145 lines
4.5 KiB
C++
145 lines
4.5 KiB
C++
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#include "wrap-sstream.hpp"
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#include "wrap-string.hpp"
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#include "luasnap.hpp"
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#include "luastack.hpp"
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#include "streambuffer.hpp"
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#include <cassert>
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class LuaByteReader {
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private:
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const char *data_;
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int64_t size_;
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public:
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LuaByteReader(const char *d, int64_t s) : data_(d), size_(s) {}
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static const char *lua_reader(lua_State *L, void *ud, size_t *size) {
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LuaByteReader *reader = (LuaByteReader*)ud;
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*size = reader->size_;
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const char *data = reader->data_;
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reader->data_ = 0;
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reader->size_ = 0;
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return data;
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}
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};
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LuaSnap::LuaSnap() {
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state_ = LuaCoreStack::newstate(eng::l_alloc);
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LuaExtStack LS(state_);
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}
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LuaSnap::~LuaSnap() {
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lua_close(state_);
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}
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void LuaSnap::serialize(StreamBuffer *sb) {
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// Lua stack should be empty.
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assert(lua_gettop(state_) == 0);
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// We'll allocate stack slots manually, to ensure
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// that the thread serializes as we expect it to.
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lua_pushnil(state_); // permstable
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lua_pushnil(state_); // regcopy
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lua_pushnil(state_); // key
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lua_pushnil(state_); // value
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LuaSpecial permstable(1);
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LuaSpecial regcopy(2);
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LuaSpecial key(3);
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LuaSpecial value(4);
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LuaCoreStack LS(state_);
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// Construct a copy of the registry table.
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LS.set(regcopy, LuaNewTable);
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LS.set(key, LuaNil);
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while (LS.next(LuaRegistry, key, value) != 0) {
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LS.rawset(regcopy, key, value);
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}
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// Remove certain things from the copy. These items
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// don't get included in the snapshot.
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//
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// From a modularity perspective, this is bad.
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//
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LS.rawset(regcopy, LUA_RIDX_MAINTHREAD, LuaNil);
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LS.rawset(regcopy, "persist", LuaNil);
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LS.rawset(regcopy, "unpersist", LuaNil);
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LS.rawset(regcopy, "world", LuaNil);
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LS.rawset(regcopy, "gui", LuaNil);
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LS.rawset(regcopy, "tnmap", LuaNil);
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LS.rawset(regcopy, "ntmap", LuaNil);
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// Get the eris permanents table from the registry.
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LS.rawget(permstable, LuaRegistry, "persist");
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assert(LS.istable(permstable));
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// Remove key and value from stack, leaving permstable and regcopy.
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lua_settop(state_, 2);
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// Write dummy length, use eris to write data, then overwrite length.
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sb->write_int64(0);
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int64_t pos1 = sb->total_writes();
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eris_dump(state_, lua_writer_into_streambuffer, sb);
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int64_t pos2 = sb->total_writes();
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sb->overwrite_int64(pos1, pos2 - pos1);
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lua_settop(state_, 0);
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}
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void LuaSnap::deserialize(StreamBuffer *sb) {
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// Lua stack should be empty.
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assert(lua_gettop(state_) == 0);
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// Get the eris data and convert it to a byte reader.
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int64_t eris_len = sb->read_int64();
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const char *eris_bytes = sb->read_bytes(eris_len);
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LuaByteReader bytereader(eris_bytes, eris_len);
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// Call eris with the permanents table and passing the snapshot as a lua_Reader.
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lua_pushstring(state_, "unpersist");
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lua_rawget(state_, LUA_REGISTRYINDEX);
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eris_undump(state_, bytereader.lua_reader, &bytereader);
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// Set up a stack frame manually. Eris deserialization
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// should have left permstable and regcopy on the stack.
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assert(lua_gettop(state_) == 2);
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[[maybe_unused]] LuaSpecial permstable(1);
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LuaSpecial regcopy(2);
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lua_pushnil(state_);
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lua_pushnil(state_);
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LuaSpecial key(3);
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LuaSpecial value(4);
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LuaCoreStack LS(state_);
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assert(LS.istable(regcopy));
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// Copy the contents of the snapshot over to the registry.
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LS.set(key, LuaNil);
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while (LS.next(regcopy, key, value) != 0) {
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LS.rawset(LuaRegistry, key, value);
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}
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lua_settop(state_, 0);
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}
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// Snapshot and rollback can trivially be implemented on top of serialize and
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// deserialize. However, it's also possible to implement snapshot and rollback
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// using an alternative technique:
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//
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// 1. When constructing the lua interpreter, use a custom memory allocator that
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// keeps track of all the memory blocks used by lua.
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//
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// 2. Snapshot simply copies all the memory blocks used by lua into a buffer.
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//
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// 3. Rollback restores lua's memory blocks back to their previous state. This
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// has the effect of restoring lua's state.
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//
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// A proof-of-concept implementation of the memory-snapshotting design was
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// created, and it worked. It is probably faster than using serialize and
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// deserialize.
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//
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// Note: even if we implement this alternative design, we still need to keep
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// serialize and deserialize around in order to implement the save-game
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// functionality. So for now, we're sticking with this design, which doesn't
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// require us to maintain any additional code.
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