Develop Reference

Task does not always return upon completion

So I am trying to build a program to control a machine. Communications with said machine is via a serial port for which I have written a driver. Continuous polling to the machine is necessary for status feedback etc. In my program I have a dedicated ExecutionEngine() class to handle serial send and receive. I also need to have two separate control sequences running, which I have put into methods RunSequenceA() and RunSequenceB() respectively. During normal operation, all three methods need to run until both control sequences finish, at which point the StopSequence() method is called. My issue is that sometimes, for whatever reason, the StopSequence() method is never called, leaving my ExecutionEngine() method in an infinite loop!
Code for ExecutionEngine():
private static void ExecutionEngine()
{
// Clear both lists in case they have old data
_commandList.Clear();
_pollingList.Clear();
// Poll while user has not yet clicked "STOP"
while (!_cTokenSource.Token.IsCancellationRequested)
{
// If there are commands to be sent, send them first
if (_commandList.Count > 0)
{
Command[] tempCommandArray;
lock (_commandList)
tempCommandArray = _commandList.ToArray();
foreach (var c in tempCommandArray)
{
if (_cTokenSource.Token.IsCancellationRequested)
break;
var response = SerialDriver.ComCycle(c.CommandBytes, _serialPort);
var success = CheckErrorReturn(response, false);
if (success)
{
AddPolling(c);
RemoveCommand(c);
}
}
}
// Do polling operation on applicable controllers
if (_pollingList.Count > 0)
{
Command[] tempPollingArray;
lock (_pollingList)
tempPollingArray = _pollingList.ToArray();
foreach (var c in tempPollingArray)
{
if (_cTokenSource.Token.IsCancellationRequested)
break;
var response = SerialDriver.ComCycle(c.PollBytes, _serialPort);
var success = ProcessPollReturn(response);
if (success)
{
c.FlagDone();
RemovePolling(c);
}
}
}
if (_commandList.Count + _pollingList.Count == 0)
{
// Will get stuck here if neither list gets new items added
Console.WriteLine("Bad place");
Thread.Sleep(500);
}
}
// Cancellation has been requested
lock (_commandList)
_commandList.Clear();
lock (_pollingList)
_pollingList.Clear();
ResetTriggers();
var endCommand = new Command("GL_SYSCMD", 0);
SerialDriver.ComCycle(endCommand.CommandBytes, _serialPort);
_serialPort.Close();
_vm.SequenceRunning = false;
return;
}
Code for running sequences:
private static async Task RunSequencesAsync()
{
var taskArray = new Task[2];
var a = new Action(RunSequenceA);
var b = new Action(RunSequenceB);
taskArray[0] = Task.Run(a);
taskArray[1] = Task.Run(b);
await Task.WhenAll(taskArray).ConfigureAwait(continueOnCapturedContext: false);
// Sometimes this never fires, WHY?
UpdateStatus("All done!");
StopSequence();
}
// Run A sequence
internal static void RunSequenceA()
{
if (_sequenceA1 != null && _sequenceA1.Count > 0)
{
foreach (var s in _sequenceA1)
{
if (_cTokenSource.Token.IsCancellationRequested)
return;
s.Execute();
if (s.Reference != null && TriggerStepCompleted != null)
TriggerStepCompleted(s, EventArgs.Empty);
}
// This part always fires
Console.WriteLine("Sequence A finished");
return;
}
else
return;
}
And finally, the methods to start and stop everything:
private static async Task StartSequenceAsync()
{
_serialPort.PortName = _vm.SelectedComPort;
_serialPort.Open();
_serialPort.DiscardInBuffer();
_serialPort.DiscardOutBuffer();
// Start
_cTokenSource = new CancellationTokenSource();
_vm.SequenceRunning = true;
var taskArray = new Task[2];
taskArray[0] = Task.Run(() => ExecutionEngine());
Thread.Sleep(50);
taskArray[1] = Task.Run(() => RunSequencesAsync());
await Task.WhenAll(taskArray).ConfigureAwait(continueOnCapturedContext: false);
}
private static void StopSequence()
{
_cTokenSource.Cancel();
}
To reiterate, the problem doesn't happen every time. In fact, most times the program runs fine. It seems that problems only arise if I manually call the StopSequence() method half way through execution. Then it's 50/50 as to whether the problem shows up. I'm pretty sure my issue is threading related, but not sure exactly what is going wrong. Any help pointing me in the right direction will be greatly appreciated!

