CondBroadcastsub

'' How can all threads wait for each other before continuing to execute their concomitant sections of code ?

''

'' This is the main code that manages the synchronization of concomitant sections of code:

''    - Each thread signals to main code that it is waiting for synchronization.

''    - The main code waits for each of all threads, then sends the synchronization signal to all threads.

''

'' The synchronization uses the following keywords from threading:

''   - In each thread : 'Condsignal' (to send signal to main code) then 'Condwait' (to wait signal from main code).

''   - In main code : 'Condwait' (to wait signal from each thread) then 'Condbroadcast' (to send signal to all threads).

'' With the associated mutexes and conditional variables and flags.

''

'' Test example highlighting the structure of threads and their behaviors, when synchronizing all threads to execute their concomitant sections of code:



Dim threadnumber As Integer = 4



'' global data for all threads

    Dim Shared restart As Integer = 0

    Dim Shared threadcount As Integer = 0

   

    Dim Shared hmutexrestart As Any Ptr

    Dim Shared hcondrestart As Any Ptr

    Dim Shared hmutexready As Any Ptr

    Dim Shared hcondready As Any Ptr



Sub mythread(ByVal p As Any Ptr)

   

    Dim id As Integer = Cast(Integer, p)

   

    '' for visualizing thread status

        Print "   Thread #" & id & " is started..."

       

    '' instead of starting user code

        Sleep id * 40, 1

       

    '' for visualizing thread status

        Print "      Thread #" & id & " is running..."

        Sleep id * 20, 1  '' just to well visualize thread interlacing

        Print "   Thread #" & id & " is waiting for synchronization..."

       

    '' for sending signal to main code

        MutexLock hmutexready

        threadcount += 1

        CondSignal hcondready

        MutexUnlock hmutexready

       

    '' for waiting signal from main code

        MutexLock hmutexrestart

        Do While restart = 0  

            CondWait hcondrestart, hmutexrestart

        Loop

        MutexUnlock hmutexrestart

       

    '' for visualizing thread status

        Print "   Thread #" & id & " is reactivated..."

       

    '' instead of synchronized user code

        Sleep id * 40, 1

       

    '' for visualizing thread status

        Print "      Thread #" & id & " is continuing..."

        Sleep id * 20, 1  '' just to well visualize thread interlacing

        Print "   Thread #" & id & " is finishing execution..."

   

End Sub





Dim threads(1 To threadnumber) As Any Ptr



hcondrestart = CondCreate()

hmutexrestart = MutexCreate()

hcondready = CondCreate()

hmutexready = MutexCreate()



'' for visualizing main code status

    Print "Start all threads from main code :"

       

'' for starting all threads

    For i As Integer = 1 To threadnumber

        threads(i) = ThreadCreate(@mythread, Cast(Any Ptr, i))

    Next i



'' for waiting for all threads waiting for synchronisation

    MutexLock hmutexready

    Do Until threadcount = threadnumber

        CondWait(hcondready, hmutexready)

    Loop

    MutexUnlock hmutexready



'' for visualizing main code status

    Print "All thread seen waiting from main code"

    Print

    Print "Reactivate all threads from main code :"

       

'' for reactivating all threads

    MutexLock hmutexrestart

    restart = 1

    CondBroadcast hcondrestart

    MutexUnlock hmutexrestart



'' for waiting for all threads to be completed

    For i As Integer = 1 To threadnumber

        If threads(i) <> 0 Then

            ThreadWait threads(i)

        End If

    Next i

   

'' for visualizing main code status

    Print "All thread seen completed from main code"



MutexDestroy hmutexready

CondDestroy hcondready

MutexDestroy hmutexrestart

CondDestroy hcondrestart



Sleep