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Subject:	RE: Does gzip support multiple processors under windows 2000?
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Date:	Fri, 23 Mar 2001 09:20:20 +1100
Message-ID:	<EA18B9FA0FE4194AA2B4CDB91F73C0EF02E285@itdomain002.itdomain.net.au>
Thread-Topic:	Does gzip support multiple processors under windows 2000?
Thread-Index:	AcCzG4KKIkZXu3pQTHOtDAF02zNozgAAjDvw
From:	"Robert Collins" <robert DOT collins AT itdomain DOT com DOT au>
To:	"Ilan Rabinovitch" <Ilan DOT Rabinovitch AT dig DOT com>, <cygwin AT cygwin DOT com>
X-MIME-Autoconverted:	from quoted-printable to 8bit by delorie.com id RAA07210

> -----Original Message-----
> From: Ilan Rabinovitch [mailto:Ilan DOT Rabinovitch AT dig DOT com]
> Sent: Friday, March 23, 2001 9:02 AM
> To: cygwin AT cygwin DOT com
> Subject: RE: Does gzip support multiple processors under windows 2000?
> 
> 
> 
> Chris,
> 
> I guess thats what Im trying to figure out.  Does it support it? 
> If not can anyone suggest a form a compression that would 
> work with multiple
> processors?
> 
> Thanks,
> Ilan

Most compression algorithms are single-threaded - there's few
opportunities for parallelism (every data bit out depends on the
immediately preceeding bits in). You could play tricks with maximum
compression lengths and reset the stream 50% through the file, then run
the 1st half through one compressor and the 2nd through another (that's
for 2 processors).. but I haven't heard of anyone doing that. (for the
most common uses og gzip it's kinda hard to know the file size to make
that work, and you can't seek stdin so you'd have to buffer internally).

In short I don't know of any parallel stream compressors. 

Your best bet is to start two operations side by side as parallel
processes - that will use both your cpu's.

Rob

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