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Add additional features to SOS DumpAsync command #18213
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1. Computing GC roots is a relatively slow operation, and doing it for every state machine object found in a large heap can be time consuming. Making it opt-in with -roots command-line flag.
2. Added -waiting command-line flag. DumpAsync will now retrieve the <>1__state field from the StateMachine, and if -waiting is specified, it'll filter down to state machines that have a state value >= 0, meaning the state machines are waiting at an await point. For example, given this program:
```C#
using System.Threading.Tasks;
class Program
{
static async Task Main() { await MethodA(0); await MethodA(int.MaxValue); }
static async Task MethodA(int delay) => await MethodB(delay);
static async Task MethodB(int delay) { await Task.Yield(); await Task.Delay(delay); }
}
```
using `!DumpAsync` outputs:
```
Address MT Size Name
#0
0000026848693438 00007ff88ea35e58 120 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[Program+<MethodB>d__2, test]]
StateMachine: Program+<MethodB>d__2 (struct)
MT Field Offset Type VT Attr Value Name
00007ff8e9bc4bc0 4000008 0 System.Int32 1 instance -2 <>1__state
00007ff8e9bd82f8 4000009 8 ...TaskMethodBuilder 1 instance 0000026848693490 <>t__builder
00007ff8e9bc4bc0 400000a 4 System.Int32 1 instance 0 delay
00007ff8e9bee4d0 400000b 10 ...able+YieldAwaiter 1 instance 0000026848693498 <>u__1
00007ff8e9bcead0 400000c 18 ...vices.TaskAwaiter 1 instance 00000268486934a0 <>u__2
Continuation: 00000268486934b0 (System.Object)
dotnet#1
0000026848693e68 00007ff88ea36cc8 112 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[Program+<MethodA>d__1, test]]
StateMachine: Program+<MethodA>d__1 (struct)
MT Field Offset Type VT Attr Value Name
00007ff8e9bc4bc0 4000004 0 System.Int32 1 instance -2 <>1__state
00007ff8e9bd82f8 4000005 8 ...TaskMethodBuilder 1 instance 0000026848693ec0 <>t__builder
00007ff8e9bc4bc0 4000006 4 System.Int32 1 instance 0 delay
00007ff8e9bcead0 4000007 10 ...vices.TaskAwaiter 1 instance 0000026848693ec8 <>u__1
Continuation: 00000268486934b0 (System.Object)
dotnet#2
0000026848693ed8 00007ff88ea37188 112 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[Program+<Main>d__0, test]]
StateMachine: Program+<Main>d__0 (struct)
MT Field Offset Type VT Attr Value Name
00007ff8e9bc4bc0 4000001 0 System.Int32 1 instance 1 <>1__state
00007ff8e9bd82f8 4000002 8 ...TaskMethodBuilder 1 instance 0000026848693f30 <>t__builder
00007ff8e9bcead0 4000003 10 ...vices.TaskAwaiter 1 instance 0000026848693f38 <>u__1
Continuation: 0000026848693f48 (System.Threading.Tasks.Task+SetOnInvokeMres)
dotnet#3
0000026848695d30 00007ff88ea35e58 120 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[Program+<MethodB>d__2, test]]
StateMachine: Program+<MethodB>d__2 (struct)
MT Field Offset Type VT Attr Value Name
00007ff8e9bc4bc0 4000008 0 System.Int32 1 instance 1 <>1__state
00007ff8e9bd82f8 4000009 8 ...TaskMethodBuilder 1 instance 0000026848695d88 <>t__builder
00007ff8e9bc4bc0 400000a 4 System.Int32 1 instance 2147483647 delay
00007ff8e9bee4d0 400000b 10 ...able+YieldAwaiter 1 instance 0000026848695d90 <>u__1
00007ff8e9bcead0 400000c 18 ...vices.TaskAwaiter 1 instance 0000026848695d98 <>u__2
Continuation: 0000026848695dd0 (System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[Program+<MethodA>d__1, test]])
dotnet#4
0000026848695dd0 00007ff88ea36cc8 112 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[Program+<MethodA>d__1, test]]
StateMachine: Program+<MethodA>d__1 (struct)
MT Field Offset Type VT Attr Value Name
00007ff8e9bc4bc0 4000004 0 System.Int32 1 instance 0 <>1__state
00007ff8e9bd82f8 4000005 8 ...TaskMethodBuilder 1 instance 0000026848695e28 <>t__builder
00007ff8e9bc4bc0 4000006 4 System.Int32 1 instance 2147483647 delay
00007ff8e9bcead0 4000007 10 ...vices.TaskAwaiter 1 instance 0000026848695e30 <>u__1
Continuation: 0000026848693ed8 (System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[Program+<Main>d__0, test]])
Found 5 state machines.
