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/**************************************************//**
@file include/os0event.h
The interface to the operating system condition variables

Created 2012-09-23 Sunny Bains (split from os0sync.h)
*******************************************************/

#ifndef os0event_h
#define os0event_h

#include "univ.i"

// Forward declaration.
struct os_event;
typedef struct os_event* os_event_t;

/** Denotes an infinite delay for os_event_wait_time() */
#define OS_SYNC_INFINITE_TIME   ULINT_UNDEFINED

/** Return value of os_event_wait_time() when the time is exceeded */
#define OS_SYNC_TIME_EXCEEDED   1

/**
Creates an event semaphore, i.e., a semaphore which may just have two states:
signaled and nonsignaled. The created event is manual reset: it must be reset
explicitly by calling os_event_reset().
@return	the event handle */
os_event_t
os_event_create(
/*============*/
	const char*	name);	/*!< in: the name of the event, if NULL
				the event is created without a name */

/**
Sets an event semaphore to the signaled state: lets waiting threads
proceed. */
void
os_event_set(
/*=========*/
	os_event_t	event);	/*!< in/out: event to set */

/**
Check if the event is set.
@return true if set */
bool
os_event_is_set(
/*============*/
	const os_event_t	event);	/*!< in: event to set */

/**
Resets an event semaphore to the nonsignaled state. Waiting threads will
stop to wait for the event.
The return value should be passed to os_even_wait_low() if it is desired
that this thread should not wait in case of an intervening call to
os_event_set() between this os_event_reset() and the
os_event_wait_low() call. See comments for os_event_wait_low(). */
int64_t
os_event_reset(
/*===========*/
	os_event_t	event);	/*!< in/out: event to reset */

/**
Frees an event object. */
void
os_event_destroy(
/*=============*/
	os_event_t&	event);	/*!< in/own: event to free */

/**
Waits for an event object until it is in the signaled state.

Typically, if the event has been signalled after the os_event_reset()
we'll return immediately because event->is_set == TRUE.
There are, however, situations (e.g.: sync_array code) where we may
lose this information. For example:

thread A calls os_event_reset()
thread B calls os_event_set()   [event->is_set == TRUE]
thread C calls os_event_reset() [event->is_set == FALSE]
thread A calls os_event_wait()  [infinite wait!]
thread C calls os_event_wait()  [infinite wait!]

Where such a scenario is possible, to avoid infinite wait, the
value returned by os_event_reset() should be passed in as
reset_sig_count. */
void
os_event_wait_low(
/*==============*/
	os_event_t	event,		/*!< in/out: event to wait */
	int64_t		reset_sig_count);/*!< in: zero or the value
					returned by previous call of
					os_event_reset(). */

/** Blocking infinite wait on an event, until signealled.
@param e - event to wait on. */
#define os_event_wait(e) os_event_wait_low((e), 0)

/**
Waits for an event object until it is in the signaled state or
a timeout is exceeded. In Unix the timeout is always infinite.
@return 0 if success, OS_SYNC_TIME_EXCEEDED if timeout was exceeded */
ulint
os_event_wait_time_low(
/*===================*/
	os_event_t	event,			/*!< in/out: event to wait */
	ulint		time_in_usec,		/*!< in: timeout in
						microseconds, or
						OS_SYNC_INFINITE_TIME */
	int64_t		reset_sig_count);	/*!< in: zero or the value
						returned by previous call of
						os_event_reset(). */
/** Initializes support for os_event objects. Must be called once,
 and before any os_event object is created. */
void os_event_global_init(void);

/** Deinitializes support for os_event objects. Must be called once,
 and after all os_event objects are destroyed. After it is called, no
new os_event is allowed to be created. */
void os_event_global_destroy(void);

/** Blocking timed wait on an event.
@param e - event to wait on.
@param t - timeout in microseconds */
#define os_event_wait_time(e, t) os_event_wait_time_low((e), (t), 0)

#endif /* !os0event_h */
