Thread Question - Sleep 0 vs Sleep 1

[Gary Beene]

Same code as my last message - different question, just trying to understand how Sleep works.

If I use Sleep 0, I expect the thread to give up the rest of the current time slice. I don't know what the time-slice for my PC, but if it is 20ms, then Sleep 0 would give up 0-20 ms, depending on how much of the current time slice the current thread had already used when Sleep was called.

If I use Sleep 1, then I expect it to give up only 1 ms of the current time slice.

If these two statements are true, then I would expect Sleep 0 would cause a thread to run more slowly than Sleep 1 (unless it just happens that Sleep 0 hits on the 19 ms mark). But that's not what I see in the code.

Can someone explain my mis-understanding of how Sleep is supposed to work?

'Compilable Example:
#Compile Exe
#Dim All
#Include "Win32API.inc"
Global hDlg As Dword, hThread As Dword
Function PBMain() As Long
   Dialog New Pixels, 0, "Test Code",300,300,200,200, %WS_OverlappedWindow To hDlg
   Control Add Button, hDlg, 100,"Start Thread", 50,10,100,20
   Control Add Label, hDlg, 200,"<main thread count>", 50,40,100,20
   Control Add Label, hDlg, 300,"<extra thread count>", 50,70,100,20
   Dialog Show Modal hDlg Call DlgProc
End Function

CallBack Function DlgProc() As Long
   If Cb.Msg = %WM_Command And Cb.Ctl = 100 And Cb.CtlMsg = %BN_Clicked Then
     Thread Create NewThread(0) To hThread       'start the new thread, argument not used
      Thread Close hThread To hThread    'suggested by PowerBASIC Inc. as good practice
      MainThread    'in the main thread, keep doing something
   End If
End Function

Function MainThread () As Long
     Local iCount&
     Do
        Incr iCount& : Control Set Text hDlg, 200, "Main" + Str$(iCount&)
        Sleep 1
     Loop Until iCount& > 500
End Function

Thread Function NewThread (ByVal x As Long) As Long
     Local iCount&
     Do
        Incr iCount& : Control Set Text hDlg, 300, "Thread" + Str$(iCount&)
        Sleep 1
     Loop Until iCount& > 500
End Function

[David Roberts]

> If I use Sleep 1, then I expect it to give up only 1 ms of the current time slice.

The current time slice is given up on Sleep no matter what its parameter is. When we return if Sleep is still active then the time slice is given up again and we belt out. With Sleep 0 when we return Sleep is no longer active and we continue where we left off.

[Michael Mattias]

SLEEP is not something you "always use" just because a program is multi-threaded.

[Tom Hanlin]

SLEEP tells the operating system that you're not doing something vitally important right now, and it can take the time to catch up on its to-do list-- process a few messages or whatever. The amount of time you specify for a SLEEP is a hint, not a command, because the SLEEP statement already says "I don't need your attention right now, take five." How much time is actually used depends on what other things the operating system wants to do, and on how accurate the clock is. If you specify a unit of 1 tick, and the clock is only accurate to within 10 ticks, well...