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Avoid starting new thread with lock

Is this possible to lock method for one thread and force another to go futher rather than waiting until first thread finish? Can this problem be resolved with static thread or some proper pattern with one instance of mendtioned below service.
For presentation purposes, it can be done with static boolen like below.
public class SomeService
{
private readonly IRepository _repo;
public SomeService(IRepository repo)
{
_repo = repo;
}
private Thread threadOne;
public static bool isLocked { get; set; }
public void StartSomeMethod()
{
if(!isLocked)
{
threadOne = new Thread(SomeMethod);
isLocked = true;
}
}
public void SomeMethod()
{
while(true)
{
lots of time
}
...
isLocked = false;
}
}
I want to avoid situation when user clicked, by accident, two times to start and accidentailly second thread starts immediatelly after first finished.

You can use lock :)
object locker = new object();
void MethodToLockForAThread()
{
lock(locker)
{
//put method body here
}
}
Now the result will be that when this method is called by a thread (any thread) it puts something like flag at the beginning of lock: "STOP! You are not allowed to go any further, you must wait!" Like red light on crossroads.
When thread that called this method first, levaes the scope, then at the beginning of the scope this "red light" changes into green.
If you want to not call the method when it is already called by another thread, the only way to do this is by using bool value. For example:
object locker = new object();
bool canAccess = true;
void MethodToLockForAThread()
{
if(!canAccess)
return;
lock(locker)
{
if(!canAccess)
return;
canAccess = false;
//put method body here
canAccess = true;
}
}
Other check of canAccess in lock scope is because of what has been told on comments. No it's really thread safe. This is kind of protection that is advisible in thread safe singleton.
EDIT
After some discussion with mjwills I have to change my mind and turn more into Monitor.TryEnter. You can use it like that:
object locker = new object();
void ThreadMethod()
{
if(Monitor.TryEnter(locker, TimeSpan.FromMiliseconds(1))
{
try
{
//do the thread code
}
finally
{
Monitor.Exit(locker);
}
} else
return; //means that the lock has not been aquired
}
Now, lock could not be aquired because of some exception or because some other thread has already acuired it. In second parameter you can pass the time that a thread will wait to acquire a lock. I gave here short time because you don't want the other thread to do the job, when first is doing it.
So this solution seems the best.
When the other thread could not acquire the lock, it will go further instead of waiting (well it will wait for 1 milisecond).

Since lock is a language-specific wrapper around Monitor class, you need Monitor.TryEnter:
public class SomeService
{
private readonly object lockObject = new object();
public void StartSomeMethod()
{
if (Monitor.TryEnter(lockObject))
{
// start new thread
}
}
public void SomeMethod()
{
try
{
// ...
}
finally
{
Monitor.Exit(lockObject);
}
}
}

You can use a AutoResetEvent instead of your isLocked flag.
AutoResetEvent autoResetEvent = new AutoResetEvent(true);
public void StartSomeMethod()
{
if(autoResetEvent.WaitOne(0))
{
//start thread
}
}
public void SomeMethod()
{
try
{
//Do your work
}
finally
{
autoResetEvent.Set();
}
}

Inform another thread, that an operation is running or finished

I have multi-threaded application, where different threads may want to perform an operation. I tried to use Mutex to make sure, that thread does not start an operation if it is already running.
System.Threading.Mutex mutex;
bool isRunning = System.Threading.Mutex.TryOpenExisting(name, out mutex);
if (!isRunning)
{
RunMethod();
}
within method I created mutex, and try to release it at the end:
var mutex = new Mutex(true, name);
try{
//do stuff, it takes some time
}
finally
{
//TODO: I want to get rid of Mutex here
}
How do I get rid of mutex? Because even after I called mutex.ReleaseMutex() and mutex.Close(), it still exists and can be found. How can I inform that operation is currently running or finished?
Is there another way to do this?

