[C#/TPL/.NET5] Task 클래스 : FromException/FromResult 정적 메소드 사용하기

■ Task 클래스의 FromException<T>/FromResult<T> 정적 메소드를 사용하는 방법을 보여준다.

▶ 예제 코드 (C#)


using System.IO;
using System.Threading;
using System.Threading.Tasks;

#region 디렉토리 크기 구하기 (비동기) - GetDirectorySizeAsync(directoryPath)

/// <summary>
/// 디렉토리 크기 구하기 (비동기)
/// </summary>
/// <param name="directoryPath">디렉토리 경로</param>
/// <returns>디렉토리 크기</returns>
public Task<long> GetDirectorySizeAsync(string directoryPath)
{
    if(!Directory.Exists(directoryPath))
    {
        return Task.FromException<long>(new DirectoryNotFoundException("디렉토리가 없습니다."));
    }
    else
    {
        string[] filePathArray = Directory.GetFiles(directoryPath, "*.*", SearchOption.AllDirectories);

        if(filePathArray.Length == 0)
        {
            return Task.FromResult(0L);
        }
        else
        {
            return Task.Run
            (
                () =>
                {
                    long totalFileLength = 0;

                    Parallel.ForEach
                    (
                        filePathArray,
                        (filePath) =>
                        {
                            FileStream fileStream = new FileStream
                            (
                                filePath,
                                FileMode.Open,
                                FileAccess.Read,
                                FileShare.ReadWrite,
                                256,
                                true
                            );

                            long fileLength = fileStream.Length;

                            Interlocked.Add(ref totalFileLength, fileLength);

                            fileStream.Close();
                        }
                    );

                    return totalFileLength;
                }
            );
        }
    }
}

#endregion

using System.IO;

using System.Threading;

using System.Threading.Tasks;

#region 디렉토리 크기 구하기 (비동기) - GetDirectorySizeAsync(directoryPath)

/// <summary>

/// 디렉토리 크기 구하기 (비동기)

/// </summary>

/// <param name="directoryPath">디렉토리 경로</param>

/// <returns>디렉토리 크기</returns>

public Task<long> GetDirectorySizeAsync(string directoryPath)

{

if(!Directory.Exists(directoryPath))

{

return Task.FromException<long>(new DirectoryNotFoundException("디렉토리가 없습니다."));

}

else

{

string[] filePathArray = Directory.GetFiles(directoryPath, "*.*", SearchOption.AllDirectories);

if(filePathArray.Length == 0)

{

return Task.FromResult(0L);

}

else

{

return Task.Run

(

() =>

{

long totalFileLength = 0;

Parallel.ForEach

(

filePathArray,

(filePath) =>

{

FileStream fileStream = new FileStream

(

filePath,

FileMode.Open,

FileAccess.Read,

FileShare.ReadWrite,

256,

true

);

long fileLength = fileStream.Length;

Interlocked.Add(ref totalFileLength, fileLength);

fileStream.Close();

}

);

return totalFileLength;

}

);

}

#endregion