(SQL Server) Async Task Chain

Demonstrates how to combine a sequence of asynchronous tasks into a single task chain to be run in a background thread.

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

-- Important: See this note about string length limitations for strings returned by sp_OAMethod calls.
--
CREATE PROCEDURE ChilkatSample
AS
BEGIN
    DECLARE @hr int
    DECLARE @iTmp0 int
    -- Important: Do not use nvarchar(max).  See the warning about using nvarchar(max).
    DECLARE @sTmp0 nvarchar(4000)
    DECLARE @sTmp1 nvarchar(4000)
    -- All Chilkat classes can be unlocked at once at the beginning of a program
    -- by calling UnlockBundle.  It requires a Bundle unlock code.
    DECLARE @chilkatGlob int
    -- Use "Chilkat_9_5_0.Global" for versions of Chilkat < 10.0.0
    EXEC @hr = sp_OACreate 'Chilkat.Global', @chilkatGlob OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    DECLARE @success int
    EXEC sp_OAMethod @chilkatGlob, 'UnlockBundle', @success OUT, 'Anything for 30-day trial.'
    IF @success <> 1
      BEGIN
        EXEC sp_OAGetProperty @chilkatGlob, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @chilkatGlob
        RETURN
      END

    DECLARE @mailman int
    -- Use "Chilkat_9_5_0.MailMan" for versions of Chilkat < 10.0.0
    EXEC @hr = sp_OACreate 'Chilkat.MailMan', @mailman OUT

    -- Set the POP3 server's hostname
    EXEC sp_OASetProperty @mailman, 'MailHost', 'pop.someMailServer.com'

    -- Set the POP3 login/password and any other requirements..
    EXEC sp_OASetProperty @mailman, 'PopUsername', 'myLogin'
    EXEC sp_OASetProperty @mailman, 'PopPassword', 'myPassword'
    EXEC sp_OASetProperty @mailman, 'PopSsl', 1
    EXEC sp_OASetProperty @mailman, 'MailPort', 995

    -- Connect to the POP3 server:
    EXEC sp_OAMethod @mailman, 'Pop3BeginSession', @success OUT
    IF Not @success
      BEGIN
        EXEC sp_OAGetProperty @mailman, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @chilkatGlob
        EXEC @hr = sp_OADestroy @mailman
        RETURN
      END

    -- Get the number of messages in the mailbox.
    DECLARE @numMessages int
    EXEC sp_OAMethod @mailman, 'GetMailboxCount', @numMessages OUT
    IF @numMessages = 0
      BEGIN

        PRINT 'No email messages in the POP3 mailbox.'
        EXEC @hr = sp_OADestroy @chilkatGlob
        EXEC @hr = sp_OADestroy @mailman
        RETURN
      END

    DECLARE @taskChain int
    -- Use "Chilkat_9_5_0.TaskChain" for versions of Chilkat < 10.0.0
    EXEC @hr = sp_OACreate 'Chilkat.TaskChain', @taskChain OUT

    -- Create async task objects to fetch each email message
    -- by its sequence number
    DECLARE @i int

    DECLARE @task int

    SELECT @i = 1
    WHILE @i <= @numMessages
      BEGIN

        EXEC sp_OAMethod @mailman, 'FetchByMsgnumAsync', @task OUT, @i
        EXEC sp_OAGetProperty @mailman, 'LastMethodSuccess', @iTmp0 OUT
        IF @iTmp0 = 0
          BEGIN
            EXEC sp_OAGetProperty @mailman, 'LastErrorText', @sTmp0 OUT
            PRINT @sTmp0
            EXEC @hr = sp_OADestroy @chilkatGlob
            EXEC @hr = sp_OADestroy @mailman
            EXEC @hr = sp_OADestroy @taskChain
            RETURN
          END

        -- Append each task to the task chain.
        EXEC sp_OAMethod @taskChain, 'Append', @success OUT, @task
        IF Not @success
          BEGIN
            EXEC sp_OAGetProperty @taskChain, 'LastErrorText', @sTmp0 OUT
            PRINT @sTmp0
            EXEC @hr = sp_OADestroy @chilkatGlob
            EXEC @hr = sp_OADestroy @mailman
            EXEC @hr = sp_OADestroy @taskChain
            RETURN
          END

        EXEC @hr = sp_OADestroy @task

        SELECT @i = @i + 1
      END

    -- 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.
    EXEC sp_OASetProperty @taskChain, 'StopOnFailedTask', 1
    EXEC sp_OAMethod @taskChain, 'Run', @success OUT
    IF Not @success
      BEGIN
        EXEC sp_OAGetProperty @taskChain, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @chilkatGlob
        EXEC @hr = sp_OADestroy @mailman
        EXEC @hr = sp_OADestroy @taskChain
        RETURN
      END

    -- 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. 
    EXEC sp_OAGetProperty @taskChain, 'Finished', @iTmp0 OUT
    WHILE @iTmp0 <> 1
      BEGIN

        -- Sleep 100 ms.
        EXEC sp_OAMethod @taskChain, 'SleepMs', NULL, 100

      END

    -- 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:
    EXEC sp_OAGetProperty @taskChain, 'StatusInt', @iTmp0 OUT
    IF @iTmp0 <> 7
      BEGIN

        PRINT 'Task did not complete.'

        EXEC sp_OAGetProperty @taskChain, 'Status', @sTmp0 OUT
        PRINT 'task chain status: ' + @sTmp0
        EXEC @hr = sp_OADestroy @chilkatGlob
        EXEC @hr = sp_OADestroy @mailman
        EXEC @hr = sp_OADestroy @taskChain
        RETURN
      END

    DECLARE @email int
    -- Use "Chilkat_9_5_0.Email" for versions of Chilkat < 10.0.0
    EXEC @hr = sp_OACreate 'Chilkat.Email', @email OUT

    DECLARE @numTasks int
    EXEC sp_OAGetProperty @taskChain, 'NumTasks', @numTasks OUT
    DECLARE @taskIdx int
    SELECT @taskIdx = 0

    WHILE (@taskIdx < @numTasks)
      BEGIN

        EXEC sp_OAMethod @taskChain, 'GetTask', @task OUT, @taskIdx

        -- Load the email object with email downloaded by this task.
        EXEC sp_OAMethod @email, 'LoadTaskResult', @success OUT, @task
        IF Not @success
          BEGIN

            PRINT 'Failed to load email object for task.'
          END
        ELSE
          BEGIN
            EXEC sp_OAGetProperty @email, 'From', @sTmp0 OUT

            EXEC sp_OAGetProperty @email, 'Subject', @sTmp1 OUT
            PRINT @sTmp0 + '; ' + @sTmp1
          END

        EXEC @hr = sp_OADestroy @task

        SELECT @taskIdx = @taskIdx + 1
      END

    EXEC @hr = sp_OADestroy @chilkatGlob
    EXEC @hr = sp_OADestroy @mailman
    EXEC @hr = sp_OADestroy @taskChain
    EXEC @hr = sp_OADestroy @email


END
GO