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How Asp.Net Requests Page

As our company delved into asynchronous transfers we noticed that we would get a random application hang every now and then.  We suspected and tried to hunt down a threading problem and along the way we learned some interesting things.

First: Asp.Net queues requests by session to prevent this problem.  Here is our test. First we built a new Page Class with some diagnostic info.

namespace WebApplication3
{
public class TestPage : Page
{

protected override void OnLoad(EventArgs e)
{
Debug.Print("strt\t" + this.GetType().Name + "Load" + " " +this.GetHashCode());
base.OnLoad(e);
Debug.Print(" stop\t" + this.GetType().Name + "Load"+ " " +this.GetHashCode());
}

protected override void OnPreRender(EventArgs e)
{
Debug.Print(" strt\t" + this.GetType().Name + "PreR"+ " " +this.GetHashCode());
base.OnPreRender(e);
Debug.Print(" stop\t" + this.GetType().Name + "PreR"+ " " +this.GetHashCode());

}
}
}
Then I setup the Default Page to add iframes to the source.  
 
public partial class _Default : TestPage
{
protected void Page_Load(object sender, EventArgs e)
{
Thread.Sleep(1000);
for (int i = 0; i < 20; i++)
{
HtmlGenericControl control = new HtmlGenericControl("iframe");
control.Attributes.Add("src", "WebForm1.aspx");
this.Form.Controls.Add(control);
}
}
}
 
Some notes here.  The Thread.Sleep makes sure that the debugger is attached and responding well enough to record things correctly.
 
Finally WebForm1.aspx.  This thing doesnt do anything but inherit from the TestPage with diagnostic information.
namespace WebApplication3
{
public partial class WebForm1 : TestPage
{
protected void Page_Load(object sender, EventArgs e)
{

}
}
}
 

Ok so the first run we make sure EnableSessionState="True" 


What this is supposed to do is make sure that only one request happens at a time.  Here is the log.


strt    default_aspxLoad 53576792
stop    default_aspxLoad 53576792
  strt    default_aspxPreR 53576792
   stop    default_aspxPreR 53576792
strt    webform1_aspxLoad 46058179
strt    webform1_aspxLoad 63986957

stop    webform1_aspxLoad 46058179
  strt    webform1_aspxPreR 46058179
   stop    webform1_aspxPreR 46058179
stop    webform1_aspxLoad 63986957
  strt    webform1_aspxPreR 63986957
   stop    webform1_aspxPreR 63986957
strt    webform1_aspxLoad 58678956
stop    webform1_aspxLoad 58678956
  strt    webform1_aspxPreR 58678956
   stop    webform1_aspxPreR 58678956
strt    webform1_aspxLoad 49300528
stop    webform1_aspxLoad 49300528
  strt    webform1_aspxPreR 49300528
   stop    webform1_aspxPreR 49300528
strt    webform1_aspxLoad 8423152
stop    webform1_aspxLoad 8423152
  strt    webform1_aspxPreR 8423152
   stop    webform1_aspxPreR 8423152
strt    webform1_aspxLoad 32996321
stop    webform1_aspxLoad 32996321
  strt    webform1_aspxPreR 32996321
   stop    webform1_aspxPreR 32996321
strt    webform1_aspxLoad 28848020
stop    webform1_aspxLoad 28848020
  strt    webform1_aspxPreR 28848020
   stop    webform1_aspxPreR 28848020
strt    webform1_aspxLoad 66504299
stop    webform1_aspxLoad 66504299
  strt    webform1_aspxPreR 66504299
   stop    webform1_aspxPreR 66504299
strt    webform1_aspxLoad 47123389
stop    webform1_aspxLoad 47123389
  strt    webform1_aspxPreR 47123389
   stop    webform1_aspxPreR 47123389
strt    webform1_aspxLoad 60889463
stop    webform1_aspxLoad 60889463
  strt    webform1_aspxPreR 60889463
   stop    webform1_aspxPreR 60889463
strt    webform1_aspxLoad 16515137
stop    webform1_aspxLoad 16515137
  strt    webform1_aspxPreR 16515137
   stop    webform1_aspxPreR 16515137
strt    webform1_aspxLoad 10378086
stop    webform1_aspxLoad 10378086
  strt    webform1_aspxPreR 10378086
   stop    webform1_aspxPreR 10378086
strt    webform1_aspxLoad 58791803
stop    webform1_aspxLoad 58791803
  strt    webform1_aspxPreR 58791803
   stop    webform1_aspxPreR 58791803
strt    webform1_aspxLoad 45784774
stop    webform1_aspxLoad 45784774
  strt    webform1_aspxPreR 45784774
   stop    webform1_aspxPreR 45784774
strt    webform1_aspxLoad 31806433
stop    webform1_aspxLoad 31806433
  strt    webform1_aspxPreR 31806433
   stop    webform1_aspxPreR 31806433
strt    webform1_aspxLoad 17398656
stop    webform1_aspxLoad 17398656
  strt    webform1_aspxPreR 17398656
   stop    webform1_aspxPreR 17398656
strt    webform1_aspxLoad 62912648
stop    webform1_aspxLoad 62912648
  strt    webform1_aspxPreR 62912648
   stop    webform1_aspxPreR 62912648
strt    webform1_aspxLoad 50833736
stop    webform1_aspxLoad 50833736
  strt    webform1_aspxPreR 50833736
   stop    webform1_aspxPreR 50833736
strt    webform1_aspxLoad 46154167
stop    webform1_aspxLoad 46154167
  strt    webform1_aspxPreR 46154167
   stop    webform1_aspxPreR 46154167
strt    webform1_aspxLoad 63078365
stop    webform1_aspxLoad 63078365
  strt    webform1_aspxPreR 63078365
   stop    webform1_aspxPreR 63078365

