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zhangzhe65
Total Points:
240
Status Points:
190
Green Belt
March 31, 2009 10:19 PM PDT
about OpenMP Critical
why?
code1
#include "stdafx.h"
#include "omp.h"
#define N 100000  
int _tmain(int argc, _TCHAR* argv[])
{
int arx[N],ary[N];
int i,max_num_x=-1,max_num_y=-1;
for(i=0;i<N;i++)
{
arx[i]=i;
ary[i]=N-i;
}
omp_set_num_threads(10);
#pragma omp parallel for
for(i=0;i<N;i++)
{
//#pragma omp critical(max_arx)
if(arx[i]>max_num_x)
max_num_x=arx[i];
//#pragma omp critical(max_ary)
if(ary[i]>max_num_y)
max_num_y=ary[i];
}

printf("max_num_x=%d  max_num_y=%d\n",max_num_x,max_num_y);
return 0;
}

and
code2
#include "stdafx.h"
#include "omp.h"
#define N 100000  
int _tmain(int argc, _TCHAR* argv[])
{
int arx[N],ary[N];
int i,max_num_x=-1,max_num_y=-1;
for(i=0;i<N;i++)
{
arx[i]=i;
ary[i]=N-i;
}
omp_set_num_threads(10);
#pragma omp parallel for
for(i=0;i<N;i++)
{
#pragma omp critical(max_arx)
if(arx[i]>max_num_x)
max_num_x=arx[i];
#pragma omp critical(max_ary)
if(ary[i]>max_num_y)
max_num_y=ary[i];
}

printf("max_num_x=%d  max_num_y=%d\n",max_num_x,max_num_y);
return 0;
}

please tell me why   the results of the two codes  are identical?   I don't know why no add #pragma omp critical ,no data race too,in code1Slide 173 .O {color:white; font-size:149%;} a:link {color:#0860A8 !important;} a:active {color:#567EB9 !important;} a:visited {color:#AA014C !important;} <!--.sld {left:0px !important; width:6.0in !important; height:4.5in !important; font-size:103% !important;} -->
Critical
Om Sachan (Intel)
Total Points:
7,270
Status Points:
6,770
Brown Belt
April 5, 2009 11:48 PM PDT
Rate
 
#1
Quoting - zhangzhe65
why?
code1
#include "stdafx.h"
#include "omp.h"
#define N 100000  
int _tmain(int argc, _TCHAR* argv[])
{
int arx[N],ary[N];
int i,max_num_x=-1,max_num_y=-1;
for(i=0;i<N;i++)
{
arx[i]=i;
ary[i]=N-i;
}
omp_set_num_threads(10);
#pragma omp parallel for
for(i=0;i<N;i++)
{
//#pragma omp critical(max_arx)
if(arx[i]>max_num_x)
max_num_x=arx[i];
//#pragma omp critical(max_ary)
if(ary[i]>max_num_y)
max_num_y=ary[i];
}

printf("max_num_x=%d  max_num_y=%d\n",max_num_x,max_num_y);
return 0;
}

and
code2
#include "stdafx.h"
#include "omp.h"
#define N 100000  
int _tmain(int argc, _TCHAR* argv[])
{
int arx[N],ary[N];
int i,max_num_x=-1,max_num_y=-1;
for(i=0;i<N;i++)
{
arx[i]=i;
ary[i]=N-i;
}
omp_set_num_threads(10);
#pragma omp parallel for
for(i=0;i<N;i++)
{
#pragma omp critical(max_arx)
if(arx[i]>max_num_x)
max_num_x=arx[i];
#pragma omp critical(max_ary)
if(ary[i]>max_num_y)
max_num_y=ary[i];
}

printf("max_num_x=%d  max_num_y=%d\n",max_num_x,max_num_y);
return 0;
}

please tell me why   the results of the two codes  are identical?   I don't know why no add #pragma omp critical ,no data race too,in code1 Slide 173<!--[if !ppt]--> .O {color:white; font-size:149%;} a:link {color:#0860A8 !important;} a:active {color:#567EB9 !important;} a:visited {color:#AA014C !important;} <!--.sld {left:0px !important; width:6.0in !important; height:4.5in !important; font-size:103% !important;} --> <!--[endif]-->
Critical

There is a data race in code1. You may use Intel(R) Thread Checker tool to confirm this.

connorisaac
Total Points:
60
Status Points:
10
Green Belt
April 9, 2009 3:19 AM PDT
Rate
 
#2 Reply to #1

There is a data race in code1. You may use Intel(R) Thread Checker tool to confirm this.


Nice One no doubt. Really cool coding.


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