Task Lianja Reference Documentation

Task

Current Version: 9.5.0.73

Represents a single task to be run in a background thread.

Object Creation

loObject = createobject("CkTask")

Properties

DebugLogFilePath
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.

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Finished
Finished As Boolean (read-only)
Introduced in version 9.5.0.52

.T. if the task status is "canceled", "aborted", or "completed". A task 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.

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Inert
Inert As Boolean (read-only)
Introduced in version 9.5.0.52

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

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KeepProgressLog
KeepProgressLog As Boolean
Introduced in version 9.5.0.52

Determines if the in-memory progress info event log is kept. The default value is .F. and therefore no log is kept. To enable progress info logging, set this property equal to .T. (prior to running the task).

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LastErrorHtml
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.

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LastErrorText
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.

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LastErrorXml
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.

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LastMethodSuccess
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.

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Live
Live As Boolean (read-only)
Introduced in version 9.5.0.52

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

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PercentDone
PercentDone As Numeric (read-only)
Introduced in version 9.5.0.52

Indicates the percent completion while the task is running. The percent completed information is only available in cases where it is possible to know the percentage completed. For some methods, it is never possible to know, such as for methods that establish TCP or TLS connections. For other methods it is always possible to know -- such as for sending email (because the size of the email to be sent is already known). For some methods, it may or may not be possible to know the percent completed. For example, if an HTTP response is "chunked", there is no Content-Length header and therefore the receiver has no knowledge of the size of the forthcoming response body.

Also, the value of the PercentDoneScale property of the asynchronous method's object determines the scale, such as 0 to 100, or 0 to 1000, etc.

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ProgressLogSize
ProgressLogSize As Numeric (read-only)
Introduced in version 9.5.0.52

What would normally be a ProgressInfo event callback (assuming Chilkat supports event callbacks for this language) is instead saved to an in-memory progress log that can be examined and pruned while the task is still running. This property returns the number of progress log entries that are currently available. (Note: the progress log is only kept if the KeepProgressLog property is turned on. By default, the KeepProgressLog is turned off.)

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ResultErrorText
ResultErrorText As Character (read-only)
Introduced in version 9.5.0.52

The LastErrorText for the task's asynchronous method.

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ResultType
ResultType As Character (read-only)
Introduced in version 9.5.0.52

Indicates the data type of the task's result. This property is only available after the task has completed. Possible values are "bool", "int", "string", "bytes", "object", and "void". For example, if the result data type is "bool", then call GetResultBool to get the boolean result of the underlying asynchronous method.

For example, if the synchronous version of the method returned a boolean, then in the asynchronous version of the method, the boolean return value is made available via the GetResultBool method.

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Status
Status As Character (read-only)
Introduced in version 9.5.0.52

The current status of the task. Possible values are:

  • "empty" -- The method call and arguments are not yet loaded into the task object. This can only happen if a task was explicitly created instead of being returned by a method ending in "Async".
  • "loaded" -- The method call and arguments are loaded into the task object.
  • "queued" -- The task is in the thread pool's queue of tasks awaiting to be run.
  • "running" -- The task is currently running.
  • "canceled" -- The task was canceled before it entered the "running" state.
  • "aborted" -- The task was canceled while it was in the running state.
  • "completed" -- The task completed. The success or failure depends on the semantics of the method call and the value of the result.

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StatusInt
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 -- The method call and arguments are not yet loaded into the task object. This can only happen if a task was explicitly created instead of being returned by a method ending in "Async".
  • 2 -- The method call and arguments are loaded into the task object.
  • 3 -- The task is in the thread pool's queue of tasks awaiting to be run.
  • 4 -- The task is currently running.
  • 5 -- The task was canceled before it entered the "running" state.
  • 6 -- The task was canceled while it was in the running state.
  • 7 -- The task completed. The success or failure depends on the semantics of the method call and the value of the result.

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TaskId
TaskId As Numeric (read-only)
Introduced in version 9.5.0.52

A unique integer ID assigned to this task. The purpose of this property is to help an application identify the task if a TaskCompleted event callback is used.

