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Path: utzoo!utcsrgv!dave
From: dave@utcsrgv.UUCP (Dave Sherman)
Newsgroups: net.unix
Subject: How to get printf to call write(2) only once?
Message-ID: <3769@utcsrgv.UUCP>
Date: Fri, 6-Apr-84 15:26:52 EST
Article-I.D.: utcsrgv.3769
Posted: Fri Apr  6 15:26:52 1984
Date-Received: Fri, 6-Apr-84 17:32:51 EST
Organization: The Law Society of Upper Canada, Toronto
Lines: 40

In running benchmarks on a particular computer to simulate our CAI
application, I seem to have run into a bottleneck in the terminal I/O,
specifically the O. This is a modified version 7 system (Perkin-Elmer
Edition VII Workbench).

It seems to me that a call to printf should trigger a single call
to write, but that's not happening. I looked at the stdio source on
our PDP-11 v7 system, and this is what happens:
	1. printf calls _doprnt
	2. _doprnt calls _strout on the whole string
	3. _strout calls the putc macro
	4. since _cnt is 0 (on a terminal line), flsbuf is
		called immediately
	5. flsbuf calls write on one character.

Now, I realize I can use setbuf to buffer stdout, but I don't want
buffered output. I simply want to reduce the number of character
interrupts generated per printf.

I suppose I can do:

myprintf(a,b,c,d)
{
	printf(a,b,c,d);
	fflush(stdout);
}
and run setbuf on stdout, but that's (a) kludgey and (b) not guaranteed
to pass the args to printf properly on any particular machine.

Any suggestions? Could _strout be modified to set a flag that _flsbuf
looks at, so that only one call to write(2) is done? Has someone done
this already?

Thanks.

Dave Sherman
The Law Society of Upper Canada
Toronto
-- 
 {allegra,cornell,decvax,ihnp4,linus,utzoo}!utcsrgv!dave