TaskChain Pascal Reference Documentation
TaskChain
Current Version: 11.5.0
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.
Create / Free
uses
Chilkat.TaskChain;
var
obj: TTaskChain;
begin
obj := TTaskChain.Create;
try
if not obj.IsValid then
raise Exception.Create('Failed to create a TTaskChain instance.');
// ... use obj ...
finally
obj.Free;
end;
end;
Allocates the underlying CkTaskChain object and returns a new TTaskChain instance. Simply adding Chilkat.TaskChain to the unit's uses clause is enough to locate and bind to the Chilkat shared library (DLL / .so / .dylib) at runtime — no separate load step is required. Check obj.IsValid after calling Create; it is False if the underlying library could not be found/loaded or the object could not be allocated (for example, when unlicensed).
Every TTaskChain created by calling Create should eventually be released by calling .Free (inherited from TObject). The destructor automatically disposes the underlying CkTaskChain handle. A native (unmanaged) memory leak occurs if the object is never freed.
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
True 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
True 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
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: True means success, False 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.
Live
True 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 True then stops execution of the task chain if any individual task fails. Task failure is defined by the standard LastMethodSuccess property. If False, then all of the tasks in the chain will be run even if some fail. The default value of this property is True.
VerboseLogging
If set to True, then the contents of LastErrorText (or LastErrorXml, or LastErrorHtml) may contain more verbose information. The default value is False. Verbose logging should only be used for debugging. The potentially large quantity of logged information may adversely affect peformance.
Version
Methods
Append
function Append(task: TChilkatBase): Boolean;
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 True for success, False for failure.
topCancel
GetTask
function GetTask(index: Integer): TChilkatBase;
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 True for success, False for failure.
topRunSynchronously
Runs the task chain synchronously. Then this method returns after all the tasks in the chain have been run.
Returns True for success, False 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 (False) 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 True.
Returns True for success, False for failure.
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