我们正在尝试测量使用同步方法与异步读取一系列文件之间的性能。预计两者之间的时间大致相同,但事实证明使用异步大约慢 5.5 倍。
这可能是由于管理线程的开销,但只是想了解您的意见。也许我们只是测量了错误的时间。
这些是正在测试的方法:
static void ReadAllFile(string filename)
{
var content = File.ReadAllBytes(filename);
}
static async Task ReadAllFileAsync(string filename)
{
using (var file = File.OpenRead(filename))
{
using (var ms = new MemoryStream())
{
byte[] buff = new byte[file.Length];
await file.ReadAsync(buff, 0, (int)file.Length);
}
}
}
这是运行它们并启动秒表的方法:
static void Test(string name, Func<string, Task> gettask, int count)
{
Stopwatch sw = new Stopwatch();
Task[] tasks = new Task[count];
sw.Start();
for (int i = 0; i < count; i++)
{
string filename = "file" + i + ".bin";
tasks[i] = gettask(filename);
}
Task.WaitAll(tasks);
sw.Stop();
Console.WriteLine(name + " {0} ms", sw.ElapsedMilliseconds);
}
全部从这里运行:
static void Main(string[] args)
{
int count = 10000;
for (int i = 0; i < count; i++)
{
Write("file" + i + ".bin");
}
Console.WriteLine("Testing read...!");
Test("Read Contents", (filename) => Task.Run(() => ReadAllFile(filename)), count);
Test("Read Contents Async", (filename) => ReadAllFileAsync(filename), count);
Console.ReadKey();
}
还有辅助写入方法:
static void Write(string filename)
{
Data obj = new Data()
{
Header = "random string size here"
};
int size = 1024 * 20; // 1024 * 256;
obj.Body = new byte[size];
for (var i = 0; i < size; i++)
{
obj.Body[i] = (byte)(i % 256);
}
Stopwatch sw = new Stopwatch();
sw.Start();
MemoryStream ms = new MemoryStream();
Serializer.Serialize(ms, obj);
ms.Position = 0;
using (var file = File.Create(filename))
{
ms.CopyToAsync(file).Wait();
}
sw.Stop();
//Console.WriteLine("Writing file {0}", sw.ElapsedMilliseconds);
}
结果:
-Read Contents 574 ms
-Read Contents Async 3160 ms
如果有人能在我们搜索堆栈和网络但找不到合适的解释时对此有所说明,我们将不胜感激。
最佳答案
测试代码有很多问题。最值得注意的是,您的“异步”测试不使用异步 I/O;对于文件流,您必须显式地将它们作为异步打开,否则您只是在后台线程上执行同步操作。此外,您的文件非常小,可以轻松缓存。
我修改了测试代码以写出更大的文件,使同步代码与异步代码具有可比性,并使异步代码成为异步代码:
static void Main(string[] args)
{
Write("0.bin");
Write("1.bin");
Write("2.bin");
ReadAllFile("2.bin"); // warmup
var sw = new Stopwatch();
sw.Start();
ReadAllFile("0.bin");
ReadAllFile("1.bin");
ReadAllFile("2.bin");
sw.Stop();
Console.WriteLine("Sync: " + sw.Elapsed);
ReadAllFileAsync("2.bin").Wait(); // warmup
sw.Restart();
ReadAllFileAsync("0.bin").Wait();
ReadAllFileAsync("1.bin").Wait();
ReadAllFileAsync("2.bin").Wait();
sw.Stop();
Console.WriteLine("Async: " + sw.Elapsed);
Console.ReadKey();
}
static void ReadAllFile(string filename)
{
using (var file = new FileStream(filename, FileMode.Open, FileAccess.Read, FileShare.Read, 4096, false))
{
byte[] buff = new byte[file.Length];
file.Read(buff, 0, (int)file.Length);
}
}
static async Task ReadAllFileAsync(string filename)
{
using (var file = new FileStream(filename, FileMode.Open, FileAccess.Read, FileShare.Read, 4096, true))
{
byte[] buff = new byte[file.Length];
await file.ReadAsync(buff, 0, (int)file.Length);
}
}
static void Write(string filename)
{
int size = 1024 * 1024 * 256;
var data = new byte[size];
var random = new Random();
random.NextBytes(data);
File.WriteAllBytes(filename, data);
}
在我的机器上,这个测试(在 Release 中构建,在调试器之外运行)产生了这些数字:
Sync: 00:00:00.4461936
Async: 00:00:00.4429566
关于c# - .NET 4.5 文件读取性能同步与异步,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/18331349/