TaskChain C++ Reference Documentation

CkTaskChain

Current Version: 11.1.0

Requires Chilkat Bundle License

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

Object Creation

// Local variable on the stack
CkTaskChain obj;

// Dynamically allocate/delete
CkTaskChain *pObj = new CkTaskChain();
// ...
delete pObj;

Properties

DebugLogFilePath

void get_DebugLogFilePath(CkString &str);
const char *debugLogFilePath(void);
void put_DebugLogFilePath(const char *ansiOrUtf8Str);

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.

More Information and Examples

Example showing how to use DebugLogFilePath.

Finished

bool get_Finished(void);

Introduced in version 9.5.0.52

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

int get_HeartbeatMs(void);
void put_HeartbeatMs(int newVal);

Introduced in version 9.5.0.52

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.

Inert

bool get_Inert(void);

Introduced in version 9.5.0.52

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

void get_LastErrorHtml(CkString &str);
const char *lastErrorHtml(void);

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.

LastErrorText

void get_LastErrorText(CkString &str);
const char *lastErrorText(void);

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.

More Information and Examples

Concept of LastErrorText LastErrorText Standard Information

LastErrorXml

void get_LastErrorXml(CkString &str);
const char *lastErrorXml(void);

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.

LastMethodSuccess

bool get_LastMethodSuccess(void);
void put_LastMethodSuccess(bool newVal);

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.

Live

bool get_Live(void);

Introduced in version 9.5.0.52

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

int get_NumTasks(void);

Introduced in version 9.5.0.52

The number of tasks contained within the task chain.

Status

void get_Status(CkString &str);
const char *status(void);

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

int get_StatusInt(void);

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

bool get_StopOnFailedTask(void);
void put_StopOnFailedTask(bool newVal);

Introduced in version 9.5.0.52

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.

More Information and Examples

Async Methods Returning an Object

Utf8

bool get_Utf8(void);
void put_Utf8(bool newVal);

When set to true, all const char * arguments and return values are interpreted as UTF-8 strings. When set to false, they are interpreted as ANSI strings.

In Chilkat v11.0.0 and later, the default value is true. Before v11.0.0, it was false.

VerboseLogging

bool get_VerboseLogging(void);
void put_VerboseLogging(bool newVal);

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

void get_Version(CkString &str);
const char *version(void);

Version of the component/library, such as "10.1.0"

More Information and Examples

How to get the Chilkat version at runtime.

Methods

Append

bool Append(CkTask &task);

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 true for success, false for failure.

More Information and Examples

Async Task Chain

Cancel

bool Cancel(void);

Introduced in version 9.5.0.52

Cancels execution of the asynchronous task chain.

Returns true for success, false for failure.

GetTask

CkTask *GetTask(int index);

Introduced in version 9.5.0.52

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

Note: The application is responsible for deleting (via the C++ delete operator) the object returned by this method.

Returns NULL on failure

More Information and Examples

Async Methods Returning an Object

Run

bool Run(void);

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 true for success, false for failure.

RunSynchronously

bool RunSynchronously(void);

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 true for success, false for failure.

SleepMs

void SleepMs(int numMs);

Introduced in version 9.5.0.52

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

Wait

bool Wait(int maxWaitMs);

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 (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.

Events

To implement an event callback, your application would define and implement a class that inherits from CkBaseProgress. Your application can implement methods to override some or all of the default/empty method implementations of the CkBaseProgress base class.

For example:

  CkTaskChain taskchain;

  MyTaskChainProgress callbackObj;

  taskchain.put_EventCallbackObject(&callbackObj);

MyTaskChainProgress example:

#include "CkBaseProgress.h"

class MyTaskChainProgress : public CkBaseProgress {

  public:
    MyTaskChainProgress();
    virtual ~MyTaskChainProgress();

    void AbortCheck(bool  *abort);

    void PercentDone(int pctDone, bool  *abort);

    void ProgressInfo(const char *name, const char *value);

    void TaskCompleted(CkTask &task);

};

AbortCheck

void AbortCheck(bool *abort);

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.

More Information and Examples

Chilkat Event Callback Examples

PercentDone

void PercentDone(int pctDone, bool *abort);

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 true. This will cause the method to terminate and return a failure status or corresponding failure value.

More Information and Examples

Chilkat Event Callback Examples

ProgressInfo

void ProgressInfo(const char *name, const char *value);

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.

More Information and Examples

Chilkat Event Callback Examples

TaskCompleted

void TaskCompleted(CkTask &task);

Called from the background thread when an asynchronous task completes.

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