一：背景

1. 讲故事

上个月有位朋友通过博客园的短消息找到我，说他的程序存在内存溢出情况，寻求如何解决。

要解决还得通过 windbg 分析啦。

二：Windbg 分析

1. 为什么会内存溢出

大家都知道内存溢出对应着 .NET 中的 OutOfMemoryException 异常，这种异常有可能是托管代码手工抛出的，也有可能是CLR层面抛出的，言外之意就是可以通过两种方式排查。

• 托管线程是否挂载着异常？

0:000> !t
ThreadCount:      23
UnstartedThread:  0
BackgroundThread: 5
PendingThread:    0
DeadThread:       17
Hosted Runtime:   no
                                                                         Lock  
       ID OSID ThreadOBJ    State GC Mode     GC Alloc Context  Domain   Count Apt Exception
   0    1 362c 00fac868     26020 Preemptive  7ED701A0:00000000 00fa6b60 0     STA 
   5    2 2d70 00fbeba0     2b220 Preemptive  7EBA7AC0:00000000 00fa6b60 0     MTA (Finalizer) 
   7    3 3264 061c8890   102a220 Preemptive  00000000:00000000 00fa6b60 0     MTA (Threadpool Worker) 
  17   15 3f98 19682b90   202b220 Preemptive  7EBB0830:00000000 00fa6b60 0     MTA 
XXXX   16    0 2845fb00     35820 Preemptive  00000000:00000000 00fa6b60 0     Ukn 
  18   14  a7c 2842b1c8   202b220 Preemptive  00000000:00000000 00fa6b60 0     MTA 
XXXX    6    0 2c9b3778   1039820 Preemptive  00000000:00000000 00fa6b60 0     Ukn (Threadpool Worker) 
XXXX   18    0 288a1318   1039820 Preemptive  00000000:00000000 00fa6b60 0     Ukn (Threadpool Worker) 
XXXX   23    0 288a22f0   1039820 Preemptive  00000000:00000000 00fa6b60 0     Ukn (Threadpool Worker) 
XXXX   10    0 2ccf3550   1039820 Preemptive  00000000:00000000 00fa6b60 0     Ukn (Threadpool Worker) 
XXXX   21    0 288a1860   1039820 Preemptive  00000000:00000000 00fa6b60 0     Ukn (Threadpool Worker) 
XXXX   12    0 288a1da8   1039820 Preemptive  00000000:00000000 00fa6b60 0     Ukn (Threadpool Worker) 
XXXX   11    0 2c993640   1039820 Preemptive  00000000:00000000 00fa6b60 0     Ukn (Threadpool Worker) 
XXXX    8    0 2ccf3a98     35820 Preemptive  00000000:00000000 00fa6b60 0     Ukn 
XXXX    9    0 2ccf2030   1039820 Preemptive  00000000:00000000 00fa6b60 0     Ukn (Threadpool Worker) 
XXXX    7    0 2c9aed88   1039820 Preemptive  00000000:00000000 00fa6b60 0     Ukn (Threadpool Worker) 
XXXX   26    0 28898308   1039820 Preemptive  00000000:00000000 00fa6b60 0     Ukn (Threadpool Worker) 
XXXX   25    0 2c492c68   1039820 Preemptive  00000000:00000000 00fa6b60 0     Ukn (Threadpool Worker) 
XXXX    4    0 2c993b88   1039820 Preemptive  00000000:00000000 00fa6b60 0     Ukn (Threadpool Worker) 
XXXX   20    0 2c9af2d0   1039820 Preemptive  00000000:00000000 00fa6b60 0     Ukn (Threadpool Worker) 
XXXX   17    0 2c9afd60   1039820 Preemptive  00000000:00000000 00fa6b60 0     Ukn (Threadpool Worker) 
XXXX   24    0 2c9b1280   1039820 Preemptive  00000000:00000000 00fa6b60 0     Ukn (Threadpool Worker) 
  23   22 2658 2c9b02a8   1029220 Preemptive  7ED5BFF8:00000000 00fa6b60 0     MTA (Threadpool Worker) 

从输出信息看，这些线程并没有挂载任何托管异常，我去。。。

• 是否在 CLR 上抛出

这主要是看 托管堆(heap) 上的内存分配或者gc回收造成的内存不足，可以用 !ao 命令。

0:000> !ao
There was no managed OOM due to allocations on the GC heap

从输出信息看也没有任何异常，尴尬了