TaskChain FoxPro Reference Documentation
TaskChain
Current Version: 11.6.0
Chilkat.TaskChain
Append multiple
Start the entire chain, run it synchronously, wait for completion, or
cancel the chain as a single coordinated operation.
Inspect whether the chain is live, finished, inert, canceled, failed, or
still running.
Retrieve tasks by index after execution to inspect each task's status,
success flag, error text, and result.
Use
Use task and chain status information together with
For an extended overview, see
TaskChain Class Overview.
Run multiple asynchronous Chilkat tasks in a defined sequence.
Chilkat.TaskChain manages a sequence of
Chilkat.Task objects and runs them one after another. It is
useful when multiple asynchronous Chilkat operations must execute in a
predictable order while still allowing the entire chain to be started,
monitored, waited on, canceled, or run synchronously. A task chain can stop
when a task fails, or continue depending on the configured behavior.
Sequential async workflow
Task objects and run them in order when one
operation must finish before the next begins.
Chain-level execution
Monitor progress and status
Access individual tasks
Stop-on-failure control
StopOnFailedTask to control whether the chain stops at
the first failed task or continues to later tasks.
Diagnostics
LastErrorText and each task's result details to troubleshoot
ordered async workflows.
TaskChain in the required order, set
StopOnFailedTask as appropriate, run the chain, wait for
completion, then inspect each task's success status and result. Use
TaskChain when operations must run sequentially; use individual
Task objects when each async operation can be managed on its
own.
Object Creation
loTaskChain = CreateObject('Chilkat.TaskChain')Visual FoxPro is a 32-bit application and therefore uses the 32-bit Chilkat ActiveX. To bind to a specific major version of Chilkat, append the major version number to the ProgID, such as CreateObject('Chilkat.TaskChain.11') for Chilkat v11.*.*.
Properties
DebugLogFilePath
If set to a file path, this property logs the LastErrorText of each Chilkat method or property call to the specified file. This logging helps identify the context and history of Chilkat calls leading up to any crash or hang, aiding in debugging.
Enabling the VerboseLogging property provides more detailed information. This property is mainly used for debugging rare instances where a Chilkat method call causes a hang or crash, which should generally not happen.
Possible causes of hangs include:
- A timeout property set to 0, indicating an infinite timeout.
- A hang occurring within an event callback in the application code.
- An internal bug in the Chilkat code causing the hang.
Finished
1 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.
HeartbeatMs
The number of milliseconds between each AbortCheck event callback. The AbortCheck callback allows an application to abort the Wait method. If HeartbeatMs is 0 (the default), no AbortCheck event callbacks will fire. Note: An asynchronous task chain running in a background thread (in one of the thread pool threads) does not fire events. The task chain's event callbacks pertain only to the Wait method.
topInert
1 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.
LastBinaryResult
This property is mainly used in SQL Server stored procedures to retrieve binary data from the last method call that returned binary data. It is only accessible if Chilkat.Global.KeepBinaryResult is set to 1. This feature allows for the retrieval of large varbinary results in an SQL Server environment, which has restrictions on returning large data via method calls, though temp tables can handle binary properties.
LastErrorHtml
Provides HTML-formatted information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.
topLastErrorText
Provides plain text information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.
LastErrorXml
Provides XML-formatted information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.
topLastMethodSuccess
Indicates the success or failure of the most recent method call: 1 means success, 0 means failure. This property remains unchanged by property setters or getters. This method is present to address challenges in checking for null or Nothing returns in certain programming languages. Note: This property does not apply to methods that return integer values or to boolean-returning methods where the boolean does not indicate success or failure.
LastStringResult
In SQL Server stored procedures, this property holds the string return value of the most recent method call that returns a string. It is accessible only when Chilkat.Global.KeepStringResult is set to TRUE. SQL Server has limitations on string lengths returned from methods and properties, but temp tables can be used to access large strings.
LastStringResultLen
The length, in characters, of the string contained in the LastStringResult property.
topLive
1 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
The number of tasks contained within the task chain.
topStatus
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 therunningstate.aborted-- The task chain was canceled while it was in the running state.completed-- The task chain completed.
StatusInt
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 therunningstate. - 6 --
aborted-- The task chain was canceled while it was in the running state. - 7 --
completed-- The task chain completed.
StopOnFailedTask
If 1 then stops execution of the task chain if any individual task fails. Task failure is defined by the standard LastMethodSuccess property. If 0, then all of the tasks in the chain will be run even if some fail. The default value of this property is 1.
VerboseLogging
If set to 1, then the contents of LastErrorText (or LastErrorXml, or LastErrorHtml) may contain more verbose information. The default value is 0. Verbose logging should only be used for debugging. The potentially large quantity of logged information may adversely affect peformance.
Version
Methods
Append
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 1 for success, 0 for failure.
Cancel
GetTask
Returns the Nth task in the chain. The 1st task is at index 0.
