.NET Framework 4.7 breaking Web Forms Page Cache

Question

User-227976983 posted

In an ASP.NET webforms context (FYI - .NET Framework 4.5.1 project), the following code works when .NET Framework 4.7 is not installed. But when Framework 4.7 is installed (which came out today), I get a NullReference exception.

public class Default : System.Web.UI.Page
{ 
  protected override void OnInit(EventArgs e) {
      string key = "key", data = "data";
      Cache.Insert(key, data, null, DateTime.Now.AddMinutes(5), TimeSpan.Zero);
      Cache[key].ToString(); // Throws NRE when 4.7 installed
  }
}

After debugging I've determined the item is being added to the cache and then immediately deleted. I found two workarounds:

1. Web.config

  <system.web>
...
    <caching>
       <cache disableExpiration="true"/>
    </caching>
...
  </system.web>

2. Change insert statement to this

Cache.Insert(key, data, null, DateTime.Now.AddMinutes(5),
   TimeSpan.Zero, CacheItemPriority.Normal, 
   (key,value,removal)=> { });

I'm very confused as to what I'm doing wrong in my first cache statement that works fine before installing v4.7. Is this a bug?

Thanks,

Fungus Man

Answer 1

User-158764254 posted

you're using conflicting arguments.  When using an absolute expiration you should not use a timespan.zero.

instead try this:

Cache.Insert(key, data, null, DateTime.Now.AddMinutes(5), System.Web.Caching.Cache.NoSlidingExpiration);

https://msdn.microsoft.com/en-us/library/4y13wyk9(v=vs.110).aspx

https://msdn.microsoft.com/en-us/library/system.web.caching.cache.noslidingexpiration(v=vs.110).aspx

Answer 2

User-227976983 posted

Hi

Thanks for your response. Tried that - exact same result. Item not being held in cache. Now Im convinced there is a bug with that insert method in .net 4.7.

Answer 3

User-227976983 posted

Actually this is a serious issue - how can I report this bug to microsoft and how long would it take to get it fixed? I dont want to use that web.config setting and Im not sure rewriting my code is use another method is appropriate.

Answer 4

User475983607 posted

Actually this is a serious issue - how can I report this bug to microsoft and how long would it take to get it fixed? I dont want to use that web.config setting and Im not sure rewriting my code is use another method is appropriate.

Your code does not wok in 4.6 either.  However, mbanavige's suggestion does work which I verified. 

Answer 5

User-227976983 posted

Thanks mgebhard - I am not sure if you caught my note in my original question: project Target framework isn't 4.7, its actually 4.5.1. All I did was install 4.7 on two servers and my workstation and neither mbanavige's nor my original code works. Its strange that the other functions accept my parameters too...

Can you, or anyone, please test the scenario I mentioned? Maybe there is a set up issue on my side.

Answer 6

User753101303 posted

Hi,

And what if you try :

Cache.Insert(key, data, null,  DateTime.UtcNow.AddMinutes(5), System.Web.Caching.Cache.NoSlidingExpiration);

 

Answer 7

User475983607 posted

ahmad.fungus

Thanks mgebhard - I am not sure if you caught my note in my original question: project Target framework isn't 4.7, its actually 4.5.1. All I did was install 4.7 on two servers and my workstation and neither mbanavige's nor my original code works. Its strange that the other functions accept my parameters too...

Can you, or anyone, please test the scenario I mentioned? Maybe there is a set up issue on my side.

I have 4.7 installed and cannot reproduce this issue.  I can only reproduce the bug if I target a framework 4.6+.  I suspect there might be other issues in the code base.

Answer 8

User-1084200161 posted

It's a bug in Cache.Insert.. you're not doing anything wrong..

You'd have to use one of the workarounds for now until this is addressed (which should be next release)..

If you can use this overload:  Cache.Insert  (String, Object, CacheDependency, DateTime, TimeSpan, CacheItemPriority, CacheItemRemovedCallback)  -- that one does not have the same bug as the Insert overload you're using..  so that should work too...  Docs for this overload https://msdn.microsoft.com/en-us/library/05kd8d77(v=vs.110).aspx

PS.  You do not need to report this bug to MSFT.. it's already been reported/noted.

Answer 9

User753101303 posted

Just installed 4.7 and on my side it seems to work just fine on my dev machine. Also if using the removal callback I can see it happens roughly when expected.

Answer 10

User-1084200161 posted

Reflect the code in that Cache.Insert overload and you'll spot the problem in about 2 seconds ;)  Especially if you then compare it with other Insert overloads that do not have this issue..

Answer 11

User475983607 posted

Reflect the code in that Cache.Insert overload and you'll spot the problem in about 2 seconds ;)  Especially if you then compare it with other Insert overloads that do not have this issue..

That's a vague response.  Can you elaborate on what you found?  Or where the bug is documented?  

I looked at the source code it looks like the right version...  

https://github.com/Microsoft/referencesource/blob/master/System.Web/Cache/cache.cs

As far as I can tell the mbanavige's answer is correct and documented in the source  well as the MS docs.  

        //
        // Summary:
        //     Used as the slidingExpiration parameter in an System.Web.Caching.Cache.Insert(System.String,System.Object)
        //     or System.Web.Caching.Cache.Add(System.String,System.Object,System.Web.Caching.CacheDependency,System.DateTime,System.TimeSpan,System.Web.Caching.CacheItemPriority,System.Web.Caching.CacheItemRemovedCallback)
        //     method call to disable sliding expirations. This field is read-only.
        public static readonly TimeSpan NoSlidingExpiration;

I suppose the method could check if the user passed TimeSpan.Zero then add the NoSlidingExpiration member to the  CacheInsertOptions() object rather than the user's argument. That might be a bit more user friendly.

Again. my finding are framework 4.5 is tolerant of TimeSpan.Zero while 4.6+ is not.  I have 4.7 installed on my machine which does not affect 4.5 as the OP suggests. If I change the target framework, that does cause a problem using TimeSpan.Zero.

Please explain what I'm missing.

Answer 12

User-1084200161 posted

Line 425 in that reference source you posted is the problem... 

Expiration timestamp is converted to UTC, but then they don't use UTC (they mistakenly use original argument into the function)... Line 425 should have had utcAbsoluteExpiration declared on LIne 422... (instead of absoluteExpiration)... and it's an oversight, unfortunately..  this is not documented anywhere (yet).

TimeSpan.Zero vs NoSlidingExpiration is not the issue, because NoSlidingExpiration *is* TimeSpan.Zero :) so it does not matter which one you put in there.. they're same.

Line 182:

public static readonly TimeSpan NoSlidingExpiration = TimeSpan.Zero;

Answer 13

User475983607 posted

Ah, got it... thanks

Answer 14

User1300272511 posted

You are right. Looks like a bug in System.Web/Cache/cache.cs and with new update it is causing issues.

Answer 15

User753101303 posted

I suspected something related and this is why I suggested earlier to pass explicitely UtcNow.AddMinutes(5) in the call and see what happens.

Answer 16

User-227976983 posted

Thanks all. I guess its not likely this will be fixed any time soon.. :(

Answer 17

User753101303 posted

And you tried/considered using explicitely DateTime.UtcNow.AddMinutes(5) as suggested earlier twice ? It seems to me it would be an easy fix and it doesn't need to be changed back once the underlying bug is fixed.