integration/luprex/core/cpp/luasnap.hpp

/////////////////////////////////////////////////////////////////////////////
//
// LUASNAP
//
// A lua interpreter that can be checkpointed (snapshotted). This makes it
// possible to roll the entire interpreter back to a previously-snapshotted
// state.
//
// To accomplish this, we take advantage of the 'allocf' parameter to
// lua_newstate.  This lets us hook the lua allocator, which in turn lets us
// find every block of memory currently in use by lua.  To snapshot, we 'memcpy'
// every block of memory that lua is using into a buffer.  To rollback, we just
// 'memcpy' the data back.
//
// The current implementation is a proof-of-concept.  It's quite wasteful of
// memory, roughly doubling the amount of RAM that LUA uses.  It's also not
// super-fast, since it allocates tons of tiny blocks.  But it totally
// works, so it demonstrate that this method of snapshot and rollback is
// feasible.
//
/////////////////////////////////////////////////////////////////////////////

#ifndef LUASNAP_HPP
#define LUASNAP_HPP

#include "luastack.hpp"

class LuaSnap {
private:
    lua_State *state_;
    std::string snapshot_;
    
public:
    LuaSnap();
    ~LuaSnap();

    // Get the lua intepreter.
    //
    lua_State *state() const { return state_; }

    // Return true if there's a saved snapshot.
    //
    bool have_snapshot() const;

    // snapshot the state of the lua interpreter.
    //
    // If there is already a snapshot, this panics.
    //
    void snapshot();

    // Rollback the lua intepreter to the snapshotted state.
    //
    // If there is no snapshot, this panics.
    //
    void rollback();
};


#endif // LUASNAP_HPP