MSL.Pool 4.0.1

Build Status

Pool

IPool<TPoolItem> is an object pool that uses the lease/release pattern. It allows for but does not require, preparation strategies. Common use cases for preparation strategies include objects that benefit from long-lived connections, like SMTP or database connections.

Github Repository

https://github.com/marklauter/pool

Nuget Package

Nuget.org Page

https://www.nuget.org/packages/MSL.Pool

Package Install

dotnet add package MSL.Pool

The Lease / Release Pattern

When the pool is instantiated, it creates a minimum number of poolable items and places them in the available items queue.

When a lease is requested, the pool attempts to dequeue an item. If an item is returned from the queue, the item is returned on a task. However, if the item queue is empty, the pool attempts to create a new item to fulfill the lease request. If the pool has reached its allocation limit, it enqueues a new lease request object into the lease request queue. Then it returns the least request's TaskCompletionSource.Task to the caller.

The caller will block on await until timing out, or until an item is released back to the pool. First, the release operation attempts to dequeue an active lease request. If a lease request is returned, the least request's task is completed with the item being released by the caller. But if the lease request queue is empty, the item will be placed in the available item queue.

Pool

IPool<TPoolItem> is implmented internally by Pool<TPoolItem>.

You can access IPool<TPoolItem> by registering it with the service collection by calling one of the IServiceCollection extensions from the Pool.DependencyInjection namespace. See Dependency Injection for more information.

IPool<TPoolItem> provides three methods with convenient overloads:

• LeaseAsync - returns an item from the pool and optionally performs a ready check
• ReleaseAsync - returns an item to the pool
• ClearAsync - clears the pool, disposes of items as required, and reinitializes the pool with PoolOptions.MinSize items

The caller is responsible for calling ReleaseAsync when it no longer needs the item. I recommend using try / finally.

var item = await pool.LeaseAsync();
try
{
    item.DoStuff();
}
finally
{
    await pool.ReleaseAsync(item);
}

Pool<TPoolItem> has three dependencies injected into the constructor:

• IIitemFactory<TPoolItem>
• IPreparationStrategy<TPoolItem>
• PoolOptions

See Dependency Injection for more information.

The pool will use an item factory to create new items as required. During the lease operation, the pool invokes a ready checker to initialize an item that isn't ready.

Pool Item Factory

Implement the IIitemFactory<TPoolItem> interface to create new items for the pool. The library provides a default pool implementation that uses IServiceProvider to construct items. To use the default implementation, call AddPool<TPoolItem> or AddPoolWithDefaultFactory<TPoolItem, TPreparationStrategy> when registering the pool with the service collection. See Dependency Injection for more information.

Pool Item Preparation Strateg

Implement the IPreparationStrategy<TPoolItem> interface to ensure an item is ready for use when leased from the pool.

There's a default IPreparationStrategy<TPoolItem> implementation that always returns true from the IsReadyAsync method. To use the default implementation with a custom item factory, call AddPool<TPoolItem> when registering the pool with the service collection. See Dependency Injection for more information.

Ready check is useful for items that may become inactive for some time, such as an SMTP connection that has been idle long enough for the server to terminate the connection.

For example, if you're implementing an SMTP connection pool, the lease operation can verify the connection to the STMP server by invoking the SMTP no-op. If the ready check fails, you can connect and authenticate to the SMTP server.

Sample SMTP connection ready check implementation using MailKit.IMailTransport:

public async ValueTask<bool> IsReadyAsync(IMailTransport item, CancellationToken cancellationToken) =>
    item.IsConnected
    && item.IsAuthenticated
    && await NoOpAsync(item, cancellationToken);

Sample SMTP connection PrepareAsync implementation using MailKit.IMailTransport:

public async Task PrepareAsync(IMailTransport item, CancellationToken cancellationToken)
{
    await item.ConnectAsync(hostOptions.Host, hostOptions.Port, hostOptions.UseSsl, cancellationToken);
    await item.AuthenticateAsync(credentials.UserName, credentials.Password, cancellationToken);
}

Dependency Injection

The ServiceCollectionExtensions class is in the Pool.DependencyInjection namespace.

• Call AddPool<TPoolItem> to register a singleton pool. Pass Action<PoolRegistrationOptions> to specify whether or not to register the default item factory and ready check implementations.
• Call AddPreparationStrategy<TPoolItem, TPreparationStrategy> to register a singleton preparation strategy.
• Call AddPoolItemFactory<TPoolItem, TFactoryImplementation> to register a singleton item factory implementation.

Sample AddPool<TPoolItem> Registration

services.AddPool<IMailTransport>(configuration, options =>
{
    // use default factory, which uses the service provider to construct pool items
    options.RegisterDefaultFactory = true;
});

Dev Log

• 12 FEB 2024 - started SMTP pool at the end of 2023, but got busy with other stuff. I'll take it up again soon though because I need it for a work project.
• 05 MAY 2024 - prepping the library for Nuget by supporting dotnet 6, 7 and 8.
• 06 MAY 2024 - published to Nuget.
• 17 MAY 2024 - added tests for out-of-order disposal scenarios.
• 17 MAY 2024 - updated readme.md
• 17 MAY 2024 - Sample/Smtp.Pool is still a work in progress.
• 18 MAY 2024 :ALERT: breaking changes.
• 18 MAY 2024 - refactored dependency injection extensions.
• 18 MAY 2024 - refactored to use ValueTask on LeaseAsync method.
• 16 JUL 2024 - better naming and cleaned up smtp sample project.