pralarm.h - mozsearch

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/*

** File:        pralarm.h

** Description: API to periodic alarms.

**

**

** Alarms are defined to invoke some client specified function at

** a time in the future. The notification may be a one time event

** or repeated at a fixed interval. The interval at which the next

** notification takes place may be modified by the client code only

** during the respective notification.

**

** The notification is delivered on a thread that is part of the

** alarm context (PRAlarm). The thread will inherit the priority

** of the Alarm creator.

**

** Any number of periodic alarms (PRAlarmID) may be created within

** the context of a single alarm (PRAlarm). The notifications will be

** scheduled as close to the desired time as possible.

**

** Repeating periodic notifies are expected to run at a fixed rate.

** That rate is expressed as some number of notifies per period where

** the period is much larger than a PRIntervalTime (see prinrval.h).

*/

#if !defined(pralarm_h)

#define pralarm_h

#include "prtypes.h"

#include "prinrval.h"

PR_BEGIN_EXTERN_C

/**********************************************************************/

/************************* TYPES AND CONSTANTS ************************/

/**********************************************************************/

typedef struct PRAlarm PRAlarm;

typedef struct PRAlarmID PRAlarmID;

typedef PRBool (PR_CALLBACK *PRPeriodicAlarmFn)(

    PRAlarmID *id, void *clientData, PRUint32 late);

/**********************************************************************/

/****************************** FUNCTIONS *****************************/

/**********************************************************************/

/***********************************************************************

** FUNCTION:    PR_CreateAlarm

** DESCRIPTION:

**  Create an alarm context.

** INPUTS:      void

** OUTPUTS:     None

** RETURN:      PRAlarm*

**

** SIDE EFFECTS:

**  This creates an alarm context, which is an object used for subsequent

**  notification creations. It also creates a thread that will be used to

** deliver the notifications that are expected to be defined. The client

** is resposible for destroying the context when appropriate.

** RESTRICTIONS:

**  None.

** MEMORY:      The object (PRAlarm) and a thread to support notifications.

** ALGORITHM:   N/A

***********************************************************************/

NSPR_API(PRAlarm*) PR_CreateAlarm(void);

/***********************************************************************

** FUNCTION:    PR_DestroyAlarm

** DESCRIPTION:

**  Destroys the context created by PR_CreateAlarm().

** INPUTS:      PRAlarm*

** OUTPUTS:     None

** RETURN:      PRStatus

**

** SIDE EFFECTS:

**  This destroys the context that was created by PR_CreateAlarm().

**  If there are any active alarms (PRAlarmID), they will be cancelled.

**  Once that is done, the thread that was used to deliver the alarms

**  will be joined.

** RESTRICTIONS:

**  None.

** MEMORY:      N/A

** ALGORITHM:   N/A

***********************************************************************/

NSPR_API(PRStatus) PR_DestroyAlarm(PRAlarm *alarm);

/***********************************************************************

** FUNCTION:    PR_SetAlarm

** DESCRIPTION:

**  Creates a periodic notifier that is to be delivered to a specified

**  function at some fixed interval.

** INPUTS:      PRAlarm *alarm              Parent alarm context

**              PRIntervalTime period       Interval over which the notifies

**                                          are delivered.

**              PRUint32 rate               The rate within the interval that

**                                          the notifies will be delivered.

**              PRPeriodicAlarmFn function  Entry point where the notifies

**                                          will be delivered.

** OUTPUTS:     None

** RETURN:      PRAlarmID*                  Handle to the notifier just created

**                                          or NULL if the request failed.

**

** SIDE EFFECTS:

**  A periodic notifier is created. The notifications will be delivered

**  by the alarm's internal thread at a fixed interval whose rate is the

**  number of interrupts per interval specified. The first notification

**  will be delivered as soon as possible, and they will continue until

**  the notifier routine indicates that they should cease of the alarm

**  context is destroyed (PR_DestroyAlarm).

** RESTRICTIONS:

**  None.

** MEMORY:      Memory for the notifier object.

** ALGORITHM:   The rate at which notifications are delivered are stated

**              to be "'rate' notifies per 'interval'". The exact time of

**              the notification is computed based on a epoch established

**              when the notifier was set. Each notification is delivered

**              not ealier than the epoch plus the fixed rate times the

**              notification sequence number. Such notifications have the

**              potential to be late by not more than 'interval'/'rate'.

**              The amount of lateness of one notification is taken into

**              account on the next in an attempt to avoid long term slew.

***********************************************************************/

NSPR_API(PRAlarmID*) PR_SetAlarm(

    PRAlarm *alarm, PRIntervalTime period, PRUint32 rate,

    PRPeriodicAlarmFn function, void *clientData);

/***********************************************************************

** FUNCTION:    PR_ResetAlarm

** DESCRIPTION:

**  Resets an existing alarm.

** INPUTS:      PRAlarmID *id               Identify of the notifier.

**              PRIntervalTime period       Interval over which the notifies

**                                          are delivered.

**              PRUint32 rate               The rate within the interval that

**                                          the notifies will be delivered.

** OUTPUTS:     None

** RETURN:      PRStatus                    Indication of completion.

**

** SIDE EFFECTS:

**  An existing alarm may have its period and rate redefined. The

**  additional side effect is that the notifier's epoch is recomputed.

**  The first notification delivered by the newly refreshed alarm is

**  defined to be 'interval'/'rate' from the time of the reset.

** RESTRICTIONS:

**  This function may only be called in the notifier for that alarm.

** MEMORY:      N/A.

** ALGORITHM:   See PR_SetAlarm().

***********************************************************************/

NSPR_API(PRStatus) PR_ResetAlarm(

    PRAlarmID *id, PRIntervalTime period, PRUint32 rate);

PR_END_EXTERN_C

#endif /* !defined(pralarm_h) */

/* prinrval.h */