NTDLS.Semaphore 2.2.4

NTDLS.Semaphore

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

Pessimistic Semaphore

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

PessimisticSemaphore using inline execution example:

An example using a PessimisticSemaphore to envelope a variable and protect it from parallel execution, Note that there are nullable and nonnullable counterpars 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 PessimisticSemaphore<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 PessimisticSemaphore using inline execution example:

An example using a PessimisticSemaphore 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 PessimisticSemaphore<List<Car>> Cars { get; set; } = new();
public CriticalSection OtherLock1 { get; set; } = new();
public CriticalSection OtherLock2 { get; set; } = new();
public CriticalSection 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 Semaphore

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.

OptimisticSemaphore using inline execution example:

An example using a CriticalSection 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 OptimisticSemaphore<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.

CriticalSection using inline execution example:

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

private CriticalSection _criticalSection = new();

private int _value;

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

License

Apache-2.0