Returns .NULL. on failure
Run
Queues the task chain to run on the internal Chilkat thread pool. Each task in the chain will run, one after the other.
Returns 1 for success, 0 for failure.
topRunSynchronously
Runs the task chain synchronously. Then this method returns after all the tasks in the chain have been run.
Returns 1 for success, 0 for failure.
topSleepMs
Convenience method to force the calling thread to sleep for a number of milliseconds.
topWait
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 (0) 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 1.
Returns 1 for success, 0 for failure.
topEvents
A Visual FoxPro application receives Chilkat ActiveX events by defining a class that IMPLEMENTS the _IChilkatEvents interface, creating an instance of it, and binding that instance to the Chilkat object with EVENTHANDLER(). Visual FoxPro requires the class to implement every method of the interface, so the class below includes a PROCEDURE for each event; leave the ones you do not need empty. The TextData and BinaryData events are defunct: they are deprecated and are never called, but their procedures must still exist because the interface declares them.
Important: Event callbacks from asynchronous method calls are generally not possible from the ActiveX. Events fire during synchronous method calls.
taskChainEventHandler = CREATEOBJECT("MyTaskChainEvents")
loTaskChain = CreateObject('Chilkat.TaskChain')
EVENTHANDLER(loTaskChain, taskChainEventHandler)
DEFINE CLASS MyTaskChainEvents AS SESSION OLEPUBLIC
IMPLEMENTS _IChilkatEvents IN "Chilkat.TaskChain"
PROCEDURE _IChilkatEvents_AbortCheck(abort As Number)
? "AbortCheck"
ENDPROC
* The BinaryData event is defunct: it is deprecated and is never called.
* The procedure must exist because the interface declares it, but it can be left empty.
PROCEDURE _IChilkatEvents_BinaryData(data As Variant)
ENDPROC
PROCEDURE _IChilkatEvents_PercentDone(pctDone As Number, abort As Number)
? "PercentDone"
ENDPROC
PROCEDURE _IChilkatEvents_ProgressInfo(name As String, value As String)
? "ProgressInfo"
ENDPROC
PROCEDURE _IChilkatEvents_TaskCompleted(task As Generic)
? "TaskCompleted"
ENDPROC
* The TextData event is defunct: it is deprecated and is never called.
* The procedure must exist because the interface declares it, but it can be left empty.
PROCEDURE _IChilkatEvents_TextData(data As String)
ENDPROC
ENDDEFINE
AbortCheck
Enables a method call to be aborted by triggering the AbortCheck event at intervals defined by the HeartbeatMs property. If HeartbeatMs is set to its default value of 0, no events will occur. For instance, set HeartbeatMs to 200 to trigger 5 AbortCheck events per second.
FoxPro event implementation:
* Add to the MyTaskChainEvents class shown in the Events overview above.
PROCEDURE _IChilkatEvents_AbortCheck(abort As Number)
* Set abort to 1 to abort the method in progress.
ENDPROC
PercentDone
This provides the percentage completion for any method involving network communications or time-consuming processing, assuming the progress can be measured as a percentage. This event is triggered only when it's possible and logical to express the operation's progress as a percentage. The pctDone argument will range from 1 to 100. For methods that finish quickly, the number of PercentDone callbacks may vary, but the final callback will have pctDone equal to 100. For longer operations, callbacks will not exceed one per percentage point (e.g., 1, 2, 3, ..., 98, 99, 100).
The PercentDone callback also acts as an AbortCheck event. For fast methods where PercentDone fires, an AbortCheck event may not trigger since the PercentDone callback already provides an opportunity to abort. For longer operations, where time between PercentDone callbacks is extended, AbortCheck callbacks enable more responsive operation termination.
To abort the operation, set the abort output argument to 1. This will cause the method to terminate and return a failure status or corresponding failure value.
FoxPro event implementation:
* Add to the MyTaskChainEvents class shown in the Events overview above.
PROCEDURE _IChilkatEvents_PercentDone(pctDone As Number, abort As Number)
* pctDone ranges from 1 to 100. Set abort to 1 to abort the method in progress.
ENDPROC
ProgressInfo
This event callback provides tag name/value pairs that detail what occurs during a method call. To discover existing tag names, create code to handle the event, emit the pairs, and review them. Most tag names are self-explanatory.
Note: Some Chilkat methods don't fire any ProgressInfo events.
FoxPro event implementation:
* Add to the MyTaskChainEvents class shown in the Events overview above.
PROCEDURE _IChilkatEvents_ProgressInfo(name As String, value As String)
? name + ": " + value
ENDPROC
TaskCompleted
Called from the background thread when an asynchronous task completes.
FoxPro event implementation:
* Add to the MyTaskChainEvents class shown in the Events overview above.
PROCEDURE _IChilkatEvents_TaskCompleted(task As Generic)
* task is the Task object that has completed.
ENDPROC