So I know this question has been asked here before, but the situation here is a little different.
I have a service Application that spawns worker threads. The main service thread is organized as so:
public void PollCrunchFilesTask()
{
try
{
var stuckDeletedServTableFiles = MaintenanceDbContext.stuckDeletedServTableFiles;
var stuckErrorStatusFiles = MaintenanceDbContext.stuckErrorStatusFiles;
while (_signalPollAutoEvent.WaitOne())
{
try
{
Poll();
lock (stuckDelLock)
{
if(stuckDeletedServTableFiles.Count > 0)
MaintenanceDbContext.DeleteFilesToBeDeletedInServiceTable(stuckDeletedServTableFiles);
}
lock (errorStatusLock)
{
if (stuckErrorStatusFiles.Count > 0)
MaintenanceDbContext.UpdateStuckErrorServiceLogEntries(stuckErrorStatusFiles);
}
}
catch (Exception ex)
{
}
}
}
catch (Exception ex)
{
}
}
Inside Poll you have this logic:
public void Poll()
{
try
{
if (ProducerConsumerQueue.Count() == 0 && ThreadCount_Diff_ActiveTasks > 0)
{
var dequeuedItems = MetadataDbContext.UpdateOdfsServiceEntriesForProcessingOnPollInterval(ThreadCount_Diff_ActiveTasks);
var handlers = Producer.GetParserHandlers(dequeuedItems);
foreach (var handler in handlers)
{
ProducerConsumerQueue.EnqueueTask(handler.Execute, CancellationTokenSource.Token);
}
}
}
catch (Exception ex)
{
}
}
That ProducerConsumerQueue.EnqueueTask(handler.Execute, CancellationTokenSource.Token); launches 4 worker threads and inside any one of these threads, the following function is called at any time:
public static int DeleteServiceEntry(string logFileName)
{
int rowsAffected = 0;
var stuckDeletedServTableFiles = MaintenanceDbContext.stuckDeletedServTableFiles;
try
{
string connectionString = GetConnectionString();
throw new Exception($"Testing Del HashSet");
using (SqlConnection connection = new SqlConnection())
{
//Attempt some query
}
}
catch (Exception ex)
{
lock (stuckDelLock)
{
stuckDeletedServTableFiles.Add(logFileName);
}
}
return rowsAffected;
}
Now I am testing the stuckDeletedServTableFiles hashset which is only called when there is an exception during a query. this is why I purposefully throw an exception. That hashset is the one that is operated on on the main service thread in the function DeleteFilesToBeDeletedInServiceTable(); who's excerpt is defined below:
public static int DeleteFilesToBeDeletedInServiceTable(HashSet<string> stuckDeletedServTableFiles)
{
int rowsAffected = 0;
string logname = String.Empty; //used to collect error log
var removedHashset = new HashSet<string>();
try
{
var dbConnString = MetadataDbContext.GetConnectionString();
string serviceTable = Constants.SERVICE_LOG_TBL;
using (SqlConnection connection = new SqlConnection(dbConnString))
{
SqlCommand cmd = new SqlCommand();
cmd.CommandType = CommandType.Text;
cmd.CommandText = $"DELETE FROM {serviceTable} WHERE LOGNAME = @LOGNAME";
cmd.Parameters.Add("@LOGNAME", SqlDbType.NVarChar);
cmd.Connection = connection;
connection.Open();
foreach (var logFname in stuckDeletedServTableFiles)
{
cmd.Parameters["@LOGNAME"].Value = logFname;
logname = logFname;
int currRowsAffected = cmd.ExecuteNonQuery();
rowsAffected += currRowsAffected;
if (currRowsAffected == 1)
{
removedHashset.Add(logFname);
Logger.Info($"Removed Stuck {logFname} Marked for Deletion from {serviceTable}");
}
}
Logger.Info($"Removed {rowsAffected} stuck files Marked for Deletion from {serviceTable}");
}
stuckDeletedServTableFiles.ExceptWith(removedHashset);
}
catch (Exception ex)
{
}
return rowsAffected;
}
Given that the hashset stuckDeletedServTableFiles is able to be accessed by multiple threads at the same time including the main service thread, I put a lock on the mainservice thread before it is operated on by DeleteFilesToBeDeletedInServiceTable() and in the function DeleteServiceEntry(). I am new to C# but I assumed this would be enough? I assume since a lock is called on the main service thread for the function DeleteFilesToBeDeletedInServiceTable(), that lock would prevent anything from using the hashset since its being operated on by the function. Why am I getting this error?
Note I am not modifying the Hashset in the forloop. I only do it after the loop is done. I am getting this error while I loop through the Hashset. I suppose because another thread is attempting to modify it. The question then is, why is a thread able to modify the hashSet when I have a lock on the function that calls it on the service level?
