I would like to implement a Multiple file downloading with pattern of single producer and multiple consumer.
What I have:
- Code which finds new links to be downloaded in a loop
- When a new link is found - it calls download function
- Download function accepts source file path and destination file path and downloads the file.
What I want to do
- I want to download X number of files simultaneously (I dont know total number of files)
- At any times I should be able to download X files simultaneously - as soon as 1 of the X file finish downloading - the calling function should be able to add new download right away - which in turn downloading right away
So I have a producer function which keeps adding new download to queue (at any time maximum X downloads)
Multiple X thread which consumes the downloads and start downloading individually. Once it finishes download - the producer should be able to add new download - which will spawn new thread.
EXAMPLE would be really appreciated
For this P/C problem all you need is a BlockingCollection<T>.
//shared and thread-safe
static BlockingCollection<string> queue = new BlockingCollection<string>(100);
// Producer
queue.Add(fileName); // will block when full
// Consumer
if (queue.TryTake(out fileName, timeOut)) // waits when empty
...
You'll want to fine-tune it a little with timeouts and CancellationTokens.
ReaderWriterLockSlim class is designed to do that.
Also, check this brilliant website about threading:
http://www.albahari.com/threading/part4.aspx#_Reader_Writer_Locks
The example comes from the website above.
class SlimDemo
{
static ReaderWriterLockSlim _rw = new ReaderWriterLockSlim();
static List<int> _items = new List<int>();
static Random _rand = new Random();
static void Main()
{
new Thread (Read).Start();
new Thread (Read).Start();
new Thread (Read).Start();
new Thread (Write).Start ("A");
new Thread (Write).Start ("B");
}
static void Read()
{
while (true)
{
_rw.EnterReadLock();
foreach (int i in _items) Thread.Sleep (10);
_rw.ExitReadLock();
}
}
static void Write (object threadID)
{
while (true)
{
int newNumber = GetRandNum (100);
_rw.EnterWriteLock();
_items.Add (newNumber);
_rw.ExitWriteLock();
Console.WriteLine ("Thread " + threadID + " added " + newNumber);
Thread.Sleep (100);
}
}
static int GetRandNum (int max) { lock (_rand) return _rand.Next(max); }
}
Use a Concurrent collection for the communication between the boss and its work crew.
Either ConcurrentQueue (if you care about the order) or ConcurrentBag.
The boss adds to ConcurrentQueue (Add method) and the crew takes from the queue (Take method). Let me know if you need code.
I would suggest looking into the Task Parallel Library. This wraps up the method calls very cleanly, and manages your multiple threads for you.
Related
I have to write a program where I'm reading from a database the queues to process and all the queues are run in parallel and managed on the parent thread using a ConcurrentDictionary.
I have a class that represents the queue, which has a constructor that takes in the queue information and the parent instance handle. The queue class also has the method that processes the queue.
Here is the Queue Class:
Class MyQueue {
protected ServiceExecution _parent;
protect string _queueID;
public MyQueue(ServiceExecution parentThread, string queueID)
{
_parent = parentThread;
_queueID = queueID;
}
public void Process()
{
try
{
//Do work to process
}
catch()
{
//exception handling
}
finally{
_parent.ThreadFinish(_queueID);
}
The parent thread loops through the dataset of queues and instantiates a new queue class. It spawns a new thread to execute the Process method of the Queue object asynchronously. This thread is added to the ConcurrentDictionary and then started as follows:
private ConcurrentDictionary<string, MyQueue> _runningQueues = new ConcurrentDictionary<string, MyQueue>();
Foreach(datarow dr in QueueDataset.rows)
{
MyQueue queue = new MyQueue(this, dr["QueueID"].ToString());
Thread t = new Thread(()=>queue.Process());
if(_runningQueues.TryAdd(dr["QueueID"].ToString(), queue)
{
t.start();
}
}
//Method that gets called by the queue thread when it finishes
public void ThreadFinish(string queueID)
{
MyQueue queue;
_runningQueues.TryRemove(queueID, out queue);
}
I have a feeling this is not the right approach to manage the asynchronous queue processing and I'm wondering if perhaps I can run into deadlocks with this design? Furthermore, I would like to use Tasks to run the queues asynchronously instead of the new Threads. I need to keep track of the queues because I will not spawn a new thread or task for the same queue if the previous run is not complete yet. What is the best way to handle this type of parallelism?
