I'm working on a project in Lua where I will be creating tables and storing them in a master table, to be erased at a later time. I will pass around references to these tables to other sibling tables.
master = {}
table.insert(master, {name = 'hello'})
table.insert(master, {name = 'world', pre = master[1]})
The problem that occurs is that when I wish to erase the reference from the master table, the reference still remains in master[2] here. Obviously my first solution was to make the tables have weak values. (through .__mode on a metatable, not shown here)
This worked, and would work, so long as I would never store a singly-referenced table within these tables.
table.insert(master, {name = 'goodbye', pre = master[2], some_table = {123}})
The third element, some_table would eventually be collected, because the tables have weak values, and this table (some_table) is not referenced anywhere else. This is undesired behavior. My latest solution involves creating "weak reference objects" to the tables within the master table. A naive implementation follows:
function WeakRef(t)
r = {__mode = 'v', __index = t, __newindex = t}
setmetatable(r, r)
return r
end
These weak reference objects act similarly to boost::weak_ptrs and accomplish my goal, but I am uncertain if they are the best solution to my problem.
Is there a better way; a more elegant solution?
Is my design, which requires this master table, perhaps flawed?
Given that:
You want master to be the "one place" where you define whether an object exists or not
Your objects can have links between them
Then probably the simplest architecture is reserving one of the members of each object as a "middle man" in charge of managing the references to others. Here're the steps:
Make master a regular table (not weak)
On each physical object, create a weak table called links (or whatever name suits your logic better)
Make all links tables weak. Use them to store references to other objects.
And this is a possible implementation. I've tried it in Lua 5.1:
local function newWeakTable()
return setmetatable({}, {__mode = "v"})
end
local master = {}
-- create two physical objects
local obj1 = { name = "obj1", links = newWeakTable() }
local obj2 = { name = "obj2", links = newWeakTable() }
-- link them
obj2.links.pre = obj1
-- insert them into master
table.insert(master, obj1)
table.insert(master, obj2)
-- master has 2 objects, and they are linked
assert(#master == 2)
assert(obj2.links.pre == obj1)
-- remove obj1 from master, and remove the variable reference
table.remove(master, 1)
obj1 = nil
-- run gc manually
collectgarbage("collect")
-- master has only 1 object now, and the link has dissapeared
assert(#master == 1)
assert(obj2.links.pre == nil)
print("Everything went as expected")
Related
I'm keeping in memory huge list of companies, and need to do lots of operations of getting individual company.
Like getting individual company "Microsoft" by its symbol "MSFT".
Would the data structure below be a proper way to model that? There should be no copy-by-value of the whole list or map.
It is ok if the individual company would be copied by value.
import tables
type
Company = object
name: string
symbol: string
description: string
CompaniesRef = ref object
list: seq[Company]
map: Table[string, Company]
# Cached data structure to keep thousands of different companies
var cached_companies: CompaniesRef
proc companies(): CompaniesRef =
if cached_companies == nil:
# Here will be a proper code of loading companies into the
# CompaniesRef data structure
cached_companies = CompaniesRef()
cached_companies
# Lots of operations of getting a specific company from the list
# or from the map by its symbol
for i in 1..1000:
# it's ok if individual company will be copied by value,
# but the whole list should be passed by reference
let company1 = companies().list[0].name
# it's ok if individual company will be copied by value
# but the whole map should be passed by reference
let company2 = companies().map["MSFT"]
That global structure should be fine as it is, an object reference is just a memory managed pointer, so passing its reference around only copies the memory address. Unless you are going to do something with that pointer, why not create it as a global? Hiding it behind a proc call reeks of the I'm-afraid-of-globals-but-can't-live-without-them-singleton pattern.
let companies = CompaniesRef()
With regards to the contents of the structure, you are storing twice each Company object, you might want to store a reference to the Company in the Table or simply use an OrderedTable if you need to keep the order of the inserted keys.