UWP app crashes (but not all the time) during function execution

I'm working on a proof of concept at the moment, just for fun (and for YouTube). The thing I am trying to prove is that I can efficiently "hack" WiFi passwords using UWP and C# for Windows. I don't know of any Wi-Fi cracking tools that are designed specifically for Windows 10 devices (PC, Tablet, XboxOne, Mobile etc)...
So I have actually managed to perform a dictionary style attack (on my own WiFi network of course). However my function seems to completely crash occasionally when running the "hack".
Please consider the fact that this is completely white hat hacking I am talking about here, nothing illegal is intended.
Any help with a reason why this crashes is appreciated...
private async void connectWiFi_Tapped(object sender, TappedRoutedEventArgs e)
{
int success = 0;
var picker = new FileOpenPicker();
picker.ViewMode = PickerViewMode.Thumbnail;
picker.SuggestedStartLocation = PickerLocationId.DocumentsLibrary;
picker.FileTypeFilter.Add(".txt");
StorageFile file = await picker.PickSingleFileAsync();
if (file != null)
{
do
{
string _line;
using (var inputStream = await file.OpenReadAsync())
using (var classicStream = inputStream.AsStreamForRead())
using (var streamReader = new StreamReader(classicStream))
{
while (streamReader.Peek() >= 0)
{
if (success == 0)
{
_line = streamReader.ReadLine();
setConnectionStatus("Status: Checking WiFi network using passphrase " + _line);
if (await checkWifiPassword(_line) == true)
{
success = 1;
setConnectionStatus("SUCCESS: Password successfully identified as " + _line);
firstAdapter.Disconnect();
var msg = new MessageDialog(connectionStatus.Text);
await msg.ShowAsync();
}
else
{
success = 0;
setConnectionStatus("FAIL: Password " + _line + "is incorrect. Checking next password...");
}
}
}
}
} while (success == 0);
}
}
This is the code that actually runs a dictionary-style "hack" on a selected network. The code to actually connect to the network is as follows:
private async Task<bool> checkWifiPassword(string passPhrase)
{
var credential = new PasswordCredential();
WiFiReconnectionKind reconnectionKind = WiFiReconnectionKind.Manual;
credential.Password = passPhrase;
var selectedNetwork = null as WiFiNetworkDisplay;
foreach (var network in ResultCollection)
{
if (WifiNetworks.SelectedItem.ToString() == network.Ssid)
{
selectedNetwork = network as WiFiNetworkDisplay;
}
}
if (selectedNetwork != null)
{
var result = await firstAdapter.ConnectAsync(selectedNetwork.AvailableNetwork, reconnectionKind, credential);
if (result.ConnectionStatus == WiFiConnectionStatus.Success)
{
return true;
}
else
{
return false;
}
}
else
{
return false;
}
}
Does anyone have any idea what I am missing here?
Any help appreciated.
Thanks

