.NET 6新增的20个API介绍

dateonly & timeonly

.net 6 引入了两种期待已久的类型 - dateonly 和 timeonly, 它们分别代表datetime的日期和时间部分。

dateonly dateonly = new(2021, 9, 25);
console.writeline(dateonly);

timeonly timeonly = new(19, 0, 0);
console.writeline(timeonly); 

dateonly dateonlyfromdate = dateonly.fromdatetime(datetime.now);
console.writeline(dateonlyfromdate); 

timeonly timeonlyfromdate = timeonly.fromdatetime(datetime.now);
console.writeline(timeonlyfromdate); 

parallel.foreachasync

它可以控制多个异步任务的并行度。

var userhandlers = new[]
{
    "users/okyrylchuk",
    "users/jaredpar",
    "users/davidfowl"
};

using httpclient client = new()
{
    baseaddress = new uri("https://api.github.com"),
};
client.defaultrequestheaders.useragent.add(new productinfoheadervalue("dotnet", "6"));

paralleloptions options = new()
{
    maxdegreeofparallelism = 3
};
await parallel.foreachasync(userhandlers, options, async (uri, token) =>
{
    var user = await client.getfromjsonasync<githubuser>(uri, token);
    console.writeline($"name: {user.name}\nbio: {user.bio}\n");
});

public class githubuser
{
    public string name { get; set; }
    public string bio { get; set; }
}

// output:
// name: david fowler
// bio: partner software architect at microsoft on the asp.net team, creator of signalr
// 
// name: oleg kyrylchuk
// bio: software developer | dotnet | c# | azure
// 
// name: jared parsons
// bio: developer on the c# compiler

argumentnullexception.throwifnull()

argumentnullexception 的小改进, 在抛出异常之前不需要在每个方法中检查 null, 现在只需要写一行, 和 response.ensuresuccessstatuscode(); 类似。

examplemethod(null);

void examplemethod(object param)
{
    argumentnullexception.throwifnull(param);
    // do something
}

priorityqueue

.net 6 新增的数据结构, priorityqueue, 队列每个元素都有一个关联的优先级，它决定了出队顺序, 编号小的元素优先出列。

priorityqueue<string, int> priorityqueue = new();

priorityqueue.enqueue("second", 2);
priorityqueue.enqueue("fourth", 4);
priorityqueue.enqueue("third 1", 3);
priorityqueue.enqueue("third 2", 3);
priorityqueue.enqueue("first", 1);

while (priorityqueue.count > 0)
{
    string item = priorityqueue.dequeue();
    console.writeline(item);
}

// output:
// first
// second
// third 2
// third 1
// fourth

randomaccess

提供基于偏移量的 api，用于以线程安全的方式读取和写入文件。

using safefilehandle handle = file.openhandle("file.txt", access: fileaccess.readwrite);

// write to file
byte[] strbytes = encoding.utf8.getbytes("hello world");
readonlymemory<byte> buffer1 = new(strbytes);
await randomaccess.writeasync(handle, buffer1, 0);

// get file length
long length = randomaccess.getlength(handle);

// read from file
memory<byte> buffer2 = new(new byte[length]);
await randomaccess.readasync(handle, buffer2, 0);
string content = encoding.utf8.getstring(buffer2.toarray());
console.writeline(content); // hello world

periodictimer

认识一个完全异步的“periodictimer”, 更适合在异步场景中使用, 它有一个方法 waitfornexttickasync。

// one constructor: public periodictimer(timespan period)
using periodictimer timer = new(timespan.fromseconds(1));

while (await timer.waitfornexttickasync())
{
    console.writeline(datetime.utcnow);
}

// output:
// 13 - oct - 21 19:58:05 pm
// 13 - oct - 21 19:58:06 pm
// 13 - oct - 21 19:58:07 pm
// 13 - oct - 21 19:58:08 pm
// 13 - oct - 21 19:58:09 pm
// 13 - oct - 21 19:58:10 pm
// 13 - oct - 21 19:58:11 pm
// 13 - oct - 21 19:58:12 pm
// ...

metrics api

.net 6 实现了 opentelemetry metrics api 规范, 内置了指标api, 通过 meter 类创建下面的指标

• counter
• histogram
• observablecounter
• observablegauge

使用的方法如下：

var builder = webapplication.createbuilder(args);
var app = builder.build();

// create meter
var meter = new meter("metricsapp", "v1.0");
// create counter
counter<int> counter = meter.createcounter<int>("requests");

app.use((context, next) =>
{
    // record the value of measurement
    counter.add(1);
    return next(context);
});

app.mapget("/", () => "hello world");
startmeterlistener();
app.run();

