I have a snippet of code that is writing to a memory stream in an asynchronous way (.NET Standard 2.1)

• Create a list of hot tasks, one per a line
• Then await when all of them will be finished
• Flush the writer buffer to the memoryStream at the end

Code:

await using var memoryStream = new MemoryStream();
await using var writer = new StreamWriter(memoryStream);

var recordTasks = stringRecordsToWrite.Select(r => writer.WriteLineAsync(r));

await Task.WhenAll(recordTasks);

await writer.FlushAsync();

var result = memoryStream.ToArray();

Questions

There are a couple of questions that bothering me:

1. There were reports that time to time some records had been skipped. Thus, I wonder, could such implementation be the root cause. I've tried to reproduce the issue locally, but, unfortunately, no success
2. Also Resharper highlights that 'writer' (within SELECT statement) is a captured variable and disposed in outer scope. Can it be a problem?

Or those are false traces, and the implementation is fine, and I should try to found the reason out in other place

CodePudding user response：

You have a single stream. It doesn't really make sense to write to it asynchronously in parallel - any number of things could go wrong. I don't even know what MemoryStream's thread safety is like, and I can't see any documentation about that. The documentation for StreamWriter explicitly states:

By default, a StreamWriter is not thread safe. See TextWriter.Synchronized for a thread-safe wrapper.

I would strongly advise you to just iterate sequentially, e.g.

foreach (var item in stringRecordsToWrite)
{
    await writer.WriteLineAsync(item);
}