一:背景
1. 讲故事
上个月有位朋友找到我,说他的程序出现了内存泄漏,不知道如何进一步分析,截图如下:
朋友这段话已经说的非常言简意赅了,那就上 windbg 说话吧。
二:Windbg 分析
1. 到底是哪一方面的泄漏
根据朋友描述,程序运行一段时间后,内存就炸了,应该没造成人员伤亡,不然也不会跟我wx聊天了,这里可以用 .time 看看当前的 process 跑了多久。
- 0:000> .time
- Debug session time: Thu Oct 21 14:54:39.000 2021 (UTC + 8:00)
- System Uptime: 6 days 4:37:27.851
- Process Uptime: 0 days 0:40:14.000
- Kernel time: 0 days 0:01:55.000
- User time: 0 days 0:07:33.000
看的出来,这个 dump 是在程序跑了 40min 之后抓的,接下来我们比较一下 process 的内存和 gc堆 占比, 看看到底是哪一块的泄漏。
- 0:000> !address -summary
- --- State Summary ---------------- RgnCount ----------- Total Size -------- %ofBusy %ofTotal
- MEM_FREE 327 7dfc`c665a000 ( 125.987 TB) 98.43%
- MEM_RESERVE 481 201`e91a2000 ( 2.007 TB) 99.74% 1.57%
- MEM_COMMIT 2307 1`507f4000 ( 5.258 GB) 0.26% 0.00%
- 0:000> !eeheap -gc
- Number of GC Heaps: 2
- ------------------------------
- GC Allocated Heap Size: Size: 0x139923528 (5260850472) bytes.
- GC Committed Heap Size: Size: 0x13bf23000 (5300695040) bytes.
2. 到底是什么占用了如此大的内存
知道是 托管层 的泄漏,感觉一下子就幸福起来了,接下来用 !dumpheap -stat 看看有没有什么大对象可挖。
- 0:000> !dumpheap -stat
- Statistics:
- MT Count TotalSize Class Name
- 00007ffdeb1fc400 5362921 128710104 xxxBLLs.xxx.BundleBiz+<>c__DisplayClass20_0
- 00007ffdeaeff140 5362929 171613728 System.Collections.Generic.List`1[[xxx.xxx, xxx]]
- 00007ffdeaeff640 5362957 171615272 xxx.BLLs.Plan.Dto.xxx[]
- 00007ffde8171e18 16146362 841456072 System.String
-
00007ffdeb210098 5362921 1415811144 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[xxx.BundleBiz+
d__20, xxx]] - 00007ffdea9ca260 5362921 2359685240 xxx.Bundle
从输出看,内存主要被 xxx.Bundle 和 AsyncTaskMethodBuilder 两大类对象给吃掉了,数量都高达 536w,这里有一个非常有意思的地方,如果你了解异步,我相信你一看就能看出 AsyncTaskMethodBuilder + VoidTaskResult 是干嘛的,按照经验,这位朋友应该误入了 异步无限递归 ,那怎么去挖呢?接着往下看。
3. 寻找问题代码
看到上面的 xxx.BundleBiz+
虽然找到了源码,但代码是 ILSpy 反编译出来的异步状态机,接下来的一个问题是,如何根据状态机代码反向寻找到 await ,async 代码呢?在 ILSpy 中有一个 used by 功能,在这里可以用起来了。
双击 used by 就能看到真正的调用代码,简化后如下:
-
public async Task DistributionBundle(List
list, List dynamic> labels)bwdList, xxx item, List sumDetails, List details, BundleParameter bundleParameter, IEnumerable< - {
- int num = 0;
- foreach (xxx detail in sumDetails)
- {
-
IEnumerable
woDetails = details.Where((xxx w) => w.Size == detail.Size && w.Color == detail.Color); - foreach (xxx item2 in woDetails)
- {
- xxx
- }
- woDetails = woDetails.OrderBy((xxx s) => s.Seq).ToList();
- num++;
- xxx
- Bundle bundle = new Bundle();
- Bundle bundle2 = bundle;
- bundle2.BundleId = await _repo.CreateBundleId();
- foreach (xxx item3 in woDetails)
- {
- item3.TaskQty = item3.WoQty + Math.Ceiling(item3.WoQty * item3.OverCutRate);
- decimal value = default(decimal);
- }
- await DistributionBundle(list, bwdList, item, sumDetails, details, bundleParameter, labels);
- }
- }
仔细看上面这段代码, 我去, await DistributionBundle(list, bwdList, item, sumDetails, details, bundleParameter, labels); 又调用了自身,看样子是某种条件下陷入了一个死递归。。。