// create and start meter listener
void startmeterlistener()
{
    var listener = new meterlistener();
    listener.instrumentpublished = (instrument, meterlistener) =>
    {
        if (instrument.name == "requests" && instrument.meter.name == "metricsapp")
        {
            // start listening to a specific measurement recording
            meterlistener.enablemeasurementevents(instrument, null);
        }
    };

    listener.setmeasurementeventcallback<int>((instrument, measurement, tags, state) =>
    {
        console.writeline($"instrument {instrument.name} has recorded the measurement: {measurement}");
    });

    listener.start();
}

检查元素是否可为空的反射api

它提供来自反射成员的可空性信息和上下文：

• parameterinfo 参数
• fieldinfo 字段
• propertyinfo 属性
• eventinfo 事件

var example = new example();
var nullabilityinfocontext = new nullabilityinfocontext();
foreach (var propertyinfo in example.gettype().getproperties())
{
    var nullabilityinfo = nullabilityinfocontext.create(propertyinfo);
    console.writeline($"{propertyinfo.name} property is {nullabilityinfo.writestate}");
}

// output:
// name property is nullable
// value property is notnull

class example
{
    public string? name { get; set; }
    public string value { get; set; }
}

检查嵌套元素是否可为空的反射api

它允许您获取嵌套元素的可为空的信息, 您可以指定数组属性必须为非空，但元素可以为空，反之亦然。

type exampletype = typeof(example);
propertyinfo notnullablearraypi = exampletype.getproperty(nameof(example.notnullablearray));
propertyinfo nullablearraypi = exampletype.getproperty(nameof(example.nullablearray));

nullabilityinfocontext nullabilityinfocontext = new();

nullabilityinfo notnullablearrayni = nullabilityinfocontext.create(notnullablearraypi);
console.writeline(notnullablearrayni.readstate);              // notnull
console.writeline(notnullablearrayni.elementtype.readstate);  // nullable

nullabilityinfo nullablearrayni = nullabilityinfocontext.create(nullablearraypi);
console.writeline(nullablearrayni.readstate);                // nullable
console.writeline(nullablearrayni.elementtype.readstate);    // nullable

class example
{
    public string?[] notnullablearray { get; set; }
    public string?[]? nullablearray { get; set; }
}

processid & processpath

直接通过 environment 获取进程id和路径。

int processid = environment.processid
string path = environment.processpath;

console.writeline(processid);
console.writeline(path);

configuration 新增 getrequiredsection()

和 di 的 getrequiredservice() 是一样的, 如果缺失, 则会抛出异常。

webapplicationbuilder builder = webapplication.createbuilder(args);
webapplication app = builder.build();

mysettings mysettings = new();

// throws invalidoperationexception if a required section of configuration is missing
app.configuration.getrequiredsection("mysettings").bind(mysettings);
app.run();

class mysettings
{
    public string? settingvalue { get; set; }
}

cspng 密码安全伪随机数生成器

您可以从密码安全伪随机数生成器 (cspng) 轻松生成随机值序列。

它对于以下场景中很有用：

密钥生成

随机数

某些签名方案中的盐

// fills an array of 300 bytes with a cryptographically strong random sequence of values.
// getbytes(byte[] data);
// getbytes(byte[] data, int offset, int count)
// getbytes(int count)
// getbytes(span<byte> data)
byte[] bytes = randomnumbergenerator.getbytes(300);

native memory api

.net 6 引入了一个新的 api 来分配本机内存, nativememory 有分配和释放内存的方法。

unsafe
{
    byte* buffer = (byte*)nativememory.alloc(100);

    nativememory.free(buffer);

    /* this class contains methods that are mainly used to manage native memory.
    public static class nativememory
    {
        public unsafe static void* alignedalloc(nuint bytecount, nuint alignment);
        public unsafe static void alignedfree(void* ptr);
        public unsafe static void* alignedrealloc(void* ptr, nuint bytecount, nuint alignment);
        public unsafe static void* alloc(nuint bytecount);
        public unsafe static void* alloc(nuint elementcount, nuint elementsize);
        public unsafe static void* alloczeroed(nuint bytecount);
        public unsafe static void* alloczeroed(nuint elementcount, nuint elementsize);
        public unsafe static void free(void* ptr);
        public unsafe static void* realloc(void* ptr, nuint bytecount);
    }*/
}

power of 2

.net 6 引入了用于处理 2 的幂的新方法。

• 'ispow2' 判断指定值是否为 2 的幂。
• 'rounduptopowerof2' 将指定值四舍五入到 2 的幂。

// ispow2 evaluates whether the specified int32 value is a power of two.
console.writeline(bitoperations.ispow2(128));            // true

