C++ :: Recursive Directory Scan - Can Use Multi-threading For Speed?
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).
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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] ....
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Dec 19, 2014
I'm writing a C++ module that is meant to recursively scan a directory and I'm curious what yall think of my strategy.
The program is a music player and so I'm trying to make the directory scanner as lightweight and efficient as I can. I've decided I want to scan the files in two passes- first I just want to get a list of all music files that are found in a directory/subdirectories and then I want to process the list and search for id3s/other tags.
As I'm a scanning the directory, I've decided to store the temporary list in a linked list where each node is containing an array of 100 strings. I did this because I obviously don't know how long the list will be and I from my understanding of the C++ vector class it basically just makes over sized arrays and moves them when it runs out of space. That sounded rather clunky to me, as did a traditional linked list.. I didn't see the point of allocating memory that many times in a row.
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Jan 20, 2015
I am doing "Virus Tracking System" Project. I have to scan the directory selected from treeview ....
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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]....
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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.
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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);
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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?
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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?
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Nov 22, 2014
#include <iostream>
#define show(variable) std::cout << #variable << " = " << variable << std::endl;
class LivingBeing {
protected:
struct Speed {
[Code] ....
Though the above works, memory is being wasted for speed types that do not pertain to many animals (a snail only crawls, a human never flies, etc...). Saving and loading their files will involve a lot of useless zeros. The problem seems simple, but I can't think of a good redesign to encapsulate speed properly for each of the many, many types of animals. Note that main() works with speed from the base class LivingBeing.
Should there be polymorphic Speed types within each Animal subtype? Then there will be a lot of identical Speed subtypes (e.g. many animals can only swim).
Something like:
class AnimalsThatOnlySwimOrCrawl : LivingBeing {
protected:
struct Speed : LivingBeing::Speed {
int swimmingSpeed, crawlingSpeed;
virtual void increase() override {swimmingSpeed *= 2; crawlingSpeed *= 2;}
[Code] .....
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Feb 16, 2012
Any example code to convert a velocity vector to speed in C++?
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May 27, 2013
Using integers faster than using floating points? Or more precise: what do you estimate as the chance that writing a custom floating point class is worth the effort?
I need to examine some C++ code for an ARM7 or ARM9 processor. Instead of using floating points, the coder had chosen to use integers only. To be able to fake floating points, a custom class was written. The coder states that he avoids using floating points as these are much how much slower. "Have you measured this?", I asked. "No, but it is known to be so", he replied.
Google taught me that most people state integers are faster than using doubles, because their operations (addition, multiplication) take less assembler instructions. But if you need those floating points, what do you estimate as the chance that writing a custom floating point class is worth the effort?
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Jun 26, 2014
On a project I'm working on, I need to update many QLabels very quickly. Each label needs to be updated at about 20 to 50 hertz and there can be over 50 labels at any given time. The problem I'm having is after running the program for about a minute, the labels freeze and the whole program crashes about 10 seconds later. If I comment out the setText() and setNum() calls and reroute the outputs to the console, it runs fine and never crashes. Why does calling SetText() and setNum() so quickly cause the program to crash and how can I prevent this?
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Feb 14, 2015
I want to create a program in windows, it will search for a process/program by name or part of its name and monitor real-time at certain intervals the data speed at each moment that are received from the internet by this process/program. So that when no data is received by the process/program the speed will be zero and i will know it.
Can i do it in c or c++ , if yes then what libraries should i look into to do it and if i can not with these then what language and libraries should i look into to create the program?
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Feb 20, 2014
I'm trying to find the fastest method to find whether or not two rectangles intersect in an effort to streamline my code. I've built this function into a rectangle class I created below.
struct rectangle{
rectangle() :X1(0), Y1(0), X2(0), Y2(0) {};
rectangle(int X1, int Y1, int X2, int Y2)
:X1(X1), Y1(Y1), X2(X2), Y2(Y2) {};
[Code].....
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Jun 2, 2012
I heard that the speed of floating point multiplication is much faster than division. Is it still the case today?
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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]...
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Feb 20, 2015
I'm using an animation program. In this program I've simulated a particle system. The particles are flying around at different and varying speeds. I've attached birds to the particles and I want to be able to control each bird's flapping animation based on its velocity; so birds moving faster will be flapping faster.
Initially, the bird's flapping animation is controlled by a parameter that goes from 0 to 100%. So not only do I need to drive the speed at which the animation goes from 0 to 100%, I need to set it on a loop so once it reaches 100%, it loops back to 0%. I'm extremely new to code so I don't think it would be wise for me to even provide a jumping off point, not that I could.
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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] ....
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Sep 17, 2014
i wrote the following code :
Code:
#include<stdio.h>#include<conio.h>
#include<stdlib.h>
int a[][4] = {15,9,10,25,6,2,4,7,32,19,42,8,21,17,18,0};
void boxes();
void display();
void main()
{int ch,r=3,c=3,t;
[Code]...
not able to esc when i press esc key.how to get rid of this.
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Dec 13, 2014
I created a program that will create a file and print a list on it. Here is the code for my program:
Code:
int controlvalue(void) {FILE *controlvalue;
controlvalue = fopen("something.txt", "a+");
/* Series of fprintfs */
fclose (controlvalue);
return 1;}
Here is an example list created by my program:
Code:
[Gifts]Candy=45
Chocolate=32
Toy=128
Robot=754
Doll=1492
Star=21
Phone=72
Skateboard=87
Frame=314
Days=365
Perfume=421
I want to get the value of "Skateboard" on file. So I need to read 9 lines. On the 9th line, the gets() loop will stop. But, what if I only want to get the value of "Skateboard" as integer (87) and not a string? Also, is it possible to scan the value of Skateboard if it's located on a different (or unknown) line?
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Jan 28, 2013
This is my code:
int main() {
int num;
printf("Please enter a number: ");
scanf("%d", num);
printf("%d", num);
return 0;
}
when i compile and run it, it stops working and doesn't printf the integer.
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Sep 19, 2014
How would I be able to let the user enter multiple heart rates which would all be separate.
Code:
printf("Enter your recorded Heart Rates ");
scanf("%d", &in_rate);
//formulas
if (gender == 'm'){
target = 226 - age;
} else if (gender == 'f'){
[Code]...
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Mar 4, 2013
This is my text file.
bak kut teh[tab]888.0[tab]989.0
spicy chicken nugget[tab]999.0[tab]978.0
I'm experiencing some problem in trying to scan and put it into an array for the food names (e.g an array for food which consist of bak kut teh and spicy chicken nugget) and another 2 array for the other individual integer into C. However there seem to be some problem with my code.
Is there a difference if I use both tab and space instead of space for all?
Code:
#include<stdio.h>
int main() {
FILE *fp;
char food[100];
char buff[BUFSIZ];
float num;
[Code] ....
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Dec 21, 2014
Is it possible to fgets() the string (or word) only after a delimiter? I yes then how?
Example: Code: printer, scanner, machine
Also, how can I sscanf() a string with an indefinite number of sizes and assign it to only one variable?
Example:
Code:
str = "I Love C programming 9000";
sscanf(str, "%s %d", strvar, intvar);
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Feb 4, 2015
I need to take an unknown amount of sorted files and then output any number that is in at least half of them... I know I need to read in the files to a vector and then iterate through them all at the same time looking at the lowest number first and so on. But I am stuck at the point of taking an unknown amount of files and putting them in a container.
This is what I have so far but the vector isn't working and I think I should be putting each file into its own vector.
string get_file(string filename)
{
ifstream in(filename);
if (in)
[Code]....
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