Thanks in advance!
About your current approach
Indeed it is not the right approach. High number of queues read from database will spawn high number of threads which might be bad. You will create a new thread each time. Better to create some threads and then re-use them. And if you want tasks, better to create LongRunning tasks and re-use them.
Suggested Design
I'd suggest the following design:
Reserve only one task to read queues from the database and put those queues in a BlockingCollection;
Now start multiple LongRunning tasks to read a queue each from that BlockingCollection and process that queue;
When a task is done with processing the queue it took from the BlockingCollection, it will then take another queue from that BlockingCollection;
Optimize the number of these processing tasks so as to properly utilize the cores of your CPU. Usually since DB interactions are slow, you can create tasks 3 times more than the number of cores however YMMV.
Deadlock possibility
They will at least not happen at the application side. However, since the queues are of database transactions, the deadlock may happen at the database end. You may have to write some logic to make your task start a transaction again if the database rolled it back because of deadlock.
Sample Code
private static void TaskDesignedRun()
{
var expectedParallelQueues = 1024; //Optimize it. I've chosen it randomly
var parallelProcessingTaskCount = 4 * Environment.ProcessorCount; //Optimize this too.
var baseProcessorTaskArray = new Task[parallelProcessingTaskCount];
var taskFactory = new TaskFactory(TaskCreationOptions.LongRunning, TaskContinuationOptions.None);
var itemsToProcess = new BlockingCollection<MyQueue>(expectedParallelQueues);
//Start a new task to populate the "itemsToProcess"
taskFactory.StartNew(() =>
{
// Add code to read queues and add them to itemsToProcess
Console.WriteLine("Done reading all the queues...");
// Finally signal that you are done by saying..
itemsToProcess.CompleteAdding();
});
//Initializing the base tasks
for (var index = 0; index < baseProcessorTaskArray.Length; index++)
{
baseProcessorTaskArray[index] = taskFactory.StartNew(() =>
{
while (!itemsToProcess.IsAddingCompleted && itemsToProcess.Count != 0) {
MyQueue q;
if (!itemsToProcess.TryTake(out q)) continue;
//Process your queue
}
});
}
//Now just wait till all queues in your database have been read and processed.
Task.WaitAll(baseProcessorTaskArray);
}
I have developed an application in c#. The class structure is as follows.
Form1 => The UI form. Has a backgroundworker, processbar, and a "ok" button.
SourceReader, TimedWebClient, HttpWorker, ReportWriter //clases do some work
Controller => Has the all over control. From "ok" button click an instance of this class called "cntrl" is created. This cntrlr is a global variable in Form1.cs.
(At the constructor of the Controler I create SourceReader, TimedWebClient,HttpWorker,ReportWriter instances. )
Then I call the RunWorkerAsync() of the background worker.
Within it code is as follows.
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
int iterator = 1;
for (iterator = 1; iterator <= this.urlList.Count; iterator++)
{
cntrlr.Vmain(iterator-1);
backgroundWorker1.ReportProgress(iterator);
}
}
At themoment ReportProgress updates the progressbar.
The urlList mentioned above has 1000 of urls. cntlr.Vamin(int i) process the whole process at themoment. I want to give the task to several threads, each one having to process 100 of urls. Though access for other instances or methods of them is not prohibited, access to ReportWriter should be limited to only one thread at a time. I can't find a way to do this. If any one have an idea or an answer, please explain.
If you do want to restrict multiple threads using the same method concurrently then I would use the Semaphore class to facilitate the required thread limit; here's how...
A semaphore is like a mean night club bouncer, it has been provide a club capacity and is not allowed to exceed this limit. Once the club is full, no one else can enter... A queue builds up outside. Then as one person leaves another can enter (analogy thanks to J. Albahari).
A Semaphore with a value of one is equivalent to a Mutex or Lock except that the Semaphore has no owner so that it is thread ignorant. Any thread can call Release on a Semaphore whereas with a Mutex/Lock only the thread that obtained the Mutex/Lock can release it.
