ASP.NET Core 选项模式源码学习Options IOptions（二）

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https://yq.aliyun.com/articles/743159

前言

上一篇文章介绍IOptions的注册,本章我们继续往下看

IOptions

IOptions是一个接口里面只有一个Values属性，该接口通过OptionsManager实现

public interface IOptions<out TOptions> where TOptions : class, new()
{
/// <summary>
/// The default configured <typeparamref name="TOptions"/> instance
/// </summary>
TOptions Value { get; }
}

OptionsManager

OptionsManager实现了IOptions<>和IOptionsSnapshot<>，他使用内部属性OptionsCache 进行缓存操作；实现IOptionsSnapshot接口Get(string name)其实就是获取我们第一章所指定的Name，通过IOptionsFactory<>创建TOptions实例

public class OptionsManager<TOptions> : IOptions<TOptions>, IOptionsSnapshot<TOptions> where TOptions : class, new()
{
private readonly IOptionsFactory<TOptions> _factory;
private readonly OptionsCache<TOptions> _cache = new OptionsCache<TOptions>(); // Note: this is a private cache

/// <summary>
/// Initializes a new instance with the specified options configurations.
/// </summary>
/// <param name="factory">The factory to use to create options.</param>
public OptionsManager(IOptionsFactory<TOptions> factory)
{
_factory = factory;
}

/// <summary>
/// The default configured <typeparamref name="TOptions"/> instance, equivalent to Get(Options.DefaultName).
/// </summary>
public TOptions Value
{
get
{
return Get(Options.DefaultName);
}
}

/// <summary>
/// Returns a configured <typeparamref name="TOptions"/> instance with the given <paramref name="name"/>.
/// </summary>
public virtual TOptions Get(string name)
{
name = name ?? Options.DefaultName;

// Store the options in our instance cache
return _cache.GetOrAdd(name, () => _factory.Create(name));
}
}

public interface IOptionsSnapshot<out TOptions> : IOptions<TOptions> where TOptions : class, new()
{
/// <summary>
/// Returns a configured <typeparamref name="TOptions"/> instance with the given name.
/// </summary>
TOptions Get(string name);
}

OptionsCache

OptionsCache采用了线程安全字典ConcurrentDictionary进行了封装用于内存缓存

public class OptionsCache<TOptions> : IOptionsMonitorCache<TOptions> where TOptions : class
{
private readonly ConcurrentDictionary<string, Lazy<TOptions>> _cache = new ConcurrentDictionary<string, Lazy<TOptions>>(StringComparer.Ordinal);

/// <summary>
/// Clears all options instances from the cache.
/// </summary>
public void Clear() => _cache.Clear();

/// <summary>
/// Gets a named options instance, or adds a new instance created with <paramref name="createOptions"/>.
/// </summary>
/// <param name="name">The name of the options instance.</param>
/// <param name="createOptions">The func used to create the new instance.</param>
/// <returns>The options instance.</returns>
public virtual TOptions GetOrAdd(string name, Func<TOptions> createOptions)
{
if (createOptions == null)
{
throw new ArgumentNullException(nameof(createOptions));
}
name = name ?? Options.DefaultName;
return _cache.GetOrAdd(name, new Lazy<TOptions>(createOptions)).Value;
}

/// <summary>
/// Tries to adds a new option to the cache, will return false if the name already exists.
/// </summary>
/// <param name="name">The name of the options instance.</param>
/// <param name="options">The options instance.</param>
/// <returns>Whether anything was added.</returns>
public virtual bool TryAdd(string name, TOptions options)
{
if (options == null)
{
throw new ArgumentNullException(nameof(options));
}
name = name ?? Options.DefaultName;
return _cache.TryAdd(name, new Lazy<TOptions>(() => options));
}

/// <summary>
/// Try to remove an options instance.
/// </summary>
/// <param name="name">The name of the options instance.</param>
/// <returns>Whether anything was removed.</returns>
public virtual bool TryRemove(string name)
{
name = name ?? Options.DefaultName;
return _cache.TryRemove(name, out var ignored);
}
}

OptionsFactory

OptionsFactory实现了 IOptionsFactory.Create(string name);,
而OptionsFactory构造函数中注入了IConfigureOptions<>和IPostConfigureOptions<>，
这里使用了IEnumerable类型标识当注册多个时候按照次数依次的执行，从如下代码中我们也看到了我们在上一章中所说的Configures和postConfigures注册先后顺序问题。

public class OptionsFactory<TOptions> : IOptionsFactory<TOptions> where TOptions : class, new()
{
private readonly IEnumerable<IConfigureOptions<TOptions>> _setups;
private readonly IEnumerable<IPostConfigureOptions<TOptions>> _postConfigures;
private readonly IEnumerable<IValidateOptions<TOptions>> _validations;

public OptionsFactory(IEnumerable<IConfigureOptions<TOptions>> setups, IEnumerable<IPostConfigureOptions<TOptions>> postConfigures) : this(setups, postConfigures, validations: null)
{ }

public OptionsFactory(IEnumerable<IConfigureOptions<TOptions>> setups, IEnumerable<IPostConfigureOptions<TOptions>> postConfigures, IEnumerable<IValidateOptions<TOptions>> validations)
{
_setups = setups;
_postConfigures = postConfigures;
_validations = validations;
}

public TOptions Create(string name)
{
var options = new TOptions();
foreach (var setup in _setups)
{
if (setup is IConfigureNamedOptions<TOptions> namedSetup)
{
namedSetup.Configure(name, options);
}
else if (name == Options.DefaultName)
{
setup.Configure(options);
}
}
foreach (var post in _postConfigures)
{
post.PostConfigure(name, options);
}

if (_validations != null)
{
var failures = new List<string>();
foreach (var validate in _validations)
{
var result = validate.Validate(name, options);
if (result.Failed)
{
failures.AddRange(result.Failures);
}
}
if (failures.Count > 0)
{
throw new OptionsValidationException(name, typeof(TOptions), failures);
}
}

return options;
}
}