C# :: MultiThread Blocking Updates During Read
Oct 6, 2014
I have a class holding my data strcuture:
// Holding real time option data - should be thread safe
public class OptionRTHolder {
ConcurrentDictionary<double, Quates> book_calls;
ConcurrentDictionary<double, Quates> book_puts;
ConcurrentDictionary<double, List<Single_qoute>> transaction_calls;
ConcurrentDictionary<double, List<Single_qoute>> transaction_puts;
ConcurrentDictionary<double, int> volume_calls;
ConcurrentDictionary<double, int> volume_puts;
DateTime curr_time;
}
I get a stream of data messages, that come in order, each message carries a time and data. I have many threads in paralell pulling messages and in turn update the data strucutre as follows:
Quates and volume data are just overrun (new value overrun former values), also thier size and meta data is fixed (they don't grow post init).
Via the list I have a problem, I would want to lock only the list I am working on. so other lists can update in paralell, what I had in mind was to warp the list in order to warp the add/get calls to make it thread safety, this I think will achieve this goal and I would like to get some assertion from this forum if you may.
Here come my real problem, there are points in time I want to read/copy this structure, during this time I want to block all updating threads as I want to freeze structure in time, is that achiveable ? Idea that I had is to use something like aquire that will get a function (update/read) and a flag that will cause a lock when the read is on...something like that.
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Jun 13, 2014
I have table called leavetable where in i have the fields eid, lfrom,lto, reason,status an employee will insert these fields in the leave form except status, status will be updated by admin but there is no unique field in the table so when the admin updates the status as cancel for an id emp001 so whereever this id is present in the table its getting updated to cancel even though it is approved previously.. How to avoid this duplication ?
SqlConnection con = new SqlConnection(Connectionstring);
con.Open();
string sql = "update leavetable set status = '"+status+"' where eid = '"+textBox1.Text+"' and noofdays = '"+textBox5.Text+"'";
[Code] .....
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Jan 24, 2012
I'm creating a small port scanning app which use a port range defined by user.My problem with the code is that I find it not efficient enough meaning that it ping very slow, especially when ports are not responding meaning that I must wait for the timeout before continuing to next port.
I want to make this small app threaded. The problem here is that I'm kind of blank of how to implement threading in my program. This is my code which is a method which does the actual checking, the other part of the code is a simple button with for loop for advancing my port number.
Code:
private void ScanPort(IPAddress address, int port) {
using (TcpClient client = new TcpClient() {
IAsyncResult result = client.BeginConnect(address, port, null, null);
if (result.AsyncWaitHandle.WaitOne((int)nudTimeout.Value, false)) txtDisplay.AppendText("Port: " + port + " is open." + Environment.NewLine);
else txtDisplay.AppendText("Port: " + port + " is closed." + Environment.NewLine);
} }
I have read some basic threading tutorial but I just don't know how to implement this piece of code so I can check ports much faster.
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Feb 19, 2013
I'm having a bit of trouble learning how to multithread a socket server. I have everything working perfectly fine, but it only accepts one client (I would like multiple clients). some sort of example (I have troubles understanding some things, unless its visual).
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Oct 20, 2014
I'm currently finishing writing some small application. I want to be able to log important information about the program execution to a logfile, and I have several questions.
First of all - I'd prefer to make the part that logs information to a file separate from the code I've already written. So, what interface should I expose to the rest of the program? Is one function void log(const char*); enough?
Another thing that came to my mind; my program runs two threads, and I want to be able to write to the log file from both threads, so the question is: Should I make sure that the writing to the file is mutually exclusive?
And if so, whose responsibility is it to make the logging to the file thread-safe? The actual part that does the logging (void log(const char*) for that matter), or the parts of the program that calls log(const char*) ?
And lastly, and probably less importantly, where is it customary to save the logfile? (the user's home folder maybe?)
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Feb 14, 2014
I have an issue where I iterate through devices and make driver API calls. Unfortunately, these calls take too much time and they are interrupting my real-time scheduler. I have 12 cores, of which one is 100% and the others are < 1%.
I'd like to multi-thread this thing. So far, I've replaced:
for (DeviceIterator d = devices.begin(); d != devices.end(); ++d) {
d->Write(words, numwords);
}
with
void* ThreadedWrite(void* p) {
WritePackage* wp = (WritePackage*)p;
wp->device->Write(wp->words, wp->numwords);
delete[] wp->words;
delete wp;
[Code]...
My problem is that this didn't improve performance at all. The main thread still takes too long to execute. Is there something I need to do to prevent the main thread from blocking?
