PowerBuilder

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. PowerBuilder

integer li_rc
integer li_Success
oleobject loo_Mailman
integer li_NumMessages
oleobject loo_TaskChain
integer i
oleobject loo_Task
oleobject loo_Email
integer li_NumTasks
integer li_TaskIdx

li_Success = 0

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

li_Success = 0

loo_Mailman = create oleobject
li_rc = loo_Mailman.ConnectToNewObject("Chilkat.MailMan")
if li_rc < 0 then
    destroy loo_Mailman
    MessageBox("Error","Connecting to COM object failed")
    return
end if

// Set the POP3 server's hostname
loo_Mailman.MailHost = "pop.example.com"

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

// Connect to the POP3 server:
li_Success = loo_Mailman.Pop3BeginSession()
if not li_Success then
    Write-Debug loo_Mailman.LastErrorText
    destroy loo_Mailman
    return
end if

// Get the number of messages in the mailbox.
li_NumMessages = loo_Mailman.GetMailboxCount()
if li_NumMessages = 0 then
    Write-Debug "No email messages in the POP3 mailbox."
    destroy loo_Mailman
    return
end if

loo_TaskChain = create oleobject
li_rc = loo_TaskChain.ConnectToNewObject("Chilkat.TaskChain")

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

for i = 1 to li_NumMessages

    loo_Task = loo_Mailman.FetchByMsgnumAsync(i)
    if loo_Mailman.LastMethodSuccess = 0 then
        Write-Debug loo_Mailman.LastErrorText
        destroy loo_Mailman
        destroy loo_TaskChain
        return
    end if

    // Append each task to the task chain.
    li_Success = loo_TaskChain.Append(loo_Task)
    if not li_Success then
        Write-Debug loo_TaskChain.LastErrorText
        destroy loo_Mailman
        destroy loo_TaskChain
        return
    end if

    destroy loo_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.
loo_TaskChain.StopOnFailedTask = 1
li_Success = loo_TaskChain.Run()
if not li_Success then
    Write-Debug loo_TaskChain.LastErrorText
    destroy loo_Mailman
    destroy loo_TaskChain
    return
end if

// 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 loo_TaskChain.Finished <> 1

    // Sleep 100 ms.
    loo_TaskChain.SleepMs(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:
if loo_TaskChain.StatusInt <> 7 then
    Write-Debug "Task did not complete."
    Write-Debug "task chain status: " + loo_TaskChain.Status
    destroy loo_Mailman
    destroy loo_TaskChain
    return
end if

loo_Email = create oleobject
li_rc = loo_Email.ConnectToNewObject("Chilkat.Email")

li_NumTasks = loo_TaskChain.NumTasks
li_TaskIdx = 0

do while (li_TaskIdx < li_NumTasks)

    loo_Task = loo_TaskChain.GetTask(li_TaskIdx)

    // Load the email object with email downloaded by this task.
    li_Success = loo_Email.LoadTaskResult(loo_Task)
    if not li_Success then
        Write-Debug "Failed to load email object for task."
    else
        Write-Debug loo_Email.From + "; " + loo_Email.Subject
    end if

    destroy loo_Task

    li_TaskIdx = li_TaskIdx + 1
loop


destroy loo_Mailman
destroy loo_TaskChain
destroy loo_Email