/* $Header: /pjproject-0.3/pjlib/include/pj/timer.h 7     10/14/05 12:26a Bennylp $ */
/* (C)1993-2003 Douglas C. Schmidt
 *
 * This file is originaly from ACE library by Doug Schmidt
 * ACE(TM), TAO(TM) and CIAO(TM) are copyrighted by Douglas C. Schmidt and his research 
 * group at Washington University, University of California, Irvine, and Vanderbilt 
 * University Copyright (c) 1993-2003, all rights reserved.
 *
 */

#ifndef __PJ_TIMER_H__
#define __PJ_TIMER_H__

/**
 * @file timer.h
 * @brief Timer Heap
 */

#include <pj/types.h>

PJ_BEGIN_DECL

/**
 * @defgroup PJ_TIMER Timer Heap Management.
 * @ingroup PJ_MISC
 * @brief
 * The timer scheduling implementation here is based on ACE library's 
 * ACE_Timer_Heap, with only little modification to suit our library's style
 * (I even left most of the comments in the original source).
 *
 * To quote the original quote in ACE_Timer_Heap_T class:
 *
 *      This implementation uses a heap-based callout queue of
 *      absolute times.  Therefore, in the average and worst case,
 *      scheduling, canceling, and expiring timers is O(log N) (where
 *      N is the total number of timers).  In addition, we can also
 *      preallocate as many \a ACE_Timer_Nodes as there are slots in
 *      the heap.  This allows us to completely remove the need for
 *      dynamic memory allocation, which is important for real-time
 *      systems.
 * @{
 *
 * \section pj_timer_examples_sec Examples
 *
 * For some examples on how to use the timer heap, please see the link below.
 *
 *  - \ref page_pjlib_timer_test
 */


/**
 * The type for internal timer ID.
 */
typedef int pj_timer_id_t;

/** 
 * Forward declaration for pj_timer_entry. 
 */
struct pj_timer_entry;

/**
 * The type of callback function to be called by timer scheduler when a timer
 * has expired.
 *
 * @param timer_heap    The timer heap.
 * @param entry         Timer entry which timer's has expired.
 */
typedef void pj_timer_heap_callback(pj_timer_heap_t *timer_heap,
				    struct pj_timer_entry *entry);


/**
 * This structure represents an entry to the timer.
 */
struct pj_timer_entry
{
    /** 
     * User data to be associated with this entry. 
     * Applications normally will put the instance of object that
     * owns the timer entry in this field.
     */
    void *user_data;

    /** 
     * Arbitrary ID assigned by the user/owner of this entry. 
     * Applications can use this ID to distinguish multiple
     * timer entries that share the same callback and user_data.
     */
    int id;

    /** 
     * Callback to be called when the timer expires. 
     */
    pj_timer_heap_callback *cb;

    /** 
     * Internal unique timer ID, which is assigned by the timer heap. 
     * Application should not touch this ID.
     */
    pj_timer_id_t _timer_id;

    /** 
     * The future time when the timer expires, which the value is updated
     * by timer heap when the timer is scheduled.
     */
    pj_time_val _timer_value;
};


/**
 * Default flag for timer heap, indicates that synchronization will be
 * used.
 */
#define PJ_TIMER_HEAP_SYNCHRONIZE	(0)

/**
 * Flag to indicate that thread synchronization is NOT needed for the 
 * timer heap.
 */
#define PJ_TIMER_HEAP_NO_SYNCHRONIZE	(1)

/**
 * Calculate memory size required to create a timer heap.
 *
 * @param count     Number of timer entries to be supported.
 * @return          Memory size requirement in bytes.
 */
PJ_DECL(pj_size_t) pj_timer_heap_mem_size(pj_size_t count);

/**
 * Create a timer heap.
 *
 * @param pool      The pool where allocations in the timer heap will be 
 *                  allocated. The timer heap will dynamicly allocate 
 *                  more storate from the pool if the number of timer 
 *                  entries registered is more than the size originally 
 *                  requested when calling this function.
 * @param count     The maximum number of timer entries to be supported 
 *                  initially. If the application registers more entries 
 *                  during runtime, then the timer heap will resize.
 * @param flag      Creation flag, currently only PJ_TIMER_HEAP_NO_SYNCHRONIZE
 *                  is recognized..
 * @param ht        Pointer to receive the created timer heap.
 *
 * @return          PJ_SUCCESS, or the appropriate error code.
 */
PJ_DECL(pj_status_t) pj_timer_heap_create( pj_pool_t *pool,
					   pj_size_t count,
					   unsigned flag,
                                           pj_timer_heap_t **ht);

/**
 * Initialize a timer entry. Application should call this function at least
 * once before scheduling the entry to the timer heap, to properly initialize
 * the timer entry.
 *
 * @param entry     The timer entry to be initialized.
 * @param id        Arbitrary ID assigned by the user/owner of this entry.
 *                  Applications can use this ID to distinguish multiple
 *                  timer entries that share the same callback and user_data.
 * @param user_data User data to be associated with this entry. 
 *                  Applications normally will put the instance of object that
 *                  owns the timer entry in this field.
 * @param cb        Callback function to be called when the timer elapses.
 *
 * @return          The timer entry itself.
 */
PJ_DECL(pj_timer_entry*) pj_timer_entry_init( pj_timer_entry *entry,
                                              int id,
                                              void *user_data,
                                              pj_timer_heap_callback *cb );

/**
 * Schedule a timer entry which will expire AFTER the specified delay.
 *
 * @param ht        The timer heap.
 * @param entry     The entry to be registered. 
 * @param delay     The interval to expire.
 * @return          PJ_SUCCESS, or the appropriate error code.
 */
PJ_DECL(pj_status_t) pj_timer_heap_schedule( pj_timer_heap_t *ht,
					     pj_timer_entry *entry, 
					     const pj_time_val *delay);

/**
 * Cancel a previously registered timer.
 *
 * @param ht        The timer heap.
 * @param entry     The entry to be cancelled.
 * @return          The number of timer cancelled, which should be one if the
 *                  entry has really been registered, or zero if no timer was
 *                  cancelled.
 */
PJ_DECL(int) pj_timer_heap_cancel( pj_timer_heap_t *ht,
				   pj_timer_entry *entry);

/**
 * Get the number of timer entries.
 *
 * @param ht        The timer heap.
 * @return          The number of timer entries.
 */
PJ_DECL(pj_size_t) pj_timer_heap_count( pj_timer_heap_t *ht );

/**
 * Get the earliest time registered in the timer heap. The timer heap
 * MUST have at least one timer being scheduled (application should use
 * #pj_timer_heap_count() before calling this function).
 *
 * @param ht        The timer heap.
 * @param timeval   The time deadline of the earliest timer entry.
 *
 * @return          PJ_SUCCESS, or PJ_ENOTFOUND if no entry is scheduled.
 */
PJ_DECL(pj_status_t) pj_timer_heap_earliest_time( pj_timer_heap_t *ht, 
					   pj_time_val *timeval);

/**
 * Poll the timer heap, check for expired timers and call the callback for
 * each of the expired timers.
 *
 * @param ht        The timer heap.
 * @param next_delay If this parameter is not NULL, it will be filled up with
 *		     the time delay until the next timer elapsed, or -1 in
 *		     the sec part if no entry exist.
 * @return          The number of timers expired.
 */
PJ_DECL(int) pj_timer_heap_poll( pj_timer_heap_t *ht, pj_time_val *next_delay);

/**
 * @}
 */

PJ_END_DECL

#endif	/* __PJ_TIMER_H__ */