[英]why is the lock keyword not working with this multi-threading implementation?
我正在嘗試將Parallel.ForEach()構造用於多線程,並且遇到一些問題。 具體來說,某些數據需要進行不同的評估,這似乎在ForEach()構造中造成了一些問題,在該構造中,某些屬性已使用來自不同線程的值進行設置。 我以為我可以用鎖簡單地包裝該特定代碼,但是問題仍然存在。 您可以通過查看以下代碼來確定問題的根源嗎:
https://dotnetfiddle.net/IDUGbP
這是內聯代碼:
using SecurityApi.Core.Models;
using SecurityApi.Core.Repositories;
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.ComponentModel.Composition;
using System.DirectoryServices.AccountManagement;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using AutoMapper;
using SecurityApi.EntityFramework;
using System.DirectoryServices;
namespace SecurityApi.Repositories
{
[Export(typeof(IADUserRepository))]
public class ADUserRepository : IADUserRepository
{
private Object etlLock = new Object();
public async Task<List<Core.Models.ADUser>> GetADUsersFromAD(string domainName)
{
var domainId = await new DomainRepository().GetDomainId(domainName);
var adUsers = new ConcurrentBag<Core.Models.ADUser>();
var adGroups = new ConcurrentBag<Core.Models.ADGroup>();
return await Task.Run(() =>
{
using (var context = new PrincipalContext(ContextType.Domain, domainName))
{
// init vars
var up = new UserPrincipal(context);
var ps = new PrincipalSearcher(up);
Core.Models.ADUser adUser;
Parallel.ForEach(
ps.FindAll().ToList(),
new ParallelOptions() { MaxDegreeOfParallelism = Environment.ProcessorCount },
result =>
{
if (!result.DistinguishedName.Contains("OU=Users")) return;
//set ad user properties
var userPrincipal = result as UserPrincipal;
adUser.Name = userPrincipal.Name;
adUser.FirstName = userPrincipal.GivenName;
adUser.LastName = userPrincipal.Surname;
lock (etlLock)
{
//get a directory entry representation for accessing special properties
var directoryEntry = result.GetUnderlyingObject() as DirectoryEntry;
//user principal name
adUser.UserPrincipalName = directoryEntry.Properties["UserPrincipalName"].Value?.ToString();
//employee id
adUser.EmployeeId = directoryEntry.Properties["EmployeeId"].Value?.ToString();
}
#endregion
adUsers.Add(adUser);
});
}
return adUsersList;
});
}
}
}
問題是臨時adUser
變量是在Parallel.ForEach
塊的外部范圍中定義的,這導致不同的線程對其進行修改。 相反,請考慮將定義移到foreach主體中,在該主體中實際設置變量。 這樣,每個線程將獲得其自己的變量。 當然,這里的問題是Parallel.Foreach是否對重復的引用進行操作,但我認為沒有。
在這里,我將如何修改您的代碼: https : //dotnetfiddle.net/gFb5z6
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