Consider this loop
while (streamReader.Peek() >= 0)
{
if (success == 0)
{
_line = streamReader.ReadLine();
setConnectionStatus("Status: Checking WiFi network using passphrase " + _line);
if (await checkWifiPassword(_line) == true)
{
success = 1;
setConnectionStatus("SUCCESS: Password successfully identified as " + _line);
firstAdapter.Disconnect();
var msg = new MessageDialog(connectionStatus.Text);
await msg.ShowAsync();
}
else
{
success = 0;
setConnectionStatus("FAIL: Password " + _line + "is incorrect. Checking next password...");
}
}
}
This can lead to and infinite loop:
Imagine the following dictionary file:
abc
bcd
cde
where abc is the correct password.
You peek the stream, you get 97 (decimal ASCII for letter a), fine.
Success is 0, as we just started.
You read the next line.
You check the password, it works, cool.
You set success to 1, show the message, etc.
User closes the message dialog, ShowAsync() returns.
End of first loop iteration, let's start another one.
You peek the stream, you get 98 (ASCII for letter b), non 0, fine.
Success is not zero, so we skip the entire body of that while, end of second loop iteration.
You peek the stream again, the pointer did not move since the last peek, so you're going to get that same 98 again.
And you skip again, infinite loop.
EDIT - there is actually another infinite loop there
I will not detail this that much, but take a look at the outer do-while loop. That loop runs until success. But if the inner loop exhausts all possibilities and does not find a correct password, success will remain 0. That means the do while will run once again, the inner loop will go through the file again, which obviously will not find a solution again, and so on.
Solution
There are many ways that code could be cleaned up, but the quick fix is to break after msg.ShowAsync();.
More details (that would belong to codereview.stackexchange.com):
Also I would not Peek the StreamReader. Use EndOfStream for that job. And you can skip the inner if, you simply break if you found a correct password. You can drop the outer loop as well. If you completed the inner loop without setting the success flag (which in turn should be a boolean) you can report to the user that no password worked.
I would do something along the lines of: (take it as a pseudo code, might not compile as it is)
private async void connectWiFi_Tapped(object sender, TappedRoutedEventArgs e)
{
var picker = new FileOpenPicker();
picker.ViewMode = PickerViewMode.Thumbnail;
picker.SuggestedStartLocation = PickerLocationId.DocumentsLibrary;
picker.FileTypeFilter.Add(".txt");
StorageFile file = await picker.PickSingleFileAsync();
if (file != null)
{
bool success = false;
string _line;
using (var inputStream = await file.OpenReadAsync())
using (var classicStream = inputStream.AsStreamForRead())
using (var streamReader = new StreamReader(classicStream))
{
while (!streamReader.EndOfStream)
{
_line = streamReader.ReadLine();
setConnectionStatus("Status: Checking WiFi network using passphrase " + _line);
if (await checkWifiPassword(_line) == true)
{
success = true;
setConnectionStatus("SUCCESS: Password successfully identified as " + _line);
firstAdapter.Disconnect();
var msg = new MessageDialog(connectionStatus.Text);
await msg.ShowAsync();
break;
}
else
{
setConnectionStatus("FAIL: Password " + _line + "is incorrect. Checking next password...");
}
}
}
if(!success){ /* report to the user*/ }
}

Bloomberg web service call for single field and single instrument taking more than 1 min

