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Interface PriorityTask

All Known Implementing Classes:

AbstractHttpSessionCollection.ExitAgent, AbstractInvocable, AbstractPriorityTask, PortalCacheProvider.FlushAgent, PriorityAggregator, PriorityFilter, PriorityProcessor, WorkManager.AbstractWork, WorkManager.CollectMembershipInfo, WorkManager.ReleaseWork, WorkManager.RequestStatus, WorkManager.ScheduleWork, WorkManager.SendFeedback

public interface PriorityTask

The PriorityTask interface allows to control the ordering in which a service schedules tasks for execution using a thread pool and limit their execution times to a specified duration. Instances of PriorityTask typically also implement either Invocable or Runnable interface.

Depending on the value returned by the getSchedulingPriority() method, the scheduling order will be one of the following:

• SCHEDULE_STANDARD - a task will be scheduled for execution in a natural (based on the request arrival time) order;
• SCHEDULE_FIRST - a task will be scheduled in front of any equal or lower scheduling priority tasks and executed as soon as any of worker threads become available;
• SCHEDULE_IMMEDIATE - a task will be immediately executed by any idle worker thread; if all of them are active, a new thread will be created to execute this task.

A best effort will be made to limit the task execution time according to the value returned by the getExecutionTimeoutMillis() method. However, it should be noted that:

• for tasks with the scheduling priority of SCHEDULE_IMMEDIATE, factors that could make the execution time longer than the timeout value are long GC pauses and high network latency;
• if the service has a task backlog (when there are more tasks scheduled for execution than the number of available worker threads), the request execution time (measured from the client's perspective) for tasks with the scheduling priorities of SCHEDULE_STANDARD or SCHEDULE_FIRST could be longer and include the time those tasks were kept in a queue before invocation;
• the corresponding service is free to cancel the task execution before the task is started and call the runCanceled(boolean) method if it's known that the client is no longer interested in the results of the task execution.

In addition to allowing control of the task execution (as scheduled and measured on the server side), the PriorityTask interface could also be used to control the request time from the calling thread perspective (measured on the client). A best effort will be made to limit the request time (the time period that the calling thread is blocked waiting for a response from the corresponding service) to the value returned by the getRequestTimeoutMillis() method.

It should be noted that the request timeout value (RT) could be grater than, equal to or less than the task execution timeout value (ET). The value of RT which is less than ET indicates that even though the task execution is allowed to take longer period of time, the client thread will not wait for a result of the execution and will be able to handle a timeout exception if it arises. Since the time spent by the task waiting in the service backlog queue does not count toward the task execution time, a value of RT that is equal or slightly greater than ET still leaves a possibility that the client thread will throw a TimeoutException before the task completes its execution normally on a server.

Since:

Coherence 3.3

Author:

gg 2006.11.02

Field Summary

static int	SCHEDULE_FIRST Scheduling value indicating that this task is to be queued in front of any equal or lower scheduling priority tasks and executed as soon as any of the worker threads become available.
static int	SCHEDULE_IMMEDIATE Scheduling value indicating that this task is to be immediately executed by any idle worker thread; if all of them are active, a new thread will be created to execute this task.
static int	SCHEDULE_STANDARD Scheduling value indicating that this task is to be queued and executed in a natural (based on the request arrival time) order.
static long	TIMEOUT_DEFAULT A special timeout value to indicate that the corresponding service's default timeout value should be used.
static long	TIMEOUT_NONE A special timeout value to indicate that this task or request can run indefinitely.

Method Summary

long	getExecutionTimeoutMillis() Obtain the maximum amount of time this task is allowed to run before the corresponding service will attempt to stop it.
long	getRequestTimeoutMillis() Obtain the maximum amount of time a calling thread is willing to wait for a result of the request execution.
int	getSchedulingPriority() Obtain this task's scheduling priority.
void	runCanceled(boolean fAbandoned) This method will be called if and only if all attempts to interrupt this task were unsuccesful in stopping the execution or if the execution was canceled before it had a chance to run at all.

Field Detail

SCHEDULE_STANDARD

static final int SCHEDULE_STANDARD

Scheduling value indicating that this task is to be queued and executed in a natural (based on the request arrival time) order.

See Also:

Constant Field Values

SCHEDULE_FIRST

static final int SCHEDULE_FIRST

Scheduling value indicating that this task is to be queued in front of any equal or lower scheduling priority tasks and executed as soon as any of the worker threads become available.

See Also:

Constant Field Values

SCHEDULE_IMMEDIATE

static final int SCHEDULE_IMMEDIATE

Scheduling value indicating that this task is to be immediately executed by any idle worker thread; if all of them are active, a new thread will be created to execute this task.

See Also:

Constant Field Values

TIMEOUT_DEFAULT

static final long TIMEOUT_DEFAULT

A special timeout value to indicate that the corresponding service's default timeout value should be used.

See Also:

Constant Field Values

TIMEOUT_NONE

static final long TIMEOUT_NONE

A special timeout value to indicate that this task or request can run indefinitely.

See Also:

Constant Field Values

Method Detail

getSchedulingPriority

int getSchedulingPriority()

Obtain this task's scheduling priority. Valid values are one of the SCHEDULE_* constants.

Returns:

this task's scheduling priority

getExecutionTimeoutMillis

long getExecutionTimeoutMillis()

Obtain the maximum amount of time this task is allowed to run before the corresponding service will attempt to stop it.

The value of TIMEOUT_DEFAULT indicates a default timeout value configured for the corresponding service; the value of TIMEOUT_NONE indicates that this task can execute indefinitely.

If, by the time the specified amount of time passed, the task has not finished, the service will attempt to stop the execution by using the Thread.interrupt() method. In the case that interrupting the thread does not result in the task's termination, the runCanceled(boolean) method will be called.

Returns:

the execution timeout value in millisecods or one of the special TIMEOUT_* values

getRequestTimeoutMillis

long getRequestTimeoutMillis()

Obtain the maximum amount of time a calling thread is willing to wait for a result of the request execution. The request time is measured on the client side as the time elapsed from the moment a request is sent for execution to the corresponding server node(s) and includes:

• the time it takes to deliver the request to the executing node(s);
• the interval between the time the task is received and placed into a service queue until the execution starts;
• the task execution time;
• the time it takes to deliver a result back to the client.

The value of TIMEOUT_DEFAULT indicates a default timeout value configured for the corresponding service; the value of TIMEOUT_NONE indicates that the client thread is willing to wait indefinitely until the task execution completes or is canceled by the service due to a task execution timeout specified by the getExecutionTimeoutMillis() value.

If the specified amount of time elapsed and the client has not received any response from the server, an RequestTimeoutException will be thrown to the caller.

Returns:

the request timeout value in milliseconds or one of the special TIMEOUT_* values

runCanceled

void runCanceled(boolean fAbandoned)

This method will be called if and only if all attempts to interrupt this task were unsuccesful in stopping the execution or if the execution was canceled before it had a chance to run at all.

Since this method is usually called on a service thread, implementors must exercise extreme caution since any delay introduced by the implementation will cause a delay of the corresponding service.

Parameters:

fAbandoned - true if the task has timed-out, but all attempts to interrupt it were unsuccesful in stopping the execution; otherwise the task was never started