Oracle® Fusion Middleware C++ API Reference for Oracle Coherence
12c (12.2.1.3.0)
E80355-01

coherence/net/PriorityTask.hpp

/*
* PriorityTask.hpp
*
* Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.
*
* Oracle is a registered trademarks of Oracle Corporation and/or its
* affiliates.
*
* This software is the confidential and proprietary information of Oracle
* Corporation. You shall not disclose such confidential and proprietary
* information and shall use it only in accordance with the terms of the
* license agreement you entered into with Oracle.
*
* This notice may not be removed or altered.
*/
#ifndef COH_PRIORITY_TASK_HPP
#define COH_PRIORITY_TASK_HPP

#include "coherence/lang.ns"

COH_OPEN_NAMESPACE2(coherence,net)


/**
* 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 PriorityTask or Runnable interface.
*
* Depending on the value returned by the #getSchedulingPriority()
* method, the scheduling order will be one of the following:
* <ul>
* <li> #schedule_standard - a task will be scheduled for execution in
*      a natural (based on the request arrival time) order;
* <li> #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;
* <li> #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.
* </ul>
*
* 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:
* <ul>
* <li> 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;
* <li> 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;
* <li> the corresponding service is free to cancel the task execution before
*      the task is started and call the #runCanceled method if it's
*      known that the client is no longer interested in the results of the
*      task execution.
* </ul>
*
* 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.
*
* @author djl  2008.05.15
*/
class COH_EXPORT PriorityTask
    : public interface_spec<PriorityTask>
    {
    // ----- PriorityTask interface -----------------------------------------

    public:
        /**
        * Obtain this task's scheduling priority. Valid values are one of the
        * SCHEDULE_* constants.
        *
        * @return  this task's scheduling priority
        */
        virtual int32_t getSchedulingPriority() const = 0;

        /**
        * 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 method will be called.
        *
        * @return the execution timeout value in millisecods or one of the
        *          special TIMEOUT_* values
        */
        virtual int64_t getExecutionTimeoutMillis() const = 0;

        /**
        * 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:
        * <ul>
        * <li> the time it takes to deliver the request to the executing
        *      node(s);
        * <li> the interval between the time the task is received and placed
        *      into a service queue until the execution starts;
        * <li> the task execution time;
        * <li> the time it takes to deliver a result back to the client.
        * </ul>
        *
        * The value of timeout_default  indicates a default timeout value
        * configured for the corresponding service; the
        * value of #timeout_none 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.
        *
        * @return the request timeout value in milliseconds or one of the
        *          special TIMEOUT_* values
        */
        virtual int64_t getRequestTimeoutMillis() const = 0;

        /**
        * 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 <b>before</b> 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.
        *
        * @param 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
        */
        virtual void runCanceled(bool fAbandoned) = 0;


    // ----- constants ------------------------------------------------------

    public:
        /**
        * Scheduling value indicating that this task is to be queued and
        * executed in a natural (based on the request arrival time) order.
        */
        static const int32_t schedule_standard = 0;

        /**
        * 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 const int32_t schedule_first = 1;

        /**
        * 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 const int32_t schedule_immediate = 2;

        /**
        * A special timeout value to indicate that the corresponding
        * service's default timeout value should be used.
        */
        static const int64_t timeout_default = 0L;

        /**
        * A special timeout value to indicate that this task or request can
        * run indefinitely.
        */
        static const int64_t timeout_none = -1L;
    };

COH_CLOSE_NAMESPACE2

#endif // COH_PRIORITY_TASK_HPP

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