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Annotate Lua packer with more comments

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sfan5 2024-02-15 16:24:15 +01:00
parent 2b97fead9e
commit 933432e62d
2 changed files with 85 additions and 23 deletions
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93
src/script/common/c_packer.cpp
View File

@ -70,6 +70,7 @@ static inline bool uses_union(int type)
}
}
// can set_into be used with these key / value types in principle?
static inline bool can_set_into(int ktype, int vtype)
{
switch (ktype) {
@ -82,7 +83,7 @@ static inline bool can_set_into(int ktype, int vtype)
}
}
// is the key suitable for use with set_into?
// is the actual key suitable for use with set_into?
static inline bool suitable_key(lua_State *L, int idx)
{
if (lua_type(L, idx) == LUA_TSTRING) {
@ -143,6 +144,13 @@ namespace {
typedef std::pair<std::string, Packer> PackerTuple;
}
/**
* Append instruction to end.
*
* @param pv target
* @param type instruction type
* @return reference to instruction
*/
static inline auto emplace(PackedValue &pv, s16 type)
{
pv.i.emplace_back();
@ -211,6 +219,13 @@ void script_register_packer(lua_State *L, const char *regname,
lua_pop(L, 1);
}
/**
* Find a packer for a metatable.
*
* @param regname metatable name
* @param out packer will be placed here
* @return success
*/
static bool find_packer(const char *regname, PackerTuple &out)
{
MutexAutoLock autolock(g_packers_lock);
@ -223,6 +238,14 @@ static bool find_packer(const char *regname, PackerTuple &out)
return true;
}
/**
* Find a packer matching the metatable of the Lua value.
*
* @param L Lua state
* @param idx Index on stack
* @param out packer will be placed here
* @return success
*/
static bool find_packer(lua_State *L, int idx, PackerTuple &out)
{
#ifndef NDEBUG
@ -254,6 +277,21 @@ static bool find_packer(lua_State *L, int idx, PackerTuple &out)
// Packing implementation
//
/**
* Keeps track of seen objects, which is needed to make circular references work.
* The first time an object is seen it remembers the instruction index.
* The caller is expected to add instructions that produce the value immediately after.
* For second, third, ... calls it pushes an instruction that references the already
* created value.
*
* @param L Lua state
* @param idx Index of value on Lua stack
* @param pv target
* @param seen Map of seen objects
* @return empty reference (first time) or reference to instruction that
* reproduces the value (otherwise)
*
*/
static VectorRef<PackedInstr> record_object(lua_State *L, int idx, PackedValue &pv,
std::unordered_map<const void *, s32> &seen)
{
@ -261,18 +299,31 @@ static VectorRef<PackedInstr> record_object(lua_State *L, int idx, PackedValue &
assert(ptr);
auto found = seen.find(ptr);
if (found == seen.end()) {
// first time, record index
assert(pv.i.size() <= S32_MAX);
seen[ptr] = pv.i.size();
return VectorRef<PackedInstr>();
}
s32 ref = found->second;
assert(ref < (s32)pv.i.size());
// reuse the value from first time
auto r = emplace(pv, INSTR_PUSHREF);
r->ref = ref;
r->sidata1 = ref;
pv.i[ref].keep_ref = true;
return r;
}
/**
* Pack a single Lua value and add it to the instruction stream.
*
* @param L Lua state
* @param idx Index of value on Lua stack. Must be positive, use absidx if not!
* @param vidx Next free index on the stack as it would look during unpacking. (v = virtual)
* @param pv target
* @param seen Map of seen objects (see record_object)
* @return reference to the instruction that creates the value
*/
static VectorRef<PackedInstr> pack_inner(lua_State *L, int idx, int vidx, PackedValue &pv,
std::unordered_map<const void *, s32> &seen)
{
@ -330,6 +381,7 @@ static VectorRef<PackedInstr> pack_inner(lua_State *L, int idx, int vidx, Packed
PackerTuple ser;
if (!find_packer(L, idx, ser))
throw LuaError("Cannot serialize unsupported userdata");
// use packer callback to turn into a void*
pv.contains_userdata = true;
r = emplace(pv, LUA_TUSERDATA);
r->sdata = ser.first;
@ -358,22 +410,28 @@ static VectorRef<PackedInstr> pack_inner(lua_State *L, int idx, int vidx, Packed
else
rtable->uidata2++; // nrec
// check if we can use a shortcut
// set_into is a shortcut that allows a pushed value
// to be directly set into a table without separately pushing
// the key and using SETTABLE.
// only works in certain circumstances, hence the check:
if (can_set_into(ktype, vtype) && suitable_key(L, -2)) {
// push only the value
auto rval = pack_inner(L, absidx(L, -1), vidx, pv, seen);
vidx++;
rval->pop = rval->type != LUA_TTABLE;
// and where to put it:
// where to put it:
rval->set_into = vi_table;
if (ktype == LUA_TSTRING)
rval->sdata = lua_tostring(L, -2);
else
rval->sidata1 = lua_tointeger(L, -2);
// pop tables after the fact
// since tables take multiple instructions to populate we have to
// pop them separately afterwards.
if (!rval->pop) {
auto ri1 = emplace(pv, INSTR_POP);
ri1->sidata1 = vidx;
ri1->sidata1 = vidx - 1;
}
vidx--;
} else {
// push the key and value
pack_inner(L, absidx(L, -2), vidx, pv, seen);
@ -392,6 +450,7 @@ static VectorRef<PackedInstr> pack_inner(lua_State *L, int idx, int vidx, Packed
lua_pop(L, 1);
}
// exactly the table should be left on stack
assert(vidx == vi_table + 1);
return rtable;
}
@ -405,6 +464,7 @@ PackedValue *script_pack(lua_State *L, int idx)
std::unordered_map<const void *, s32> seen;
pack_inner(L, idx, 1, pv, seen);
// allocate last for exception safety
return new PackedValue(std::move(pv));
}
@ -414,14 +474,15 @@ PackedValue *script_pack(lua_State *L, int idx)
void script_unpack(lua_State *L, PackedValue *pv)
{
lua_newtable(L); // table at index top to track ref indices -> objects
// table that tracks objects for keep_ref / PUSHREF (key = instr index)
lua_newtable(L);
const int top = lua_gettop(L);
int ctr = 0;
for (size_t packed_idx = 0; packed_idx < pv->i.size(); packed_idx++) {
auto &i = pv->i[packed_idx];
// If leaving values on stack make sure there's space (every 5th iteration)
// Make sure there's space on the stack (if applicable)
if (!i.pop && (ctr++) >= 5) {
lua_checkstack(L, 5);
ctr = 0;
@ -449,7 +510,8 @@ void script_unpack(lua_State *L, PackedValue *pv)
lua_remove(L, top + i.sidata2);
continue;
case INSTR_PUSHREF:
lua_pushinteger(L, i.ref);
// retrieve from top table
lua_pushinteger(L, i.sidata1);
lua_rawget(L, top);
break;
@ -476,7 +538,7 @@ void script_unpack(lua_State *L, PackedValue *pv)
PackerTuple ser;
sanity_check(find_packer(i.sdata.c_str(), ser));
ser.second.fout(L, i.ptrdata);
i.ptrdata = nullptr; // ownership taken by callback
i.ptrdata = nullptr; // ownership taken by packer callback
break;
}
@ -486,13 +548,14 @@ void script_unpack(lua_State *L, PackedValue *pv)
}
if (i.keep_ref) {
// remember in top table
lua_pushinteger(L, packed_idx);
lua_pushvalue(L, -2);
lua_rawset(L, top);
}
if (i.set_into) {
if (!i.pop)
if (!i.pop) // set will consume
lua_pushvalue(L, -1);
if (uses_sdata(i.type))
lua_rawseti(L, top + i.set_into, i.sidata1);
@ -504,7 +567,7 @@ void script_unpack(lua_State *L, PackedValue *pv)
}
}
// as part of the unpacking process we take ownership of all userdata
// as part of the unpacking process all userdata is "used up"
pv->contains_userdata = false;
// leave exactly one value on the stack
lua_settop(L, top+1);
@ -523,7 +586,7 @@ PackedValue::~PackedValue()
if (i.type == LUA_TUSERDATA && i.ptrdata) {
PackerTuple ser;
if (find_packer(i.sdata.c_str(), ser)) {
// tell it to deallocate object
// tell packer to deallocate object
ser.second.fout(nullptr, i.ptrdata);
} else {
assert(false);
@ -536,7 +599,6 @@ PackedValue::~PackedValue()
// script_dump_packed
//
#ifndef NDEBUG
void script_dump_packed(const PackedValue *val)
{
printf("instruction stream: [\n");
@ -550,7 +612,7 @@ void script_dump_packed(const PackedValue *val)
printf(i.sidata2 ? "POP(%d, %d)" : "POP(%d)", i.sidata1, i.sidata2);
break;
case INSTR_PUSHREF:
printf("PUSHREF(%d)", i.ref);
printf("PUSHREF(%d)", i.sidata1);
break;
case LUA_TNIL:
printf("nil");
@ -593,4 +655,3 @@ void script_dump_packed(const PackedValue *val)
}
printf("]\n");
}
#endif

