一：背景

1. 講故事

上個(gè)月中旬，星球里的一位朋友在微信找我，說(shuō)他的程序跑著跑著內(nèi)存會(huì)不斷的緩慢增長(zhǎng)并無(wú)法釋放，尋求如何解決 ？

得，看樣子星球還得好好弄！！！😂😂😂 ?不管怎么說(shuō)，先上 windbg 說(shuō)話。

二：Windbg 分析

1. 經(jīng)驗(yàn)推理

從朋友的截圖看，有大量的 8216 字節(jié)的 byte[]，這表示什么呢？追隨本系列的朋友應(yīng)該知道，有一篇 某三甲醫(yī)院 的內(nèi)存暴漲的dump中，也同樣有此 size= (8216-24=8192) 的 byte[] 數(shù)組， 他的問(wèn)題是 Oracle 中讀取某大字段時(shí)sdk里的 OraBuf 出了問(wèn)題，換句話說(shuō)，這肯定又是底層或者第三方庫(kù)中的池對(duì)象搞出來(lái)的東西，接下來(lái)從 托管堆 看起。

2. 查看托管堆

0:000>?!dumpheap?-stat Statistics: 00007ffe107248f0???483707?????15478624?System.Threading.PreAllocatedOverlapped 00007ffe1079c160???483744?????15479808?System.Threading.ThreadPoolBoundHandle 00007ffe1079cff8???483701?????23217648?System.Threading._IOCompletionCallback 00007ffe106e7a90???483704?????23217792?Microsoft.Win32.SafeHandles.SafeFileHandle 00007ffe1079b088???483703?????30956992?System.IO.FileSystemWatcher+AsyncReadState 00007ffe1079ceb0???483707?????34826904?System.Threading.OverlappedData 00007ffe1079ccb0???483707?????34826904?System.Threading.ThreadPoolBoundHandleOverlapped 0000016c64651080???245652???1473128080??????Free 00007ffe105abf30???488172???3977571092?System.Byte[]

掃完托管堆，臥槽 ，byte[] 沒(méi)吸引到我，反而被 System.IO.FileSystemWatcher+AsyncReadState 吸引到了，畢竟被 System.IO.FileSystemWatcher 折騰多次了，它已經(jīng)深深打入了我的腦海。。。畢竟讓程序卡死，讓句柄爆高的都是它。。。這一回八成又是它惹的禍，看樣子還是有很多程序員栽在這里哈。

為做到嚴(yán)謹(jǐn)，我還是從最大的 System.Byte[] 入手，按size對(duì)它進(jìn)行分組再按totalsize降序，丑陋的腳本我就不發(fā)了，直接上腳本的輸出結(jié)果。

!dumpheap?-mt?00007ffe105abf30 size=8216,count=483703,totalsize=3790M size=8232,count=302,totalsize=2M size=65560,count=6,totalsize=0M size=131096,count=2,totalsize=0M size=4120,count=11,totalsize=0M size=56,count=301,totalsize=0M size=88,count=186,totalsize=0M size=848,count=16,totalsize=0M size=152,count=85,totalsize=0M size=46,count=242,totalsize=0M size=279,count=38,totalsize=0M!dumpheap?-mt?00007ffe105abf30?-min?0n8216?-max?0n8216?-short0000016c664277f0 0000016c66432a48 0000016c6648ef88 0000016c6649daa8 0000016c6649fb00 0000016c664a8b90 ...

