B4J Question Run processes simultaneously

jroriz · May 28, 2019

Hi.
I would like the Sub LongProcess to be executed SIMULTANEOUSLY, ie the 3 processes beginning and ending at the same time.
As it is in the code, they start together, but the second only ends after the end of the first, and the third after the end of the second.
Can anyone help?

B4X:

Sub AppStart (Form1 As Form, Args() As String)
    MainForm = Form1
    MainForm.Show
    
    LongProcess(0)
    LongProcess(1)
    LongProcess(2)

End Sub

Sub LongProcess(ix As Int)
    Log("start time: " & ix & " " & DateTime.Time(DateTime.Now))
    Sleep(0)
    For x = 1 To 300000000
        
    Next
    Log("end time: " & ix & " " & DateTime.Time(DateTime.Now))
End Sub

log:

Waiting for debugger to connect...
Program started.
start time: 0 12:13:41
start time: 1 12:13:41
start time: 2 12:13:41
end time: 0 12:13:42
end time: 1 12:13:44
end time: 2 12:13:46

DonManfred · May 28, 2019

Watch the resumeable subs tutorial and get familar with resumeable subs.

jroriz · May 28, 2019

Thanks for your attention. This was the best I got after following the tutorial. I made several attempts but I did not succeed.

agraham · May 28, 2019

In a B4J program all your code runs on the single main thread so you cannot achieve true simultaneous execution. Even using Resumable Subs you will still get consecutive execution of your Subs. You can achieve a measure of simultaneity by running each Sub on a separate thread, each of which might execute a different core of your CPU or might be time sliced with other threads on the same CPU core. What actually happens is outside your control.

Even if you use threads although the processes may start at the same time they will never all end at same time owing to uncertainties in the execution process.

You don't say why you want to simultaneous execution but I doubt that it is really necessary. If you want to try my B4A Threading library https://www.b4x.com/android/forum/threads/threading-library.6775/ should work in B4J in release mode.

jroriz · May 28, 2019

agraham said:
In a B4J program all your code runs on the single main thread so you cannot achieve true simultaneous execution. Even using Resumable Subs you will still get consecutive execution of your Subs. You can achieve a measure of simultaneity by running each Sub on a separate thread, each of which might execute a different core of your CPU or might be time sliced with other threads on the same CPU core. What actually happens is outside your control.

Even if you use threads although the processes may start at the same time they will never all end at same time owing to uncertainties in the execution process.

You don't say why you want to simultaneous execution but I doubt that it is really necessary. If you want to try my B4A Threading library https://www.b4x.com/android/forum/threads/threading-library.6775/ should work in B4J in release mode.

I need to show 4 different information on the screen, starting from a common information.
The problem is that each of these information takes about 4 seconds to complete, and one does not depend on the other.
My wish is to finish the process in 4 seconds, doing the four processes together.
I do not know if I could make myself clear.
I will try your lib.
Thanks.

agraham · May 28, 2019

You cannot directly access screen elements from a thread. You will need to call a Sub that runs on the main thread to access screen elements using the RunOnGuiThread method.

MarkusR · May 28, 2019

jroriz said:
each of these information takes about 4 seconds to complete

nonstop or is there a delay as example wainting for a http response?

its more like this, as soon you use sleep the sub interrupts and other continue until the sleep there.

B4X:

Sub LongProcess(ix As Int)
    Log("start time: " & ix & " " & DateTime.Time(DateTime.Now))   
    For x = 1 To 100000
        Sleep(0)
    Next
    Log("end time: " & ix & " " & DateTime.Time(DateTime.Now))
End Sub

jroriz · May 28, 2019

MarkusR said:
nonstop or is there a delay as example wainting for a http response?

In fact it is a mathematical process that has 5000 interactions.

MarkusR · May 28, 2019

jroriz said:
In fact it is a mathematical process that has 5000 interactions.

then i think the resumeable subs make no sense for you.

Erel · May 29, 2019

You should do it like this:

B4X:

Sub LongProcess(ix As Int)
    Log("start time: " & ix & " " & DateTime.Time(DateTime.Now))

    For x = 1 To 300000000
        if x Mod 1000000 = 0 Then Sleep(0) 'try different values
    Next
    Log("end time: " & ix & " " & DateTime.Time(DateTime.Now))
End Sub

This will allow you four processes to run together (on the same thread, but still together).

B4J Question Run processes simultaneously

jroriz

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