B4J Question Wait for used as asyncstreams timeout

[Chris2]

In the following code from here, can someone please explain to me why b needs to be an array (as opposed to a single boolean), and b(1) set as true at the end of the two subs?
b(1) doesn't appear to be actually used anywhere?

'usage
ReadData(5000)
Wait For DataReceived (Success As Boolean, Data() As Byte)


Sub ReadData (Timeout As Int)
 Dim b() As Boolean = Array As Boolean(False)
 TimeOutImpl(Timeout, b)
 Wait For Astream_NewData(Data() As Byte)
 If b(0) = false Then CallSubDelayed3(Me, "DataReceived", True, Data)
 b(1) = true
End Sub

Sub TimeOutImpl(Duration As Int, b() As Boolean)
 Sleep(Duration)
 If b(0) = false Then CallSubDelayed3(Me, "DataReceived", False, Null)
 b(1) = true
End Sub

 

[agraham]

I think the b(1) references are a typo and they should be b(0) as b() is an array with a length of one. Here an array is used instead of a global flag to signal that one or other of the ReadData or TimeOutImpl waits has expired. As Java/B4X parameters are passed by value just using a boolean as a flag won't work as assignment to parameter values don't propagate back to the caller. However if an array value is passed as a parameter the parameter value is actually a reference to the array and so a change in a value in the array will be seen by the caller.

 

[Chris2]

OK, thanks.
So, just to help my understanding, would the following, using a global boolean flag be equivalent?
(albeit perhaps less elegant, and susceptible to problems if the global boolean b is changed somewhere else or ReadData is called more than once)

Process_Globals
 Private b as Boolean
End Sub

'usage
ReadData(5000)
Wait For DataReceived (Success As Boolean, Data() As Byte)


Sub ReadData (Timeout As Int)
 b = False
 TimeOutImpl(Timeout, b)
 Wait For Astream_NewData(Data() As Byte)
 If b = false Then CallSubDelayed3(Me, "DataReceived", True, Data)
 b = true
End Sub

Sub TimeOutImpl(Duration As Int)
 Sleep(Duration)
 If b = false Then CallSubDelayed3(Me, "DataReceived", False, Null)
 b = true
End Sub

 

[OliverA]

So, would the following, using a global boolean flag be equivalent?

Yes, but now you make both routines (ReadData and TimeOutImpl) dependent on a global variable, whereas before they were not.