MutexLocksub

'Example of mutual exclusion for synchronization between 2 threads

'by using 2 Mutexes only (by self lock and mutual unlock):

'The Producer works one time, then the Consumer works one time.

'

'Principle of synchronisation by mutual exclusion

'(initial condition: mut#A and mut#B locked)

'

'          Thread#A              XORs              Thread#B

'Do_something#A_with_exclusion          MutexLock(mut#A)

'MutexUnlock(mut#A)                       Do_something#B_with_exclusion

'.....                                  MutexUnlock(mut#B)

'MutexLock(mut#B)                       .....



'----------------------------------------------------------------------



Dim Shared produced As Any Ptr

Dim Shared consumed As Any Ptr

Dim consumer_id As Any Ptr

Dim producer_id As Any Ptr





Sub consumer ( ByVal param As Any Ptr )

    For i As Integer = 0 To 9

        MutexLock produced

        Print , ",consumer gets:" ; i

        MutexUnlock consumed

        Sleep 5, 1

    Next i

End Sub



Sub producer ( ByVal param As Any Ptr )

    For i As Integer = 0 To 9

        Print "Producer puts:" ; i;

        MutexUnlock produced

        MutexLock consumed

    Sleep 5, 1

Next i

End Sub





produced = MutexCreate

consumed = MutexCreate

If ( produced = 0 ) Or ( consumed = 0 ) Then

    Print "Error creating mutexes! Exiting..."

    Sleep

    End

End If



MutexLock produced

MutexLock consumed



consumer_id = ThreadCreate ( @ consumer )

producer_id = ThreadCreate ( @ producer )

If ( producer_id = 0 ) Or ( consumer_id = 0 ) Then

    Print "Error creating threads! Exiting..."

    Sleep

    End

End If



ThreadWait consumer_id

ThreadWait producer_id



MutexDestroy consumed

MutexDestroy produced



Sleep

' 'Threadcreate' launches one time the user-defined Sub in a separate execution thread

'    (which runs simultaneously with the rest of the main code).

' If you want obtain a periodically display from the thread,

'    you must put (into the thread) a [Do...Loop] block with a 'Sleep x, 1' to adjust the display period

'    and a flag to exit the loop (and terminate the thread).

'

' Warning:

' - Each thread has not its own memory of cursor position, so for that and other reasons, it is mandatory

'      to apply an exclusion between displaying from the main code (main thread) and displaying from the user thread,

'      by using a 'Mutex' ([Mutexlock...Mutexunlock] block).

'   At beginning of each display block both into main thread and user thread,

'      the initial cursor position must also be re-initialized.

' - The input keywords (like keyboard, mouse) cannot be safely run when the screen is locked,

'      therefore a such keyword must be outside of any [Screenlock...Screenunlock] block (outside this block in its own thread,

'      and protected of block of another thread by a 'Mutex').

'

' See below a rustic program, but showing all these constraints:





Dim Shared As Any Ptr sync   '' pointer to Mutex

Dim Shared As Byte quit = 0  '' flag to end user thread

Dim As Any Ptr handle        '' pointer to thread handle



Sub ProcedureThread (ByVal param As Any Ptr)  '' param not used in thread body

    Do

        MutexLock(sync)       '' Mutex for exclusion of displaying

            ScreenLock        '' keyword after Mutexlock

                Locate 1, 70  '' re-initialize cursor position

                Print Date

                Locate , 71

                Print Time;

            ScreenUnlock      '' keyword before Mutexunlock

        MutexUnlock(sync)     '' end exclusion

        Sleep 100, 1          '' ajust display period

    Loop Until quit <> 0      '' test for exit thread

End Sub





Screen 12

Locate 1, 62

Print "Date:"

Locate , 62

Print "Time:";

Locate 15, 20

Print "Mouse (position):"

Locate , 20

Print "Mouse (buttons) :";

Locate 30, 2

Print "<any_key> or <click on window close button>: exit";



sync = MutexCreate                          '' create Mutex (before Threadcreate)

handle = ThreadCreate(@ProcedureThread, 0)  '' launch thread



Dim As String s

Do

    MutexLock(sync)                     '' Mutex for exclusion of displaying

        Dim As Long x, y, b

        GetMouse x, y , , b             '' keyword outside [Screenlock...Screenunlock] and protected by Mutex

        ScreenLock                      '' keyword after Mutexlock

            Locate 15, 37               '' re-initialize cursor position

            Print Using "######"; x; y

            Locate , 43

            Print Using "##"; b;

        ScreenUnlock                    '' Keyword before Mutexunlock

        s = Inkey                       '' keyword outside [Screenlock...Screenunlock] and protected by Mutex

    MutexUnlock(sync)                   '' end exclusion

    Sleep 10, 1                         '' ajust display period

Loop Until s <> ""

 

quit = Not quit     '' order thread end

ThreadWait(handle)  '' wait for thread end

MutexDestroy(sync)  '' free Mutex