B4J Question Wait For and Ctrl+S causing 'java.lang.NullPointerException'

cyiwin · Sep 8, 2019

I'm trying to use 'Wait For'. It works but whenever I do a code change in debug mode and press ctrl+s, my program crashes.

here is an example of what I'm doing.

B4X:

Sub Process_Globals
    Private fx As JFX
    Private MainForm As Form
End Sub

Sub AppStart (Form1 As Form, Args() As String)
    MainForm = Form1
    Wait For (Job_Current_Time) Complete (Success As Boolean)
    Log("Job_Current_Time = " & Success)
End Sub

Sub Job_Current_Time As ResumableSub
    Log("Http.Get_Current_Time")
    Dim job As HttpJob : job.Initialize("", Me)
    job.Download("http://worldtimeapi.org/api/timezone/America/Los_Angeles")
    
    Wait For (job) JobDone(job As HttpJob)
    If job.Success Then
        Dim jobstring As String = job.GetString
        Dim JSON As JSONParser : JSON.Initialize(jobstring)
        Dim m As Map = JSON.NextObject
        Log(m)
    Else
        LogError(job.JobName & "     " & job.ErrorMessage)
    End If
    job.Release
    
    Return job.Success
End Sub

On my computer, placing a break point (red dot) anywhere in Subs AppStart or Job_Current_Time and using ctrl+s causes the error "java.lang.NullPointerException". Where is my mistake?

Thanks

amykonio · Sep 8, 2019

What version of B4J are you using? In 7.80 (current beta) it works fine.
I do a change in debug mode, and I save it without any error.

DonManfred · Sep 8, 2019

cyiwin said:
job.Release

Return job.Success

you are accessing the job after you released it.

B4X:

Sub Job_Current_Time As ResumableSub
    dim success as boolean
    Log("Http.Get_Current_Time")
    Dim job As HttpJob : job.Initialize("", Me)
    job.Download("http://worldtimeapi.org/api/timezone/America/Los_Angeles")
    
    Wait For (job) JobDone(job As HttpJob)
    success = job.success
    If job.Success Then
        Dim jobstring As String = job.GetString
        Dim JSON As JSONParser : JSON.Initialize(jobstring)
        Dim m As Map = JSON.NextObject
        Log(m)
    Else
        LogError(job.JobName & "     " & job.ErrorMessage)
    End If
    job.Release
    
    Return success
End Sub

amykonio · Sep 8, 2019

DonManfred said:
you are accessing the job after you released it.

You are right. He is doing that but for some reason when I debug that part of code in beta (7.80) it works...

cyiwin · Sep 8, 2019

Thanks for the replies.

DonManfred said:
you are accessing the job after you released it.

I updated the code so it doesn't return Job.Success. I still get the same error.

B4X:

Sub Process_Globals
    Private fx As JFX
    Private MainForm As Form
End Sub

Sub AppStart (Form1 As Form, Args() As String)
    MainForm = Form1
    Wait For (Job_Current_Time) Complete (Success As Boolean)
    Log("Job_Current_Time = " & Success)
End Sub

Sub Job_Current_Time As ResumableSub
    Log("Http.Get_Current_Time")
    Dim job As HttpJob : job.Initialize("", Me)
    job.Download("http://worldtimeapi.org/api/timezone/America/Los_Angeles")
    
    Wait For (job) JobDone(job As HttpJob)
    Dim success As Boolean
    If job.Success Then
        success = True
        Dim jobstring As String = job.GetString
        Dim JSON As JSONParser : JSON.Initialize(jobstring)
        Dim m As Map = JSON.NextObject
        Log(m)
    Else
        LogError(job.JobName & "     " & job.ErrorMessage)
    End If
    job.Release
    
    Return success
End Sub

amykonio said:
What version of B4J are you using?

I was using 7.51, I installed 7.80 beta, but I still get the same error when I press Ctrl+S.

EnriqueGonzalez · Sep 8, 2019

amykonio said:
You are right. He is doing that but for some reason when I debug that part of code in beta (7.80) it works...
View attachment 83746

This is expected. Compilation of debug and release makes different assumptions therefore yielding different ways to read the code by the compiler. You should always make some tests on release.

amykonio · Sep 8, 2019

Enrique Gonzalez R said:
This is expected. Compilation of debug and release makes different assumptions therefore yielding different ways to read the code by the compiler. You should always make some tests on release.

Yes... Before testing in debug mode i tried the same code in release. It run without any problem. Also the issue was mentioned to happen while debugging.
Maybe we use different version of java. I use JDK 1.8.0_201.

amykonio · Sep 8, 2019

cyiwin said:
I was using 7.51, I installed 7.80 beta, but I still get the same error when I press Ctrl+S.

And what version of jdk? We must do something different.

amykonio · Sep 8, 2019

Also what happens if you place the breakpoint in line 12 or 13 instead of line 14?

amykonio · Sep 8, 2019

From my testing the issue happens when you place a breakpoint after the wait for statement in line 13 in appstart or after the wait for statement in Job_Current_Time sub.
And yes that way I also receive the java.lang.NullPointerException.
Maybe because the code at that point works in a separate thread? So the executed code will be different than the on in the IDE?

cyiwin · Sep 8, 2019

amykonio said:
And what version of jdk? We must do something different.

I'm also using jdk1.80_201.

I also tried it on a different computer using jdk-9. I get the exact same error.

amykonio said:
Also what happens if you place the breakpoint in line 12 or 13 instead of line 14?

breakpoints at lines 12 and 13 work fine, no crashes.

To recreate the problem:

place a breakpoint at line 14
run in debug mode
when the program halts on line 14, press Ctrl+S

For both my computers this causes a crash and error "java.lang.NullPointerException"

cyiwin · Sep 8, 2019

amykonio said:
From my testing the issue happens when you place a breakpoint after the wait for statement in line 13 in appstart or after the wait for statement in Job_Current_Time sub.
And yes that way I also receive the java.lang.NullPointerException.
Maybe because the code at that point works in a separate thread? So the executed code will be different than the on in the IDE?

I see. I rely on hot code swapping a lot, is there a way to kill the 'Wait For' process when it's done?

amykonio · Sep 8, 2019

cyiwin said:
I see. I rely on hot code swapping a lot, is there a way to kill the 'Wait For' process when it's done?

I'm not sure. The following:

Maybe because the code at that point works in a separate thread?

was a question. I don't know how this code is transformed to java, and how the ctrl-s may affect it after changes.
Personally I rarely modify the code while debugging.
I think Erel is the most appropriate person to answer your question.

cyiwin · Sep 8, 2019

amykonio said:
was a question. I don't know how this code is transformed to java, and how the ctrl-s may affect it after changes.
Personally I rarely modify the code while debugging.
I think Erel is the most appropriate person to answer your question.

Thanks for your time and help!

Erel · Sep 9, 2019

I see it as well. It will be checked.

B4J Question Wait For and Ctrl+S causing 'java.lang.NullPointerException'

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