I am making a Bloomberg web service GetData call for the "DEBT_TO_EQUITY_FUNDAMENTALS_TKR" field. I am setting secmaster = true and asking for a single instrument with a CUSIP identifier (with yellowkey = MarketSector.Corp).
This strikes me as a fairly lightweight call having seen people asking for thousands of instruments and dozens of fields at once.
I have played around with setting lots of different settings but I just can't get this request to return in a few seconds. It gives me the correct return value but it takes longer than 60 seconds.
Any idea if it is possible to get such a request to execute and return in a few seconds?
Thanks
EDIT - Here is the code I am running:
public string GetFundamentalTicker(string identifier, InstrumentType identifierType = InstrumentType.CUSIP)
{
PerSecurityWS ps = new PerSecurityWS();
try
{
log.DebugFormat("Cert path is: {0}", CertPath);
X509Certificate2 clientCert = new X509Certificate2(CertPath, "<password_redacted>");
ps.ClientCertificates.Add(clientCert);
}
catch (Exception e)
{
log.ErrorFormat("Error in cert setup - {0} - {1}", e.Message, e.InnerException == null ? "" : e.InnerException.Message);
return null;
}
//Set request header
GetDataHeaders getDataHeaders = new GetDataHeaders();
getDataHeaders.secmaster = true;
getDataHeaders.secmasterSpecified = true;
//getDataHeaders.fundamentals = true;
//getDataHeaders.fundamentalsSpecified = true;
//getDataHeaders.programflag = ProgramFlag.oneshot;//unnecessary - defaults to this anyway
//getDataHeaders.programflagSpecified = true;
//getDataHeaders.pricing = true;
getDataHeaders.secid = identifierType;
getDataHeaders.secidSpecified = true;
SubmitGetDataRequest sbmtGtDtreq = new SubmitGetDataRequest();
sbmtGtDtreq.headers = getDataHeaders;
sbmtGtDtreq.fields = new string[] {
"DEBT_TO_EQUITY_FUNDAMENTALS_TKR"
};
int currentFundYear = DateTime.Now.Year;
//var fundYears = new List<int>();
List<Instrument> fundYearInstruments = new List<Instrument>();
Instrument fundYearInstrument = null;
fundYearInstrument = new Instrument();
fundYearInstrument.id = identifier;
fundYearInstrument.typeSpecified = true;
fundYearInstrument.type = identifierType;
fundYearInstrument.yellowkey = MarketSector.Corp;
fundYearInstrument.yellowkeySpecified = true;
//fundYearInstrument.overrides = new Override[] {};//{ new Override() { field = "EQY_FUND_YEAR", value = currentFundYear.ToString() } };
fundYearInstruments.Add(fundYearInstrument);
//fundYears.Add(-1);
Instrument[] instr = fundYearInstruments.ToArray();
Instruments instrs = new Instruments();
instrs.instrument = instr;
sbmtGtDtreq.instruments = instrs;
try
{
SubmitGetDataResponse sbmtGtDtResp = ps.submitGetDataRequest(sbmtGtDtreq);
RetrieveGetDataRequest rtrvGtDrReq = new RetrieveGetDataRequest();
rtrvGtDrReq.responseId = sbmtGtDtResp.responseId;
RetrieveGetDataResponse rtrvGtDrResp;
do
{
System.Threading.Thread.Sleep(POLL_INTERVAL);
rtrvGtDrResp = ps.retrieveGetDataResponse(rtrvGtDrReq);
}
while (rtrvGtDrResp.statusCode.code == DATA_NOT_AVAILABLE);
if (rtrvGtDrResp.statusCode.code == SUCCESS)
{
for (int i = 0; i < rtrvGtDrResp.instrumentDatas.Length; i++)
{
for (int j = 0; j < rtrvGtDrResp.instrumentDatas[i].data.Length; j++)
{
if (rtrvGtDrResp.instrumentDatas[i].data[j].value == "N.A." || rtrvGtDrResp.instrumentDatas[i].data[j].value == "N.S." || rtrvGtDrResp.instrumentDatas[i].data[j].value == "N.D.")
rtrvGtDrResp.instrumentDatas[i].data[j].value = null;
return rtrvGtDrResp.instrumentDatas[i].data[j].value;
}
}
return null;
}
else if (rtrvGtDrResp.statusCode.code == REQUEST_ERROR)
{
log.ErrorFormat("Error in the submitted request: {0}", rtrvGtDrResp.statusCode.description);
return null;
}
}
catch (Exception e)
{
log.ErrorFormat("Error in GetData - {0} - {1}", e.Message, e.InnerException == null ? "" : e.InnerException.Message);
return null;
}
return null;
}
Poll interval is 5 seconds and the SOAP web service url is:
https://software.bloomberg.com/datalicensewp/dlws.wsdl

I am having the same issue. I found out that there is a difference between making the same call to Bloomberg API from, for example, console app (works very fast) and web service (takes a lot of time to start session). And the difference is that console app runs under the same user as bbcomm process, whereas web service (or actually iis process) runs under System account. You can try to log out all users on the PC where web service is hosted and then try to make the call. In this case, I guess, bbcomm goes under System account as no one else is logged in and works fast. It worked for me and the call was answered instantly.

