PureBasic

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. PureBasic

IncludeFile "CkTask.pb"
IncludeFile "CkEmail.pb"
IncludeFile "CkTaskChain.pb"
IncludeFile "CkMailMan.pb"

Procedure ChilkatExample()

    success.i = 0

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

    success = 0

    mailman.i = CkMailMan::ckCreate()
    If mailman.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; Set the POP3 server's hostname
    CkMailMan::setCkMailHost(mailman, "pop.example.com")

    ; Set the POP3 login/password and any other requirements..
    CkMailMan::setCkPopUsername(mailman, "myLogin")
    CkMailMan::setCkPopPassword(mailman, "myPassword")
    CkMailMan::setCkPopSsl(mailman, 1)
    CkMailMan::setCkMailPort(mailman, 995)

    ; Connect to the POP3 server:
    success = CkMailMan::ckPop3BeginSession(mailman)
    If Not success
        Debug CkMailMan::ckLastErrorText(mailman)
        CkMailMan::ckDispose(mailman)
        ProcedureReturn
    EndIf

    ; Get the number of messages in the mailbox.
    numMessages.i = CkMailMan::ckGetMailboxCount(mailman)
    If numMessages = 0
        Debug "No email messages in the POP3 mailbox."
        CkMailMan::ckDispose(mailman)
        ProcedureReturn
    EndIf

    taskChain.i = CkTaskChain::ckCreate()
    If taskChain.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; Create async task objects to fetch each email message
    ; by its sequence number
    i.i
    task.i

    For i = 1 To numMessages

        task = CkMailMan::ckFetchByMsgnumAsync(mailman,i)
        If CkMailMan::ckLastMethodSuccess(mailman) = 0
            Debug CkMailMan::ckLastErrorText(mailman)
            CkMailMan::ckDispose(mailman)
            CkTaskChain::ckDispose(taskChain)
            ProcedureReturn
        EndIf

        ; Append each task to the task chain.
        success = CkTaskChain::ckAppend(taskChain,task)
        If Not success
            Debug CkTaskChain::ckLastErrorText(taskChain)
            CkMailMan::ckDispose(mailman)
            CkTaskChain::ckDispose(taskChain)
            ProcedureReturn
        EndIf

        CkTask::ckDispose(task)

    Next

    ; 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.
    CkTaskChain::setCkStopOnFailedTask(taskChain, 1)
    success = CkTaskChain::ckRun(taskChain)
    If Not success
        Debug CkTaskChain::ckLastErrorText(taskChain)
        CkMailMan::ckDispose(mailman)
        CkTaskChain::ckDispose(taskChain)
        ProcedureReturn
    EndIf

    ; 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 CkTaskChain::ckFinished(taskChain) <> 1

        ; Sleep 100 ms.
        CkTaskChain::ckSleepMs(taskChain,100)

    Wend

    ; 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:
    If CkTaskChain::ckStatusInt(taskChain) <> 7
        Debug "Task did not complete."
        Debug "task chain status: " + CkTaskChain::ckStatus(taskChain)
        CkMailMan::ckDispose(mailman)
        CkTaskChain::ckDispose(taskChain)
        ProcedureReturn
    EndIf

    email.i = CkEmail::ckCreate()
    If email.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    numTasks.i = CkTaskChain::ckNumTasks(taskChain)
    taskIdx.i = 0

    While (taskIdx < numTasks)

        task = CkTaskChain::ckGetTask(taskChain,taskIdx)

        ; Load the email object with email downloaded by this task.
        success = CkEmail::ckLoadTaskResult(email,task)
        If Not success
            Debug "Failed to load email object for task."
        Else
            Debug CkEmail::ckFrom(email) + "; " + CkEmail::ckSubject(email)
        EndIf

        CkTask::ckDispose(task)

        taskIdx = taskIdx + 1
    Wend


    CkMailMan::ckDispose(mailman)
    CkTaskChain::ckDispose(taskChain)
    CkEmail::ckDispose(email)


    ProcedureReturn
EndProcedure