C :: Threading With OpenMP
Apr 10, 2013
I wrote code that finds the number of prime numbers in a range entered by the user. Now I'm attempting to make it run in parallel with the number of threads I assign it to have. I'm using blocking technique, so I'm assigning, in this scenario, 4 threads - 1/4 of the numbers in the range to the first array, and the next 1/4 of the numbers in the range to the next array and so on. Then I want to execute the prime number counting code in parallel. I'm using openMP to do this. I'm having difficulty setting it all up properly. I have a little experience with pthreads but little with openMP and am struggling in how this should be done.
Code:
#include <stdio.h>
#include <stdlib.h>
#include <omp.h>
[Code]....
View 2 Replies
ADVERTISEMENT
Dec 19, 2012
I am using map for assigning an identifiers for a line from file in c++. Also i am using IDs for a pattern in line {name, operator, val} which is separated by ';'. I am using read_pub() for calculating how many patterns are there in a line.
#include<stdio.h>
#include<stdlib.h>
#include<iostream>
#include<fstream>
#include<omp.h>
#include<map>
#include <sstream>
using namespace std;
struct predicate {
[Code] ....
View 1 Replies
View Related
May 20, 2013
I'm quite new to openMP, mostly used pthreads and mpi before. Now I like to tinker a bit with openMP, but haven't found any good docs, reference list or similar.
What's the equivalent to pthread's mutex lock in openMP?
Code:
#pragma omp parallel for
for(i=0; i<n ; i++){
// Do something intelligent...
// If needed handle a shared variable.
}
How do I protect the shared variable?
View 1 Replies
View Related
Oct 14, 2014
I'm trying to write a small brute force application in C on Ubuntu 14.04.1 using Code::Blocks with gcc-4.8.2. It's nothing special and just for practice.The focus is on a parallel procedure that generates strings by use of OpenMP. Every time a string is generated, the counter variable should be incremented. At the end, regardless of whether the search string was matched or not, it outputs the correct number of all generated strings (counts).It works fine so far.Here is my source code example:
Code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <omp.h>
/* Global variables */
const char Literals[] = "abcdefghijklmnopqrstuvwxyz";
const int NLiterals = sizeof( Literals ) - 1; // NLiterals = 26 Bytes.
const char SearchString[] = "test"; // I.e. until 'test' there are 355414 counts.
char MatchString[16];
}
[code]...
This should speed up the process of generating strings. But if I do so, always when the program has a match the number of counted strings is wrong. Here are some possible "wrong" outputs: Code: Match: 'test'! 40710 tries. <-- number of tries (counts) is wrong! or Code: Match: 'test'! 40375 tries. <-- number of tries (counts) is wrong! But if the program doesn't have a match (i.e. when I change SearchString to something like the following line), then the number of counts is correct: Code: const char SearchString[] = "test0"; The only thing I have to do before, is to change the follow line from:
Code:
printf( "
No match! %u tries.
", Count / 8 ); to Code: printf( "
No match! %u tries.
", Count );
But also it can happen that there is no output. Like an infinite or endless loop. How can I improve the source code in order that the correct number of counts is always displayed and what can be the reason for the endless loops time after time? Both issues appears only by the use of Code: #pragma omp for schedule( dynamic ).
View 5 Replies
View Related
May 22, 2013
I'm trying to implement Parallel loop with OpenMP. I just googled and got the below sample, but it seems its not executing parallely. It takes same amount time for code which is with parallel and without parallel.
Without Parallel : It takes 39 secs.
-----------------
for (int I=0;I<100000;I++){
cout<<I<<" ";
}
With Parallel : It takes 39 secs.
--------------
#include<omp.h>
#pragma omp parallel {
#pragma omp for
for (int I=0;I<100000;I++) {
cout<<I<<endl;
}
}
Why parallel is not working and it takes same time. My machine is Dual Core.
View 4 Replies
View Related
Jun 13, 2013
I'm wondering if there is a library for C++ that supports threading over the network, maybe with a threading pool and a specific protocol; or if there is just a de-facto protocol for doing threading over the network.
View 10 Replies
View Related
May 13, 2014
I've written some code that I am currently threading but I am unsure how to pass by reference, or rather why my pass by reference is failing.
I am passing an array of floats by reference, this works fine when not threaded but I am given the error that float*&field does not match std::reference_wrapper<float*>.
Anyways. Here's the code.
The method:
diffuse(int b, float*& field, float*& pField, float diffFactor, float dt, int iteration)
The thread:
std::thread diffuseThread(diffuse, 1, std::ref(u), std::ref(prevU), visc, dt, iteration);
View 14 Replies
View Related
Jun 12, 2012
I'm using MS' optimizing compiler CL 13.10 (one from VCToolkit 2003) along with WinAPI threading functions and is being compiled as a C console program.
I was wondering how to implement threading in a production setting? I've seen and tried various examples, but they all show basically the same thing - startup in main, run their function, clean up, and then the program exits.
