New Optimization idea


#1

I have a couple of classes like so…

class Foo
def step1
@mine = Hash.new
# Perhaps stuff things into @mine
end

def step2
@mine.each_pair do |key,value|
# Do stuff
end
end
end

Profiling with my “new” profiler shows that I’m creating many many Hash
objects, probably way more than I need. In fact most of them are empty.

Optimization trick…

class Object
FROZEN_EMPTY_HASH = Hash.new.freeze
end

class Foo
@@hash_cache = Hash.new

def step1
@mine = @@hash_cache
# Perhaps stuff things into @mine
if @mine.empty?
@mine = FROZEN_EMPTY_HASH
else
@@hash_cache = Hash.new
end
end

def step2
@mine.each_pair do |key,value|
# Do stuff
end
end
end

John C. Phone : (64)(3) 358 6639
Tait Electronics Fax : (64)(3) 359 4632
PO Box 1645 Christchurch Email : removed_email_address@domain.invalid
New Zealand

Carter’s Clarification of Murphy’s Law.

“Things only ever go right so that they may go more spectacularly wrong
later.”

From this principle, all of life and physics may be deduced.


#2

John C. wrote:

  # Do stuff

class Object
@mine = FROZEN_EMPTY_HASH
end
You could as well leave the member nil and change the getter
appropriately:

class Foo
def mine() @mine || FROZEN_EMPTY_HASH end
def step2() mine.each_pair …
end

Or do the test in step2…
@mine and @mine.each_pair

Kind regards

robert

#3

On Wed, 29 Mar 2006, Robert K. wrote:

You could as well leave the member nil and change the getter appropriately:

class Foo
def mine() @mine || FROZEN_EMPTY_HASH end
def step2() mine.each_pair …
end

Or do the test in step2…
@mine and @mine.each_pair

I didn’t want to do that since @mine.each and .has_key? was going to be
evaluated often and in many places.
ie. The optimization tweak would have been a shot gun
hack all over the place.

However, if anybody had listened to me about the Null Object pattern and
nil…

I wouldn’t have had to do anything.

John C. Phone : (64)(3) 358 6639
Tait Electronics Fax : (64)(3) 359 4632
PO Box 1645 Christchurch Email : removed_email_address@domain.invalid
New Zealand

Carter’s Clarification of Murphy’s Law.

“Things only ever go right so that they may go more spectacularly wrong
later.”

From this principle, all of life and physics may be deduced.


#4

On Mar 27, 2006, at 1:18 PM, John C. wrote:

  # Do stuff
end

end
end

Profiling with my “new” profiler shows that I’m creating many many
Hash objects, probably way more than I need. In fact most of them
are empty.

Optimization trick…

Maybe it is just me, but I find your original code much easier to
read and intuitive than your second version. There is just too much
wonky-thought going on in the second version and it’ll make it easy
to get it wrong (esp if this pattern spreads throughout a large code
base). I don’t know what your real code is doing, but creating empty
hashes seems fine to me. They don’t actually cost all that much:

% time ruby -e ‘1_000_000.times do Hash.new; end’

real 0m7.107s
user 0m3.432s
sys 0m0.101s

(with itunes running in the background no less)

One suggestion I could make is to recycle if you really are making
too many empty hashes. If you are running step1/2 in a loop and doing
a lot of such work, only reinstantiate @mine if you need to:

def initialize
@mine = Hash.new
end

def step1
@mine = Hash.new unless @mine.empty?
# …
end

That is only a teeny change to your original logic and meets your
goals of creating less hashes. I can read that and grok the intent
immediately. I can’t with your rewrite.


_why: zenspider’s most intense moments of solice are immediately
following the slaughter […]
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#5

On Thu, 30 Mar 2006, Ryan D. wrote:

Maybe it is just me, but I find your original code much easier to read and
intuitive than your second version. There is just too much wonky-thought
going on in the second version and it’ll make it easy to get it wrong (esp if

Like any optimization, premature, it’s the root of all programming evil.
In my case profiling showed up a case where I was starting to consume
significant non-GC’able memory resources which were slowing the system
as
a whole.

In this case it was worth it. In general, no.

John C. Phone : (64)(3) 358 6639
Tait Electronics Fax : (64)(3) 359 4632
PO Box 1645 Christchurch Email : removed_email_address@domain.invalid
New Zealand

Carter’s Clarification of Murphy’s Law.

“Things only ever go right so that they may go more spectacularly wrong
later.”

From this principle, all of life and physics may be deduced.