實例化NSObject導致內存不足崩潰

Question

運行下面的代碼時，應用程序在下面的堆棧跟蹤中崩潰（約30秒後）。我覺得這很奇怪，因爲我期望垃圾收集器清理這個內存。我們的應用程序有一個類似的模式，並與類似的堆棧跟蹤崩潰。

註釋掉實例化NSObject成員的行使應用程序運行時不會崩潰。將實例化字節數組的行註釋掉會使應用運行更長時間，但仍然崩潰。

樂器報告一個非常好的恆定實時字節爲應用程序和儀器會導致應用程序運行更長時間沒有崩潰，但它仍然崩潰（大約10分鐘後）。不斷的Live Bytes讓我感覺垃圾收集器正在工作。

代碼：

using System.Threading; 
using MonoTouch.Foundation; 
using MonoTouch.UIKit; 

namespace MyExample 
{ 
    public class Application 
    { 
     static void Main (string[] args) 
     { 
      UIApplication.Main(args); 
     } 
    } 

    public partial class AppDelegate : UIApplicationDelegate 
    { 
     public override bool FinishedLaunching (UIApplication app, NSDictionary options) 
     { 
      Thread testThread = new Thread(BreakMe); 
      testThread.Start(); 

      window.MakeKeyAndVisible(); 
      return true; 
     } 

     private void BreakMe() 
     { 
      while(true) 
      { 
       using (var arPool = new NSAutoreleasePool()) 
       { 
        MyGarbage garbage = new MyGarbage(); 
       } 
      } 
     } 

     private class MyGarbage 
     { 
      byte[] _Foo = new byte[100000]; 
      NSObject _Bar = new NSObject(); 
     } 
    } 
} 

應用程序輸出：

Mprotect failed at 0x493c000 (length 4096) with errno 12 
Stacktrace: 

    at (wrapper managed-to-native) System.Array.CreateInstanceImpl (System.Type,int[],int[]) <0xffffffff> 
    at System.Array.CreateInstance (System.Type,int[]) <0x000bc> 
    at System.Array.CreateInstance (System.Type,int) <0x00057> 
    at System.MonoCustomAttrs.GetCustomAttributes (System.Reflection.ICustomAttributeProvider,System.Type,bool) <0x000db> 
    at System.MonoCustomAttrs.GetCustomAttribute (System.Reflection.ICustomAttributeProvider,System.Type,bool) <0x00033> 
    at System.Attribute.GetCustomAttribute (System.Reflection.MemberInfo,System.Type,bool) <0x0003f> 
    at MonoTouch.ObjCRuntime.Class.GetHandle (System.Type) <0x00037> 
    at MonoTouch.Foundation.NSObject.AllocIfNeeded() <0x00063> 
    at MonoTouch.Foundation.NSObject..ctor (MonoTouch.Foundation.NSObjectFlag) <0x00027> 
    at MonoTouch.Foundation.NSAutoreleasePool..ctor() <0x00037> 
    at MyExample.AppDelegate.BreakMe() [0x00000] in Main.cs:30 
    at (wrapper runtime-invoke) object.runtime_invoke_dynamic (intptr,intptr,intptr,intptr) <0x000cb> 

Native stacktrace: 

    0 MyExample      0x002db308 mono_handle_native_sigsegv + 404 
    1 MyExample      0x002fa5dc sigabrt_signal_handler + 148 
    2 libsystem_c.dylib     0x369c972f _sigtramp + 42 
    3 libsystem_c.dylib     0x369be3bb pthread_kill + 58 
    4 libsystem_c.dylib     0x369b6bff abort + 78 
    5 MyExample      0x0041e484 GC_remap + 200 
    6 MyExample      0x00411ee4 GC_allochblk_nth + 1536 
    7 MyExample      0x00411894 GC_allochblk + 96 
    8 MyExample      0x0041d94c GC_new_hblk + 116 
    9 MyExample      0x00413c3c GC_allocobj + 188 
    10 MyExample      0x0041859c GC_generic_malloc_inner + 352 
    11 MyExample      0x004187ac GC_generic_malloc + 132 
    12 MyExample      0x00418c60 GC_malloc + 208 
    13 MyExample      0x003a67dc mono_object_allocate + 64 
    14 MyExample      0x003a7240 mono_array_new_full + 828 
    15 MyExample      0x00341324 ves_icall_System_Array_CreateInstanceImpl + 896 
    16 MyExample      0x0012cf3c (wrapper managed-to-native) System.Array:CreateInstanceImpl (System.Type,int[],int[]) + 80 
    17 MyExample      0x0012d23c System.Array:CreateInstance (System.Type,int) + 88 
    18 MyExample      0x0018b70c System.MonoCustomAttrs:GetCustomAttributes (System.Reflection.ICustomAttributeProvider,System.Type,bool) + 220 
    19 MyExample      0x0018b560 System.MonoCustomAttrs:GetCustomAttribute (System.Reflection.ICustomAttributeProvider,System.Type,bool) + 52 
    20 MyExample      0x00131fd0 System.Attribute:GetCustomAttribute (System.Reflection.MemberInfo,System.Type,bool) + 64 
    21 MyExample      0x000795ec MonoTouch.ObjCRuntime.Class:GetHandle (System.Type) + 56 
    22 MyExample      0x00077e60 MonoTouch.Foundation.NSObject:AllocIfNeeded() + 100 
    23 MyExample      0x0007779c MonoTouch.Foundation.NSObject:.ctor (MonoTouch.Foundation.NSObjectFlag) + 40 
    24 MyExample      0x00074d10 MonoTouch.Foundation.NSAutoreleasePool:.ctor() + 56 
    25 MyExample      0x00002c34 MyExample.AppDelegate:BreakMe() + 164 
    26 MyExample      0x001f3e3c (wrapper runtime-invoke) object:runtime_invoke_dynamic (intptr,intptr,intptr,intptr) + 204 
    27 MyExample      0x002c4658 mono_jit_runtime_invoke + 3032 
    28 MyExample      0x003a34a8 mono_runtime_invoke + 140 
    29 MyExample      0x003a48f0 mono_runtime_delegate_invoke + 136 
    30 MyExample      0x003cb31c start_wrapper + 752 
    31 MyExample      0x003f09a0 thread_start_routine + 240 
    32 MyExample      0x0041f9ac GC_start_routine + 132 
    33 libsystem_c.dylib     0x369be311 _pthread_start + 248 
    34 libsystem_c.dylib     0x369bfbbc start_wqthread + 0 

Answer 1

對此的真實答案是，懷疑是Why is our MonoTouch app breaking in the garbage collector? It is not out of memory問題，這是內存管理器問題。堆棧跟蹤對我來說非常熟悉。

Answer 2

你已經把分配器與垃圾收集賽跑。如果您對演示進行簡單更改並添加：

System.GC.Collect(); 

在循環中，您將看到它不再崩潰。

這裏發生了什麼是你正在儘可能快地分配。當GC耗盡內存時，它將擴展堆並收集。接下來的幾次循環運行時間更長，然後由於堆積較大而再次收集，但最終比賽丟失。

在我放棄之前，對上述的小修改進行了10分鐘的測試。