Duplicate entries on server response .net

Scenario
One windows service polls a url every two minutes to retrieve certain data.
If any data has been added since the previous call, the data is retrieved and stored otherwise the loop carries on.
Issue
Sometimes a request takes more than two minutes to return a response.
When this happens, the next request is still made and finds new data, since the previous request hasn't return a response yet
This results in duplicate entries when the data is stored.
What I've tried
I tried to handle that by using a boolean like so:
Boolean InProgress = true;
foreach (var item in Lists)
{
\\Make a request and return new data (if any)
InProgress = false;
if (InProgress = false)
{
\\Store new data
}
}
This doesn't solve the issue. I believe I'm using the boolean in wrong place, but I'm not sure where it should.
This is the loop that makes the request and store the data
void serviceTimer_Elapsed(object sender, ElapsedEventArgs e)
{
try
{
Data getCredentials = new Data();
DataTable credentials = getCredentials.loadCredentials();
Boolean InProgress = true;
for (int i = 0; i < credentials.Rows.Count; i++)
{
if (credentials != null)
{
var PBranchID = (int)credentials.Rows[i]["PortalBranchID"];
var negRef = (int)credentials.Rows[i]["NegotiatorRef"];
var Username = credentials.Rows[i]["Username"].ToString();
var Password = credentials.Rows[i]["Password"].ToString();
var Domain = credentials.Rows[i]["Domain"].ToString();
var FooCompanyBaseUrl = "https://" + Domain + ".FooCompany.com/";
Data getCalls = new Data();
DataTable calls = getCalls.loadCalls(PBranchID);
//If it's not the first call
if (calls != null && calls.Rows.Count > 0)
{
//Makes a call
DateTime CreatedSince = DateTime.SpecifyKind((DateTime)calls.Rows[0]["LastSuccessOn"], DateTimeKind.Local);
string IssueListUrl = FooCompany.WebApi.V2.URLs.Issues(BaseUrl, null, CreatedSince.ToUniversalTime(), null);
FooCompany.WebApi.V2.DTO.PrevNextPagedList resultIssueList;
resultIssueList = FooCompany.WebApi.Client.Helper.Utils.Getter<Foocompany.WebApi.V2.DTO.PrevNextPagedList>(IssueListUrl, Username, Password);
InProgress = false;
if (InProgress == false)
{
if (resultIssueList.Items.Count > 0)
{
//If call returns new issues, save call
Data saveCalls = new Data();
saveCalls.saveCalls(PBranchID);
foreach (var item in resultIssueList.Items)
{
var Issue = FooCompany.WebApi.Client.Helper.Utils.Getter<FooCompany.WebApi.V2.DTO.Issue>(item, Username, Password);
string TenantSurname = Issue.Surname;
string TenantEmail = Issue.EmailAddress;
Data tenants = new Data();
int tenantPropRef = Convert.ToInt32(tenants.loadTenantPropRef(PBranchID, TenantSurname, TenantEmail));
Data Properties = new Data();
DataTable propAddress = Properties.loadPropAddress(PBranchID, tenantPropRef);
var Address1 = propAddress.Rows[0]["Address1"];
var Address2 = propAddress.Rows[0]["Address2"];
var AddressFolder = Address1 + "," + Address2;
if (!Directory.Exists("path"))
{
Directory.CreateDirectory("path");
}
string ReportPDFDestination = "path";
if (File.Exists(ReportPDFDestination))
{
File.Delete(ReportPDFDestination);
}
FooCompany.WebApi.Client.Helper.Utils.DownloadFileAuthenticated(FooCompany.WebApi.V2.URLs.IssueReport(BaseUrl, Issue.Id), Username, Password, ReportPDFDestination);
//Store data
}
IssueListUrl = resultIssueList.NextURL;
}
}
}
else
{
continue;
}
}
}
catch (Exception ex)
{
//write to log
}
}
Question
I'm sure there is a better way than a boolean.
Could anyone advice a different method to handle the issue properly?
Thanks.
Solution
I ended up using a combination of both Thomas and Mason suggestions. I wrapped a lock statement around the main function of my windows service and used a boolean inside the function section that makes the call to the remote server.
Tested many times and it's error free.

