DataFlex

Async Task Chain

See more Async Examples

Demonstrates how to combine a sequence of asynchronous tasks into a single task chain to be run in a background thread. DataFlex

Use ChilkatAx-win32.pkg

Procedure Test
    Boolean iSuccess
    Handle hoMailman
    Integer iNumMessages
    Handle hoTaskChain
    Integer i
    Variant vTask
    Handle hoTask
    Handle hoEmail
    Integer iNumTasks
    Integer iTaskIdx
    String sTemp1
    String sTemp2
    Integer iTemp1
    Boolean bTemp1

    Move False To iSuccess

    // This example assumes the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    Move False To iSuccess

    Get Create (RefClass(cComChilkatMailMan)) To hoMailman
    If (Not(IsComObjectCreated(hoMailman))) Begin
        Send CreateComObject of hoMailman
    End

    // Set the POP3 server's hostname
    Set ComMailHost Of hoMailman To "pop.example.com"

    // Set the POP3 login/password and any other requirements..
    Set ComPopUsername Of hoMailman To "myLogin"
    Set ComPopPassword Of hoMailman To "myPassword"
    Set ComPopSsl Of hoMailman To True
    Set ComMailPort Of hoMailman To 995

    // Connect to the POP3 server:
    Get ComPop3BeginSession Of hoMailman To iSuccess
    If (Not iSuccess) Begin
        Get ComLastErrorText Of hoMailman To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Get the number of messages in the mailbox.
    Get ComGetMailboxCount Of hoMailman To iNumMessages
    If (iNumMessages = 0) Begin
        Showln "No email messages in the POP3 mailbox."
        Procedure_Return
    End

    Get Create (RefClass(cComChilkatTaskChain)) To hoTaskChain
    If (Not(IsComObjectCreated(hoTaskChain))) Begin
        Send CreateComObject of hoTaskChain
    End

    // Create async task objects to fetch each email message
    // by its sequence number

    For i From 1 To iNumMessages

        Get ComFetchByMsgnumAsync Of hoMailman i To vTask
        If (IsComObject(vTask)) Begin
            Get Create (RefClass(cComChilkatTask)) To hoTask
            Set pvComObject Of hoTask To vTask
        End
        Get ComLastMethodSuccess Of hoMailman To bTemp1
        If (bTemp1 = False) Begin
            Get ComLastErrorText Of hoMailman To sTemp1
            Showln sTemp1
            Procedure_Return
        End

        // Append each task to the task chain.
        Get ComAppend Of hoTaskChain vTask To iSuccess
        If (Not iSuccess) Begin
            Get ComLastErrorText Of hoTaskChain To sTemp1
            Showln sTemp1
            Procedure_Return
        End

        Send Destroy of hoTask

    Loop

    // At this point, no tasks have actually started running.
    // All we've done so far is to create tasks for the work that will be done
    // when the task chain is run.

    // Start the task chain running in a background thread.
    // Each task is run one after the other (on the same background thread) until all tasks have completed.
    // The task chain will stop at the first task that fails.
    Set ComStopOnFailedTask Of hoTaskChain To True
    Get ComRun Of hoTaskChain To iSuccess
    If (Not iSuccess) Begin
        Get ComLastErrorText Of hoTaskChain To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // The application is now free to do anything else
    // while the emails are being downloaded

    // For this example, we'll simply sleep and periodically
    // check to see if the taskchain if finished. 
    While ((ComFinished(hoTaskChain)) <> True)

        // Sleep 100 ms.
        Send ComSleepMs To hoTaskChain 100

    Loop

    // A finished task chain could be one that was canceled, aborted, or truly finished.  

    // If the task chain "completed", then it ran to completion.  A "completed" task will
    // have a StatusInt equal to 7.   If the task finished, but was not completed, then it must've
    // been aborted or canceled:
    Get ComStatusInt Of hoTaskChain To iTemp1
    If (iTemp1 <> 7) Begin
        Showln "Task did not complete."
        Get ComStatus Of hoTaskChain To sTemp1
        Showln "task chain status: " sTemp1
        Procedure_Return
    End

    Get Create (RefClass(cComChilkatEmail)) To hoEmail
    If (Not(IsComObjectCreated(hoEmail))) Begin
        Send CreateComObject of hoEmail
    End

    Get ComNumTasks Of hoTaskChain To iNumTasks
    Move 0 To iTaskIdx

    While (iTaskIdx < iNumTasks)

        Get ComGetTask Of hoTaskChain iTaskIdx To vTask
        If (IsComObject(vTask)) Begin
            Get Create (RefClass(cComChilkatTask)) To hoTask
            Set pvComObject Of hoTask To vTask
        End

        // Load the email object with email downloaded by this task.
        Get ComLoadTaskResult Of hoEmail vTask To iSuccess
        If (Not iSuccess) Begin
            Showln "Failed to load email object for task."
        End
        Else Begin
            Get ComFrom Of hoEmail To sTemp1
            Get ComSubject Of hoEmail To sTemp2
            Showln sTemp1 "; " sTemp2
        End

        Send Destroy of hoTask

        Move (iTaskIdx + 1) To iTaskIdx
    Loop



End_Procedure