I don't know the proper terminology, but I was looking for two maybe three functions to run simultaneously with a loop in main. I tried a small test program and was wondering if it's setup correctly.
A structure is used as the argument for each function.
int running = 1; // global variable
DWORD WINAPI function_1(LPVOID);
DWORD WINAPI function_2(LPVOID);
main() {
HANDLE hndThreads[2];
DWORD threadIDs[2];
[code].....
Right now, function_2 is just a copy of function_1's definition. Everything *appears* to do what I want, but is it setup correctly?
View 2 Replies
View Related
Nov 1, 2013
I want to make a thread outside an int main() method; and this code below gives an error of (paraphrasing) 'no constructor found for thread for type void()'
#include <thread>;
class Board(){
//Lines Later
[Code]....
Is there any way to accomplish threading outside the main and in a class?
View 1 Replies
View Related
Feb 6, 2014
Is there a way of knowing which indices a thread is assigned in a parallel openMP scope?
View 6 Replies
View Related
Apr 11, 2013
I recently picked up multithreading with OpenMP, so it is still new to me. While processing data, I would like to store it in a vector, as shown here:
vector<int> vect;
#pragma omp parallel for
for(int c=0; c<500; ++c) {
vect.push_back(c)
}
However, since it is multithreaded, I would like (and need!) to have one dedicated vector per thread. I haven't been able to find an example of how to do this online. Is it even possible?
View 1 Replies
View Related
Dec 9, 2014
I'm trying to optimize this code using openMP. The line I added made it run about twice as fast but I'm trying to figure out how to make it even faster. Could reshaping the loops potentially increase the speed?
//4 threads
int listsize=15000;
#pragma omp parallel for shared(f) private(i,j,hash)
for(i = 0; i < listsize; i++) {
printf("Thread: %d i: %zu wl_size: %zu
",omp_get_thread_num(),i,wl_size);
for (j = 0; j < num; j++) {
h = f[j] (getw(list, i));
c[h] = 1;
} }
View 2 Replies
View Related
May 2, 2013
I am trying to parallelize some of my code with OpenMP. When I switch to using multiple threads I start getting random numbers that are out of the expected range.
Here is a small example:
Code:
#include <stdio.h>
#include </usr/local/include/gsl/gsl_rng.h>
#include </usr/local/include/gsl/gsl_randist.h>
int main() {
int mySeed=0;
const gsl_rng_type *T;
T = gsl_rng_ranlxs2;
gsl_rng *r_1 ;
[Code] .....
gsl_rng_uniform should only output number in the range [0,1) but with multiple threads it outputs larger number as well.
View 2 Replies
View Related
Mar 25, 2013
I need do read a text file from memory card using threading.
I am able to do it with out using thread but because of some limitations, i have to do it with threading only.
Here is the code to read file from memory card with out thread:
Code: ##########################################
#include <stdio.h>
#include <stdlib.h>
#include <XMC4500.h> /* SFR declarations of the selected device */
#include <DAVE3.h> /* Declarations from DAVE3 Code
#include <stdio.h>
#include <string.h>
#include <stdbool.h>
[Code]...
View 4 Replies
View Related
May 11, 2014
In our Qt application, we have to load several files on application start-up starting from a root directory.
We are recursively scanning the directories and loading the files.
The total time it takes is about 12 seconds. Can we reduce this time if we use multi-threading?
I have heard that multi-threading does not work everywhere and it increases code complexity and debugging issues.
Would multi-threading solve the above problem? We want it to be platform independent (Mac, Linux, Windows).
View 9 Replies
View Related
Feb 25, 2013
When I put boost::thread Thread; in my struct I get the error error C2248: 'boost::thread::thread' : cannot access private member declared in class 'boost::thread'
The whole struct is
struct Player {
bool key[256];
char nameString[64];
bool lMouseButton;
bool rMouseButton;
double mouseX;
double mouseY;
[Code] ....
View 1 Replies
View Related
Feb 10, 2012
I have a SSD and I am trying to use it to simulate my program I/O performance, however, IOPS calculated from my program is much much faster than IOMeter.
My SSD is PLEXTOR PX-128M3S, by IOMeter, its max 512B random read IOPS is around 94k (queue depth is 32). However my program (32 windows threads) can reach around 500k 512B IOPS, around 5 times of IOMeter!!! I did data validation but didn't find any error in data fetching. It's because my data fetching in order?
I paste my code belwo (it mainly fetch 512B from file and release it; I did use 4bytes (an int) to validate program logic and didn't find problem).
#include <stdio.h>
#include <Windows.h>
/*
** Purpose: Verify file random read IOPS in comparison with IOMeter
**/
//Global variables
long completeIOs = 0;
long completeBytes = 0;
int threadCount = 32;
unsigned long long length = 1073741824; //4G test file
[Code] ....
View 1 Replies
View Related