I don't use often weak tables. However now I need to manage certain attributes for my objects which should be stored somewhere else. Thats when weak tables come in handy. My issue is, that they don't work es expected. I need weak keys, so that the entire key/value pair is removed, when the key is no longer referenced and I need strong values, since what is stored are tables with meta information which is only used inside that table, which also have a reference to the key, but somehow those pairs are never collected.
Code example:
local key = { }
local value = {
ref = key,
somevalue = "Still exists"
}
local tab = setmetatable({}, { __mode = "k" })
tab[key] = value
function printtab()
for k, v in pairs(tab) do
print(v.somevalue)
end
end
printtab()
key = nil
value = nil
print("Delete values")
collectgarbage()
printtab()
Expected output:
Still exists
Delete values
Got:
Still exists
Delete values
Still exists
Why is the key/value pair not deleted? The only reference to value is effectivly a weak reference inside tab, and the reference inside value is not relevant, since the value itself is not used anywhere.
Ephemeron tables are supported since Lua 5.2.
The Lua 5.2 manual says:
A table with weak keys and strong values is also called an ephemeron table. In an ephemeron table, a value is considered reachable only if its key is reachable. In particular, if the only reference to a key comes through its value, the pair is removed.
Lua 5.1 does not support ephemeron tables correctly.
You are making too many assumptions about the garbage collector. Your data will be collected eventually. In this particular example it should work if you call collectgarbage() twice, but if you have some loops in your weak table it might take even longer.
EDIT: this actually only matters when you're waiting for the __cg event
I went over your code in more detail and noticed you have another problem.
Your value is referencing the key as well, creating a loop that is probably just too much for the GC of your Lua version to handle. In PUC Lua 5.3 this works as expected, but in LuaJIT the loop seems to keep the value from being collected.
This actually makes a lot of sense if you think about it; from what I can tell, the whole thing works by first removing weak elements from a table when they're not referenced anywhere else and thus leave them to be collected normally the next time the GC runs.
However, when this step runs, the key is still in the table, so the (not weak) value is a valid reference in the GCs eyes, as it is accessible from the code. So the GC kind of deadlocks itself into not being able to remove the key-value pair.
Possible solutions would be:
Don't save a reference to the key in the value
Make the value a weak table as well so it doesn't count as a reference either
Upgrade to another Lua version
Wrap the reference in a weak-valued single-element array
you can change the code like this. Then you will get the expected output. tips: do not reference key variable when you want it to be week.
local key = { }
local value = {
-- ref = key,
somevalue = "Still exists"
}
local tab = setmetatable({}, { __mode = "k" })
tab[key] = value
function printtab()
for k, v in pairs(tab) do
print(v.somevalue)
end
end
printtab()
key = nil
value = nil
print("Delete values")
collectgarbage()
printtab()
This is for a simple script I'm writing for an oldschool MUD game for those who know what that is.
Basically I am searching through one table (which I'm reading from gmcp) and trying to search the value's on that table to see if any of them match any of the value's on another table which I'm storing the value's I'm looking for.
I've successfully managed to do it with singular value's by simply using a "for" loop to grab the value from gmcp and store it as a variable and then using another "for" loop to search the other table to see if any of the values there match the variable.
Trouble is, it only works for a singular value and misses all the others if there is more than one value I need to check in that table.
The code I have is as follows,
for _, v in pairs(gmcptable) do
checkvalue = v
end
for _, v in pairs(mytable) do
if v == checkvalue then
echo("yay")
else
echo("no!")
end
end
again this works fine for gmcp tables with one value, but fails if more. I tried doing this to,
for _, v in pairs(gmcptable) do
checkvalue = v
for _, v in pairs(mytable) do
if v == checkvalue then
echo("yay")
else
echo("no!")
end
end
end
my hope was that it might set the variable, run the second for loop to check the variable and then repeat for the next value on the gmcp table since it's a for loop and the second loop was within the loop, but that didn't work either. I also tried making my own function to add to the mix and simplify it,
function searchtable(table, element)
for _, v in pairs(table) do
if v == element then
return true
else
return false
end
end
end
for _, v in pairs(gmcptable) do
if searchtable(mytable, v) == true then
echo("yay")
else
echo("no!")
end
end
that was a bust also... I'm sure I'm just overlooking something or showing what an amateur I am, but I've googled loads and tried everything I can think of, but I'm just self taught and only recently started understanding how tables and for loops even work. Hopefully someone out there can get back to me with something that works soonish!
