NTDLS.Semaphore

?? Be sure to check out the NuGet package: https://www.nuget.org/packages/NTDLS.Semaphore

Pessimistic Critical Resource

Provides various classes to protect a variable from parallel / non-sequential thread access by always acquiring an exclusive lock on the resource.

PessimisticCriticalResource using inline execution example:

An example using a PessimisticCriticalResource to envelope a variable and protect it from parallel execution, Note that there are nullable and non-nullable counterparts and also template/generics of each method to allow you to return various types from the delegate execution.

public class Car
{
    public string? Name { get; set; }
    public int NumerOhWheels { get; set; }
}

public PessimisticCriticalResource<List<Car>> Cars { get; set; } = new();

public void Add(Car car)
{
    Cars.Use((obj) => obj.Add(car));
}

public Car? GetByName(string name)
{
    return Cars.Use((obj) => obj.Where(o=>o.Name == name).FirstOrDefault());
}

public bool TryAdd(Car car)
{
    //Since TryUse<T> can return values, we have to pass the result of the try out though a variable.
    Cars.TryUse(out bool wasLockObtained, (obj) => obj.Add(car));
    return wasLockObtained;
}

public bool TryAdd(Car car, int timeout)
{
    //Since TryUse<T> can return values, we have to pass the result of the try out though a variable.
    Cars.TryUse(out bool wasLockObtained, timeout, (obj) => obj.Add(car));
    return wasLockObtained;
}

Multi PessimisticCriticalResource using inline execution example:

An example using a PessimisticCriticalResource to envelope a variable and protect it and others from parallel execution.

public class Car
{
    public string? Name { get; set; }
    public int NumerOhWheels { get; set; }
}

public PessimisticCriticalResource<List<Car>> Cars { get; set; } = new();
public PessimisticSemaphore OtherLock1 { get; set; } = new();
public PessimisticSemaphore OtherLock2 { get; set; } = new();
public PessimisticSemaphore OtherLock3 { get; set; } = new();

public void Add(Car car)
{
    Cars.Use((obj) => obj.Add(car));
}

public Car? GetByName(string name)
{
    return Cars.Use((obj) => obj.Where(o => o.Name == name).FirstOrDefault());
}

public bool TryAdd(Car car)
{
    //Since TryUse<T> can return values, we have to pass the result of the try out though a variable.
    Cars.TryUse(out bool wasLockObtained, (obj) => obj.Add(car));
    return wasLockObtained;
}

public bool TryAdd(Car car, int timeout)
{
    //Since TryUse<T> can return values, we have to pass the result of the try out though a variable.
    Cars.TryUse(out bool wasLockObtained, timeout, (obj) => obj.Add(car));
    return wasLockObtained;
}

public Car? TryGet(string name, int timeout)
{
    return Cars.TryUseAll(new[] { OtherLock1, OtherLock2, OtherLock3 }, timeout, out bool wasLockObtained, (obj) =>
    {
        //We only get here if we are able to lock "Cars" and OtherLock1, OtherLock2 and OtherLock3
        return obj.Where(o => o.Name == name).FirstOrDefault();
    });
}

Optimistic Critical Resource

Protects a variable from parallel / non-sequential thread access but controls read-only and exclusive access separately to prevent read operations from blocking other read operations.it is up to the developer to determine when each lock type is appropriate. Note: read-only locks only indicate intention, the resource will not disallow modification of the resource, but this will lead to race conditions.

OptimisticCriticalResource using inline execution example:

An example using a OptimisticCriticalResource to protect a portion of code from parallel execution while not allowing reads to block reads.

public class Car
{
    public string? Name { get; set; }
    public int NumerOhWheels { get; set; }
}

public OptimisticCriticalResource<List<Car>> Cars { get; set; } = new();

public void Add(Car car)
{
    Cars.Write((obj) => obj.Add(car));
}

public Car? GetByName(string name)
{
    return Cars.Read((obj) => obj.Where(o=>o.Name == name).FirstOrDefault());
}

public bool TryAdd(Car car)
{
    //Since TryUse<T> can return values, we have to pass the result of the try out though a variable.
    Cars.TryWrite(out bool wasLockObtained, (obj) => obj.Add(car));
    return wasLockObtained;
}

public bool TryAdd(Car car, int timeout)
{
    //Since TryUse<T> can return values, we have to pass the result of the try out though a variable.
    Cars.TryWrite(out bool wasLockObtained, timeout, (obj) => obj.Add(car));
    return wasLockObtained;
}

Critical Section

Protects an area of code from parallel / non-sequential thread access.

PessimisticSemaphore using inline execution example:

An example using a PessimisticSemaphore to protect a portion of code from parallel execution.

private PessimisticSemaphore _pessimisticSemaphore = new();

private int _value;

public int Value
{
    get
    {
        return _pessimisticSemaphore.Use(() => _value);
    }
    set
    {
        _pessimisticSemaphore.Use(() => _value = value);
    }
}

Thread ownership tracking

If you need to keep track of which thread owns each semaphore and/or critical sections then you can enable "ThreadOwnershipTracking" by calling ThreadOwnershipTracking.Enable(). Once this is enabled, it is enabled for the life of the application so this is only for debugging deadlock/race-condition tracking. You can evaluate the ownership by evaluating the dictonary "ThreadOwnershipTracking.LockRegistration" or and instance of "PessimisticSemaphore" or "PessimisticCriticalResource" CurrentOwnerThread.

Enabling Thread Ownership Tracking

An example of enabling the thread ownerhsip mechanism.

ThreadOwnershipTracking.Enable();

License

Apache-2.0