Same, like CodingGorilla said, using events is easier.
I hope I understand your question well.
This example shows some events techniques:
Waiting for a thread has been started.
The use of waiting on multiple events (WaitHandle.WaitAny())
How to terminate a thread, safe.
Testing an event state without waiting (.WaitOne(0))
Here is an example:
public class MultiThreadedExample : IDisposable
{
private Thread _thread;
private ManualResetEvent _terminatingEvent = new ManualResetEvent(false);
private ManualResetEvent _runningEvent = new ManualResetEvent(false);
private ManualResetEvent _threadStartedEvent = new ManualResetEvent(false);
public MultiThreadedExample()
{
_thread = new Thread(MyThreadMethod);
_thread.Start();
_threadStartedEvent.WaitOne();
}
private void MyThreadMethod()
{
_threadStartedEvent.Set();
var events = new WaitHandle[] { _terminatingEvent, _runningEvent };
while (WaitHandle.WaitAny(events) != 0) // <- WaitAny returns index within the array of the event that was Set.
{
try
{
// do work......
}
finally
{
// reset the event. so it can be triggered again.
_runningEvent.Reset();
}
}
}
public bool TryStartWork()
{
// .Set() will return if the event was set.
return _runningEvent.Set();
}
public bool IsRunning
{
get { return _runningEvent.WaitOne(0); }
}
public void Dispose()
{
// break the whileloop
_terminatingEvent.Set();
// wait for the thread to terminate.
_thread.Join();
}
}

C# thread accesed to if block, whose condition returns false

This block of code is being accessed by many threads
// All code is from same class
public void ExecuteCommand(IAsciiCommand command, IAsciiCommandSynchronousResponder responder)
{
lock (commander)
{
if (commander.IsConnected)
{
commander.ExecuteCommand(command, responder);
}
}
}
public void Disconnect()
{
var tmp = commander.IsConnected;
commander.Disconnect();
if (commander.IsConnected != tmp && !commander.IsConnected)
{
OnPropertyChanged("IsConnected");
}
}
And eventually i get this:
How is this possible, that thread accessed into if statement, whose condition returns false? How can i fix it?

This is happening because the check and the call lack atomicity. Here is a sequence of events that could lead to an exception:
Two threads, A and B, are reaching the condition at the same time
Thread A checks the condition, which returns true, so it enters the if block
At the same time, thread scheduler decides that thread A has exhausted its time slot, and suspends it
Thread B calls Disconnect
Thread scheduler resumes thread A, which is inside the if condition. However, the command is no longer connected
This causes the exception
You can fix it by locking commander inside Disconnect().
public void Disconnect()
{
bool doEvent;
lock(commander) {
var tmp = commander.IsConnected;
commander.Disconnect();
doEvent = (commander.IsConnected != tmp && !commander.IsConnected)
}
// Run OnPropertyChanged outside the locked context
if (doEvent)
{
OnPropertyChanged("IsConnected");
}
}

You need to lock on a static object. Right now you're creating separate locks based on the object your are working with (commander). Try this:
public class WhatEverClassHasTheExecuteCommandMethod
{
private static object _lock = new object();
public void ExecuteCommand(IAsciiCommand command, IAsciiCommandSynchronousResponder responder)
{
lock (_lock)
if (commander.IsConnected)
commander.ExecuteCommand(command, responder);
}
}

If you are not locking while disconnecting, it's entirely possible to get a race condition. The basic solution is to add a lock inside the Disconnect method:
public void Disconnect()
{
lock (commander)
{
var tmp = commander.IsConnected;
commander.Disconnect();
if (commander.IsConnected != tmp && !commander.IsConnected)
OnPropertyChanged("IsConnected");
}
}

Is this an appropriate place to invoke Thread.Abort()?