UPDATE!
#Piglet Okay so, gmcptable was actually me trying to simplify the question for those who could answer the coding question. gmcptable actually is a long list of tables received by my client via the connection from the server the game this is for. so in all actuality, I have 3 tables I'm parsing data from. "gmcp.Char.Items.List.items", "gmcp.Char.Items.Add" and "gmcp.Char.Items.Remove". Now gmcp.Char.Items.List.items is the list of everything in the room I'm in within the game. gmcp.Char.Items.Add is the list of anything that enter the room and is sent each time anything enters the room aside from other players and gmcp.Char.Items.Remove is the same, but for when anything leaves the room. I'm trying to use this information to create a targeting table that will automatically add desired targets to my targeting que and remove them if they are not in the room. the room list (gmcp.Char.Items.List) is updated only when I enter or exit the room and possibly when I look, but for now I'm assuming it doesn't update when I look because that will be a whole other problem to solve later.
I currently have a simple script in what my client ID's as a trigger, this is set to fire once when I log into the game in question and the script define the tables that hold the value's I'm cross referencing the gmcp tables with to figure out if it's information I want added to my target table, this script also defines the target table as empty, which is meant to ensure that for the duration of the session, both tables exist and are defined.
I then added three separate scripts that parse the three gmcp tables and figure out whether that are on my desired targets table and if so adds it or in the of the case of the remove table checks if its currently on the targets table and if so removes it. below I'll show the current scripts I'm using (which have changed several times over since yesterday and might change again before I get a look at any future replies to this. I will also include a what the gmcp tables in question look like and if I'm currently seeing any error or debug details from my client I'll include that as well.
log on trigger
match on > ^Password correct\. in perl regex
bashtargets = {}
bashlist = {
"a baby rat",
"a young rat",
"a rat",
"an old rat",
"a black rat"
}
(the above trigger appears to be working properly and I can print the tables accurately)
script in the room
event handlers > gmcp.Char.Items.List
for _, v in pairs(gmcp.Char.Items.List.items) do
bashname = v.name
bashid = v.id
for _, v in pairs(bashlist) do
if v == bashname then
table.insert(bashtargets, bashid)
end
end
end
script addcheck
event handlers "gmcp.Char.Items.Add"
for _, v in pairs(gmcp.Char.Items.Add) do
addname = v.name
addid = v.id
for _, v in pairs(bashlist) do
if v == addname then
table.insert(bashtargets, addid)
end
end
end
script removecheck
event handlers "gmcp.Char.Items.Remove"
for _, v in pairs(gmcp.Char.Items.Remove) do
delid = v.id
for _, v in pairs(bashtargets) do
if v == delid then
table.remove(bashtargets, delid)
end
end
end
gmcp table "gmcp.Char.Items"
{
Remove = {
location = "room",
item = {
id = "150558",
name = "a filthy gutter mutt",
attrib = "m"
}
},
Add = {
location = "room",
item = {
id = "150558",
name = "a filthy gutter mutt",
attrib = "m"
}
},
List = {
location = "room",
items = {
{
id = "59689",
name = "a statue of a decaying gargoyle",
icon = "profile"
},
{
id = "84988",
name = "a gas lamp"
},
{
id = "101594",
attrib = "t",
name = "a monolith sigil",
icon = "rune"
},
{
id = "196286",
name = "a wooden sign"
},
{
id = "166410",
name = "Lain, the Lamplighter",
attrib = "m"
}
}
}
}
I have parsed the information successfully several times, so I've got the right tables and syntax and what have you where gmcp is concerned.
using this I have also managed to get it to half work. currently the set up seems to capture single targets at a time even if there are dozens and add that one, sometimes it oddly enough adds the same target 3 - 5 times for some reason, not sure why, haven't been able to figure it out yet.
these two error messages have been output by my client repeatedly, no idea what to do about them though or how to fix them... "left the room" and "entered the room" are the names currently assigned to the scripts for adding and removing data from the tables in my client.
