B4J Question What is the recommended way to perform a time-consuming task?

[xulihang]

There is a sub which is time consuming. I try to make it a resumable sub but it is still making the UI not responsive.

So I use the Threading library to call the sub.

Private th As Thread
th.Initialise("th")
Dim map1 As Map
map1.Initialize
map1.Put("mat",Mat)
map1.Put("geometries",geometries)
th.Start(Me,"Detect",Array As Map(map1))
wait for th_Ended(endedOK As Boolean, error As String)

It works but on some devices, the th_Ended event is never triggered. One of my users is reporting this: https://github.com/xulihang/ImageTrans-docs/issues/1029

I can reproduce this on a Linux Virtual machine with limited CPU cores. It works fine on my regular macOS and Windows devices.

 

[Erel]

A resumable sub runs on the main thread, so it won't help with CPU intensive tasks.

Does your solution work with Sub th_Ended ... instead of Wait For?

 

[xulihang]

I modified the code like the following. If it takes too long, mark it as time out and stop using Threading.

Private MergeBoxesIsTimeOut as Boolean = False

Private Sub MergeBoxesUILess(filename As String,srcMat As cvMat,horizontal As Boolean,Xweight As Double,Yweight As Double) As ResumableSub
    MergeBoxesAsync(filename,srcMat,horizontal,Xweight,Yweight)
    wait for Merged(Success As Boolean)
    Return ""
End Sub

Sub MergeBoxesAsync(filename As String,srcMat As cvMat,horizontal As Boolean,Xweight As Double,Yweight As Double)
    If MergeBoxesIsTimeOut Then
        wait for (MergeBoxesUILessImpl(filename,srcMat,horizontal,Xweight,Yweight)) complete (done As Object)
        CallSubDelayed2(Me, "Merged", True)
    Else
        Dim b() As Boolean = Array As Boolean(False)
        MergeBoxesTimeOut(5000, b)
        th.Start(Me,"MergeBoxesUILessImpl",Array(filename,srcMat,horizontal,Xweight,Yweight))
        wait for th_Ended(endedOK As Boolean, error As String)
        If b(0) = False Then
            b(0) = True
            CallSubDelayed2(Me, "Merged", True)
        End If
    End If
End Sub

Sub MergeBoxesTimeOut(Duration As Int, b() As Boolean)
    Sleep(Duration)
    If b(0) = False Then
        MergeBoxesIsTimeOut = True
        b(0) = True
        Log("time out")
        CallSubDelayed2(Me, "Merged", False)
    End If
End Sub

Private Sub MergeBoxesUILessImpl(filename As String,srcMat As cvMat,horizontal As Boolean,Xweight As Double,Yweight As Double) As ResumableSub
'heavy work here
End Sub