C++ :: Accessing And Working With Vector From Multiple Threads
Oct 20, 2014
I have a vector that I would like to access and work with from multiple threads. I have created an example below to illustrate the functionality that I would like to accomplish.
The goals are to be (1) high speed, (2) thread safe, and (3) *if possible* continue to use vectors as my larger project uses vectors all over the place and as such I would like to maintain that.
However, if I need to switch from vectors to something else then I am open to that as well.
The following example below compiles but crashes rather quickly because it is not thread safe.
How I can fix the example below which I can then apply to my larger project?
#include <string>
#include <vector>
#include <ctime>
#include <thread>
#include <iostream>
#include <random>
#include <atomic>
#include <algorithm>
enum EmployeeType {
[Code] ....
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Aug 7, 2013
I'm currently working on a server for handling clients in a 2d online game and I wrote some regular fstream file code for handling the file that stores their information and I was about to implement it into the server, then I realized there might be a problem having it open multiple times concurrently, so I googled it and came up with
posts like
[URL]
I'm wondering if I can just treat it like everything else or will I have to do something specific for opening on multiple threads?
p.s. I did read those posts but I'm very new to multithreading
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Sep 18, 2013
I'm doing work on chat messenger and facing difficulty to run multiple threads at the same time. Here is the sample code.
void menu();
void groupChat();
void personalChat();
int main() {
sf::Thread thread(&menu());
thread.launch();
[Code] ....
In my program, after menu when he selects a choice, next display of menu wait the termination of the selected thread.
while i want to show menu right after when a menu is selected.
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Jan 16, 2015
I am trying to retrieve the elements in an array to print them. I am pretty sure I have everything right, but it is not working. There are 5 values in the array {3, 4, 10, 5, 6}, but the first two elements (supposed to be 3,4) are coming out a 0,-2654238590. The last three elements are coming out correct.
void addDynArr(DynArr *v, TYPE val) {
/* FIXME: You will write this function */
assert(v != 0);
//resize if necessary
if(v->size >= v->capacity)
[Code] ....
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Apr 9, 2013
I have a big un-editable program, A, which I need to run for like a 1000 different input files. It takes about 15 minutes for each file, so a little parallelisation wouldn't hurt.
I have installed openmpi and it works fine. I have made a small program, B, which selects an input file, moves it to another directory, calls program A with the path to the selected input file and then - when A is done - selects a new input file etc. It should loop until there are no more files in the initial directory.
The problem is this: When I have several processors they might pick the same file and that leads to errors. I have a working program, but it is not pretty.
Code:
#include <stdio.h>
#include <mpi.h>
#include <dirent.h>
#include <string.h>
#include <stdlib.h>
int main(int argc, char *argv[]) {
int num_procs, procs_id, i, exit;
struct dirent *ent;
[Code]...
Every time a processor tries to move a file that another processor has just moved, the output shows an error message before looping to the next file and trying again. It works, but it is a bit annoying. So my questions are:
1) Can I switch off the error message somehow?
2) Is there a better way to do this?
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Jan 30, 2013
I have the following map: myMap<string,vector<int>>. I now want to look through my map to see if a key exists and if it does, retrieve one of the int values from within that vector. What would be the best way to do this? Right now I have the following:
What would be the best way to look for a key and get one of the int values from its vector value? Right now I'm doing something like this:
[code]
map<string,vector<unsigned int>>::iterator it;
it = wordMap.find(someWord);
if(it == wordMap.end){
cout << "No matching entry";
} else{
// this is where I'd want to access the value (the vector) of the map
}
Is there a better way to do this?
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May 9, 2013
I have a pointer to a vector of objects, each object has an array and a couple of strings. how to access the data in the objects via the pointer.
Best tree::chooseSplit(vector <pgm> *ptr)
{
Best splits;
cout<<ptr[1].filePath; //not working!!!
}
filepath is a string in the pgm object. i also need to be able to access elements in an array that also exists in pgm.
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Jul 24, 2013
How I can use class functions in a vector. I have 2 classes:
Gamemode class
bullets class
Inside the Gamemode class I declared: vector<bullets> Bullet and bullets * b.