[ERROR:] object:<event handler function> function:<left the room>
<Lua error:[string "return left the room"]:1: '<eof>' expected near 'the'>
[ERROR:] object:<event handler function> function:<entered the room>
<Lua error:[string "return entered the room"]:1: '<eof>' expected near 'the'>
I have no idea what '' means though, or why it's expected near 'the' it's all got my head pounding though...
I can see through the debug feature on my client that all the handlers are being sent by the server so it's not the gmcp... I'm not actually seeing any bugs on the debug feature (which btw is separate from the error feature that keeps putting out those other two errors I mentions.
anyways that's my update... Hopefully that give some people a better handle on what I'm doing wrong so I can get this figured out and learn something new.
Thanks again in advance and extra thanks to you #Piglet for you answer I definitely learned something new from it and thought it was very helpful.
In your first attempt you have 2 separate loops. You overwrite checkvalue for every element in gmcptable. Once you enter your second loop checkvalue will have the value last asigned in your first loop. So you only have 1 checkvalue and you only run across your table once as you only run your second loop once.
for _, v in pairs(gmcptable) do
checkvalue = v
end
for _, v in pairs(mytable) do
if v == checkvalue then
echo("yay")
else
echo("no!")
end
end
Your second attempt should work if I understood your problem.
You iterate over every element of gmcptable and compare it to every element in mytable. So whenever gmcptable contains a value that is also contained in mytable you should get a "yay".
for _, v in pairs(gmcptable) do
checkvalue = v
for _, v in pairs(mytable) do
if v == checkvalue then
echo("yay")
else
echo("no!")
end
end
end
One remark on your third attempt with a function. You should not call arguments table as you will then have no access to the global table functions inside your function. A call to table.sort for example would result in an error as you will index your local parameter table instead.
Okay so I tinkered with it a bit more tonight and kept getting the same error, eventually I googled the error and came to understand that the error was an end of file error, the client I use uses the name of a script as the name for a function if you don't declare it in the actual script, or at least that is my understanding of it, and so I didn't bother defining the function, and if I added an additional end to the script the client threw up another error because it wasn't defined, so I guess the client adds it's own definition to the function but doesn't add it's own end to the function which created the mix up. So long story short, the solution was to define each of the scripts as a function and add another end to close the function and that fixed the problem.
Thanks again to #Piglet for his answer, it was very helpful and dead accurate too! Thanks mate!
I'm facing a problem while using Drools.
I try to update an attribute from a nested member. The update seems to work, but the when clause do not consider it.
I have 2 Obj object, sharing the same Cpt object.
Cpt cpt = new Cpt();
Obj obj1 = new Obj("obj1");
obj1.setComposant("R2");
obj1.counter = cpt;
Obj obj2 = new Obj("obj2");
obj2.setComposant("R2");
obj2.counter = cpt;
kSession.insert(obj2);
kSession.insert(obj1);
My rule is define as:
rule "R2"
when
m : Obj(composant == "R2" && counter.value == 0)
then
System.out.println(m.getName() + " " + m.getCounter().getValue());
m.getCounter().increment();
end
I was expecting Obj1 to match the when clause, then update the value of the counter (from 0 to 1). So the Obj2 should not match the where clause.
But in fact, it does, even if the display is as I expected :
obj1 0
obj2 1
Can someone explain me what am I doing wrong ?
All reactions of the Drools Rule Engine with respect to changes in the set of facts require to be notified by using one of the extensions for the Right Hand Side language. You need to call update(f) for the modified fact object f, or you may use the modify(f){...} statement.
However... Changing a contained object X via the reference from fact A and telling the Engine that fact A has been modified will not make it see that fact B, also referencing X, has been changed as well.
