使用dotnet-dump 查找 .net core 3.0 占用CPU 100%的原因解析

公司的产品一直紧跟 .net core 3.0 preview 不断升级, 部署到 Linux 服务器后, 偶尔会出现某个进程CPU占用100%.
　　由于服务部署在云上, 不能使用远程调试; 在局域网内的Linux 服务器或 Windows开发机上又不能重现这个问题, 联想到Java的jstack, 很是羡慕啊. 想到.net core 已经出来这么久了, 还是试着找找看吧, 结果还真找到一篇博客Introducing diagnostics improvements in .NET Core 3.0

　　这篇文章介绍了3个工具

•dotnet-counters: 实时统计runtime的状况, 包括 CPU、内存、GC、异常等
•dotnet-trace: 类似性能探测器
•dotnet-dump: 程序崩溃时使用该工具

　　这次使用的是dotnet-dump, 即使程序没有崩溃, 也可以dump程序快照, 用于分析

实验环境

ubuntu-16.04.5-desktop-amd64
SDK 3.0.100-preview6-012264

1. 新建一个简单Console程序(只能是 .net core 3.0的程序, 不支持 .net core 2.2), 模拟CPU占用100%的情况

1 2	`mkdir NetCoreDumpTest && cd NetCoreDumpTest` `dotnet` `new` `console`

编辑Program.cs

									namespace NetCoreDumpTest

									{

									 using System;

									 using System.Threading.Tasks;

									 class Program

									 {

									  static void Main(string[] args)

									  {

									   Task.Factory.StartNew(() => PrintNumber("Print", 5));

									   Console.WriteLine("Press any key to exit.");

									   Console.ReadKey();

									  }

									  static void PrintNumber(string message, int startNumber)

									  {

									   var number = startNumber;

									   while (true)

									    Console.WriteLine($"{message} {number++}");

									  }

									 }

									}

2. 安装dotnet-dump

dotnet tool install --global dotnet-dump --version 1.0.4-preview6.19311.1

提示

If you are using bash, you can add it to your profile by running the following command:
cat << \EOF >> ~/.bash_profile
# Add .NET Core SDK tools
export PATH="$PATH:/home/****/.dotnet/tools"
EOF
You can add it to the current session by running the following command:
export PATH="$PATH:/home/****/.dotnet/tools"
You can invoke the tool using the following command: dotnet-dump
Tool 'dotnet-dump' (version '1.0.4-preview6.19311.1') was successfully installed.

建议将 $HOME/.dotnet/tools加入到PATH, 好吧, 照着做吧, 记得使用下面的命令使设置立即生效

source ~/.bash_profile

3. 使用 dotnet NetCoreDumpTest.dll 启动我们的问题程序, 然后使用 ps -ef | grep dotnet 查看程序的进程ID, 可以看到进程ID是 3411

									ps -ef | grep dotnet

									z*****e  3411 1464 22 07:51 pts/8 00:00:59 dotnet NetCoreDumpTest.dll

									z*****e  3431 2935 0 07:55 pts/9 00:00:00 grep --color=auto dotnet

针对进程3411, 我们还需要知道是哪个线程占CPU, 使用 top -Hp 3411 可以列出所有线程, 由于top每隔3秒刷新一次, 所以可能需要多观察几秒才能看到具体是哪个线程占用CPU比较高, 这里我们可以看到是PID=3418的线程(Linux的进程ID和线程ID请自行了解一下).

