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

　　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

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 dotnetz*****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.

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

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

好了, 可以看到它是一个字符串, 内容为 "Print"

假如message是一个复杂类型, 可以查看Fields下面的信息进一步查看

clrstack 还有一个实验性质的参数 -i, 协助查看各种变量信息, 需要用到lldb, 按照官方教程, 我暂时没有实验成功.

查看进程ID和线程ID, 更方便的方法是 htop(需要安装), 然后按 F4 进行过滤, 输入dotnet 即可

这张图是重新运行问题程序的结果, 进程ID和线程ID与前面不一样

第二行白色的是进程ID=1650, 第一行CPU占用高, 是问题线程ID=1658

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