This is where you should reconsider your design. Is it really necessary to have an X shared via references from A and B? Or: what about making X a fact and updating it? The latter may mean that you have to rewrite your rules, making the relation between Obj and Cpt visible on the left hand side. But, in my experience, it is usually better to have this than some complex mechanism propagating update notifications from some joint contained object to its parents.
Edit What I mean by "making the relation visible" is shown by the rule below:
rule "R2"
when
Obj(composant == "R2", $counter: counter )
$c: Cpt( this == $counter, value == 0)
then
modify( $c ){ increment() }
end
I need to use a string value as a table, in order to restore points to a player when they reconnect to a game server.
This string value is their profile ID, which never changes and I need to put data inside the string value (Kills, deaths, head shots) in order to effectively restore these points. I have had a quick look on the internet but I have not found much because I don't know what this specific thing is actually called.
To make it easier, here's what I have so far:
if (not Omega.Playertable) then
Omega.Playertable = {};
System.LogAlways("Set static record table on first connect");
end
local ID = g_gameRules.game:GetProfileId(player.id);
if (not Omega.Playertable.ID) then
table.insert(Omega.Playertable, ID);
Omega.Playertable.g_gameRules.game:GetProfileId(player.id).Kills=0;
Omega.Playertable.g_gameRules.game:GetProfileId(player.id).Deaths=0;
Omega.Playertable.g_gameRules.game:GetProfileId(player.id).Headshots=0;
else
local Kills=Omega.Playertable.g_gameRules.game:GetProfileId(player.id).Kills;
local Deaths=Omega.Playertable.g_gameRules.game:GetProfileId(player.id).Deaths;
local Headshots=Omega.Playertable.g_gameRules.game:GetProfileId(player.id).Headshots;
g_gameRules.game:SetSynchedEntityValue(playerId, 101, Kills);
g_gameRules.game:SetSynchedEntityValue(playerId, 100, Deaths);
g_gameRules.game:SetSynchedEntityValue(playerId, 102, Headshots);
end
As you can see, I've tried adding their ID into the table and adding info based on this. I cannot get the system to read the 'ID' value that I set before, so I tried adding the code that gets the ID instead, and it doesn't work. The ID is unique to each player so I cannot use a simple number system for this.
Could someone point out to me what I have done wrong here? If I manage to fix the problem, I will answer my own question on here so that it can be helpful to other users.
It seems to me that you are using the wrong table indexing syntax.
Indexing a table by a variables value in Lua is done with the [] syntax.
Furthermore, in Lua Foo.bar is syntactic sugar for Foo["bar"] both formats are interchangeable, but the . variant has limitations on which characters you can use with it. For example Foo["\n.*#%!"] is a valid table index, but you certainly can't write this: Foo.\n.*#%!
Also table.insert(t, v) inserts v at the end of the array part of the table. That means if you do this
foo = {};
foo.X = "Some value";
table.insert(foo, "X");
This is what you get
{
X = "Some value"
[1] = "X"
}
That means, if I apply this to the code you gave us, this is what you probably had in mind:
if (not Omega.Playertable) then
Omega.Playertable = {};
System.LogAlways("Set static record table on first connect");
end
local ID = g_gameRules.game:GetProfileId(player.id);
if (not Omega.Playertable[ID]) then
Omega.Playertable[ID] = {};
Omega.Playertable[ID].Kills=0;
Omega.Playertable[ID].Deaths=0;
Omega.Playertable[ID].Headshots=0;
else
local Kills = Omega.Playertable[ID].Kills;
local Deaths = Omega.Playertable[ID].Deaths;
local Headshots = Omega.Playertable[ID].Headshots;
g_gameRules.game:SetSynchedEntityValue(playerId, 101, Kills);
g_gameRules.game:SetSynchedEntityValue(playerId, 100, Deaths);
g_gameRules.game:SetSynchedEntityValue(playerId, 102, Headshots);
end
Try this:
s="35638846.12.34.45"
id,kills,deaths,headshots=s:match("(.-)%.(.-)%.(.-)%.(.-)$")
print(id,kills,deaths,headshots)
But note that these values are strings. If you're using them as numbers, use tonumber to convert them.