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Aug 3, 2013
How do I find an error in a multithreading program (written in C)? I get an address, but when I put it into psp-addr2line, i get
??
??:0
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Apr 20, 2014
My problem: I want to make an application that is going to block the action of some files (It is anticheat files actually).
how do I make code to block the application's action?
Maybe there is another way to do that? I need to use Cheat Engine in game, and anticheat blocks it, so I thought if I'll block the activity of the anticheat it couldn't detect the Cheat Engine...
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Apr 22, 2013
I wanted to create an asynchronous/non-blocking udp client server application where the client and server were supposed to chat away with each other without waiting for each other's turns. I came to know that this could be done by select()... here is my Server(Mentioning only the communication part):
Code:
fd_set readfds,writefds;
while(1){
FD_ZERO(&readfds);
FD_ZERO(&writefds);
FD_SET(sd,&readfds);
FD_SET(sd,&writefds);
int rv = select(n, &readfds, NULL, NULL, NULL);
[Code] .....
At first on the server side I wrote:
int rv = select(n, &readfds, &writefds, NULL, NULL);
But that led to the printing of an entire empty array on the server console when the server initialised in addition to the fact that communication between the server and client was not proper. removing "&writefds" did remove the redundant data but the improper communication issue still persists...
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Nov 18, 2013
Let's have global dynamic array p defined as
volatile int p[];
Let's use it in a multithread application, where every thread can change array's size by
new_p = realloc(p, new_size);
if (!new_p) exit 1;
p = new_p;
For simplify assume that we have no problems with it's size and indexing.
Expression like
int x = p[i];
is unsafe cause thread (1) takes the pointer and (2) add the index. Executing of this thread may be stoped after first step before second step. In this time other thread can realloc the array, which move it to some other place in memory. Executing second step after it will add index to wrong pointer. So we will have segmentation fault.
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Mar 5, 2015
I have a thread that fetch elements from a std:queue, which are pushed from other threads. My question is how can I fetch elements from the queue in a blocking mode, what I mean is if there are no elements in the queue then the fetch call will block until at least one element is pushed. Of course I want to do it this way to avoid polling.
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Mar 27, 2014
I am writing an application that needs to temporarily disable the Play/Pause button that appears on multimedia keyboards.
Normally, a key can be blocked quite easily by installing a low level keyboard hook (WH_KEYBOARD_LL) where the KeyboardProc intercepts the key (in this case VK_MEDIA_PLAY_PAUSE) and returns a "1" instead of calling CallNextHookEx. I have tried this with other keys (including the Windows key VK_LWIN) and this works perfectly. I also have no problems with this method under Windows 7 where all keys, including VK_MEDIA_PLAY_PAUSE get blocked.
Windows 8 is a different story. When my application has input focus, everything works as expected, meaning the VK_MEDIA_PLAY_PAUSE key gets blocked and no other application responds to it. However, when my application loses focus, my hook procedure gets called (this was verified by sending out a OutputDebugString) but other applications respond to key even though I return a "1". As soon as my app gets focus again, everything is block as it should.
After some investigation, I found that the multimedia keys not only generate keystrokes but also generate WM_APPCOMMAND messages so I added ShellProc (WH_SHELL) hook with the following hook procedure:
LRESULT __declspec(dllexport)__stdcall CALLBACK ShellProc(int nCode,WPARAM wParam,LPARAM lParam) {
// Do we have to handle this message?
if (nCode == HSHELL_APPCOMMAND) {
OutputDebugStringX(">>>>> HSHELL_APPCOMMAND");
[code]....
This procedure is only getting called when my app has input focus. Whenever I have input focus and return "1" the Play/Pause command gets blocked. As soon as I lose focus the procedure does not get called/hooked.
As I have mentioned, the code works for other keys, just not the multimedia keys.
Alternatively, another way of blocking the multimedia keyboards Play/Pause button?
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Dec 8, 2013
Is possible read text form keyboard using read() function? or which is best way in ansi creplace input command form basic language. for numbers and text...
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May 15, 2013
I want to read the contents of a file block (512 bytes) by block using low I/O read statements. Each record is 64 bytes long and has a pre-defined structure. The first 4 bytes are an unsigned integer; the next 20 bytes are ascii text, etc.
I have a buffer which I can access with buf[0] to buf[63] to read the first record and then buf[64] to buf[127] for the second, etc. However, I was wondering how to map a record so that I can refer to an integer as an integer and a float as float, etc. I can't create a struct and move the 64 bytes to it, as I will have alllignment/padding problems.
