Lianja

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. Lianja

llSuccess = .F.

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

llSuccess = .F.

loMailman = createobject("CkMailMan")

// 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 = .T.
loMailman.MailPort = 995

// Connect to the POP3 server:
llSuccess = loMailman.Pop3BeginSession()
if (not llSuccess) then
    ? loMailman.LastErrorText
    release loMailman
    return
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
    return
endif

loTaskChain = createobject("CkTaskChain")

// 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 = .F.) then
        ? loMailman.LastErrorText
        release loMailman
        release loTaskChain
        return
    endif

    // Append each task to the task chain.
    llSuccess = loTaskChain.Append(loTask)
    if (not llSuccess) then
        ? loTaskChain.LastErrorText
        release loMailman
        release loTaskChain
        return
    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 = .T.
llSuccess = loTaskChain.Run()
if (not llSuccess) then
    ? loTaskChain.LastErrorText
    release loMailman
    release loTaskChain
    return
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 <> .T.

    // 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
    return
endif

loEmail = createobject("CkEmail")

lnNumTasks = loTaskChain.NumTasks
lnTaskIdx = 0

do while (lnTaskIdx < lnNumTasks)

    loTask = loTaskChain.GetTask(lnTaskIdx)

    // Load the email object with email downloaded by this task.
    llSuccess = loEmail.LoadTaskResult(loTask)
    if (not llSuccess) 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