces original function as embedded
  // object with a substitution one.
  static void ReplaceRefToNestedFunction(Handle<JSValue> parent_function_shared,
                                         Handle<JSValue> orig_function_shared,
                                         Handle<JSValue> subst_function_shared);

  // Checks listed functions on stack and return array with corresponding
  // FunctionPatchabilityStatus statuses; extra array element may
  // contain general error message. Modifies the current stack and
  // has restart the lowest found frames and drops all other frames above
  // if possible and if do_drop is true.
  static Handle<JSArray> CheckAndDropActivations(
      Handle<JSArray> shared_info_array, bool do_drop);

  // Restarts the call frame and completely drops all frames above it.
  // Return error message or NULL.
  static const char* RestartFrame(JavaScriptFrame* frame);

  // A copy of this is in liveedit-debugger.js.
  enum FunctionPatchabilityStatus {
    FUNCTION_AVAILABLE_FOR_PATCH = 1,
    FUNCTION_BLOCKED_ON_ACTIVE_STACK = 2,
    FUNCTION_BLOCKED_ON_OTHER_STACK = 3,
    FUNCTION_BLOCKED_UNDER_NATIVE_CODE = 4,
    FUNCTION_REPLACED_ON_ACTIVE_STACK = 5
  };

  // Compares 2 strings line-by-line, then token-wise and returns diff in form
  // of array of triplets (pos1, pos1_end, pos2_end) describing list
  // of diff chunks.
  static Handle<JSArray> CompareStrings(Handle<String> s1,
                                        Handle<String> s2);
};


// A general-purpose comparator between 2 arrays.
class Comparator {
 public:
  // Holds 2 arrays of some elements allowing to compare any pair of
  // element from the first array and element from the second array.
  class Input {
   public:
    virtual int GetLength1() = 0;
    virtual int GetLength2() = 0;
    virtual bool Equals(int index1, int index2) = 0;

   protected:
    virtual ~Input() {}
  };

  // Receives compare result as a series of chunks.
  class Output {
   public:
    // Puts another chunk in result list. Note that technically speaking
    // only 3 arguments actually needed with 4th being derivable.
    virtual void AddChunk(int pos1, int pos2, int len1, int len2) = 0;

   protected:
    virtual ~Output() {}
  };

  // Finds the difference between 2 arrays of elements.
  static void CalculateDifference(Input* input,
                                  Output* result_writer);
};

#endif  // ENABLE_DEBUGGER_SUPPORT


} }  // namespace v8::internal

#endif /* V*_LIVEEDIT_H_ */