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TaskSuccess
TaskSuccess As Boolean (read-only)
Introduced in version 9.5.0.52

This is the value of the LastMethodSuccess property of the underlying task object. This property is only valid for those methods where the LastMethodSuccess property would be valid had the method been called synchronously.

Important: This property is only meaningful for cases where the underlying method call has a non-boolean return value (such as for methods that return strings, other Chilkat objects, or integers). If the underlying method call returns a boolean, then call the GetResultBool() method instead to get the boolean return value.

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UserData
UserData As Character
Introduced in version 9.5.0.52

An application may use this property to attach some user-specific information with the task, which may be useful if a TaskCompleted event callback is used.

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VerboseLogging
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.

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Version
Version As Character (read-only)

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

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Methods

Cancel
Cancel() As Boolean
Introduced in version 9.5.0.52

Marks an asynchronous task for cancellation. The expected behavior depends on the current status of the task as described here:

  • "loaded" - If the task has been loaded but has not yet been queued to run in the thread pool, then there is nothing to do. (There is nothing to cancel because the task's Run method has not yet been called.) The task will remain in the "loaded" state.
  • "queued" - The task is marked for cancellation, is dequeued, and will not run. The task's status changes immediately to "canceled".
  • "running" - The already-running task is marked for cancellation. The task's status will eventually change to "aborted" when the asynchronous method returns. At that point in time, the ResultErrorText property will contain the "LastErrorText" of the method call. In the case where a task is marked for cancellation just at the time it's completing, the task status may instead change to "completed".
  • "canceled", "aborted", "completed" - In these cases the task has already finished, and there will be no change in status.
Cancel returns .T. if the task was in the "queued" or "running" state when it was marked for cancellation. Cancel returns .F. if the task was in any other state.

Important: Calling the Cancel method marks a task for cancellation. It sets a flag in memory that the running task will soon notice and then abort. It is important to realize that your application is likely calling Cancel from the main UI thread, whereas the asynchronous task is running in a background thread. If the task was in the "running" state when Cancel was called, it will still be in the "running" state when Cancel returns. It will take a short amount of time until the task actually aborts. This is because operating systems schedule threads in time slices, and the thread needs one or more time slices to notice the cancellation flag and abort. After calling Cancel, your application might wish to call the Wait method to wait until the task has actually aborted, or it could periodically check the task's status and then react once the status changes to "aborted".

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ClearProgressLog
ClearProgressLog()
Introduced in version 9.5.0.52

Removes all entries from the progress info log.

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GetResultBool
GetResultBool() As Boolean
Introduced in version 9.5.0.52

Returns the boolean result of the task.

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GetResultInt
GetResultInt() As Numeric
Introduced in version 9.5.0.52

Returns the integer result of the task.

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GetResultString
GetResultString() As Character
Introduced in version 9.5.0.52

Returns the string result of the task.

Returns .F. on failure

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ProgressInfoName
ProgressInfoName(index As Numeric) As Character
Introduced in version 9.5.0.52

Returns the name of the Nth progress info event logged. The 1st entry is at index 0.

Returns .F. on failure

More Information and Examples
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ProgressInfoValue
ProgressInfoValue(index As Numeric) As Character
Introduced in version 9.5.0.52

Returns the value of the Nth progress info event logged. The 1st entry is at index 0.

Returns .F. on failure

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RemoveProgressInfo
RemoveProgressInfo(index As Numeric)
Introduced in version 9.5.0.52

Removes the Nth progress info log entry.

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Run
Run() As Boolean
Introduced in version 9.5.0.52

Queues the task to run on the internal Chilkat thread pool.

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

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RunSynchronously
RunSynchronously() As Boolean
Introduced in version 9.5.0.52

Runs the task synchronously. Then this method returns after the task has been run.

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

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SaveLastError
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.

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SleepMs
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. (This does not cause the task's background thread to sleep.)

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Wait
Wait(maxWaitMs As Numeric) As Boolean
Introduced in version 9.5.0.52

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

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

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