Parallel.ForEach 通过 AuthorizationRuleCollection

Question

希望有人能指出我在这里做错了什么。我有一个读取文件访问规则的进程，我正在尝试运行并行处理它。

这是我目前的代码：

public List<FolderAccessRule> GetSecurityGroupsForFolder(long importId, string subdirectory, bool includeInherited)
    {
        ConcurrentQueue<FolderAccessRule> groups = new ConcurrentQueue<FolderAccessRule>();
        ConcurrentQueue<Exception> exceptions = new ConcurrentQueue<Exception>();

        DirectoryInfo dInfo = new DirectoryInfo(subdirectory);
        DirectorySecurity dSecurity = dInfo.GetAccessControl();

        AuthorizationRuleCollection authorizationRuleCollection = dSecurity.GetAccessRules(true, includeInherited, typeof(NTAccount));
        Parallel.ForEach( authorizationRuleCollection,
            fsar =>
            {
                try
                {
                    FolderAccessRule group = this.GetGroup(fsar);
                    if (group != null)
                    {
                        groups.Enqueue(group);
                    }
                }
                catch (Exception e)
                {
                    exceptions.Enqueue(e);
                }
            });

        foreach (Exception e in exceptions)
        {
            string message = string.Concat(e.GetType(), "Exception getting Directory info for  ", subdirectory);
            this.RecordException(message, subdirectory, e);
        }

        return groups.ToList();
    }

这（对于未经训练的人来说）看起来应该有效。但是 Parallel.ForEach 不会编译，因为它会给出错误：

The type arguments for method 'System.Threading.Tasks.Parallel.ForEach<TSource>
(System.Collections.Generic.IEnumerable<TSource>, System.Action<TSource>)' cannot be inferred from the usage.
Try specifying the type arguments explicitly.

我也试过将违规行更改为：

Parallel.ForEach<FileSystemAccessRule>( authorizationRuleCollection, fsar =>

但还是不开心

那么，我做错了什么？提前致谢。

Answer 1

将authorizationRuleCollection.OfType<AuthorizationRule>()传递给Parallel.ForEach，例如：

var typedColletion=authorizationRuleCollection.OfType<AuthorizationRule>();
Parallel.ForEach(typedColletion);

错误是因为AuthorizationRuleCollection doesn't implement IEnumerable<T> but only IEnumerable，其元素是Object。当泛型不可用时，这是较旧（.NET 2.0 之前）集合的常见模式。

较新的 .NET 类 return/expect 通用集合。通过调用 OfType<T>() or Cast<T>()，您可以有效地将源 IEnumerable 转换为 IEnumerable<T>.

区别在于OfType<T>() will filter out incompatible elements, while Cast<T>()如果发现任何不兼容的元素将抛出。

这两种方法背后的 code 并不神奇，在参考源中它只是对源 IEnumerable:

的迭代器

    public static IEnumerable<TResult> OfType<TResult>(this IEnumerable source) {
        if (source == null) throw Error.ArgumentNull("source");
        return OfTypeIterator<TResult>(source);
    }

    static IEnumerable<TResult> OfTypeIterator<TResult>(IEnumerable source) {
        foreach (object obj in source) {
            if (obj is TResult) yield return (TResult)obj;
        }
    }

Parallel.ForEach 通过 AuthorizationRuleCollection

Parallel.ForEach over AuthorizationRuleCollection

.net

c#

parallel-processing

access-rules