memory usage

[saito]

Sorry this may be quite basic but just wanted to confirm it:

Let's say that I have a proc which generates a large dict and returns
it. Then when used, the caller assigns it to a variable.

How much memory is used, 10mb or 20mb? (let's ignore any extra memory
needed to manage the dict structure and the proc calls).


proc generate_10mb_dict {a b c} {
# generate a large dict, in d

return $d
}

set my_data [generate_10mb_dict $a $b $c]


what is the ram use at this point?

[Rich]

Post by saito
Let's say that I have a proc which generates a large dict and returns
it. Then when used, the caller assigns it to a variable.
How much memory is used, 10mb or 20mb? (let's ignore any extra memory
needed to manage the dict structure and the proc calls).
proc generate_10mb_dict {a b c} {
# generate a large dict, in d
return $d
}
set my_data [generate_10mb_dict $a $b $c]
what is the ram use at this point?

Given your sample code, the usage is the amount taken up by the dict.

If the dict is 10mb (as you suggest) then after "set my_data" the ram
usage is 10mb.

[saito]

Post by Rich
Given your sample code, the usage is the amount taken up by the dict.
If the dict is 10mb (as you suggest) then after "set my_data" the ram
usage is 10mb.

Thank you!

[Harald Oehlmann]

Post by saito

Post by Rich
Given your sample code, the usage is the amount taken up by the dict.
If the dict is 10mb (as you suggest) then after "set my_data" the ram
usage is 10mb.

Thank you!

Yes, TCL uses generally shared values with referent count.
And each item is reference counted. And with TCL 9, even sublists are
reference counted, e.g. stored only once.

That means:

set d [dict create a [string repeat a 100000]]

-> d and a are reference counted.

dict set d b [dict get $d a]

does not copy the string, but reference it twice.

A copy of the data is only done, if the data gets different:

dict set d b "[dict get $d b]q"

Now, dict item a and b are differently and thus b is copied.

Anyway, it is endlessly complicated...

Harald

[saito]

Post by Harald Oehlmann
Now, dict item a and b are differently and thus b is copied.
Anyway, it is endlessly complicated...

:-)

Thanks for the details. That makes sense.