15
src/script/common/c_packer.h
View File

@ -39,30 +39,31 @@ extern "C" {
#define INSTR_PUSHREF (-12)
/**
* Represents a single instruction that pushes a new value or works with existing ones.
* Represents a single instruction that pushes a new value or operates with existing ones.
*/
struct PackedInstr
{
s16 type; // LUA_T* or INSTR_*
u16 set_into; // set into table on stack
bool keep_ref; // is referenced later by INSTR_PUSHREF?
bool keep_ref; // referenced later by INSTR_PUSHREF?
bool pop; // remove from stack?
// Note: the remaining members are named by type, not usage
union {
bool bdata; // boolean: value
lua_Number ndata; // number: value
struct {
u16 uidata1, uidata2; // table: narr, nrec
u16 uidata1, uidata2; // table: narr | nrec
};
struct {
/*
SETTABLE: key index, value index
SETTABLE: key index | value index
POP: indices to remove
otherwise w/ set_into: numeric key, -
PUSHREF: index of referenced instr | unused
otherwise w/ set_into: numeric key | unused
*/
s32 sidata1, sidata2;
};
void *ptrdata; // userdata: implementation defined
s32 ref; // PUSHREF: index of referenced instr
};
/*
- string: value
@ -78,7 +79,7 @@ struct PackedInstr
/**
* A packed value can be a primitive like a string or number but also a table
* including all of its contents. It is made up of a linear stream of
* 'instructions' that build the final value when executed.
* instructions that build the final value when executed.
*/
struct PackedValue
{