What is the standard way to deal with records in C?
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Mar 30, 2013
What is the most efficient way to read a bit at a particular position in a byte?
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Nov 27, 2014
I need it to be faster as possible, so poking here and there looks like that a command line utility in C under linux, should do the job fine.I'm aiming at two goals: the first one is to read the raw sector content (means get the 512 bytes of a sector), the second one would be to take this occasion to study the ANSI C language ( I was coding, but too many years ago, quick basic :-) ) and I like to develop in some RAW disk content manipulation analyzing and so on.
For first test I'd like to sequentially read the sectors and print them to screen until a break happen and this would also tuning and benchmarking the whole situation. I'll add a counter to evaluate the average speed (sectors per second)
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Jan 21, 2014
I'm working on a program that reads from a .dat file that has names and numbers associated with the name. What the big picture it will be able to take those names and numbers find the avg of certain peoples scores and display these numbers or names who have the highest etc.
So to keep this short in my main I have it call the class and pass "Even.dat" as a char * fname my questions is how do I go about reading this .dat file? I know sorting it will use a sort algorithm which I will be using a bubble sort. But I haven't worked with ofstream and ifstream very much so some tips would be great! Here's an example of what the .dat file contains
David 42
Rebecca 83
Jonathan 79
Matthew 77
Rose 7
Melanie 75
int main() {
StudentStat StatEven("Even.dat");
[code]....
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Oct 6, 2013
#include "stdafx.h"
#include "iostream"
#include "conio.h"
#include "windows.h"
using namespace std;
void main(){
HDC hdc = GetDC(NULL);
DWORD color = GetPixel(hdc, 500, 500);
[Code] ....
From this code I think it reads pixel from screenshot. I want to read from file. I think I have to change this line
HDC hdc = GetDC(NULL);
but I don't know how to?
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Mar 18, 2015
im trying to make a program which will tell which key i pressed and then it will print in msgbox, but i cant figure out how to read the key in loops, like i tried getasynkey (imported to my c# console app) with value around -32676 or -32767 i ( i found it on internet) and it only shows the key once, i want to do like while my key is pressed, then it will spam my console with key pressed, is there any way to do it?
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Dec 9, 2014
I am a learner in C#. I want to read a particular value from the CSV file. I have learned the getting the csv file into a datatable through browsing. See the following code and my CSV file format. The following code displays all the values.... Say, I want to get what is the 'Volume' for 'ID' = 90.
CSV file (IDVolumeName.csv)
ID:Volume:Name
100:5600:A
95:5000:B
90:4500:C
85:4000:D
Code:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
using System.Data;
[Code] ....
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Apr 22, 2013
I have a code for reading a series of data from a text file.The code was shown below I don't know why I can't successfully read file. (Can open successfully)
btw: the text file and source code were located at the same directory.
#include <stdio.h>
#include <stdlib.h>
int main(){
int numOfAtoms;
[Code]....
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Oct 18, 2014
I read correctly in MatLab some data by serial port of a device, but in C... nothing.
Code: #include <cstdlib>
#include <stdio.h>
int main(void)
{
FILE *in;
char linha[30];
while(1)
{
// Abrir porta COM de onde se ligou a placa
in = fopen( "COM8", "r" );
if( in == NULL )
{
[code].....
The message "ERRO: no consigo abrir porta COM " don't appear, so I haven't error there. I just do not see anything in the terminal.
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Nov 24, 2014
When reading a binary .img why is it when you read it by slurping in the file, then save it to a string and cout, you don't see the binary but random garbage?
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Nov 24, 2013
When I tried to run my code I keep getting a "Segmentation fault".
I am trying to write a code that read from a file and put the data into a structure.
The file look like the following:
2001,ABBIGAEL,5
1994,ABBIGAIL,5
1996,ABBIGAIL,8
1997,ABBIGAIL,13
The file have 31 lines.
Code:
#include <stdio.h>
#include <string.h>
int main() {
/* Define a daydata structure */
typedef struct {
[Code]....
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Oct 17, 2013
I have a c source file:
Code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <regex.h>
typedef struct
[Code] .....
But the problem is i get a seg fault at the read function.
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Mar 3, 2013
How can I erase the data stored in /tmp/a.txt after every run of this code?
Code:
#include <stdio.h> // IO operations
#include <unistd.h> //for pid, ppid, fork functions
#include <sys/types.h> //for pid_t type, kill function
#include <stdlib.h> //for exit function
#include <signal.h> //for kill function
#include <sys/types.h>
#include <sys/stat.h>
[Code]...
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