C# “之间有什么区别吗?”;等待任务。运行();返回&引用;及;返回任务。运行();?
以下两段代码在概念上是否存在差异:C# “之间有什么区别吗?”;等待任务。运行();返回&引用;及;返回任务。运行();?,c#,async-await,C#,Async Await,以下两段代码在概念上是否存在差异: async Task TestAsync() { await Task.Run(() => DoSomeWork()); } 及 Task TestAsync() { return Task.Delay(1000); } 生成的代码是否也不同 编辑:以避免与任务混淆。运行,类似情况: async Task TestAsync() { await Task.Delay(1000); } 及 Task TestAsync(
async Task TestAsync()
{
await Task.Run(() => DoSomeWork());
}
及
Task TestAsync()
{
return Task.Delay(1000);
}
生成的代码是否也不同
编辑:以避免与任务混淆。运行
,类似情况:
async Task TestAsync()
{
await Task.Delay(1000);
}
及
Task TestAsync()
{
return Task.Delay(1000);
}
最新更新:除了公认的答案之外,处理LocalCallContext
的方式也有所不同:这两个示例确实不同。当一个方法被标记为async
关键字时,编译器会在后台生成一个状态机。这就是在等待一个可等待的事件被等待之后,负责恢复延续的原因
相反,当一个方法没有标记为async
时,您就失去了wait
waitables的功能。(也就是说,在方法本身内部;调用方仍然可以等待该方法。)但是,通过避免使用async
关键字,您不再生成状态机,这可能会增加相当多的开销(将局部变量提升到状态机的字段,将其他对象提升到GC)
在这样的示例中,如果您能够避免async wait
并直接返回一个waitable,那么应该这样做以提高方法的效率
请看和,它们与您的问题和此答案非常相似
Program.TestAsync()
”是一个返回“Task
”的异步方法,因此返回关键字后面不能跟有对象表达式。您是否打算返回“任务”
一定是这样
async Task TestAsync()
{
await Task.Run(() => DoSomeWork());
}
async
/内部的更多信息,请等待
.method private hidebysig
instance class [mscorlib]System.Threading.Tasks.Task TestAsync () cil managed
{
.custom instance void [mscorlib]System.Runtime.CompilerServices.AsyncStateMachineAttribute::.ctor(class [mscorlib]System.Type) = (
01 00 25 53 4f 54 65 73 74 50 72 6f 6a 65 63 74
2e 50 72 6f 67 72 61 6d 2b 3c 54 65 73 74 41 73
79 6e 63 3e 64 5f 5f 31 00 00
)
.custom instance void [mscorlib]System.Diagnostics.DebuggerStepThroughAttribute::.ctor() = (
01 00 00 00
)
// Method begins at RVA 0x216c
// Code size 62 (0x3e)
.maxstack 2
.locals init (
[0] valuetype SOTestProject.Program/'<TestAsync>d__1',
[1] class [mscorlib]System.Threading.Tasks.Task,
[2] valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder
)
IL_0000: ldloca.s 0
IL_0002: ldarg.0
IL_0003: stfld class SOTestProject.Program SOTestProject.Program/'<TestAsync>d__1'::'<>4__this'
IL_0008: ldloca.s 0
IL_000a: call valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder::Create()
IL_000f: stfld valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder SOTestProject.Program/'<TestAsync>d__1'::'<>t__builder'
IL_0014: ldloca.s 0
IL_0016: ldc.i4.m1
IL_0017: stfld int32 SOTestProject.Program/'<TestAsync>d__1'::'<>1__state'
IL_001c: ldloca.s 0
IL_001e: ldfld valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder SOTestProject.Program/'<TestAsync>d__1'::'<>t__builder'
IL_0023: stloc.2
IL_0024: ldloca.s 2
IL_0026: ldloca.s 0
IL_0028: call instance void [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder::Start<valuetype SOTestProject.Program/'<TestAsync>d__1'>(!!0&)
IL_002d: ldloca.s 0
IL_002f: ldflda valuetype [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder SOTestProject.Program/'<TestAsync>d__1'::'<>t__builder'
IL_0034: call instance class [mscorlib]System.Threading.Tasks.Task [mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder::get_Task()
IL_0039: stloc.1
IL_003a: br.s IL_003c
IL_003c: ldloc.1
IL_003d: ret
} // end of method Program::TestAsync
.method私有隐藏
实例类[mscorlib]System.Threading.Tasks.Task TestAsync()cil托管
{
.custom instance void[mscorlib]System.Runtime.CompilerServices.AsyncStateMachineAttribute::.ctor(类[mscorlib]System.Type)=(
01 00 25 53 4f 54 65 73 74 50 72 6f 6a 65 63 74
2e 50 72 6f 67 72 61 6d 2b 3c 54 65 73 74 41 73
79 6e 63 3e 64 5f 5f 31 00 00
)
.custom instance void[mscorlib]System.Diagnostics.DebuggerStepThroughAttribute::.ctor()=(
01 00 00 00
)
//方法从RVA 0x216c开始
//代码大小62(0x3e)
.maxstack 2
.init(
[0]valuetype SOTestProject.Program/'d___1',
[1] 类[mscorlib]System.Threading.Tasks.Task,