Now, for your case we are able to use Semaphores to limit concurrency and prevent too many threads from executing a particular piece of code at once. In the following example five threads try to enter a night club that only allows entry to three...
class BadAssClub
{
static SemaphoreSlim sem = new SemaphoreSlim(3);
static void Main()
{
for (int i = 1; i <= 5; i++)
new Thread(Enter).Start(i);
}
// Enfore only three threads running this method at once.
static void Enter(int i)
{
try
{
Console.WriteLine(i + " wants to enter.");
sem.Wait();
Console.WriteLine(i + " is in!");
Thread.Sleep(1000 * (int)i);
Console.WriteLine(i + " is leaving...");
}
finally
{
sem.Release();
}
}
}
Note, that SemaphoreSlim is a lighter weight version of the Semaphore class and incurs about a quarter of the overhead. it is sufficient for what you require.
I hope this helps.
I think I would have used the ThreadPool, instead of background worker, and given each thread 1, not 100 url's to process. The thread pool will limit the number of threads it starts at once, so you wont have to worry about getting 1000 requests at once. Have a look here for a good example
http://msdn.microsoft.com/en-us/library/3dasc8as.aspx
Feeling a little more adventurous? Consider using TPL DataFlow to download a bunch of urls:
var urls = new[]{
"http://www.google.com",
"http://www.microsoft.com",
"http://www.apple.com",
"http://www.stackoverflow.com"};
var tb = new TransformBlock<string, string>(async url => {
using(var wc = new WebClient())
{
var data = await wc.DownloadStringTaskAsync(url);
Console.WriteLine("Downloaded : {0}", url);
return data;
}
}, new ExecutionDataflowBlockOptions{MaxDegreeOfParallelism = 4});
var ab = new ActionBlock<string>(data => {
//process your data
Console.WriteLine("data length = {0}", data.Length);
}, new ExecutionDataflowBlockOptions{MaxDegreeOfParallelism = 1});
tb.LinkTo(ab); //join output of producer to consumer block
foreach(var u in urls)
{
tb.Post(u);
}
tb.Complete();
Note how you can control the parallelism of each block explicitly, so you can gather in parallel but process without going concurrent (for example).
Just grab it with nuget. Easy.
I am using a BlockingCollection to process some files and then upload them to a server.
Right now I have a single Producer that recurses the file system and compresses certain files to a temporary location. Once it has finished with a file it adds my own object to the BlockingCollection that contain information, such as, File Name, File Path, Modified date, etc. The Consumer then grabs this object and uses it to upload the file. When the Producer has finished searching the file system and working on files it calls the BlockingCollection.CompleteAdding() method to signal the Consumer that it has finished.
What I would like to do is increase the number of Producers to 2 or more. The reason being that the compression process takes a while and on multi core processors I'm only taking advantage of 1 core. This causes the Producer to sometimes fall behind the Consumer on faster networks.
My question is, when I have multiple Producers and only one Consumer how can I signal the Consumer that all of the Producers have finished their work? If I call the BlockingCollection.CompleteAdding() method on one of the Producers I could still have one or more other producers still working.
You can use a semaphore in your Producer code before calling the BlockingCollection.CompleteAdding(). The semaphore is shared by all the Producer instances, when the last producer has finished it can call the method. The semaphore can be implemented as a simple counter, increment the counter when a Producer is created, decrement it when your producer ends its job. If the counter reaches zero then the BlockingCollection.CompleteAdding() can be called.
I use something like this to have multiple producers and consumers. It is just a very simple solution not optimized for production code.
public class ManageBatchProcessing
{
private BlockingCollection<Action> blockingCollection;
public void Process()
{
blockingCollection = new BlockingCollection<Action>();
int numberOfBatches = 10;
Process(HandleProducers, HandleConsumers, numberOfBatches);
}
private void Process(Action<int> produce, Action<int> consume, int numberOfBatches)
{
produce(numberOfBatches);
consume(numberOfBatches);
}
private void HandleConsumers(int numberOfBatches)
{
var consumers = new List<Task>();
for (var i = 1; i <= numberOfBatches; i++)
{
consumers.Add(Task.Factory.StartNew(() =>
{
foreach (var action in blockingCollection.GetConsumingEnumerable())
{
action();
}
}));
}
Task.WaitAll(consumers.ToArray());
}
private void HandleProducers(int numberOfBatches)
{
var producers = new List<Task>();
for (var i = 0; i <= numberOfBatches; i++)
{
producers.Add(Task.Factory.StartNew(() =>
{
blockingCollection.Add(() => YourProdcerMethod());
}));
}
Task.WaitAll(producers.ToArray());
blockingCollection.CompleteAdding();
}
}
I think I may need to re-think my design. I'm having a hard time narrowing down a bug that is causing my computer to completely hang, sometimes throwing an HRESULT 0x8007000E from VS 2010.