I have some code that I borrowed from Steve Marx. The main block is used in an azure worker role thread to take out a lease on an azure blob. This provides a locking mechanism for synchronizing across multiple worker instances when you only want one instance to process a job at a time. However since you might have jobs that will take longer to complete than a blob lease timeout, a new thread is spawned to renew the blob lease every so often.
This renewal thread sleeps and renews on an infinite loop. When the main thread exits (via Dispose in the class' consumer), renewalThread.Abort() is invoked. This causes all kinds of ThreadAbortExceptions to be thrown in the worker role.
I'm wondering, is this a better way to handle this? What I don't like about it is that you can have several renewal threads that remain asleep after the consumer that spawned them has been disposed. Is there anything bad about the code below? If so, is there a better way? Or is Thread.Abort() appropriate here?
public class AutoRenewLease : IDisposable
{
private readonly CloudBlockBlob _blob;
public readonly string LeaseId;
private Thread _renewalThread;
private volatile bool _isRenewing = true;
private bool _disposed;
public bool HasLease { get { return LeaseId != null; } }
public AutoRenewLease(CloudBlockBlob blob)
{
_blob = blob;
// acquire lease
LeaseId = blob.TryAcquireLease(TimeSpan.FromSeconds(60));
if (!HasLease) return;
// keep renewing lease
_renewalThread = new Thread(() =>
{
try
{
while (_isRenewing)
{
Thread.Sleep(TimeSpan.FromSeconds(40.0));
if (_isRenewing)
blob.RenewLease(AccessCondition
.GenerateLeaseCondition(LeaseId));
}
}
catch { }
});
_renewalThread.Start();
}
~AutoRenewLease()
{
Dispose(false);
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (_disposed) return;
if (disposing && _renewalThread != null)
{
//_renewalThread.Abort();
_isRenewing = false;
_blob.ReleaseLease(AccessCondition
.GenerateLeaseCondition(LeaseId));
_renewalThread = null;
}
_disposed = true;
}
}
Update
Let's say you have an azure worker role deployed with 2 or more instances. Let's also say you have a job that both instances have the ability to process for you. During the worker roles Run method you might have something like this:
public override void Run()
{
while (true)
{
foreach (var task in _workforce)
{
var job = task.Key;
var workers = task.Value;
foreach (var worker in workers)
worker.Perform((dynamic)job);
}
Thread.Sleep(1000);
}
}
Every second, the role will check to see if certain jobs are scheduled to run, and if they are, process them. However to avoid having both role instances process the same job, you first take out a lease on a blob. By doing that, the other instance cannot access the blob, so it is effectively blocked until the first instance is finished processing. (Note: taking out a new lease happens within the .Perform method above.)
Now, let's say a job can take anywhere from 1 to 100 seconds to complete. There is a built-in timeout on blob leases, so if you want to keep the other role blocked until the process is finished, you have to periodically renew that lease, to keep it form timing out. That is what the above class encapsulates -- automatically renewing a lease until you dispose of it as a consumer.
My question is mainly about the sleep timeout in the renewalThread. Say the job completed in 2 seconds. The renewalThread will gracefully exit (I think) but not for another 38 seconds. That is where the meat of uncertainty in my question lies. The original code invoked renewalThread.Abort(), which caused it to cease immediately. Is it better to do that, or let it sleep and exit gracefully at a later time? If you are heartbeating the role's Run method at once per second, you could have up to 40 of these renewal threads waiting to exit gracefully. If you have different jobs blocking on different blobs, that number gets multiplied by the number of blobs being leased. However if you do it with Thread.Abort(), you get just as many ThreadAbortExceptions sizzling on the stack.

As I understand it, you have a job that requires a lease on some object. That lease can expire, so you want something to continually renew the lease as long as the job is running.
You don't need a thread in a sleep loop. You need a timer. For example:
public class AutoRenewLease : IDisposable
{
private readonly CloudBlockBlob _blob;
public readonly string LeaseId;
private System.Threading.Timer _renewalTimer;
private volatile bool _isRenewing = true;
private bool _disposed;
public bool HasLease { get { return LeaseId != null; } }
public AutoRenewLease(CloudBlockBlob blob)
{
_blob = blob;
// acquire lease
LeaseId = blob.TryAcquireLease(TimeSpan.FromSeconds(60));
if (!HasLease) return;
_renewalTimer = new System.Threading.Timer(x =>
{
if (_isRenewing)
{
blob.RenewLease(AccessCondition
.GenerateLeaseCondition(LeaseId));
}
}, null, TimeSpan.FromSeconds(40), TimeSpan.FromSeconds(40));
~AutoRenewLease()
{
Dispose(false);
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (_disposed) return;
if (disposing && _renewalTimer != null)
{
_isRenewing = false;
_renewalTimer.Dispose();
_blob.ReleaseLease(AccessCondition
.GenerateLeaseCondition(LeaseId));
_renewalTimer = null;
}
_disposed = true;
}
}
There's no need to waste the resources that a thread uses just so that it can sleep most of the time. Using a timer eliminates polling and also eliminates the need for Thread.Abort.

Abort should be avoided whenever possible. There are some places you really need it, but for this scenario I think we can do it better without abort.
Make it simple with ManualResetEvent, This will stop your thread gracefully and immediately without the use of Abort.
private ManualResetEvent jobSignal = new ManualResetEvent(false);
public AutoRenewLease(CloudBlockBlob blob)
{
_blob = blob;
// acquire lease
LeaseId = blob.TryAcquireLease(TimeSpan.FromSeconds(60));
if (!HasLease) return;
// keep renewing lease
_renewalThread = new Thread(() =>
{
try
{
while (_isRenewing)
{
if(jobSignal.WaitOne(TimeSpan.FromSeconds(40.0)))
{
//Disposed so stop working
jobSignal.Dispose();
jobSignal = null;
return;
}
if (_isRenewing)
blob.RenewLease(AccessCondition
.GenerateLeaseCondition(LeaseId));
}
}
catch (Exception ex) {//atleast log it }
});
_renewalThread.Start();
}
protected virtual void Dispose(bool disposing)
{
if (_disposed) return;
if (disposing && _renewalThread != null)
{
jobSignal.Set();//Signal the thread to stop working
_isRenewing = false;
_blob.ReleaseLease(AccessCondition
.GenerateLeaseCondition(LeaseId));
_renewalThread = null;
}
_disposed = true;
}
Hope this helps.

