Re: advice on efficient socket programming sought

Hi Philippe,

on Sat, 19 Jul 2008 09:11:20 +0200, you wrote:

> 2008/7/18 Janko Mivšek:
>> Hi Philippe,
>>
>> By efficient you mean receiving and sending a lot such data? Or what  
>> kind of
>> efficiency you want to achieve?
>
> The data comes in chunks up to 8k. I just want to read it fast with as
> little unnecessary copies as possible. Same for writing.

I do sort of this, taking the buffer's size from the actual network's  
capabilities. Also, I only send/receive strings, the user must know what a  
string is for socket in Squeak. The first k characters (k digits,  
delimiter is Character space) that I send/receive are # of characters of  
the whole string.

So I have no 8k limit, the limit I make use of is the underlying TCP/IP  
stack's/socket's capabilities (which may be influenced by hw/vendor  
limitations and/or plugin's consideration). But as with networking in  
general: only less is more, for example it would be worth considering MTU  
when sending (if you can find out from Smalltalk/plugin is another  
matter). Ping some "far, far away" IP addresses with 32 bytes and then  
with 8k to see the difference (or see one of the routers complaining ;)

Back to Smalltalk, pasted from my NetworkContext.st:

>> #createBuffer
  	buffer := String new: ((socket getOption: 'SO_RCVBUF') at: 2).
  	position := 0

>> #receiveSomeData
	^ position := position
	 + (socket receiveSomeDataInto: buffer startingAt: position + 1)

>> #sendData: aString
	"user is expected to send chunks in size of buffer"
	^ socket sendData: aString

>> #waitForData
	^ socket waitForDataFor: nTimeUnits "YMMV"

>> #fetchFromBuffer
	| chunk |
	(buffer == nil or: [position == nil])
	  ifTrue: [self createBuffer; waitForData; receiveSomeData]
	  ifFalse: [socket dataAvailable ifTrue: [self receiveSomeData]].
	"if not enough available, ^ self fetchFromBuffer"
	"now process from buffer whatever there was made available"
	"copy available chars to chunk or (re-)use some writeStream"
	"adjust position and copy remainder to buffer's beginning"
	^ chunk

Observe use of the words "seconds" and "milliseconds" for timeout units in  
the comments of Socket implementation. For other possible  
misunderstandings with Squeak socket's ifClosed: ifTimeOut: (I didn't  
paste these if's into the above) see

- http://bugs.squeak.org/view.php?id=6951
-  
http://lists.squeakfoundation.org/pipermail/squeak-dev/2008-February/125927.html

HTH.

/Klaus

> Cheers
> Philippe