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?
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
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.
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)
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:
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 }
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
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?
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'
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);
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.
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?
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?
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 ?
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
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?
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.
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.