You seems to have a problem of synchronisation, just surround the code that iterate though the List with a lock, and you will be fine.
public class MyClass{
private readonly object internalLock= new object();
private bool AlreadyRunning { get; set; }
void serviceTimer_Elapsed(object sender, ElapsedEventArgs e)
{
if(AlreadyRunning){
return;
}
try{
lock(internalLock){
Thread.MemoryBarrier();
if(AlreadyRunning){
return;
}
AlreadyRunning = true;
...Do all the things...
}
}
catch(Exception e){
..Exception handling
}
finally
{
AlreadyRunning = false;
}
}

bool InProgress=false;
void serviceTimer_Elapsed(object sender, ElapsedEventArgs e)
{
if(!InProgress)
{
InProgress=true;
//retrieve data
InProgress=false;
}
}
Your InProgress variable needs to be declared outside the event handler. When you enter the method, check to see if it's already running. If it is, then we do nothing. If it's not running, then we say it's running, retrieve our data, then reset our flag to say we've finished running.
You'll probably need to add appropriate locks for thread safety, similar to Thomas's answer.

C# false http response

I have a thread that returns a site's http response status, but sometimes my program returns false results. and after a while it gives good results.
False result:
it takes a big a mount of time to check, and then it says that (for example) Google is down, which is quite not reasonable, but after a few seconds it returns good results
Can you take a look and tell me whats wrong? or how I can I improve it?
Checks all sites in datagrid:
private void CheckSites()
{
if (CheckSelected())
{
int rowCount = dataGrid.BindingContext[dataGrid.DataSource, dataGrid.DataMember].Count;
string url;
for (int i = 0; i < rowCount; i++)
{
url = dataGrid.Rows[i].Cells[2].Value.ToString();
if (url != null)
{
Task<string[]> task = Task.Factory.StartNew<string[]>
(() => checkSite(url));
// We can do other work here and it will execute in parallel:
//Loading...
// When we need the task's return value, we query its Result property:
// If it's still executing, the current thread will now block (wait)
// until the task finishes:
string[] result = task.Result;
selectRows();
if (result[0] != System.Net.HttpStatusCode.OK.ToString() && result[0] != System.Net.HttpStatusCode.Found.ToString() && result[0] != System.Net.HttpStatusCode.MovedPermanently.ToString())
{
//bad
notifyIcon1.ShowBalloonTip(5000, "Site Down", dataGrid.Rows[i].Cells[2].Value.ToString() + ", has a status code of:" + result, ToolTipIcon.Error);
dataGrid.Rows[i].DefaultCellStyle.BackColor = System.Drawing.Color.Wheat;
TimeSpan ts;
TimeSpan timeTaken = TimeSpan.Parse(result[1]);
dataGrid.Rows[i].Cells[3].Value = result[0];
dataGrid.Rows[i].Cells[3].Style.BackColor = System.Drawing.Color.Red;
dataGrid.Rows[i].Cells[4].Value = timeTaken.Seconds.ToString() + "." + String.Format("{0:0.00000}", timeTaken.Milliseconds.ToString()) + " seconds.";
string sec = (DateTime.Now.Second < 10) ? "0" + DateTime.Now.Second.ToString() : DateTime.Now.Second.ToString();
string min = (DateTime.Now.Minute < 10) ? "0" + DateTime.Now.Minute.ToString() : DateTime.Now.Minute.ToString();
string hour = (DateTime.Now.Hour < 10) ? "0" + DateTime.Now.Hour.ToString() : DateTime.Now.Hour.ToString();
dataGrid.Rows[i].Cells[5].Value = hour + ":" + min + ":" + sec;
//loadbar
}
else if (result[0] == "catch")//catch
{
notifyIcon1.ShowBalloonTip(10000, "SITE DOWN", dataGrid.Rows[i].Cells[1].Value.ToString() + ", Error:" +result[1], ToolTipIcon.Error);
dataGrid.Rows[i].Cells[3].Value = result[1];
dataGrid.Rows[i].Cells[3].Style.BackColor = System.Drawing.Color.Red;
//loadbar
}
else
{
//good
TimeSpan timeTaken = TimeSpan.Parse(result[1]);
dataGrid.Rows[i].Cells[3].Value = result[0];