有些朋友可能要问,除了经验之外,能从 dump 中分析出来吗?当然可以,从 500w+ 中抽一个看看它的 !gcroot 即可。
- 0:000> !DumpHeap /d -mt 00007ffdeb210098
- Address MT Size
- 000001a297913a68 00007ffdeb210098 264
- 000001a297913b70 00007ffdeb210098 264
- 0:000> !gcroot 000001a297913a68
- Thread 5ac:
- 000000470B1EE4E0 00007FFE45103552 System.Threading.Tasks.Task.SpinThenBlockingWait(Int32, System.Threading.CancellationToken) [/_/src/System.Private.CoreLib/shared/System/Threading/Tasks/Task.cs @ 2922]
- rbp+10: 000000470b1ee550
-
-> 000001A297A25D88 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions+
d__4, Microsoft.Extensions.Hosting.Abstractions]] - -> 000001A29796D8C0 Microsoft.Extensions.Hosting.Internal.Host
- ...
- -> 000001A298213248 System.Data.SqlClient.TdsParserStateObjectNative
- -> 000001A32E6AB700 System.Threading.Tasks.TaskFactory`1+<>c__DisplayClass38_0`1[[System.Data.SqlClient.SqlDataReader, System.Data.SqlClient],[System.Data.CommandBehavior, System.Data.Common]]
- -> 000001A32E6AB728 System.Threading.Tasks.Task`1[[System.Data.SqlClient.SqlDataReader, System.Data.SqlClient]]
- -> 000001A32E6ABB18 System.Threading.Tasks.StandardTaskContinuation
- -> 000001A32E6ABA80 System.Threading.Tasks.ContinuationTaskFromResultTask`1[[System.Data.SqlClient.SqlDataReader, System.Data.SqlClient]]
- -> 000001A32E6AB6C0 System.Action`1[[System.Threading.Tasks.Task`1[[System.Data.SqlClient.SqlDataReader, System.Data.SqlClient]], System.Private.CoreLib]]
- -> 000001A32E6AB428 System.Data.SqlClient.SqlCommand+<>c__DisplayClass130_0
- ...
-
-> 000001A32E6ABC08 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.String, System.Private.CoreLib],[Dapper.SqlMapper+
d__34`1[[System.String, System.Private.CoreLib]], Dapper]] -
-> 000001A32E6ABD20 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.String, System.Private.CoreLib],[xxx.DALs.xxx.BundleRepo+
d__12, xxx]] -
-> 000001A32E6ABD98 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[xxx.BundleBiz+
d__20, xxx]] -
-> 000001A32E6A6BD8 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[xxx.BundleBiz+
d__20, xxx]] -
-> 000001A433250520 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[xxx.BundleBiz+
d__20, xxx]] -
-> 000001A32E69E0F8 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[xxx.BundleBiz+
d__20, xxx]] -
-> 000001A433247D28 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[xxx.BundleBiz+
d__20, xxx]] -
-> 000001A433246330 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[xxx.BundleBiz+
d__20, xxx]] -
-> 000001A32E69A568 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[xxx.BundleBiz+
d__20, xxx]] -
-> 000001A433245408 System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1+AsyncStateMachineBox`1[[System.Threading.Tasks.VoidTaskResult, System.Private.CoreLib],[xxx.BundleBiz+
d__20, xxx]] - ...