I have a console application (that I will later convert to a service) that handles transferring files based on a database queue.
I am throttling the threads allowed to transfer. This is because some systems we are connecting to can only contain a certain number of connections from certain accounts.
For example, System A can only accept 3 simultaneous connections (which means 3 separate threads). Each one of these threads has their own unique connection object, so we shouldn't run in to any synchronization problems since they aren't sharing a connection.
We want to process the files from those systems in cycles. So, for example, we will allow 3 connections that can transfer up to 100 files per connection. This means, to move 1000 files from System A, we can only process 300 files per cycle, since 3 threads are allowed with 100 files each. Therefore, over the lifetime of this transfer, we will have 10 threads. We can only run 3 at a time. So, there will be 3 cycles, and the last cycle will only use 1 thread to transfer the last 100 files. (3 threads x 100 files = 300 files per cycle)
The current architecture by example is:
A System.Threading.Timer checks the queue every 5 seconds for something to do by calling GetScheduledTask()
If there's nothing to, GetScheduledTask() simply does nothing
If there is work, create a ThreadPool thread to process the work [Work Thread A]
Work Thread A sees that there are 1000 files to transfer
Work Thread A sees that it can only have 3 threads running to the system it is getting files from
Work Thread A starts three new work threads [B,C,D] and transfers
Work Thread A waits for B,C,D [WaitHandle.WaitAll(transfersArray)]
Work Thread A sees that there are still more files in the queue (should be 700 now)
Work Thread A creates a new array to wait on [transfersArray = new TransferArray[3] which is the max for System A, but could vary on system
Work Thread A starts three new work threads [B,C,D] and waits for them [WaitHandle.WaitAll(transfersArray)]
The process repeats until there are no more files to move.
Work Thread A signals that it is done
I am using ManualResetEvent to handle the signaling.
My questions are:
Is there any glaring circumstance which would cause a resource leak or problem that I am experiencing?
Should I loop thru the array after every WaitHandle.WaitAll(array) and call array[index].Dispose()?
The Handle count under the Task Manager for this process slowly creeps up
I am calling the initial creation of Worker Thread A from a System.Threading.Timer. Is there going to be any problems with this? The code for that timer is:
(Some class code for scheduling)
private ManualResetEvent _ResetEvent;
private void Start()
{
_IsAlive = true;
ManualResetEvent transferResetEvent = new ManualResetEvent(false);
//Set the scheduler timer to 5 second intervals
_ScheduledTasks = new Timer(new TimerCallback(ScheduledTasks_Tick), transferResetEvent, 200, 5000);
}
private void ScheduledTasks_Tick(object state)
{
ManualResetEvent resetEvent = null;
try
{
resetEvent = (ManualResetEvent)state;
//Block timer until GetScheduledTasks() finishes
_ScheduledTasks.Change(Timeout.Infinite, Timeout.Infinite);
GetScheduledTasks();
}
finally
{
_ScheduledTasks.Change(5000, 5000);
Console.WriteLine("{0} [Main] GetScheduledTasks() finished", DateTime.Now.ToString("MMddyy HH:mm:ss:fff"));
resetEvent.Set();
}
}
private void GetScheduledTask()
{
try
{
//Check to see if the database connection is still up
if (!_IsAlive)
{
//Handle
_ConnectionLostNotification = true;
return;
}
//Get scheduled records from the database
ISchedulerTask task = null;
using (DataTable dt = FastSql.ExecuteDataTable(
_ConnectionString, "hidden for security", System.Data.CommandType.StoredProcedure,
new List<FastSqlParam>() { new FastSqlParam(ParameterDirection.Input, SqlDbType.VarChar, "#ProcessMachineName", Environment.MachineName) })) //call to static class
{
if (dt != null)
{
if (dt.Rows.Count == 1)
{ //Only 1 row is allowed
DataRow dr = dt.Rows[0];
//Get task information
TransferParam.TaskType taskType = (TransferParam.TaskType)Enum.Parse(typeof(TransferParam.TaskType), dr["TaskTypeId"].ToString());
task = ScheduledTaskFactory.CreateScheduledTask(taskType);
task.Description = dr["Description"].ToString();
task.IsEnabled = (bool)dr["IsEnabled"];
