path: root/storage/innobase/os/os0event.cc

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

/**************************************************//**
@file os/os0event.cc
The interface to the operating system condition variables.

Created 2012-09-23 Sunny Bains
*******************************************************/

#include "os0event.h"
#include "ut0mutex.h"

#ifdef _WIN32
#include <windows.h>
#include <synchapi.h>
#endif /* _WIN32 */

#ifdef _WIN32
/** Native condition variable. */
typedef CONDITION_VARIABLE	os_cond_t;
#else
/** Native condition variable */
typedef pthread_cond_t		os_cond_t;
#endif /* _WIN32 */

/** InnoDB condition variable. */
struct os_event {
	os_event() UNIV_NOTHROW;

	~os_event() UNIV_NOTHROW;

	/**
	Destroys a condition variable */
	void destroy() UNIV_NOTHROW
	{
#ifndef _WIN32
		int	ret = pthread_cond_destroy(&cond_var);
		ut_a(ret == 0);
#endif /* !_WIN32 */

		mutex.destroy();
	}

	/** Set the event */
	void set() UNIV_NOTHROW
	{
		mutex.enter();

		if (!m_set) {
			broadcast();
		}

		mutex.exit();
	}

	int64_t reset() UNIV_NOTHROW
	{
		mutex.enter();

		if (m_set) {
			m_set = false;
		}

		int64_t	ret = signal_count;

		mutex.exit();

		return(ret);
	}

	/**
	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->m_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->m_set == true]
	thread C calls os_event_reset() [event->m_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 reset() should be passed in as
	reset_sig_count. */
	void wait_low(int64_t reset_sig_count) UNIV_NOTHROW;

	/**
	Waits for an event object until it is in the signaled state or
	a timeout is exceeded.
	@param time_in_usec - timeout in microseconds,
			or OS_SYNC_INFINITE_TIME
	@param reset_sig_count- zero or the value returned by
			previous call of os_event_reset().
	@return	0 if success, OS_SYNC_TIME_EXCEEDED if timeout was exceeded */
	ulint wait_time_low(
		ulint		time_in_usec,
		int64_t		reset_sig_count) UNIV_NOTHROW;

	/** @return true if the event is in the signalled state. */
	bool is_set() const UNIV_NOTHROW
	{
		mutex.enter();
		bool is_set = m_set;
		mutex.exit();
		return is_set;
	}

private:
	/**
	Initialize a condition variable */
	void init() UNIV_NOTHROW
	{

		mutex.init();

#ifdef _WIN32
		InitializeConditionVariable(&cond_var);
#else
		{
			int	ret;

			ret = pthread_cond_init(&cond_var, NULL);
			ut_a(ret == 0);
		}
#endif /* _WIN32 */
	}

	/**
	Wait on condition variable */
	void wait() UNIV_NOTHROW
	{
#ifdef _WIN32
		if (!SleepConditionVariableCS(&cond_var, mutex, INFINITE)) {
			ut_error;
		}
#else
		{
			int	ret;

			ret = pthread_cond_wait(&cond_var, mutex);
			ut_a(ret == 0);
		}
#endif /* _WIN32 */
	}

	/**
	Wakes all threads waiting for condition variable */
	void broadcast() UNIV_NOTHROW
	{
		m_set = true;
		++signal_count;

#ifdef _WIN32
		WakeAllConditionVariable(&cond_var);
#else
		{
			int	ret;

			ret = pthread_cond_broadcast(&cond_var);
			ut_a(ret == 0);
		}
#endif /* _WIN32 */
	}

	/**
	Wakes one thread waiting for condition variable */
	void signal() UNIV_NOTHROW
	{
#ifdef _WIN32
		WakeConditionVariable(&cond_var);
#else
		{
			int	ret;

			ret = pthread_cond_signal(&cond_var);
			ut_a(ret == 0);
		}
#endif /* _WIN32 */
	}

	/**
	Do a timed wait on condition variable.
	@param abstime - timeout
	@param time_in_ms - timeout in milliseconds.
	@return true if timed out, false otherwise */
	bool timed_wait(
#ifndef _WIN32
		const timespec*	abstime
#else
		DWORD		time_in_ms
#endif /* !_WIN32 */
	);

private:
	bool			m_set;		/*!< this is true when the
						event is in the signaled
						state, i.e., a thread does
						not stop if it tries to wait
						for this event */
	int64_t			signal_count;	/*!< this is incremented
						each time the event becomes
						signaled */
	mutable OSMutex		mutex;		/*!< this mutex protects
						the next fields */


	os_cond_t		cond_var;	/*!< condition variable is
						used in waiting for the event */

protected:
	// Disable copying
	os_event(const os_event&);
	os_event& operator=(const os_event&);
};

/**
Do a timed wait on condition variable.
@param abstime - absolute time to wait
@param time_in_ms - timeout in milliseconds
@return true if timed out */
bool
os_event::timed_wait(
#ifndef _WIN32
	const timespec*	abstime
#else
	DWORD		time_in_ms
#endif /* !_WIN32 */
)
{
#ifdef _WIN32
	BOOL		ret;

	ret = SleepConditionVariableCS(&cond_var, mutex, time_in_ms);

	if (!ret) {
		DWORD	err = GetLastError();

