我正在尝试动态锁定线程,但是无论我如何尝试,总会发生某种竞争状况,这似乎是由多个线程同时启动任务引起的,但我一直无法找到很好的答案。
这里是一个示例:
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
public class Example
{
public static readonly Object padLock = new Object();
public readonly static ConcurrentDictionary<string, object> locks = new
ConcurrentDictionary<string, object>();
public static List<string> processes = new List<string>();
public static void Main()
{
//Add random list of processes (just testing with one for now)
for (var i = 0; i < 1; i++) {
processes.Add("random" + i.ToString());
}
while (true)
{
foreach (var process in processes )
{
var currentProc = process ;
lock (padLock)
{
if (!locks.ContainsKey(currentProc))
{
System.Threading.Tasks.Task.Factory.StartNew(() =>
{
if (!locks.ContainsKey(currentProc))
{
var lockObject = locks.GetOrAdd(currentProc, new object());
lock (lockObject)
{
Console.WriteLine("Currently Executing " + currentProc);
Console.WriteLine("Ended Executing " + currentProc);
((IDictionary)locks).Remove(currentProc);
}
}
});
}
}
// Thread.Sleep(0);
}
}
Console.ReadLine();
}
}
输出:
Started 1
Finished 1
Started 1
Finished 1
Started 1
Finished 1
但有时会得到:
Started 1
Started 1
Finished 1
这是不希望的,动态锁应该将其锁定并仅执行一次
答案 0 :(得分:3)
我将您的要求读为“获取进程列表,然后使用多个线程对它们中的每一个仅执行一次。”
就我的示例而言,假设Foo(process)
进行的工作单元只能执行一次。
这是一个非常普遍的需求,有几种模式。
此技术可以为循环的每次迭代使用不同的线程,该线程将同时执行。
Parallel.ForEach(processes, process => Foo(process));
是;这是一行代码。
如果Foo()
是异步的,则此技术适用。它只是为所有进程安排任务,然后等待它们,然后让SynchronizationContext对其进行排序。
var tasks = processes.Select( p => Foo(process) );
await Task.WhenAll(tasks);
这使用producer-consumer pattern,这是一个线程添加到队列中而另一个线程从队列中获取的传统方式。通过从队列中删除一项,该项将有效地“锁定”,以便其他线程不会尝试对其进行处理。
BlockingCollection<string>() queue = new BlockingCollection<string>();
void SetUpQueue()
{
for (int i=0; i<100; i++) queue.Add(i.ToString());
queue.CompleteAdding();
}
void Worker()
{
while (queue.Count > 0 || !queue.IsAddingCompleted)
{
var item = queue.Take();
Foo(item);
}
}
答案 1 :(得分:1)
尽管我不知道您要做什么,但是您看到的行为是因为您正在从多个线程中发送Console.WriteLine垃圾邮件,但它们的打印顺序不正确。我通过将时间戳附加到Console.WriteLine来验证这一点:
public class Example
{
public static readonly Object padLock = new Object();
public readonly static ConcurrentDictionary<string, object> locks = new ConcurrentDictionary<string, object>();
public static List<string> processes = new List<string>();
[ThreadStatic]
private static bool flag = false;
public static void Main()
{
//Add random list of processes (just testing with one for now)
for (var i = 0; i < 10; i++)
{
processes.Add(i.ToString());
}
while (true)
{
foreach (var process in processes)
{
var currentProc = process;
if (!locks.ContainsKey(currentProc))
{
var lockObject = locks.GetOrAdd(currentProc, new object());
Task.Factory.StartNew(() =>
{
lock (lockObject)
{
if (flag) throw new Exception();
flag = true;
Console.WriteLine("Currently Executing " + currentProc);
Thread.Sleep(0); // You can siimulate work here
Console.WriteLine("Ended Executing " + currentProc);
flag = false;
((IDictionary)locks).Remove(currentProc);
}
});
}
}
}
}
}
运行方式为:
....
Ended Executing 1 4025734
Currently Executing 1 4026419
Ended Executing 1 4028737
Currently Executing 1 4029565
Ended Executing 1 4030472
Currently Executing 1 4031643
Currently Executing 1 3659670
Ended Executing 1 4032900
Currently Executing 1 4033582
Ended Executing 1 4034318
Ended Executing 1 4032786
Currently Executing 1 4038042
Ended Executing 1 4042484
Currently Executing 1 4044967
Currently Executing 1 4007282
...