 

So the first request does not seem to be blocking additional requests as seen in red.  Whoops!  We didn't use Session so asp.net hasn't made us a session (this is retarded I know).

So we made a change to TestPage.

public class TestPage : Page
{

protected override void OnLoad(EventArgs e)
{
Session["dumb"] = true;
Debug.Print("strt\t" + this.GetType().Name + "Load" + " " +this.GetHashCode());
base.OnLoad(e);
Debug.Print(" stop\t" + this.GetType().Name + "Load"+ " " +this.GetHashCode());
}

protected override void OnPreRender(EventArgs e)
{
Debug.Print(" strt\t" + this.GetType().Name + "PreR"+ " " +this.GetHashCode());
base.OnPreRender(e);
Debug.Print(" stop\t" + this.GetType().Name + "PreR"+ " " +this.GetHashCode());

}
}

}

 

See now we set ["Dumb"]=true.

 

Ok so here is the next trace with that fix.

 

strt    default_aspxLoad 6100737
stop    default_aspxLoad 6100737
  strt    default_aspxPreR 6100737
   stop    default_aspxPreR 6100737
strt    webform1_aspxLoad 6299240
stop    webform1_aspxLoad 6299240
  strt    webform1_aspxPreR 6299240
   stop    webform1_aspxPreR 6299240
strt    webform1_aspxLoad 50224890
stop    webform1_aspxLoad 50224890
  strt    webform1_aspxPreR 50224890
   stop    webform1_aspxPreR 50224890
strt    webform1_aspxLoad 51844981
stop    webform1_aspxLoad 51844981
  strt    webform1_aspxPreR 51844981
   stop    webform1_aspxPreR 51844981
strt    webform1_aspxLoad 54842390
stop    webform1_aspxLoad 54842390
  strt    webform1_aspxPreR 54842390
   stop    webform1_aspxPreR 54842390
strt    webform1_aspxLoad 44186085
stop    webform1_aspxLoad 44186085
  strt    webform1_aspxPreR 44186085
   stop    webform1_aspxPreR 44186085
strt    webform1_aspxLoad 307537
stop    webform1_aspxLoad 307537
  strt    webform1_aspxPreR 307537
   stop    webform1_aspxPreR 307537
strt    webform1_aspxLoad 36642531
stop    webform1_aspxLoad 36642531
  strt    webform1_aspxPreR 36642531
   stop    webform1_aspxPreR 36642531
strt    webform1_aspxLoad 8761922
stop    webform1_aspxLoad 8761922
  strt    webform1_aspxPreR 8761922
   stop    webform1_aspxPreR 8761922
strt    webform1_aspxLoad 44283204
stop    webform1_aspxLoad 44283204
  strt    webform1_aspxPreR 44283204
   stop    webform1_aspxPreR 44283204
strt    webform1_aspxLoad 37119060
stop    webform1_aspxLoad 37119060
  strt    webform1_aspxPreR 37119060
   stop    webform1_aspxPreR 37119060
strt    webform1_aspxLoad 46442220
stop    webform1_aspxLoad 46442220
  strt    webform1_aspxPreR 46442220
   stop    webform1_aspxPreR 46442220
strt    webform1_aspxLoad 51538364
stop    webform1_aspxLoad 51538364
  strt    webform1_aspxPreR 51538364
   stop    webform1_aspxPreR 51538364
strt    webform1_aspxLoad 65304700
stop    webform1_aspxLoad 65304700
  strt    webform1_aspxPreR 65304700
   stop    webform1_aspxPreR 65304700
strt    webform1_aspxLoad 45154067
stop    webform1_aspxLoad 45154067
  strt    webform1_aspxPreR 45154067
   stop    webform1_aspxPreR 45154067
strt    webform1_aspxLoad 24313979
stop    webform1_aspxLoad 24313979
  strt    webform1_aspxPreR 24313979
   stop    webform1_aspxPreR 24313979
strt    webform1_aspxLoad 30823158
stop    webform1_aspxLoad 30823158
  strt    webform1_aspxPreR 30823158
   stop    webform1_aspxPreR 30823158
strt    webform1_aspxLoad 32261192
stop    webform1_aspxLoad 32261192
  strt    webform1_aspxPreR 32261192
   stop    webform1_aspxPreR 32261192
strt    webform1_aspxLoad 5695327
stop    webform1_aspxLoad 5695327
  strt    webform1_aspxPreR 5695327
   stop    webform1_aspxPreR 5695327
strt    webform1_aspxLoad 14547257
stop    webform1_aspxLoad 14547257
  strt    webform1_aspxPreR 14547257
   stop    webform1_aspxPreR 14547257
strt    webform1_aspxLoad 65008279
stop    webform1_aspxLoad 65008279
  strt    webform1_aspxPreR 65008279
   stop    webform1_aspxPreR 65008279