		/* FQDN=msdn.microsoft.com
		@see http://$FQDN/en-us/library/ms686301%28VS.85%29.aspx,

		"Condition variables are subject to spurious wakeups
		(those not associated with an explicit wake) and stolen wakeups
		(another thread manages to run before the woken thread)."
		Check for both types of timeouts.
		Conditions are checked by the caller.*/
		if (err == WAIT_TIMEOUT || err == ERROR_TIMEOUT) {
			return(true);
		}
	}

	ut_a(ret);

	return(false);
#else
	int	ret;

	ret = pthread_cond_timedwait(&cond_var, mutex, abstime);

	switch (ret) {
	case 0:
	case ETIMEDOUT:
		/* We play it safe by checking for EINTR even though
		according to the POSIX documentation it can't return EINTR. */
	case EINTR:
		break;

	default:
		ib::error() << "pthread_cond_timedwait() returned: " << ret
			<< ": abstime={" << abstime->tv_sec << ","
			<< abstime->tv_nsec << "}";
		ut_error;
	}

	return(ret == ETIMEDOUT);
#endif /* _WIN32 */
}

/**
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->m_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->m_set == true]
thread C calls os_event_reset() [event->m_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 reset() should be passed in as
reset_sig_count. */
void
os_event::wait_low(
	int64_t		reset_sig_count) UNIV_NOTHROW
{
	mutex.enter();

	if (!reset_sig_count) {
		reset_sig_count = signal_count;
	}

	while (!m_set && signal_count == reset_sig_count) {

		wait();

		/* Spurious wakeups may occur: we have to check if the
		event really has been signaled after we came here to wait. */
	}

	mutex.exit();
}

/**
Waits for an event object until it is in the signaled state or
a timeout is exceeded.
@param time_in_usec - timeout in microseconds, or OS_SYNC_INFINITE_TIME
@param reset_sig_count - zero or the value returned by previous call
	of os_event_reset().
@return	0 if success, OS_SYNC_TIME_EXCEEDED if timeout was exceeded */
ulint
os_event::wait_time_low(
	ulint		time_in_usec,
	int64_t		reset_sig_count) UNIV_NOTHROW
{
	bool		timed_out = false;

#ifdef _WIN32
	DWORD		time_in_ms;

	if (time_in_usec != OS_SYNC_INFINITE_TIME) {
		time_in_ms = DWORD(time_in_usec / 1000);
	} else {
		time_in_ms = INFINITE;
	}
#else
	struct timespec	abstime;

	if (time_in_usec != OS_SYNC_INFINITE_TIME) {
		struct timeval	tv;
		int		ret;
		ulint		sec;
		ulint		usec;

		ret = ut_usectime(&sec, &usec);
		ut_a(ret == 0);

		tv.tv_sec = sec;
		tv.tv_usec = usec;

		tv.tv_usec += time_in_usec;

		abstime.tv_sec = tv.tv_sec + tv.tv_usec / 1000000;
		abstime.tv_nsec = tv.tv_usec % 1000000 * 1000;
	} else {
		abstime.tv_nsec = 999999999;
		abstime.tv_sec = (time_t) ULINT_MAX;
	}

	ut_a(abstime.tv_nsec <= 999999999);

#endif /* _WIN32 */

	mutex.enter();

	if (!reset_sig_count) {
		reset_sig_count = signal_count;
	}

	do {
		if (m_set || signal_count != reset_sig_count) {

			break;
		}

#ifndef _WIN32
		timed_out = timed_wait(&abstime);
#else
		timed_out = timed_wait(time_in_ms);
#endif /* !_WIN32 */

	} while (!timed_out);

	mutex.exit();

	return(timed_out ? OS_SYNC_TIME_EXCEEDED : 0);
}

/** Constructor */
os_event::os_event() UNIV_NOTHROW
{
	init();

	m_set = false;

	/* We return this value in os_event_reset(),
	which can then be be used to pass to the
	os_event_wait_low(). The value of zero is
	reserved in os_event_wait_low() for the case
	when the caller does not want to pass any
	signal_count value. To distinguish between
	the two cases we initialize signal_count
	to 1 here. */

	signal_count = 1;
}

/** Destructor */
os_event::~os_event() UNIV_NOTHROW
{
	destroy();
}

/**
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 sync_os_reset_event.
@return	the event handle */
os_event_t os_event_create(const char*)
{
	return(UT_NEW_NOKEY(os_event()));
}

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

/**
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 */
{
	event->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().
@return	current signal_count. */
int64_t
os_event_reset(
/*===========*/
	os_event_t	event)			/*!< in/out: event to reset */
{
	return(event->reset());
}

/**
Waits for an event object until it is in the signaled state or
a timeout is exceeded.
@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(). */
{
	return(event->wait_time_low(time_in_usec, reset_sig_count));
}

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

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: event to wait */
	int64_t		reset_sig_count)	/*!< in: zero or the value
						returned by previous call of
						os_event_reset(). */
{
	event->wait_low(reset_sig_count);
}

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

{
	UT_DELETE(event);
	event = NULL;
}