fis-gtm/sr_port/wcs_backoff.c

/****************************************************************
 *								*
 *	Copyright 2001, 2012 Fidelity Information Services, Inc	*
 *								*
 *	This source code contains the intellectual property	*
 *	of its copyright holder(s), and is made available	*
 *	under a license.  If you do not know the terms of	*
 *	the license, please stop and do not read further.	*
 *								*
 ****************************************************************/

#include "mdef.h"
#include "sleep_cnt.h"

#ifdef VMS
# include <lib$routines.h>
#endif
#include "gtm_stdlib.h"
#include "gt_timer.h"
#ifdef UNIX
# include "random.h"
#endif
#include "wcs_backoff.h"

GBLREF int4 process_id;

void wcs_backoff(unsigned int sleepfactor)
{
	/* wcs_backoff provides a layer over hiber_start that produces a [pseudo] random sleep varying
	 * to a maximum sleep time it is intended to be used in as part of a contention backoff
	 * where the argument is the attempt count. If the counter starts at 0, the invocation would
	 * typically be:
	 *   if (count) wcs_backoff(count);
	 */

#	if defined(VMS)
	int4		day;
	double		randfloat;
#	endif
	static int4	seed = 0;
	uint4		sleep_ms;

	assert(sleepfactor);
	if (0 == sleepfactor)
		return;
	if (sleepfactor > MAXSLPTIME)
		sleepfactor = MAXSLPTIME;
#	ifdef UNIX
	if (0 == seed)
	{
		init_rand_table();
		seed = 1;
	}
	sleep_ms = ((uint4)(get_rand_from_table() % sleepfactor));
#	elif defined(VMS)
	if (0 == seed)				/* Seed random number generator */
	{
		lib$day(&day, 0, &seed);
		seed *= process_id;
		srandom(seed);
	}
	randfloat = ((double)random()) / RAND_MAX;
 	sleep_ms = ((uint4)(sleepfactor * randfloat));
#	else
#	error "Unsupported platform"
#	endif
	if (0 == sleep_ms)
		return;				/* We have no wait this time */
	if (1000 > sleep_ms)			/* Use simpler sleep for shorties */
	{
		SHORT_SLEEP(sleep_ms);
	}
	else
		hiber_start(sleep_ms);		/* Longer sleeps use brute force */
	return;
}