task.IsProcessing = (bool)dr["IsProcessing"];
task.IsManualLaunch = (bool)dr["IsManualLaunch"];
task.ProcessMachineName = dr["ProcessMachineName"].ToString();
task.NextRun = (DateTime)dr["NextRun"];
task.PostProcessNotification = (bool)dr["NotifyPostProcess"];
task.PreProcessNotification = (bool)dr["NotifyPreProcess"];
task.Priority = (TransferParam.Priority)Enum.Parse(typeof(TransferParam.SystemType), dr["PriorityId"].ToString());
task.SleepMinutes = (int)dr["SleepMinutes"];
task.ScheduleId = (int)dr["ScheduleId"];
task.CurrentRuns = (int)dr["CurrentRuns"];
task.TotalRuns = (int)dr["TotalRuns"];
SchedulerTask scheduledTask = new SchedulerTask(new ManualResetEvent(false), task);
//Queue up task to worker thread and start
ThreadPool.QueueUserWorkItem(new WaitCallback(this.ThreadProc), scheduledTask);
}
}
}
}
catch (Exception ex)
{
//Handle
}
}
private void ThreadProc(object taskObject)
{
SchedulerTask task = (SchedulerTask)taskObject;
ScheduledTaskEngine engine = null;
try
{
engine = SchedulerTaskEngineFactory.CreateTaskEngine(task.Task, _ConnectionString);
engine.StartTask(task.Task);
}
catch (Exception ex)
{
//Handle
}
finally
{
task.TaskResetEvent.Set();
task.TaskResetEvent.Dispose();
}
}
0x8007000E is an out-of-memory error. That and the handle count seem to point to a resource leak. Ensure you're disposing of every object that implements IDisposable. This includes the arrays of ManualResetEvents you're using.
If you have time, you may also want to convert to using the .NET 4.0 Task class; it was designed to handle complex scenarios like this much more cleanly. By defining child Task objects, you can reduce your overall thread count (threads are quite expensive not only because of scheduling but also because of their stack space).
I'm looking for answers to a similar problem (Handles Count increasing over time).
I took a look at your application architecture and like to suggest you something that could help you out:
Have you heard about IOCP (Input Output Completion Ports).
I'm not sure of the dificulty to implement this using C# but in C/C++ it is a piece of cake.
By using this you create a unique thread pool (The number of threads in that pool is in general defined as 2 x the number of processors or processors cores in the PC or server)
You associate this pool to a IOCP Handle and the pool does the work.
See the help for these functions:
CreateIoCompletionPort();
PostQueuedCompletionStatus();
GetQueuedCompletionStatus();
In General creating and exiting threads on the fly could be time consuming and leads to performance penalties and memory fragmentation.
There are thousands of literature about IOCP in MSDN and in google.
I think you should reconsider your architecture altogether. The fact that you can only have 3 simultaneously connections is almost begging you to use 1 thread to generate the list of files and 3 threads to process them. Your producer thread would insert all files into a queue and the 3 consumer threads will dequeue and continue processing as items arrive in the queue. A blocking queue can significantly simplify the code. If you are using .NET 4.0 then you can take advantage of the BlockingCollection class.
public class Example
{
private BlockingCollection<string> m_Queue = new BlockingCollection<string>();
public void Start()
{
var threads = new Thread[]
{
new Thread(Producer),
new Thread(Consumer),
new Thread(Consumer),
new Thread(Consumer)
};
foreach (Thread thread in threads)
{
thread.Start();
}
}
private void Producer()
{
while (true)
{
Thread.Sleep(TimeSpan.FromSeconds(5));
ScheduledTask task = GetScheduledTask();
if (task != null)
{
foreach (string file in task.Files)
{
m_Queue.Add(task);
}
}
}
}
private void Consumer()
{
// Make a connection to the resource that is assigned to this thread only.
while (true)
{
string file = m_Queue.Take();
// Process the file.
}
}
}
I have definitely oversimplified things in the example above, but I hope you get the general idea. Notice how this is much simpler as there is not much in the way of thread synchronization (most will be embedded in the blocking queue) and of course there is no use of WaitHandle objects. Obviously you would have to add in the correct mechanisms to shut down the threads gracefully, but that should be fairly easy.