									top -Hp 3411

									 PID USER  PR NI VIRT RES SHR S %CPU %MEM  TIME+ COMMAND

									 3418 z*****e 20 0 2997700 29060 22400 R 10.3 1.4 0:20.68 dotnet

									 3411 z*****e 20 0 2997700 29060 22400 S 0.0 1.4 0:00.11 dotnet

									 3412 z*****e 20 0 2997700 29060 22400 S 0.0 1.4 0:00.02 dotnet

									 3413 z*****e 20 0 2997700 29060 22400 S 0.0 1.4 0:00.00 dotnet

									 3414 z*****e 20 0 2997700 29060 22400 S 0.0 1.4 0:00.00 dotnet

									 3415 z*****e 20 0 2997700 29060 22400 S 0.0 1.4 0:00.01 dotnet

									 3416 z*****e 20 0 2997700 29060 22400 S 0.0 1.4 0:00.00 dotnet

									 3417 z*****e 20 0 2997700 29060 22400 S 0.0 1.4 0:00.00 dotnet

									 3421 z*****e 20 0 2997700 29060 22400 S 0.0 1.4 0:00.00 dotnet

获取dump, 只能正对进程进行dump, 所以我们输入的是 3411

									dotnet-dump collect -p 3411

									Writing minidump with heap to /tmp/core_20190623_075649

									Complete

4. 分析

dotnet-dump analyze core_20190623_075649

使用clrthreads 查看所有线程

>clrthreads
ThreadCount:      4
UnstartedThread: 0
BackgroundThread: 3
PendingThread:    0
DeadThread:       0
Hosted Runtime:   no
                                                                                                        Lock
DBG   ID OSID ThreadOBJ           State GC Mode     GC Alloc Context                  Domain           Count Apt Exception
   0    1 d53 0000000001307D80    20020 Preemptive 0000000000000000:0000000000000000 0000000001306450 1     Ukn
   4    2 d57 000000000135BBD0    21220 Preemptive 0000000000000000:0000000000000000 0000000001306450 0     Ukn (Finalizer)
   6    3 d59 00007F666C0009F0 1020220 Preemptive 0000000000000000:0000000000000000 0000000001306450 0     Ukn (Threadpool Worker)
   7    4 d5a 000000000130DA40 1021220 Preemptive 00007F6678106860:00007F6678106F20 0000000001306450 1     Ukn (Threadpool Worker)

我们关心的线程3418的16进制是d5a, 也就是最后一行, 它的DBG是7, 我们需要使用 setthread 7, 将其设置为当前操作的线程

然后使用 clrstack 获取线程调用信息

									> setthread 7

									> clrstack

									OS Thread Id: 0xd5a (7)

									  Child SP    IP Call Site

									00007F6715561558 00007f671a2bd4bd [InlinedCallFrame: 00007f6715561558] Interop+Sys.Write(System.Runtime.InteropServices.SafeHandle, Byte*, Int32)

									00007F6715561558 00007f669f669a9e [InlinedCallFrame: 00007f6715561558] Interop+Sys.Write(System.Runtime.InteropServices.SafeHandle, Byte*, Int32)

									00007F6715561540 00007F669F669A9E ILStubClass.IL_STUB_PInvoke

									00007F67155615E0 00007F669F67333E System.ConsolePal.Write(Microsoft.Win32.SafeHandles.SafeFileHandle, Byte*, Int32, Boolean)

									00007F67155616A0 00007F669F67360C System.ConsolePal.Write(Microsoft.Win32.SafeHandles.SafeFileHandle, Byte[], Int32, Int32, Boolean) [/_/src/System.Console/src/System/ConsolePal.Unix.cs @ 1236]

									00007F67155616C0 00007F669F672B2A System.IO.StreamWriter.Flush(Boolean, Boolean) [/_/src/System.Private.CoreLib/shared/System/IO/StreamWriter.cs @ 261]

									00007F6715561710 00007F669F6729F3 System.IO.StreamWriter.WriteLine(System.String) [/_/src/System.Private.CoreLib/shared/System/IO/StreamWriter.cs @ 474]

									00007F6715561760 00007F669F6727D3 System.IO.TextWriter+SyncTextWriter.WriteLine(System.String) [/_/src/System.Private.CoreLib/shared/System/IO/TextWriter.cs @ 891]

									00007F67155617A0 00007F669F672770 System.Console.WriteLine(System.String) [/_/src/System.Console/src/System/Console.cs @ 550]

									00007F67155617C0 00007F669F663791 NetCoreDumpTest.Program.PrintNumber(System.String, Int32) [/home/zhouke/NetCoreDumpTest/Program.cs @ 18]