[2] valuetype[mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder
)
IL_0000:ldloca.s 0
IL_0002:ldarg.0
IL_0003:stfld类SOTestProject.Program SOTestProject.Program/'d__1'::'4_this'
IL_0008:ldloca.s 0
IL_000a:调用valuetype[mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder[mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder::Create()
IL_000f:stfld valuetype[mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder SOTestProject.Program/'d_1':'t_builder'
IL_0014:ldloca.s 0
IL_0016:ldc.i4.m1
IL_0017:stfld int32 SOTestProject.Program/'d__1'::'1__状态'
IL_001c:ldloca.s 0
IL_001e:ldfld valuetype[mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder SOTestProject.Program/'d_1':'t_builder'
IL_0023:stloc.2
IL_0024:ldloca.s 2
IL_0026:ldloca.s 0
IL_0028:调用实例void[mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder::Start(!!0&)
IL_002d:ldloca.s 0
IL_002f:ldflda valuetype[mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder SOTestProject.Program/'d_1':'t_builder'
IL_0034:调用实例类[mscorlib]System.Threading.Tasks.Task[mscorlib]System.Runtime.CompilerServices.AsyncTaskMethodBuilder::get_Task()
IL_0039:stloc.1
IL_003a:br.s IL_003c
IL_003c:ldloc.1
IL_003d:ret
}//方法结束程序::TestAsync
及
Task TestAsync()
{
return Task.Delay(1000);
}
.method私有隐藏
实例类[mscorlib]System.Threading.Tasks.Task TestAsync2()cil托管
{
//方法从RVA 0x21d8开始
//代码大小23(0x17)
.maxstack 2
.init(
[0]类[mscorlib]System.Threading.Tasks.Task CS$1$0000
)
IL_0000:没有
IL_0001:ldarg.0
IL_0002:ldftn实例类[mscorlib]System.Threading.Tasks.Task SOTestProject.程序::'b_4'()
IL_0008:newobj实例无效类[mscorlib]System.Func`1::.ctor(对象,本机int)
IL_000d:调用类[mscorlib]System.Threading.Tasks.Task[mscorlib]System.Threading.Tasks.Task::Run(类[mscorlib]System.Func`1)
IL_0012:stloc.0
IL_0013:br.s IL_0015
IL_0015:ldloc.0
IL_0016:ret
}//方法结束程序::TestAsync2
async Task TestAsync()
{
await Task.Delay(1000);
}
及
Task TestAsync()
{
return Task.Delay(1000);
}
?
我被这个问题弄糊涂了。让我用另一个问题回答你的问题来澄清一下。两者之间有什么区别
Func<int> MakeFunction()
{
Func<int> f = ()=>1;
return ()=>f();
}
Func MakeFunction()
{
Func f=()=>1;
return()=>f();
}
及
Task TestAsync()
{
return Task.Delay(1000);
}
Func MakeFunction()
{
返回()=>1;
}
?
无论我的两件事之间有什么区别,你的两件事之间也有同样的区别。一个主要区别在于异常传播。异常,在
异步任务
方法中抛出,获取存储在返回的Task
对象中,并保持休眠状态,直到通过await Task
、Task.Wait()
、Task.Result
或Task.GetAwaiter().GetResult()
观察到该任务。即使从async
方法的同步部分抛出,它也是以这种方式传播的
考虑以下代码,其中OneTestAsync
和AnotherTestAsync
static async Task OneTestAsync(int n)
{
await Task.Delay(n);
}
static Task AnotherTestAsync(int n)
{
return Task.Delay(n);
}
// call DoTestAsync with either OneTestAsync or AnotherTestAsync as whatTest
static void DoTestAsync(Func<int, Task> whatTest, int n)
{
Task task = null;
try
{
// start the task
task = whatTest(n);
// do some other stuff,
// while the task is pending
Console.Write("Press enter to continue");
Console.ReadLine();
task.Wait();
}
catch (Exception ex)
{
Console.Write("Error: " + ex.Message);
}
}
Press enter to continue
Error: One or more errors occurred.await Task.Delay
Error: 2nd
Error: The value needs to be either -1 (signifying an infinite timeout), 0 or a positive integer.
Parameter name: millisecondsDelayError: 1st
// async
async Task<int> MethodAsync(int arg)
{
if (arg < 0)
throw new ArgumentException("arg");
// ...
return 42 + arg;
}
// non-async
Task<int> MethodAsync(int arg)
{
var task = new Task<int>(() =>
{
if (arg < 0)
throw new ArgumentException("arg");
// ...
return 42 + arg;
});
task.RunSynchronously(TaskScheduler.Default);
return task;
}
static async Task TestAsync()
{
await Task.Delay(1000);
}
void Form_Load(object sender, EventArgs e)
{
TestAsync().Wait(); // dead-lock here
}
Task TestAsync()
{
return Task.Delay(1000);
}