gecko-dev/xpcom/threads/nsITimer.idl

/* -*- Mode: C++; tab-width: 2; 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/. */

#include "nsISupports.idl"

interface nsIObserver;
interface nsIEventTarget;

%{C++
/**
 * The signature of the timer callback function passed to initWithFuncCallback.
 * This is the function that will get called when the timer expires if the
 * timer is initialized via initWithFuncCallback.
 *
 * @param aTimer the timer which has expired
 * @param aClosure opaque parameter passed to initWithFuncCallback
 */
class nsITimer;
typedef void (*nsTimerCallbackFunc) (nsITimer *aTimer, void *aClosure);
%}

native nsTimerCallbackFunc(nsTimerCallbackFunc);

/**
 * The callback interface for timers.
 */
interface nsITimer;

[function, scriptable, uuid(a796816d-7d47-4348-9ab8-c7aeb3216a7d)]
interface nsITimerCallback : nsISupports
{
  /**
   * @param aTimer the timer which has expired
   */
  void notify(in nsITimer timer);
};

%{C++
// Two timer deadlines must differ by less than half the PRIntervalTime domain.
#define DELAY_INTERVAL_LIMIT    PR_BIT(8 * sizeof(PRIntervalTime) - 1)
%}

/**
 * nsITimer instances must be initialized by calling one of the "init" methods
 * documented below.  You may also re-initialize (using one of the init()
 * methods) an existing instance to avoid the overhead of destroying and
 * creating a timer.  It is not necessary to cancel the timer in that case.
 *
 * By default a timer will fire on the thread that created it.  Set the .target
 * attribute to fire on a different thread.  Once you have set a timer's .target
 * and called one of its init functions, any further interactions with the timer
 * (calling cancel(), changing member fields, etc) should only be done by the
 * target thread, or races may occur with bad results like timers firing after
 * they've been canceled, and/or not firing after re-initiatization.
 */
[scriptable, uuid(193fc37a-8aa4-4d29-aa57-1acd87c26b66)]
interface nsITimer : nsISupports
{
  /* Timer types */

  /**
   * Type of a timer that fires once only.
   */
  const short TYPE_ONE_SHOT           = 0;

  /**
   * After firing, a TYPE_REPEATING_SLACK timer is stopped and not restarted
   * until its callback completes.  Specified timer period will be at least
   * the time between when processing for last firing the callback completes
   * and when the next firing occurs.
   *
   * This is the preferable repeating type for most situations.
   */
  const short TYPE_REPEATING_SLACK    = 1;
  
  /**
   * An TYPE_REPEATING_PRECISE repeating timer aims to have constant period
   * between firings.  The processing time for each timer callback should not
   * influence the timer period.  However, if the processing for the last
   * timer firing could not be completed until just before the next firing
   * occurs, then you could have two timer notification routines being
   * executed in quick succession.  Furthermore, if your callback processing
   * time is longer than the timer period, then the timer will post more
   * notifications while your callback is running.  For example, if a
   * REPEATING_PRECISE timer has a 10ms period and a callback takes 50ms,
   * then by the time the callback is done there will be 5 events to run the
   * timer callback in the event queue.  Furthermore, the next scheduled time
   * will always advance by exactly the delay every time the timer fires.
   * This means that if the clock increments without the timer thread running
   * (e.g. the computer is asleep) when the timer thread gets to run again it
   * will post all the events that it "missed" while it wasn't running.  Use
   * this timer type with extreme caution.  Chances are, this is not what you
   * want.
   */
  const short TYPE_REPEATING_PRECISE  = 2;

  /**
   * A TYPE_REPEATING_PRECISE_CAN_SKIP repeating timer aims to have constant
   * period between firings.  The processing time for each timer callback
   * should not influence the timer period.  However this timer type
   * guarantees that it will not queue up new events to fire the callback
   * until the previous callback event finishes firing.  If the callback
   * takes a long time, then the next callback will be scheduled immediately
   * afterward, but only once, unlike TYPE_REPEATING_PRECISE.  If you want a
   * non-slack timer, you probably want this one.
   */
  const short TYPE_REPEATING_PRECISE_CAN_SKIP  = 3;

  /**
   * Initialize a timer that will fire after the said delay.
   * A user must keep a reference to this timer till it is 
   * is no longer needed or has been cancelled.
   *
   * @param aObserver   the callback object that observes the 
   *                    ``timer-callback'' topic with the subject being
   *                    the timer itself when the timer fires:
   *
   *                    observe(nsISupports aSubject, => nsITimer
   *                            string aTopic,        => ``timer-callback''
   *                            wstring data          =>  null
   *
   * @param aDelay      delay in milliseconds for timer to fire
   * @param aType       timer type per TYPE* consts defined above
   */
  void init(in nsIObserver aObserver, in unsigned long aDelay, 
            in unsigned long aType);


  /**
   * Initialize a timer to fire after the given millisecond interval.
   * This version takes a function to call and a closure to pass to
   * that function.
   *
   * @param aFunc      The function to invoke
   * @param aClosure   An opaque pointer to pass to that function
   * @param aDelay     The millisecond interval
   * @param aType      Timer type per TYPE* consts defined above
   */
  [noscript] void initWithFuncCallback(in nsTimerCallbackFunc aCallback,
                                       in voidPtr aClosure,
                                       in unsigned long aDelay, 
                                       in unsigned long aType);

  /**
   * Initialize a timer to fire after the given millisecond interval.
   * This version takes a function to call.
   *
   * @param aFunc      nsITimerCallback interface to call when timer expires
   * @param aDelay     The millisecond interval
   * @param aType      Timer type per TYPE* consts defined above
   */
  void initWithCallback(in nsITimerCallback aCallback,
                        in unsigned long aDelay, 
                        in unsigned long aType);

  /**
   * Cancel the timer.  This method works on all types, not just on repeating
   * timers -- you might want to cancel a TYPE_ONE_SHOT timer, and even reuse
   * it by re-initializing it (to avoid object destruction and creation costs
   * by conserving one timer instance).
   */
  void cancel();
  
  /**
   * The millisecond delay of the timeout.
   *
   * NOTE: Re-setting the delay on a one-shot timer that has already fired
   * doesn't restart the timer. Call one of the init() methods to restart
   * a one-shot timer.
   */
  attribute unsigned long delay;
  
  /**
   * The timer type - one of the above TYPE_* constants.
   */  
  attribute unsigned long type;

  /**
   * The opaque pointer pass to initWithFuncCallback.
   */  
  [noscript] readonly attribute voidPtr closure;

  /**
   * The nsITimerCallback object passed to initWithCallback.
   */
  readonly attribute nsITimerCallback callback;

  /**
   * The nsIEventTarget where the callback will be dispatched. Note that this
   * target may only be set before the call to one of the init methods above.
   * 
   * By default the target is the thread that created the timer.
   */
  attribute nsIEventTarget target;
};

%{C++
#define NS_TIMER_CONTRACTID "@mozilla.org/timer;1"
#define NS_TIMER_CALLBACK_TOPIC "timer-callback"
%}