从调用栈来看,代码貌似是从数据库读取记录的过程中陷入死循环的。
4. 为什么没有出现栈溢出
一看到无限循环,我相信很多朋友肯定要问,为啥没出现堆栈溢出,毕竟默认的线程栈空间仅仅 1M 而已,从 !gcroot 上看,这些引用都是挂在 5ac 线程上,也就是下面输出的 主线程 ,而且主线程栈也非常干净。
- 0:000> !t
- ThreadCount: 30
- UnstartedThread: 0
- BackgroundThread: 24
- PendingThread: 0
- DeadThread: 5
- Hosted Runtime: no
- Lock
- DBG ID OSID ThreadOBJ State GC Mode GC Alloc Context Domain Count Apt Exception
- 0 1 5ac 000001A29752CDF0 202a020 Preemptive 0000000000000000:0000000000000000 000001a29754c570 0 MTA
- 4 2 1e64 000001A29752A490 2b220 Preemptive 0000000000000000:0000000000000000 000001a29754c570 0 MTA (Finalizer)
- ...
- 0:000> !clrstack
- OS Thread Id: 0x5ac (0)
- Child SP IP Call Site
- 000000470B1EE1D0 00007ffe5eb30544 [GCFrame: 000000470b1ee1d0]
- 000000470B1EE318 00007ffe5eb30544 [HelperMethodFrame_1OBJ: 000000470b1ee318] System.Threading.Monitor.ObjWait(Boolean, Int32, System.Object)
- 000000470B1EE440 00007ffe45103c25 System.Threading.ManualResetEventSlim.Wait(Int32, System.Threading.CancellationToken)
- 000000470B1EE4E0 00007ffe45103552 System.Threading.Tasks.Task.SpinThenBlockingWait(Int32, System.Threading.CancellationToken) [/_/src/System.Private.CoreLib/shared/System/Threading/Tasks/Task.cs @ 2922]
- 000000470B1EE550 00007ffe451032cf System.Threading.Tasks.Task.InternalWaitCore(Int32, System.Threading.CancellationToken) [/_/src/System.Private.CoreLib/shared/System/Threading/Tasks/Task.cs @ 2861]
- 000000470B1EE5D0 00007ffe45121b04 System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(System.Threading.Tasks.Task) [/_/src/System.Private.CoreLib/shared/System/Runtime/CompilerServices/TaskAwaiter.cs @ 143]
- 000000470B1EE600 00007ffe4510482d System.Runtime.CompilerServices.TaskAwaiter.GetResult() [/_/src/System.Private.CoreLib/shared/System/Runtime/CompilerServices/TaskAwaiter.cs @ 106]
- 000000470B1EE630 00007ffe4de36595 Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.Run(Microsoft.Extensions.Hosting.IHost) [/_/src/Hosting/Abstractions/src/HostingAbstractionsHostExtensions.cs @ 49]
- 000000470B1EE660 00007ffde80f3b4b xxx.Program.Main(System.String[])
- 000000470B1EE8B8 00007ffe47c06c93 [GCFrame: 000000470b1ee8b8]
- 000000470B1EEE50 00007ffe47c06c93 [GCFrame: 000000470b1eee50]
如果你稍微了解一点异步的玩法,你应该知道这其中有一个 IO完成端口 的概念,它可以实现 句柄 和 ThreadPool 的绑定,无限递归只不过是进了 IO完成端口 的待回调队列中而已,理论上和栈空间没什么关系,也就不会出现栈溢出了。
三:总结
本次内存泄漏的事故主要还是因为程序员的大意,也许是长期的 996 给弄恍惚了 ??????,有了这些信息,修正起来相信会非常简单。
原文链接:https://mp.weixin.qq.com/s/kf2sIB3LykSsPV_Zg8ncTw