									00007F6715561800 00007F669F6636D9 NetCoreDumpTest.Program+<>c.<Main>b__0_0()

									00007F6715561820 00007F669F1872A1 System.Threading.Tasks.Task.InnerInvoke() [/_/src/System.Private.CoreLib/shared/System/Threading/Tasks/Task.cs @ 2466]

									00007F6715561840 00007F669F18CBC2 System.Threading.Tasks.Task+<>c.<.cctor>b__274_0(System.Object) [/_/src/System.Private.CoreLib/shared/System/Threading/Tasks/Task.cs @ 2445]

									00007F6715561850 00007F669F171AF2 System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(System.Threading.Thread, System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object) [/_/src/System.Private.CoreLib/shared/System/Threading/ExecutionContext.cs @ 289]

									00007F6715561890 00007F669F187111 System.Threading.Tasks.Task.ExecuteWithThreadLocal(System.Threading.Tasks.Task ByRef, System.Threading.Thread) [/_/src/System.Private.CoreLib/shared/System/Threading/Tasks/Task.cs @ 2406]

									00007F6715561910 00007F669F186F28 System.Threading.Tasks.Task.ExecuteEntryUnsafe(System.Threading.Thread) [/_/src/System.Private.CoreLib/shared/System/Threading/Tasks/Task.cs @ 2344]

									00007F6715561930 00007F669F186EBB System.Threading.Tasks.Task.ExecuteFromThreadPool(System.Threading.Thread)

									00007F6715561940 00007F669F17B754 System.Threading.ThreadPoolWorkQueue.Dispatch() [/_/src/System.Private.CoreLib/shared/System/Threading/ThreadPool.cs @ 663]

									00007F67155619C0 00007F669F169A5B System.Threading._ThreadPoolWaitCallback.PerformWaitCallback() [/_/src/System.Private.CoreLib/src/System/Threading/ThreadPool.CoreCLR.cs @ 29]

									00007F6715561D50 00007f6718a1ccaf [DebuggerU2MCatchHandlerFrame: 00007f6715561d50]

哗啦啦一大片, 有点Java调用堆栈的味道, 不过我们还是找到了我们的问题代码

1	`NetCoreDumpTest.Program.PrintNumber(System.String, Int32)`

有时候我们想知道传入的什么参数导致CPU占用高, 可以给clrstack加上参数 -a

									> clrstack -a

									..............

									00007F0DD6FFC7C0 00007F0D6EEF3791 NetCoreDumpTest.Program.PrintNumber(System.String, Int32) [/home/zhouke/NetCoreDumpTest/Program.cs @ 18]

									  PARAMETERS:

									    message (0x00007F0DD6FFC7E8) = 0x00007f0d4800b8b0

									    startNumber (0x00007F0DD6FFC7E4) = 0x0000000000000005

									  LOCALS:

									    0x00007F0DD6FFC7E0 = 0x000000000014e42b

									    0x00007F0DD6FFC7DC = 0x0000000000000001

									...............

可以看到PARAMETERS里, startNumber作为值类型, 可以直接看到数值为5, 而message是引用类型, 指向0x00007f0d4800b8b0, 这时候需要用到 dumpobj 命令

									> dumpobj 0x00007f0d4800b8b0

									Name:    System.String

									MethodTable: 00007f0d6ef70f90

									EEClass:   00007f0d6eede1c0

									Size:    32(0x20) bytes

									File:    /home/zhouke/dotnet/shared/Microsoft.NETCore.App/3.0.0-preview6-27804-01/System.Private.CoreLib.dll

									String:   Print

									Fields:

									       MT  Field  Offset         Type VT   Attr      Value Name

									00007f0d6ef6a138 400022b    8     System.Int32 1 instance        5 _stringLength

									00007f0d6ef66f38 400022c    c     System.Char 1 instance        50 _firstChar

									00007f0d6ef70f90 400022d   108    System.String 0  static 00007f0d47fff360 Empty