Stream buffering issue
- by Kolyunya
The mod_rewrite documentation states that it is a strict requirement to disable in(out)put buffering in a rewrite program.
Keeping that in mind I've written a simple program (I do know that it lacks the EOF check but this is not an issue and it saves one condition check per loop):
#include <stdio.h>
#include <stdlib.h>
int main ( void )
{
setvbuf(stdin,NULL,_IOLBF,4200);
setvbuf(stdout,NULL,_IOLBF,4200);
int character;
while ( 42 )
{
character = getchar();
if ( character == '-' )
{
character = '_';
}
putchar(character);
}
return 42 - 42;
}
After making some measurements I was shocked - it was over 9,000 times slower than the demo Perl script provided by the documentation:
#!/usr/bin/perl
$| = 1; # Turn off I/O buffering
while (<STDIN>) {
s/-/_/g; # Replace dashes with underscores
print $_;
}
Now I have two related questions:
Question 1. I believe that the streams may be line buffered since Apache sends a new line after each path. Am I correct? Switching my program to
setvbuf(stdin,NULL,_IOLBF,4200);
setvbuf(stdout,NULL,_IOLBF,4200);
makes it twice as fast as Perl one. This should not hit Apache's performance, should it?
Question 2. How can one write a program in C which will use unbuffered streams (like Perl one) and will perform as fast as Perl one?