Multiple calls (at once) to a method that can only run one at a time

I have a business logic method that has to be finished before it can be called again. Multiple clients have the ability to call it at once:
public void DoSomething() {}
I was thinking about solving it by making the method private, and creating a new public method to put the requests on a queue:
public void QueueSomeWork()
{
// put on a Queue object
// How will DoSomething get invoked now?
}
private void DoSomething() {}
I'm trying to solve this issue in an elegant way. My issue is how DoSomething() will know to run. I thought about creating a timer to check the queue, but then it would be running 24/7 for something that happens maybe twice per year.
Another thought is to have DoSomething() fire an event when it's done that something else would subscribe to, pick some work off the queue, and call DoSomething(). Is there a better way?

Why don't you use a lock guard?
Eg :
private static Object lockGuard = new Object();
public void DoSomething()
{
lock (lockGuard)
{
//logic gere
}
}
Locking a resource will prevent access from multiple threads in the same time.
More on lock : http://msdn.microsoft.com/en-us/library/c5kehkcz(v=vs.110).aspx

If the numbers are not so high (it depends how DoSomething internals consume resource); I would go with this:
public static async void QueueSomeWork()
{
await Task.Run(() => { DoSomething(); });
}
static readonly object lockObject = new object();
static void DoSomething()
{
lock (lockObject)
{
// implementation
}
}
And if the numbers are higher, you should put a limit on number of allowed queued tasks:
static long numberOfQueuedTasks = 0;
const long MAX_TASKS = 10000; // it depends how DoSomething internals consume resource
public static async void QueueSomeWork()
{
if (numberOfQueuedTasks > MAX_TASKS)
{
var wait = new SpinWait();
while (numberOfQueuedTasks > MAX_TASKS) wait.SpinOnce();
}
await Task.Run(() => { Interlocked.Increment(ref numberOfQueuedTasks); DoSomething(); });
}
static readonly object lockObject = new object();
static void DoSomething()
{
try
{
lock (lockObject)
{
// implementation
}
}
finally
{
Interlocked.Decrement(ref numberOfQueuedTasks);
}
}

Simple way of doing it is by decorating the method with MethodImplOptions.Synchronized, whose function is similar to the synchronized keyword in Java:
[MethodImpl(MethodImplOptions.Synchronized)]
private void DoSomething()
{
// ...
}
The main downside is that this will lock on the current instance, which might lead to deadlock if you're already using locking elsewhere.

Here is an idea. You'd probably want to lock the doSomethingCount when using it, but as for queuing the DoSomething and going on this might work because it runs on a separate thread. Since you were ok with a queue, I assume you want fire and forget and don't actually need to block the caller.
// This will increment the count and kick off the process of going through
// the calls if it isn't already running. When it is done, it nulls out the task again
// to be recreated when something is queued again.
public static void QueueSomething()
{
doSomethingCount++;
if (doSomethingTask == null)
{
doSomethingTask =
Task.Run((Action)(() =>
{
while (doSomethingCount > 0)
{
DoSomething();
doSomethingCount--;
}
}))
.ContinueWith(t => doSomethingTask = null);
}
}
// I just put something in here that would take time and have a measurable result.
private static void DoSomething()
{
Thread.Sleep(50);
thingsDone++;
}
// These two guys are the data members needed.
private static int doSomethingCount = 0;
private static Task doSomethingTask;
// This code is just to prove that it works the way I expected. You can use it too.
public static void Run()
{
for (int i = 0; i < 10; i++)
{
QueueSomething();
}
while (thingsDone < 10)
{
Thread.Sleep(100);
}
thingsDone = 0;
QueueSomething();
while (thingsDone < 1)
{
Thread.Sleep(100);
}
Console.WriteLine("Done");
}
// This data point is just so I could test it. Leaving it in so you can prove it yourself.
private static int thingsDone = 0;

if this is code-only issue, the lock solution is good. But sometimes you run a DB transaction, where series of objects (records) have to be modified with no interference. Good example is when you re-run sequence enumeration of DB records. You can create a lock table in DB and lock a specific defined record in it for update first thing in the transaction. This will prevent other transactions created by your application (in the same code area) to even get to the table you updating. And second call will only proceed after the first one is done. Just a tip.