# each! vs foreach parallel timings

Jay Norwood via Digitalmars-d-learn digitalmars-d-learn at puremagic.com
Sun Dec 27 11:30:53 PST 2015

```I'm doing some re-writing and measuring.  The basic task is to
take 10K samples (in struct S samples below) and calculate some
metrics (just per sample for now).  It isn't evident to me how to
write the parallel foreach in the same format as each!, so I just
used the loop form that I understood.

Measured times below are for processing three simple metrics 100
times on 10K samples. This parallel mode could be very useful in
my work, which involves processing a bunch of hardware
performance data.

This is on windows, corei5, DMD32 D Compiler v2.069.2, debug
build.

each! time:59 ms
parallel! time:20 ms

import std.stdio;
import std.algorithm;
import std.conv;
import std.range;
import std.typecons;
import std.parallelism;
import std.array;
import std.traits;
import std.datetime;

struct S { int sn; ulong a; ulong b; ulong c; ulong d; double e;
ulong f; ulong m1; double m2; double m3;}

void apply_metrics(int i,ref S s){
with(s){
m1 = a+b;
m2 = (c+d)/e;
m3 = (c+f)/e;
sn = i;
}
}

int main()
{

S samples;
// initialize some values
foreach ( int i, ref s; samples){
int j=i+1;
with (s){
a=j; b=j*2; c=j*3; d=j*4; e=j*10; f=j*5;
}
}

auto sw = StopWatch(AutoStart.yes);
// apply several functions on each  sample, also number the
samples
foreach(j;iota(100))
samples[].each!((int i, ref a)=>apply_metrics(i,a));
writeln("each! time:", sw.peek().msecs, " ms");

auto sw2 = StopWatch(AutoStart.yes);
// do the same as above, but in parallel
foreach(j;iota(100))
foreach( i, ref a; parallel(samples[])){ apply_metrics(i,a);}
writeln("parallel! time:", sw2.peek().msecs, " ms");
return 0;
}
```