從輸出結(jié)果看，size=8216 的 byte[] 有 48w 個(gè)，然后腳本也列出了一些 8216 大小的 address 地址，接下來(lái)用 !gcroot 看下這些地址的引用。

0:000>?!gcroot?0000016c664277f0 HandleTable:0000016C65FC28C0?(async?pinned?handle)->?0000016C6628DEB0?System.Threading.OverlappedData->?0000016C664277F0?System.Byte[]Found?1?unique?roots?(run?'!gcroot?-all'?to?see?all?roots). 0:000>?!gcroot?0000016c667c80d0 HandleTable:0000016C65FB7920?(async?pinned?handle)->?0000016C663260F8?System.Threading.OverlappedData->?0000016C667C80D0?System.Byte[]

從輸出中可以看到這些 byte[] 都是 async pinned，也就是當(dāng)異步IO回來(lái)的時(shí)候需要給 byte[] 填充的存儲(chǔ)空間，接下來(lái)我們看看如何通過(guò) OverlappedData 找到源碼中定義為 8192 大小的 byte[] 地方。

如果你了解 FileSystemWatcher ，反向查找鏈大概是這樣的 OverlappedData -> ThreadPoolBoundHandleOverlapped -> System.IO.FileSystemWatcher+AsyncReadState -> Buffer[]， 這中間涉及到 ThreadPool 和 SafeHandle 的綁定。

0:000>?!do?0000016C663260F8 Name:????????System.Threading.OverlappedData MethodTable:?00007ffe1079ceb0 EEClass:?????00007ffe107ac8d0 Size:????????72(0x48)?bytes File:????????C:\Program?Files\dotnet\shared\Microsoft.NETCore.App\5.0.10\System.Private.CoreLib.dll Fields:MT????Field???Offset?????????????????Type?VT?????Attr????????????Value?Name 00007ffe106e3c08??40009ce????????8??System.IAsyncResult??0?instance?0000000000000000?_asyncResult 00007ffe104a0c68??40009cf???????10????????System.Object??0?instance?0000016c66326140?_callback 00007ffe1079cb60??40009d0???????18?...eading.Overlapped??0?instance?0000016c663260b0?_overlapped 00007ffe104a0c68??40009d1???????20????????System.Object??0?instance?0000016c667c80d0?_userObject 00007ffe104af508??40009d2???????28??????????????????PTR??0?instance?00000171728f66e0?_pNativeOverlapped 00007ffe104aee60??40009d3???????30????????System.IntPtr??1?instance?0000000000000000?_eventHandle 00007ffe104ab258??40009d4???????38?????????System.Int32??1?instance????????????????0?_offsetLow 00007ffe104ab258??40009d5???????3c?????????System.Int32??1?instance????????????????0?_offsetHigh 0:000>?!do?0000016c663260b0 Name:????????System.Threading.ThreadPoolBoundHandleOverlapped MethodTable:?00007ffe1079ccb0 EEClass:?????00007ffe107ac858 Size:????????72(0x48)?bytes File:????????C:\Program?Files\dotnet\shared\Microsoft.NETCore.App\5.0.10\System.Private.CoreLib.dll Fields:MT????Field???Offset?????????????????Type?VT?????Attr????????????Value?Name 00007ffe1079ceb0??40009d6????????8?...ng.OverlappedData??0?instance?0000016c663260f8?_overlappedData 00007ffe1079b818??40009c0???????10?...ompletionCallback??0?instance?0000016f661ab8a0?_userCallback 00007ffe104a0c68??40009c1???????18????????System.Object??0?instance?0000016c667ca0e8?_userState 00007ffe107248f0??40009c2???????20?...locatedOverlapped??0?instance?0000016c66326090?_preAllocated 00007ffe104af508??40009c3???????30??????????????????PTR??0?instance?00000171728f66e0?_nativeOverlapped 00007ffe1079c160??40009c4???????28?...adPoolBoundHandle??0?instance?0000000000000000?_boundHandle 00007ffe104a7238??40009c5???????38???????System.Boolean??1?instance????????????????0?_completed 00007ffe1079b818??40009bf??????738?...ompletionCallback??0???static?0000016f661ab990?s_completionCallback 0:000>?!do?0000016c667ca0e8 Name:????????System.IO.FileSystemWatcher+AsyncReadState MethodTable:?00007ffe1079b088 EEClass:?????00007ffe107a9dc0 Size:????????64(0x40)?bytes File:????????C:\Program?Files\dotnet\shared\Microsoft.NETCore.App\5.0.10\System.IO.FileSystem.Watcher.dll Fields:MT????Field???Offset?????????????????Type?VT?????Attr????????????Value?Name 00007ffe104ab258??400002b???????30?????????System.Int32??1?instance????????????????1?<Session>k__BackingField 00007ffe105abf30??400002c????????8????????System.Byte[]??0?instance?0000016c667c80d0?<Buffer>k__BackingField 00007ffe106e7a90??400002d???????10?...es.SafeFileHandle??0?instance?0000016c66326028?<DirectoryHandle>k__BackingField 00007ffe1079c160??400002e???????18?...adPoolBoundHandle??0?instance?0000016c66326058?<ThreadPoolBinding>k__BackingField 00007ffe107248f0??400002f???????20?...locatedOverlapped??0?instance?0000016c66326090?<PreAllocatedOverlapped>k__BackingField 00007ffe1079b8c8??4000030???????28?...eSystem.Watcher]]??0?instance?0000016c66326078?<WeakWatcher>k__BackingField

