Task C Reference Documentation
Task
Current Version: 10.1.0
Represents a single task to be run in a background thread.
Create/Dispose
HCkTask instance = CkTask_Create(); // ... CkTask_Dispose(instance);
Creates an instance of the HCkTask object and returns a handle ("void *" pointer). The handle is passed in the 1st argument for the functions listed on this page.
Objects created by calling CkTask_Create must be freed by calling this method. A memory leak occurs if a handle is not disposed by calling this function. Also, any handle returned by a Chilkat "C" function must also be freed by the application by calling the appropriate Dispose method, such as CkTask_Dispose.
Callback Functions
Provides the opportunity for a method call to be aborted. If TRUE is returned, the operation in progress is aborted. Return FALSE to allow the current method call to continue. This callback function is called periodically based on the value of the HeartbeatMs property. (If HeartbeatMs is 0, then no callbacks are made.) As an example, to make 5 AbortCheck callbacks per second, set the HeartbeatMs property equal to 200.
See Also:C Example using Callback Functions
Provides the percentage completed for any method that involves network communications or time-consuming processing (assuming it is a method where a percentage completion can be measured). This callback is only called when it is possible to know a percentage completion, and when it makes sense to express the operation as a percentage completed. The pctDone argument will have a value from 1 to 100. For methods that complete very quickly, the number of PercentDone callbacks will vary, but the final callback should have a value of 100. For long running operations, no more than one callback per percentage point will occur (for example: 1, 2, 3, ... 98, 99, 100).
This callback counts as an AbortCheck callback, and takes the place of the AbortCheck event when it fires.
The return value indicates whether the method call should be aborted, or whether it should proceed. Return TRUE to abort, and FALSE to proceed.
This is a general callback that provides name/value information about what is happening at certain points during a method call. To see the information provided in ProgressInfo callbacks, if any, write code to handle this event and log the name/value pairs. Most are self-explanatory.
Called in the background thread when an asynchronous task completes. (Note: When an async method is running, all callbacks are in the background thread.)
Properties
DebugLogFilePath
void CkTask_putDebugLogFilePath(HCkTask cHandle, const char *newVal);
const char *CkTask_debugLogFilePath(HCkTask cHandle);
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:
- a timeout related property was set to 0 to explicitly indicate that an infinite timeout is desired,
- the hang is actually a hang within an event callback (i.e. it is a hang within the application code), or
- there is an internal problem (bug) in the Chilkat code that causes the hang.
Finished
TRUE 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.
topHeartbeatMs
void CkTask_putHeartbeatMs(HCkTask cHandle, int newVal);
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 running in a background thread (in one of the thread pool threads) does not fire events. The task's event callbacks pertain only to the Wait method.
topInert
TRUE if the task status is "empty" or "loaded". When a task is inert, it has been loaded but is not scheduled to run yet.
topKeepProgressLog
void CkTask_putKeepProgressLog(HCkTask cHandle, BOOL newVal);
Determines if the in-memory progress info event log is kept. The default value is FALSE and therefore no log is kept. To enable progress info logging, set this property equal to TRUE (prior to running the task).
topLastErrorHtml
const char *CkTask_lastErrorHtml(HCkTask cHandle);
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.
topLastErrorText
const char *CkTask_lastErrorText(HCkTask cHandle);
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.
LastErrorXml
const char *CkTask_lastErrorXml(HCkTask cHandle);
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.
topLastMethodSuccess
void CkTask_putLastMethodSuccess(HCkTask cHandle, BOOL newVal);
Indicate whether the last method call succeeded or failed. A value of TRUE indicates success, a value of FALSE 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 = TRUE and failure = FALSE.
- 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 TRUE. For example, a method that returns no value (such as a "void" in C++) will technically always succeed.
topLive
TRUE 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.
topPercentDone
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.
topProgressLogSize
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.)
topResultErrorText
const char *CkTask_resultErrorText(HCkTask cHandle);
The LastErrorText for the task's asynchronous method.
topResultType
const char *CkTask_resultType(HCkTask cHandle);
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.
topStatus
const char *CkTask_status(HCkTask cHandle);
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.
StatusInt
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.
TaskId
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.
topTaskSuccess
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.
topUserData
void CkTask_putUserData(HCkTask cHandle, const char *newVal);
const char *CkTask_userData(HCkTask cHandle);
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.
topUtf8
void CkTask_putUtf8(HCkTask cHandle, BOOL newVal);
When set to TRUE, all "const char *" arguments are interpreted as utf-8 strings. If set to FALSE (the default), then "const char *" arguments are interpreted as ANSI strings. Also, when set to TRUE, and Chilkat method returning a "const char *" is returning the utf-8 representation. If set to FALSE, all "const char *" return values are ANSI strings.
topVerboseLogging
void CkTask_putVerboseLogging(HCkTask cHandle, 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.
topVersion
const char *CkTask_version(HCkTask cHandle);
Methods
Cancel
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.
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".
topClearProgressLog
Removes all entries from the progress info log.
topCopyResultBytes
Returns the binary bytes result of the task. The bytes are copied to the caller.
Returns TRUE for success, FALSE for failure.
topGetResultBool
Returns the boolean result of the task.
topGetResultBytes
Returns the binary bytes result of the task. The bytes are transferred to the caller, not copied. Call CopyResultBytes instead to copy the result bytes.
Returns TRUE for success, FALSE for failure.
topGetResultInt
Returns the integer result of the task.
topGetResultString
const char *CkTask_getResultString(HCkTask cHandle);
ProgressInfoName
const char *CkTask_progressInfoName(HCkTask cHandle, int index);
Returns the name of the Nth progress info event logged. The 1st entry is at index 0.
Returns TRUE for success, FALSE for failure.
ProgressInfoValue
const char *CkTask_progressInfoValue(HCkTask cHandle, int index);
Returns the value of the Nth progress info event logged. The 1st entry is at index 0.
Returns TRUE for success, FALSE for failure.
topRemoveProgressInfo
Removes the Nth progress info log entry.
topRun
Queues the task to run on the internal Chilkat thread pool.
Returns TRUE for success, FALSE for failure.
topRunSynchronously
Runs the task synchronously. Then this method returns after the task has been run.
Returns TRUE for success, FALSE for failure.
topSleepMs
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.)
topWait
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 (FALSE) 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 TRUE.
Returns TRUE for success, FALSE for failure.
top