// rounduptopowerof2 rounds the specified t:system.uint32 value up to a power of two.
console.writeline(bitoperations.rounduptopowerof2(200)); // 256

waitasync on task

您可以更轻松地等待异步任务执行, 如果超时会抛出 “timeoutexception”

task operationtask = dosomethinglongasync();

await operationtask.waitasync(timespan.fromseconds(5));

async task dosomethinglongasync()
{
    console.writeline("dosomethinglongasync started.");
    await task.delay(timespan.fromseconds(10));
    console.writeline("dosomethinglongasync ended.");
}

// output:
// dosomethinglongasync started.
// unhandled exception.system.timeoutexception: the operation has timed out.

新的数学api

新方法:

• sincos
• reciprocalestimate
• reciprocalsqrtestimate

新的重载：

• min, max, abs, sign, clamp 支持 nint 和 nuint
• divrem 返回一个元组, 包括商和余数。

// new methods sincos, reciprocalestimate and reciprocalsqrtestimate
// simultaneously computes sin and cos
(double sin, double cos) = math.sincos(1.57);
console.writeline($"sin = {sin}\ncos = {cos}");

// computes an approximate of 1 / x
double recest = math.reciprocalestimate(5);
console.writeline($"reciprocal estimate = {recest}");

// computes an approximate of 1 / sqrt(x)
double recsqrtest = math.reciprocalsqrtestimate(5);
console.writeline($"reciprocal sqrt estimate = {recsqrtest}");

// new overloads
// min, max, abs, clamp and sign supports nint and nuint
(nint a, nint b) = (5, 10);
nint min = math.min(a, b);
nint max = math.max(a, b);
nint abs = math.abs(a);
nint clamp = math.clamp(abs, min, max);
nint sign = math.sign(a);
console.writeline($"min = {min}\nmax = {max}\nabs = {abs}");
console.writeline($"clamp = {clamp}\nsign = {sign}");

// divrem variants return a tuple
(int quotient, int remainder) = math.divrem(2, 7);
console.writeline($"quotient = {quotient}\nremainder = {remainder}");

// output:
// sin = 0.9999996829318346
// cos = 0.0007963267107331026
// reciprocal estimate = 0.2
// reciprocal sqrt estimate = 0.4472135954999579
// min = 5
// max = 10
// abs = 5
// clamp = 5
// sign = 1
// quotient = 0
// remainder = 2

collectionsmarshal.getvaluerefornullref

这个是在字典中循环或者修改结可变结构体时用, 可以减少结构的副本复制, 也可以避免字典重复进行哈希计算，这个有点晦涩难懂，有兴趣的可以看看这个

https://github.com/dotnet/runtime/issues/27062

dictionary<int, mystruct> dictionary = new()
{
    { 1, new mystruct { count = 100 } }
};

int key = 1;
ref mystruct value = ref collectionsmarshal.getvaluerefornullref(dictionary, key);
// returns unsafe.nullref<tvalue>() if it doesn't exist; check using unsafe.isnullref(ref value)
if (!unsafe.isnullref(ref value))
{
    console.writeline(value.count); // output: 100

    // mutate in-place
    value.count++;
    console.writeline(value.count); // output: 101
}

struct mystruct
{
    public int count { get; set; }
}

configurehostoptions

ihostbuilder 上的新 configurehostoptions api, 可以更简单的配置应用。

public class program
{
    public static void main(string[] args)
    {
        createhostbuilder(args).build().run();
    }

    public static ihostbuilder createhostbuilder(string[] args) =>
        host.createdefaultbuilder(args)
            .configurehostoptions(o =>
            {
                o.shutdowntimeout = timespan.fromminutes(10);
            });
}

async scope

.net 6 引入了一种新的createasyncscope方法, 当您处理 iasyncdisposable 的服务时现有的createscope方法会引发异常, 使用 createasyncscope 可以完美解决。

await using var provider = new servicecollection()
        .addscoped<example>()
        .buildserviceprovider();

await using (var scope = provider.createasyncscope())
{
    var example = scope.serviceprovider.getrequiredservice<example>();
}

class example : iasyncdisposable
{
    public valuetask disposeasync() => default;
}

加密类简化

• decryptcbc
• decryptcfb
• decryptecb
• encryptcbc
• encryptcfb
• encryptecb

static byte[] decrypt(byte[] key, byte[] iv, byte[] ciphertext)
{
    using (aes aes = aes.create())
    {
        aes.key = key;
        return aes.decryptcbc(ciphertext, iv, paddingmode.pkcs7);
    }
}

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