If the user presses the shoot button a new bullets class will be added to the Bullet vector:
b = new bullets;
Bullet.push_back(b)
Bow I'd like to check all objects in the Bullet vector for the collision() function inside the bullets class.
I already set up a for loop which counts from 0 to the end of the vector:
for( int i=0;i<Bullet.size;i++)
{
}
My idea was to do something like:
if(Bullet[i].collision()) then erase Bullet[i]
But that doesn't work...
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May 1, 2015
so lets assume i have a nested vector in a set or vice versa o in a more general form a container in a container example...
Code:
std::set<vector<int> > my_tuple;
How do i access individual elements of lets say the first vector in the set! Or the last element in the 3rd vector?
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Apr 30, 2013
I have a vector (structures) in a struct (instances). I make a declaration of this struct called instance. The vector is a 3-layer vector of pointers, like so:
vector < vector < vector<scene::IAnimatedMeshSceneNode*> > > structures; (The type is from Irrlicht 3D). I have 3 nested "for" loops which looks similar to the following:
for (int a = 0; a < instance.structures.size(); a++) { /*note:vector size previously set*/
for (int b = 0; b < instance.structures[a].size(); b++){
for (int c = 0; c < instance.structures[a][b].size(); c++) {
if (1) { //checking value of variable not included in snippet
(instance.structures)[a][b][c] = smgr->addAnimatedMeshSceneNode(fl);
(instance.structures)[a][b][c]->setPosition(renderPos);
}
}
}
}
The problem is in these two lines, I think:
(instance.structures)[a][b][c] = smgr->addAnimatedMeshSceneNode(fl);
(instance.structures)[a][b][c]->setPosition(renderPos);
These are currently referencing the pointers, it seems. The program compiles but crashes at this point. I need them to reference the values of the pointers. Problem is, I don't know where to put the dereference operator (*). Where should it go?
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Oct 26, 2014
i have this vector:
#ifndef new_thing_Inventory_h
#define new_thing_Inventory_h
#include <vector>
#include <string>
using namespace std;
class Inventory {
[code]....
so i know i need to use .push_back or .pop_back, but the program im using dosn't even recognize that inventory is a created vector.
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Aug 19, 2013
I have a settings class and a settingItem class. The settings class has a vector of settingItems. The vector is not working:
error C2065: 'settingItem' : undeclared identifier
error C2923: 'std::vector' : 'settingItem' is not a valid template type argument for parameter '_Ty'
with code line:
vector<settingItem> settings;
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Oct 9, 2013
I keep getting a segmentation error when ever I have the following code...
int main(void) {
//Section 1
unsigned long val = 12;
std::vector<unsigned long> vval;
for(unsigned long i = 0; i < 100; ++i) {
vval.push_back((unsigned long)0);
[Code] ....
Error: *** Error in `/home/alex/projects/bignum/build/bignum': free(): invalid pointer: 0x00007ffff75b5b88 ***
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x80a46)[0x7ffff7274a46]
compiler is clang++ 3.2
It doesn't happen if I restructure it so that bignum::num is not a pointer to an std::vector<unsigned long>
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Sep 24, 2014
I'm trying to make a 2d shooter with SDL and I got as far as having multiple bullets but they act as one when a bullet goes off screen. I shoot 1st bullet, then I shoot 2nd bullet. 1st bullet goes off screen (deletes) and 2nd bullet disappears. I shoot 3rd bullet, 2nd bullet reappears where it disappeared and repeat.
class Bullet {
public:
static const int BULLET_WIDTH = 15;
static const int BULLET_HEIGHT = 25;
static const int BULLET_VEL = 5;
Bullet();
//xFire, yFire - position relative to player
[Code] ....
I'm guessing the problem is in the bullet_move function, but I just don't know what to do.
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Mar 17, 2014
I wud like to delete multiple values from a vector using indexes as my values r not fixed they may change so using indexes i want to delete
For example: vector<int> v={1,2,3,4,5};
I want to erase 3,4,0 indexes
So resulting vector is 2,3
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Nov 22, 2013
How could I search a vector element with multiple strings
i.e. vector.at(i) = This is a test
How could I search that to look for the word "test" in that element?
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Mar 16, 2012
Two questions:
1. I have some vector<unsigned char> containing binary data. I would like to combine them into one std::string. How is the correct way to accomplish this?
