Visual FoxPro

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. Visual FoxPro

LOCAL lnSuccess
LOCAL loMailman
LOCAL lnNumMessages
LOCAL loTaskChain
LOCAL i
LOCAL loTask
LOCAL loEmail
LOCAL lnNumTasks
LOCAL lnTaskIdx

lnSuccess = 0

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

lnSuccess = 0

loMailman = CreateObject('Chilkat.MailMan')

* Set the POP3 server's hostname
loMailman.MailHost = "pop.example.com"

* Set the POP3 login/password and any other requirements..
loMailman.PopUsername = "myLogin"
loMailman.PopPassword = "myPassword"
loMailman.PopSsl = 1
loMailman.MailPort = 995

* Connect to the POP3 server:
lnSuccess = loMailman.Pop3BeginSession()
IF (NOT lnSuccess) THEN
    ? loMailman.LastErrorText
    RELEASE loMailman
    CANCEL
ENDIF

* Get the number of messages in the mailbox.
lnNumMessages = loMailman.GetMailboxCount()
IF (lnNumMessages = 0) THEN
    ? "No email messages in the POP3 mailbox."
    RELEASE loMailman
    CANCEL
ENDIF

loTaskChain = CreateObject('Chilkat.TaskChain')

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

FOR i = 1 TO lnNumMessages

    loTask = loMailman.FetchByMsgnumAsync(i)
    IF (loMailman.LastMethodSuccess = 0) THEN
        ? loMailman.LastErrorText
        RELEASE loMailman
        RELEASE loTaskChain
        CANCEL
    ENDIF

    * Append each task to the task chain.
    lnSuccess = loTaskChain.Append(loTask)
    IF (NOT lnSuccess) THEN
        ? loTaskChain.LastErrorText
        RELEASE loMailman
        RELEASE loTaskChain
        CANCEL
    ENDIF

    RELEASE loTask

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.
loTaskChain.StopOnFailedTask = 1
lnSuccess = loTaskChain.Run()
IF (NOT lnSuccess) THEN
    ? loTaskChain.LastErrorText
    RELEASE loMailman
    RELEASE loTaskChain
    CANCEL
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. 
DO WHILE loTaskChain.Finished <> 1

    * Sleep 100 ms.
    loTaskChain.SleepMs(100)

ENDDO

* 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 (loTaskChain.StatusInt <> 7) THEN
    ? "Task did not complete."
    ? "task chain status: " + loTaskChain.Status
    RELEASE loMailman
    RELEASE loTaskChain
    CANCEL
ENDIF

loEmail = CreateObject('Chilkat.Email')

lnNumTasks = loTaskChain.NumTasks
lnTaskIdx = 0

DO WHILE (lnTaskIdx < lnNumTasks)

    loTask = loTaskChain.GetTask(lnTaskIdx)

    * Load the email object with email downloaded by this task.
    lnSuccess = loEmail.LoadTaskResult(loTask)
    IF (NOT lnSuccess) THEN
        ? "Failed to load email object for task."
    ELSE
        ? loEmail.From + "; " + loEmail.Subject
    ENDIF

    RELEASE loTask

    lnTaskIdx = lnTaskIdx + 1
ENDDO

RELEASE loMailman
RELEASE loTaskChain
RELEASE loEmail