ReadAsync Causing OPC Server Thread Leak

[qwas368]

Below is the test code I used. As you can see, this is an infinite loop continuously reading data through ReadAsync.

for (; ;)
{
    Logger logger = new Logger(nameof(OpcController), nameof(GetItemValues));
    using var server = new OpcDaServer(_opcClientConfigSection.ProgId);
    server.Connect();
    using OpcDaGroup group = server.AddGroup(Guid.NewGuid().ToString("N"));
    OpcDaItemDefinition[] definitions = items
        .Select(x => new OpcDaItemDefinition
        {
            ItemId = x,
            IsActive = true
        })
        .ToArray();
    OpcDaItemResult[] results = group.AddItems(definitions);
    OpcDaItemValue[] values = await group.ReadAsync(group.Items);
}

However, after running it, you can see through Task Manager that the Process Threads of the OPC Server keep increasing.

Then I found that changing await group.ReadAsync(group.Items) to group.ReadAsync(group.Items).Result can avoid the issue, but obviously, this is not the root cause. So I tried to find the real cause in the source code

TitaniumAS.Opc.Client/TitaniumAS.Opc.Client/Da/Internal/Requests/ReadAsyncRequest.cs

Line 14 in 77e34b6

private readonly TaskCompletionSource<OpcDaItemValue[]> _tcs = new TaskCompletionSource<OpcDaItemValue[]>();

and discovered that adding TaskCreationOptions.RunContinuationsAsynchronously to the following code can solve the problem.

private readonly TaskCompletionSource<OpcDaItemValue[]> _tcs = new TaskCompletionSource<OpcDaItemValue[]>(TaskCreationOptions.RunContinuationsAsynchronously);

Honestly, I am not familiar with Async and don't understand the underlying principle. I hope someone can help explain.

[zhshFLY]

我也遇到了类似的问题，我使用您上面提到的异步读取的方法读取数据时，发现我的opcda服务器会变得很卡，一直到整个程序退出后服务器才恢复正常，同样的情况下我使用同步读取的方法就没有出现这样的问题，应该是这个异步的方法没有封装好，我怀疑是异步读取方法里面的第二参数有问题，具体情况还没研究明白。