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Copy-on-write fork
- From: "Chris January" <chris at atomice dot net>
- To: <cygwin at cygwin dot com>
- Date: Sat, 20 Apr 2002 03:06:55 +0100
- Subject: Copy-on-write fork
This is mainly a question aimed at Christopher Faylor, but maybe someone
else knows the answer.
My question is, with regard to Chris's post "Re: copy-on-write (oh well)"
[http://www.cygwin.com/ml/cygwin-developers/2000-07/msg00026.html], does
anyone know why a copy-on-write implementation of fork takes longer than the
current Cygwin version??
BTW, I've not had any problems forking beyond the first level using the
example code from 'Window NT/2000 Native API reference'. What problems did
you encounter Chris? My test case is probably not rigorous enough.
A test program and statistics are shown below which clearly show Cygwin's
fork implementation in the lead.
#include <unistd.h>
#include <stdio.h>
#include <windows.h>
int main(void) {
int pid, i;
DWORD dwStartTicks, dwEndTicks;
dwStartTicks = GetTickCount();
for (i=0;i<100;i++) {
pid = fork();
if (!pid)
exit(0);
}
dwEndTicks = GetTickCount();
printf("average fork time = %g ms\n", (dwEndTicks -
dwStartTicks)/1000.0);
}
test uses the copy-on-write implementation
test2 uses Cygwin's implementation
$ time ./test
average fork time = 3.345 ms
real 0m3.391s
user 0m0.020s
sys 0m0.030s
$ time ./test2
average fork time = 1.972 ms
real 0m2.043s
user 0m0.060s
sys 0m0.220s
Regards
Chris
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