It turns out the source of this strange problem was not related to architecture but rather because of converting the solution from 3.5 to 4.0. I re-created the solution, performing no code changes, and the problem never occurred again.
I have an application that has many cases. Each case has many multipage tif files. I need to covert the tf files to pdf file. Since there are so many file, I thought I could thread the conversion process. I'm currently limiting the process to ten conversions at a time (i.e ten treads). When one conversion completes, another should start.
This is the current setup I'm using.
private void ConvertFiles()
{
List<AutoResetEvent> semaphores = new List<AutoResetEvet>();
foreach(String fileName in filesToConvert)
{
String file = fileName;
if(semaphores.Count >= 10)
{
WaitHandle.WaitAny(semaphores.ToArray());
}
AutoResetEvent semaphore = new AutoResetEvent(false);
semaphores.Add(semaphore);
ThreadPool.QueueUserWorkItem(
delegate
{
Convert(file);
semaphore.Set();
semaphores.Remove(semaphore);
}, null);
}
if(semaphores.Count > 0)
{
WaitHandle.WaitAll(semaphores.ToArray());
}
}
Using this, sometimes results in an exception stating the WaitHandle.WaitAll() or WaitHandle.WaitAny() array parameters must not exceed a length of 65. What am I doing wrong in this approach and how can I correct it?
There are a few problems with what you have written.
1st, it isn't thread safe. You have multiple threads adding, removing and waiting on the array of AutoResetEvents. The individual elements of the List can be accessed on separate threads, but anything that adds, removes, or checks all elements (like the WaitAny call), need to do so inside of a lock.
2nd, there is no guarantee that your code will only process 10 files at a time. The code between when the size of the List is checked, and the point where a new item is added is open for multiple threads to get through.
3rd, there is potential for the threads started in the QueueUserWorkItem to convert the same file. Without capturing the fileName inside the loop, the thread that converts the file will use whatever value is in fileName when it executes, NOT whatever was in fileName when you called QueueUserWorkItem.
This codeproject article should point you in the right direction for what you are trying to do: http://www.codeproject.com/KB/threads/SchedulingEngine.aspx
EDIT:
var semaphores = new List<AutoResetEvent>();
foreach (String fileName in filesToConvert)
{
String file = fileName;
AutoResetEvent[] array;
lock (semaphores)
{
array = semaphores.ToArray();
}
if (array.Count() >= 10)
{
WaitHandle.WaitAny(array);
}
var semaphore = new AutoResetEvent(false);
lock (semaphores)
{
semaphores.Add(semaphore);
}
ThreadPool.QueueUserWorkItem(
delegate
{
Convert(file);
lock (semaphores)
{
semaphores.Remove(semaphore);
}
semaphore.Set();
}, null);
}
Personally, I don't think I'd do it this way...but, working with the code you have, this should work.
Are you using a real semaphore (System.Threading)? When using semaphores, you typically allocate your max resources and it'll block for you automatically (as you add & release). You can go with the WaitAny approach, but I'm getting the feeling that you've chosen the more difficult route.
Looks like you need to remove the handle the triggered the WaitAny function to proceed
if(semaphores.Count >= 10)
{
int index = WaitHandle.WaitAny(semaphores.ToArray());
semaphores.RemoveAt(index);
}
So basically I would remove the:
semaphores.Remove(semaphore);
call from the thread and use the above to remove the signaled event and see if that works.
Maybe you shouldn't create so many events?
// input
var filesToConvert = new List<string>();
Action<string> Convert = Console.WriteLine;
// limit
const int MaxThreadsCount = 10;
var fileConverted = new AutoResetEvent(false);
long threadsCount = 0;
// start
foreach (var file in filesToConvert) {
if (threadsCount++ > MaxThreadsCount) // reached max threads count
fileConverted.WaitOne(); // wait for one of started threads
Interlocked.Increment(ref threadsCount);
ThreadPool.QueueUserWorkItem(
delegate {
Convert(file);
Interlocked.Decrement(ref threadsCount);
fileConverted.Set();
});
}
// wait
while (Interlocked.Read(ref threadsCount) > 0) // paranoia?
fileConverted.WaitOne();