上面的 <Buffer>k__BackingField 就是當(dāng)初丟給 OverlappedData 作為 異步IO 讀寫(xiě)的緩沖，然后看下 System.IO.FileSystemWatcher+AsyncReadState 的源碼。

有了這些原理之后，接下來(lái)就可以問(wèn)朋友是否有對(duì) appsettings 設(shè)置了 reloadonchange=true 的情況，朋友找了下代碼，寫(xiě)法大概如下：

public?object?GetxxxFlag() {string?value?=?AppConfig.GetConfig("appsettings.json").GetValue("xxxx",?"0");return?new{state?=?200,data?=?value}; }public?class?AppConfig {public?static?AppConfig?GetConfig(string?settingfile?=?"appsettings.json"){return?new?AppConfig(settingfile);} }public?class?AppConfig {private?AppConfig(string?settingfile){_config?=?new?ConfigurationBuilder().AddJsonFile(settingfile,?optional:?true,?reloadOnChange:?true).Build();_settingfile?=?settingfile;} }

從源碼邏輯看，我猜測(cè)朋友將 ?GetConfig 方法標(biāo)記成 static 后就以為是單例化了，再次調(diào)用不會(huì)重復(fù) new AppConfig(settingfile)，所以問(wèn)題就出在這里。

不過(guò)有意思的是，前面二篇的 FileSystemWatcher 都會(huì)造成程序卡死，那這一篇為啥沒(méi)有呢？恰好他沒(méi)有在程序根目錄中放日志文件，不然的話。。。😄😄😄，可萬(wàn)萬(wàn)沒(méi)想到逃過(guò)了卡死卻沒(méi)逃過(guò)一個(gè) watcher 默認(rèn) 8byte 空間的靈魂拷問(wèn)。。。😂😂😂

三：總結(jié)

總的來(lái)說(shuō)，設(shè)置 reloadOnChange: true 一定要慎重， 可能它會(huì)造成你的程序卡死，句柄泄漏，內(nèi)存泄漏 等等！！！改進(jìn)方案我就不說(shuō)了，參考我前面的系列文章吧。

END

工作中的你，是否已遇到 ...?

1. CPU爆高

2. 內(nèi)存暴漲

3. 資源泄漏

4. 崩潰死鎖

5. 程序呆滯

等緊急事件，全公司都指望著你能解決...? 危難時(shí)刻才能展現(xiàn)你的技術(shù)價(jià)值，作為專注于.NET高級(jí)調(diào)試的技術(shù)博主，歡迎微信搜索: 一線碼農(nóng)聊技術(shù)，免費(fèi)協(xié)助你分析Dump文件，希望我能將你的踩坑經(jīng)驗(yàn)分享給更多的人。

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總結(jié)

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