So great!  It finally works.  Now lets break it on purpose.  We setup this line in both pages.
EnableSessionState="ReadOnly"
 

Here is our log we can see that the first 2 requests to webform1 are made at the same time causing  a thread exception.

strt    default_aspxLoad 22177797
stop    default_aspxLoad 22177797
  strt    default_aspxPreR 22177797
   stop    default_aspxPreR 22177797
strt    webform1_aspxLoad 58758044
strt    webform1_aspxLoad 60402358
stop    webform1_aspxLoad 60402358
stop    webform1_aspxLoad 58758044
  strt    webform1_aspxPreR 60402358
  strt    webform1_aspxPreR 58758044
   stop    webform1_aspxPreR 60402358
   stop    webform1_aspxPreR 58758044
strt    webform1_aspxLoad 33970112
stop    webform1_aspxLoad 33970112
  strt    webform1_aspxPreR 33970112
   stop    webform1_aspxPreR 33970112
strt    webform1_aspxLoad 12544008
stop    webform1_aspxLoad 12544008
  strt    webform1_aspxPreR 12544008
   stop    webform1_aspxPreR 12544008
strt    webform1_aspxLoad 47231162
stop    webform1_aspxLoad 47231162
  strt    webform1_aspxPreR 47231162
   stop    webform1_aspxPreR 47231162
strt    webform1_aspxLoad 63638306
stop    webform1_aspxLoad 63638306
  strt    webform1_aspxPreR 63638306
   stop    webform1_aspxPreR 63638306
strt    webform1_aspxLoad 57701674
stop    webform1_aspxLoad 57701674
  strt    webform1_aspxPreR 57701674
   stop    webform1_aspxPreR 57701674
strt    webform1_aspxLoad 29746117
stop    webform1_aspxLoad 29746117
  strt    webform1_aspxPreR 29746117
   stop    webform1_aspxPreR 29746117
strt    webform1_aspxLoad 3884878
stop    webform1_aspxLoad 3884878
  strt    webform1_aspxPreR 3884878
   stop    webform1_aspxPreR 3884878
strt    webform1_aspxLoad 45476154
stop    webform1_aspxLoad 45476154
  strt    webform1_aspxPreR 45476154
   stop    webform1_aspxPreR 45476154
strt    webform1_aspxLoad 42317455
stop    webform1_aspxLoad 42317455
  strt    webform1_aspxPreR 42317455
   stop    webform1_aspxPreR 42317455
strt    webform1_aspxLoad 60918874
stop    webform1_aspxLoad 60918874
  strt    webform1_aspxPreR 60918874
   stop    webform1_aspxPreR 60918874
strt    webform1_aspxLoad 54806812
stop    webform1_aspxLoad 54806812
  strt    webform1_aspxPreR 54806812
   stop    webform1_aspxPreR 54806812
strt    webform1_aspxLoad 59055457
stop    webform1_aspxLoad 59055457
  strt    webform1_aspxPreR 59055457
   stop    webform1_aspxPreR 59055457
strt    webform1_aspxLoad 64646201
stop    webform1_aspxLoad 64646201
  strt    webform1_aspxPreR 64646201
   stop    webform1_aspxPreR 64646201
strt    webform1_aspxLoad 62849758
stop    webform1_aspxLoad 62849758
  strt    webform1_aspxPreR 62849758
   stop    webform1_aspxPreR 62849758
strt    webform1_aspxLoad 26235852
stop    webform1_aspxLoad 26235852
  strt    webform1_aspxPreR 26235852
strt    webform1_aspxLoad 2135755
stop    webform1_aspxLoad 2135755
   stop    webform1_aspxPreR 26235852
  strt    webform1_aspxPreR 2135755
   stop    webform1_aspxPreR 2135755
strt    webform1_aspxLoad 6565686
stop    webform1_aspxLoad 6565686
  strt    webform1_aspxPreR 6565686
   stop    webform1_aspxPreR 6565686
strt    webform1_aspxLoad 8372655
stop    webform1_aspxLoad 8372655
  strt    webform1_aspxPreR 8372655
   stop    webform1_aspxPreR 8372655

So in summary asp.net only makes one request at a time as long as you initialize the session, set the EnableSessionState=True (which is the default).  So if you think Asp.Net is causing threading issues think again.

1 comment:

Home Automation said...

Michael, I am trying to read from a com port in Silverlight. Using your code, i can write to COM port but I cannot read any commands com.ReadString(). Silverlight Textbox is not showing any commands that the com port is receiving. I am wondering if the com.ReadString is blocking any threads. Can you please provide your code and see if you can still read com ports?