```
while using `!DumpAsync -waiting` outputs only:
```
Address MT Size Name
#0
0000026848693ed8 00007ff88ea37188 112 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[Program+<Main>d__0, test]]
StateMachine: Program+<Main>d__0 (struct)
MT Field Offset Type VT Attr Value Name
00007ff8e9bc4bc0 4000001 0 System.Int32 1 instance 1 <>1__state
00007ff8e9bd82f8 4000002 8 ...TaskMethodBuilder 1 instance 0000026848693f30 <>t__builder
00007ff8e9bcead0 4000003 10 ...vices.TaskAwaiter 1 instance 0000026848693f38 <>u__1
Continuation: 0000026848693f48 (System.Threading.Tasks.Task+SetOnInvokeMres)
dotnet#1
0000026848695d30 00007ff88ea35e58 120 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[Program+<MethodB>d__2, test]]
StateMachine: Program+<MethodB>d__2 (struct)
MT Field Offset Type VT Attr Value Name
00007ff8e9bc4bc0 4000008 0 System.Int32 1 instance 1 <>1__state
00007ff8e9bd82f8 4000009 8 ...TaskMethodBuilder 1 instance 0000026848695d88 <>t__builder
00007ff8e9bc4bc0 400000a 4 System.Int32 1 instance 2147483647 delay
00007ff8e9bee4d0 400000b 10 ...able+YieldAwaiter 1 instance 0000026848695d90 <>u__1
00007ff8e9bcead0 400000c 18 ...vices.TaskAwaiter 1 instance 0000026848695d98 <>u__2
Continuation: 0000026848695dd0 (System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[Program+<MethodA>d__1, test]])
dotnet#2
0000026848695dd0 00007ff88ea36cc8 112 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[Program+<MethodA>d__1, test]]
StateMachine: Program+<MethodA>d__1 (struct)
MT Field Offset Type VT Attr Value Name
00007ff8e9bc4bc0 4000004 0 System.Int32 1 instance 0 <>1__state
00007ff8e9bd82f8 4000005 8 ...TaskMethodBuilder 1 instance 0000026848695e28 <>t__builder
00007ff8e9bc4bc0 4000006 4 System.Int32 1 instance 2147483647 delay
00007ff8e9bcead0 4000007 10 ...vices.TaskAwaiter 1 instance 0000026848695e30 <>u__1
Continuation: 0000026848693ed8 (System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[Program+<Main>d__0, test]])
Found 3 state machines.
```
skipping the two state machines that have a `<>1__state` field value of -2 (meaning it's completed). Note that this change has the somewhat unfortunate impact of taking a dependency on what's effectively an implementation detail of Roslyn, but the value the filtering provides is deemed to be worth it. This design is unlikely to change in the future, and as with other diagnostic/debugging features that rely on such details, it can be updated if Roslyn ever changes its scheme. In the meantime, the code will output a warning message if it can't find the state field.
3. If a state machine is found to have 0 roots but also to have a <>1__state value >= 0, that suggests it was dropped without having been completed, which is likely a sign of an application bug. The command now prints out an information message to highlight that state. For example, this program:
```C#
using System;
using System.Threading.Tasks;
class Program
{
static void Main()
{
Task.Run(async () => await new TaskCompletionSource<bool>().Task);
Console.ReadLine();
}
}
```
when processed with `!DumpAsync -roots` results in:
```
Address MT Size Name
#0
0000020787fb5b30 00007ff88ea1afe8 112 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Boolean, System.Private.CoreLib],[Program+<>c+<<Main>b__0_0>d, test]]
StateMachine: Program+<>c+<<Main>b__0_0>d (struct)
MT Field Offset Type VT Attr Value Name
00007ff8e9bc4bc0 4000003 0 System.Int32 1 instance 0 <>1__state
00007ff8e9bd0b88 4000004 8 ...Private.CoreLib]] 1 instance 0000020787fb5b88 <>t__builder
00007ff8e9bffd58 4000005 10 ...Private.CoreLib]] 1 instance 0000020787fb5b90 <>u__1
Continuation: 0000020787fb3fc8 (System.Threading.Tasks.UnwrapPromise`1[[System.Boolean, System.Private.CoreLib]])
GC roots:
Incomplete state machine (<>1__state == 0) with 0 roots.
Found 1 state machines.
```
mikem8361
approved these changes
May 31, 2018
|
FYI @leculver |
stephentoub
added a commit
to dotnet/buildtools
that referenced
this pull request
Jun 1, 2018
dotnet/coreclr#18160 and dotnet/coreclr#18213 added a new `dumpasync` command to sos that will dump out data on async methods currently in use. Including this in the core dump analysis has similar value to dumping out all call stacks, in that it'll give us more details into what was going on in the process.
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#18160 added a DumpAsync command to SOS. This adds a few additional features to it:
Computing GC roots is a relatively slow operation, and doing it for every state machine object found in a large heap can be time consuming. Making it opt-in with -roots command-line flag.
Added -waiting command-line flag. DumpAsync will now retrieve the <>1__state field from the StateMachine, and if -waiting is specified, it'll filter down to state machines that have a state value >= 0, meaning the state machines are waiting at an await point. For example, given this program:
using
!DumpAsyncoutputs:while using
!DumpAsync -waitingoutputs only:skipping the two state machines that have a
<>1__statefield value of -2 (meaning it's completed). Note that this change has the somewhat unfortunate impact of taking a dependency on what's effectively an implementation detail of Roslyn, but the value the filtering provides is deemed to be worth it. This design is unlikely to change in the future, and as with other diagnostic/debugging features that rely on such details, it can be updated if Roslyn ever changes its scheme. In the meantime, the code will output a warning message if it can't find the state field.when processed with
!DumpAsync -rootsresults in:cc: @jkotas, @danmosemsft, @noahfalk, @jaredpar, @mikem8361