dataGrid.Rows[i].Cells[3].Style.BackColor = System.Drawing.Color.LightGreen;
dataGrid.Rows[i].Cells[4].Value = timeTaken.Seconds.ToString() + "." + String.Format("{0:0.00000}", timeTaken.Milliseconds.ToString()) + " seconds.";
string sec = (DateTime.Now.Second < 10) ? "0" + DateTime.Now.Second.ToString() : DateTime.Now.Second.ToString();
string min = (DateTime.Now.Minute < 10) ? "0" + DateTime.Now.Minute.ToString() : DateTime.Now.Minute.ToString();
string hour = (DateTime.Now.Hour < 10) ? "0" + DateTime.Now.Hour.ToString() : DateTime.Now.Hour.ToString();
dataGrid.Rows[i].Cells[5].Value = hour + ":" + min + ":" + sec;
//loadbar
}
selectRows();
}
}
}
}
Checks a site:
/////////////////////////////////
////Check datagrid websites-button - returns response
/////////////////////////////////
private string[] checkSite(string url)
{
string[] response = new string[2];
url = dataGrid.Rows[0].Cells[2].Value.ToString();
if (url != null)
{
try
{
HttpWebRequest httpReq;
httpReq.Timeout = 10000;
//loadbar
dataGrid.Rows[0].DefaultCellStyle.BackColor = System.Drawing.Color.Wheat;
System.Diagnostics.Stopwatch timer = new System.Diagnostics.Stopwatch();
timer.Start();
HttpWebResponse httpRes = (HttpWebResponse)httpReq.GetResponse(); //httpRes.Close();
timer.Stop();
//loadbar
HttpStatusCode httpStatus = httpRes.StatusCode;
response[0] = httpStatus.ToString();
response[1] = timer.Elapsed.ToString();//*
httpRes.Close();
return response;
}
catch (Exception he)
{
response[0] = "catch";
response[1] = he.Message;
return response;
}
}
response[0] = "catch";
response[1] = "No URL entered";
return response;
//dataGrid.Rows[i].DefaultCellStyle.BackColor = System.Drawing.Color.Blue;
}
Thanks in advance.

Assuming the code provided is the actual code used:
First of all, your definition of 'False result' and 'Good result' is wrong. If you expect A but get B, that doesn't mean B is invalid. If your wife is giving birth and you expect a boy but it turns out the be a girl, its not a false result. Just unexpected.
That said: lets analyze your work: If it takes a long long time to check a site only to finally get a ??? result which isn't a 200 response code. We can almost savely assume you are dealing with a timeout. If your router, google or any fundamental network device in between is having problems, its expected to get an unexpected answer. "Timeout", "Bad Request", "Server not available" etc. Why would this happen? Its impossible to say for certain without having direct access to your environment.
Looking at your code however, i see that you're using the default TaskScheduler for making each check run as a task in the background (assuming you havent changed the default task scheduler which would be a vey bad practice to begin with). The default task scheduler, schedules each task on the threadpool which results in many many tasks running simultanious. Here we have a good candidate for overloading your network. Many sites (esspecially google) are kinda sensitive for handling many requests from the same source (esspecially if the frequency is high) so maybe google is blocking you temporarily or holding you back. Again, at this point it's pure speculation but the fact that you're running all checks simultaniously (unless the thread pool is on his max) is very likely the cause of your problem.
UPDATE
I would recommend working with a LimitedConcurrencyTaskScheduler ( see here: http://blogs.msdn.com/b/pfxteam/archive/2010/04/09/9990424.aspx ). Here you can limit the amount of tasks that can be run asynchronously. You have to do some testing for what number works ideally in your situation. Also make sure that the frequency is not 'too' high. Its hard to define what is too high, only testing can proof that.

