Swift

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. Swift

func chilkatTest() {
    var success: Bool = false

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

    success = false

    let mailman = CkoMailMan()!

    // Set the POP3 server's hostname
    mailman.mailHost = "pop.example.com"

    // Set the POP3 login/password and any other requirements..
    mailman.popUsername = "myLogin"
    mailman.popPassword = "myPassword"
    mailman.popSsl = true
    mailman.mailPort = 995

    // Connect to the POP3 server:
    success = mailman.pop3BeginSession()
    if !success {
        print("\(mailman.lastErrorText!)")
        return
    }

    // Get the number of messages in the mailbox.
    var numMessages: Int = mailman.getMailboxCount().intValue
    if numMessages == 0 {
        print("No email messages in the POP3 mailbox.")
        return
    }

    let taskChain = CkoTaskChain()!

    // Create async task objects to fetch each email message
    // by its sequence number
    var i: Int
    var task: CkoTask?

    for i = 1; i <= numMessages; i++ {

        task = mailman.fetch(byMsgnumAsync: i)
        if mailman.lastMethodSuccess == false {
            print("\(mailman.lastErrorText!)")
            return
        }

        // Append each task to the task chain.
        success = taskChain.append(task: task)
        if !success {
            print("\(taskChain.lastErrorText!)")
            return
        }

        task = nil

    }

    // 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.
    taskChain.stopOnFailedTask = true
    success = taskChain.run()
    if !success {
        print("\(taskChain.lastErrorText!)")
        return
    }

    // 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 taskChain.finished != true {

        // Sleep 100 ms.
        taskChain.sleepMs(numMs: 100)

    }

    // 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 taskChain.statusInt.intValue != 7 {
        print("Task did not complete.")
        print("task chain status: \(taskChain.status!)")
        return
    }

    let email = CkoEmail()!

    var numTasks: Int = taskChain.numTasks.intValue
    var taskIdx: Int = 0

    while (taskIdx < numTasks) {

        task = taskChain.getTask(index: taskIdx)

        // Load the email object with email downloaded by this task.
        success = email.loadTaskResult(task: task)
        if !success {
            print("Failed to load email object for task.")
        }
        else {
            print("\(email.from!); \(email.subject!)")
        }

        task = nil

        taskIdx = taskIdx + 1
    }


}