This is my best guess for sample code:
Code:
vector<unsigned char> data; //conatins some data
vector<unsigned char> data2; //contains more data
string temp(data.begin(), data.end());
temp.append(data2.begin(), data2.end());
Will this code work with binary data, or will it null terminate?
2. A similar problem.. I have some unsigned char* variables, and I want to combine them into one std::string. How can I accomplish this? will the member append() work here? or will it null terminate? Something like:
Code:
unsigned char* data; //conatins some data
unsigned char* data2; //contains more data
string temp(reinterpret_cast<const char*>(data));
temp.append(string(reinterpret_cast<const char*>(data2)));
Will the above sample code work without null termination?
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Nov 11, 2013
I've to use SIGNALS to control threads. Here's my code without the use of signals as I'm no good at that
Code:
#include <pthread.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
}
[code]....
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Jun 30, 2014
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
int turn = 1;
int counter = 0;
int t, n;
[Code] ....
I found this program in a forum and it creates 1 to t threads with each thread pointing to the next and the last thread pointing to the first thread and it allows each thread to sequentially take a turn until all threads have taken n turns. That is when the program ends.
My doubt is if we see in void *tFunc(void *arg) function, first thread locks the mutex and then wait there forever till it's turn comes.Lets say if I spwan 1000 threads and they have take 10 turns each sequentially and what if a 550th thread locks the mutex as soon as the program starts and waiting for its turn which will never happen because still (turn=1) which means it's first thread's turn and first 549 threads have to complete their 1st turn before this 550 threda's turn comes.Doesnt this result in deadlock?
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Apr 29, 2014
how to encapsulate two threads in a class?
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Aug 31, 2014
Here's my code,
#include <iostream>
#include <unistd.h>
#include <thread>
using namespace std;
void Blink();
[Code] .....
The problem is i don't want to use local vars , is ther anyway do end the loop safely(removing all the vars used in function and etc) without using a local var ?
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Apr 18, 2014
#include <stdio.h>
#include <pthread.h>
int i; // loop control variable
int *id; // array used to pass parameter of id
int nThreads; // #threads
[Code]....
I want to know where I am going wrong. I am strong in java but not in c so that may be my problem.
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Aug 31, 2014
I had a requirement where i needed to create a thread and if the execution of thread is not completed in 5 minutes i needed to terminate its execution and continue with other part of the code.
I used the below code to create the thread
_beginthread(FuncnCall,0,NULL);
HANDLE hThread = GetCurrentThread();
Then after this code, I used the below code to check for 5 minutes
for (int i=1;i<=0;i++) {
printf("Value of i=%d
",i);
if(threadFinished) {
break;
} else {
Sleep(1000);
}
}
After this if the value of "threadFinished" is false then i am terminating the thread like below
if(threadFinished == false) {
TerminateThread(hThread,0);
CloseHandle(hThread);
}
The Problem here is, after terminating the thread, the program abruptly closes by giving fatal error. Looks like memory leakage is happening after terminating the thread. Is it not the right way to safely exit the thread?
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Feb 6, 2014
Is there a way of knowing which indices a thread is assigned in a parallel openMP scope?
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Jun 2, 2014
I am on a little project involving TCP socket-programming and multiple threads but need passing structures between two threads.
The first thread receives data with respective ID, temp, etc,.. Each ID is a list-item of a linked list and every ID has again a linked list of all the received data.
The second thread just have to access the list and perform some manipulations on it.
My solution: pass the head pointer of the linked list. Easy enough, right? Somehow, I am stuck receiving error message:" dereferencing pointer to incomplete type."
For the sake of ease and simplicity I just added a stripped down version of the project.
The magic (or not) happens in MainProcess.c: The Data thread should receive the pointer (a think) from the Connection thread.
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May 9, 2013
I am doing something wrong since for me 4 threads perform 2 times slower then 1.I have 2 vectors with bunch of data to process, there is no concurrency (not moving elements and are independent of each other) so i just need to calculate some data from one and copy result in another.
LARGE_INTEGER getFrequency()
{
LARGE_INTEGER frequency;
QueryPerformanceFrequency(&frequency);
return frequency;
[code].....
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