In order to simulate your scenario, I have created a Winform with data grid and a button. On load of the form, I programmatically creates list of url’s (in a table) and bind to data grid. And on button click, we start the download process. In concise, the you have to write more defensive code and the following code only a skeleton of how you can fix the issue.
using System;
using System.Data;
using System.Net;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace app
{
public partial class Form1 : Form
{
DataTable urls = new DataTable();
public Form1()
{
InitializeComponent();
}
//Fill your uri's and bind to a data grid.
void InitTable()
{
//Silly logic to simulate your scenario.
urls = new DataTable();
urls.Columns.Add(new DataColumn("Srl", typeof(string)));
urls.Columns.Add(new DataColumn("Urls", typeof(Uri)));
urls.Columns.Add(new DataColumn("Result", typeof(string)));
DataRow dr = urls.NewRow();
dr["Srl"] = "1";
dr["Urls"] = new Uri("http://www.microsoft.com");
dr["Result"] = string.Empty;
urls.Rows.Add(dr);
dr = urls.NewRow();
dr["Srl"] = "2";
dr["Urls"] = new Uri("http://www.google.com");
dr["Result"] = string.Empty;
urls.Rows.Add(dr);
dr = urls.NewRow();
dr["Srl"] = "3";
dr["Urls"] = new Uri("http://www.stackoverflow.com");
dr["Result"] = string.Empty;
urls.Rows.Add(dr);
urls.AcceptChanges();
}
void UpdateResult()
{
dataGridView1.DataSource = urls;
}
//Important
// This example will freeze UI. You can avoid this while implementing
//background worker or pool with some event synchronization. I haven't covered those area since
//we are addressing different issue. Let me know if you would like to address UI freeze
//issue. Or can do it your self.
private void button1_Click(object sender, EventArgs e)
{
//Create array for Task to parallelize multiple download.
var tasks = new Task<string[]>[urls.Rows.Count];
//Initialize those task based on number of Uri's
for(int i=0;i<urls.Rows.Count;i++)
{
int index = i;//Do not change this. This is to avoid data race
//Assign responsibility and start task.
tasks[index] = new Task<string[]>(
() => checkSite(
new TaskInput(urls.Rows[index]["Urls"].ToString(), urls.Rows[index]["Srl"].ToString())));
tasks[index].Start();
}
//Wait for all task to complete. Check other overloaded if interested.
Task.WaitAll(tasks);
//block shows how to access result from task
foreach (var item in tasks)
{
DataRow[] rows=urls.Select("Srl='"+item.Result[2]+"'");
foreach (var row in rows)
row["Result"]=item.Result[0]+"|"+item.Result[1];
}
UpdateResult();
}
//This is dummy method which in your case 'Check Site'. You can have your own
string[] checkSite(TaskInput input)
{
string[] response = new string[3];
if (input != null)
{
try
{
WebResponse wResponse = WebRequest.Create(input.Url).GetResponse();
response[0] = wResponse.ContentLength.ToString();
response[1] = wResponse.ContentType;
response[2] = input.Srl;
return response;
}
catch (Exception he)
{
response[0] = "catch";
response[1] = he.Message;
response[2] = input.Srl;
return response;
}
}
response[0] = "catch";
response[1] = "No URL entered";
response[2] = input.Srl;
return response;
}
private void Form1_Load(object sender, EventArgs e)
{
InitTable();
UpdateResult();
}
}
//Supply custom object for simplicity
public class TaskInput
{
public TaskInput(){}
public TaskInput(string url, string srl)
{
Url = url;
Srl = srl;
}
public string Srl { get; set; }
public string Url { get; set; }
}
}