TaskChain Lianja Reference Documentation

TaskChain

Represents a chain of asynchronous tasks to be run in sequence in a background thread.

Object Creation

loObject = createobject("CkTaskChain")

Properties

DebugLogFilePath As Character

If set to a file path, causes each Chilkat method or property call to automatically append it's LastErrorText to the specified log file. The information is appended such that if a hang or crash occurs, it is possible to see the context in which the problem occurred, as well as a history of all Chilkat calls up to the point of the problem. The VerboseLogging property can be set to provide more detailed information.

This property is typically used for debugging the rare cases where a Chilkat method call hangs or generates an exception that halts program execution (i.e. crashes). A hang or crash should generally never happen. The typical causes of a hang are:

  1. a timeout related property was set to 0 to explicitly indicate that an infinite timeout is desired,
  2. the hang is actually a hang within an event callback (i.e. it is a hang within the application code), or
  3. there is an internal problem (bug) in the Chilkat code that causes the hang.

Finished As Boolean (read-only)

Introduced in version 9.5.0.52

.T. if the task status is "canceled", "aborted", or "completed". A task chain can only reach the "canceled" status if it was activated via the Run method, made it onto the internal thread pool thread's queue, was waiting for a pool thread to become available, and was then canceled prior to the task actually starting.

Inert As Boolean (read-only)

Introduced in version 9.5.0.52

.T. if the task status is "empty" or "loaded". When a task chain is inert, it has been loaded but is not scheduled to run yet.

LastErrorHtml As Character (read-only)

Provides information in HTML format about the last method/property called. If a method call returns a value indicating failure, or behaves unexpectedly, examine this property to get more information.

LastErrorText As Character (read-only)

Provides information in plain-text format about the last method/property called. If a method call returns a value indicating failure, or behaves unexpectedly, examine this property to get more information.

Concept of LastErrorText

LastErrorText Standard Information

LastErrorXml As Character (read-only)

Provides information in XML format about the last method/property called. If a method call returns a value indicating failure, or behaves unexpectedly, examine this property to get more information.

LastMethodSuccess As Boolean

Introduced in version 9.5.0.52

Indicate whether the last method call succeeded or failed. A value of .T. indicates success, a value of .F. indicates failure. This property is automatically set for method calls. It is not modified by property accesses. The property is automatically set to indicate success for the following types of method calls:

  • Any method that returns a string.
  • Any method returning a Chilkat object, binary bytes, or a date/time.
  • Any method returning a standard boolean status value where success = .T. and failure = .F..
  • Any method returning an integer where failure is defined by a return value less than zero.

Note: Methods that do not fit the above requirements will always set this property equal to .T.. For example, a method that returns no value (such as a "void" in C++) will technically always succeed.

Live As Boolean (read-only)

Introduced in version 9.5.0.52

.T. if the task status is "queued" or "running". When a task chain is live, it is either already running, or is on the thread pool thread's queue waiting for a thread to become available.

NumTasks As Numeric (read-only)

Introduced in version 9.5.0.52

The number of tasks contained within the task chain.

Status As Character (read-only)

Introduced in version 9.5.0.52

The current status of the task chain. Possible values are:

  • "empty" -- No tasks have yet been appended to the task chain.
  • "loaded" -- The task chain has been loaded (appended) with one or more task objects.
  • "queued" -- The task chain is in the thread pool's queue of tasks awaiting to be run.
  • "running" -- The task chain is currently running.
  • "canceled" -- The task chain was canceled before it entered the "running" state.
  • "aborted" -- The task chain was canceled while it was in the running state.
  • "completed" -- The task chain completed.

StatusInt As Numeric (read-only)

Introduced in version 9.5.0.52

The current status of the task as an integer value. Possible values are:

  • 1 -- "empty" -- No tasks have yet been appended to the task chain.
  • 2 -- "loaded" -- The task chain has been loaded (appended) with one or more task objects.
  • 3 -- "queued" -- The task chain is in the thread pool's queue of tasks awaiting to be run.
  • 4 -- "running" -- The task chain is currently running.
  • 5 -- "canceled" -- The task chain was canceled before it entered the "running" state.
  • 6 -- "aborted" -- The task chain was canceled while it was in the running state.
  • 7 -- "completed" -- The task chain completed.

StopOnFailedTask As Boolean

Introduced in version 9.5.0.52

If .T. then stops execution of the task chain if any individual task fails. Task failure is defined by the standard LastMethodSuccess property. If .F., then all of the tasks in the chain will be run even if some fail. The default value of this property is .T..

Async Methods Returning an Object

VerboseLogging As Boolean

If set to .T., then the contents of LastErrorText (or LastErrorXml, or LastErrorHtml) may contain more verbose information. The default value is .F.. Verbose logging should only be used for debugging. The potentially large quantity of logged information may adversely affect peformance.

Version As Character (read-only)

Version of the component/library, such as "9.5.0.63"

Methods

Append(task As CkTask) As Boolean

Introduced in version 9.5.0.52

Appends a task to the task chain. Can fail if the task is already part of another chain. (A task can only be part of a single chain.)

Returns .T. for success, .F. for failure.

Async Task Chain

Cancel() As Boolean

Introduced in version 9.5.0.52

Cancels execution of the asynchronous task chain.

Returns .T. for success, .F. for failure.

GetTask(index As Numeric) As CkTask

Introduced in version 9.5.0.52

Returns the Nth task in the chain. The 1st task is at index 0.

Returns .F. on failure

Async Methods Returning an Object

Run() As Boolean

Introduced in version 9.5.0.52

Queues the task chain to run on the internal Chilkat thread pool. Each task in the chain will run, one after the other.

Returns .T. for success, .F. for failure.

RunSynchronously() As Boolean

Introduced in version 9.5.0.52

Runs the task chain synchronously. Then this method returns after all the tasks in the chain have been run.

Returns .T. for success, .F. for failure.

SaveLastError(path As Character) As Boolean

Saves the last-error information (the contents of LastErrorXml) to an XML formatted file.

Returns .T. for success, .F. for failure.

SleepMs(numMs As Numeric)

Introduced in version 9.5.0.52

Convenience method to force the calling thread to sleep for a number of milliseconds.

Wait(maxWaitMs As Numeric) As Boolean

Introduced in version 9.5.0.52

Waits for the task chain to complete. Returns when all of the tasks in the chain have completed, or after maxWaitMs milliseconds have elapsed. (A maxWaitMs value of 0 is to wait indefinitely.) Returns (.F.) if the task chain has not yet been started by calling the Run method, or if the maxWaitMs expired. If the task chain completed, was already completed, was canceled, or aborted, then this method returns .T..

Returns .T. for success, .F. for failure.