1.\"- 2.\" Copyright (c) 2017 Dag-Erling Smørgrav 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24.\" SUCH DAMAGE. 25.\" 26.Dd March 11, 2022 27.Dt RATECHECK 9 28.Os 29.Sh NAME 30.Nm ratecheck , 31.Nm ppsratecheck 32.Nd "event rate limiting" 33.Sh SYNOPSIS 34.In sys/time.h 35.Ft int 36.Fn ratecheck "struct timeval *lasttime" "const struct timeval *mininterval" 37.Ft int 38.Fn ppsratecheck "struct timeval *lasttime" "int *curpps" "int maxpps" 39.Sh DESCRIPTION 40The 41.Nm ratecheck 42and 43.Nm ppsratecheck 44functions facilitate rate-limiting of arbitrary events. 45The former enforces a minimum interval between events while the latter 46enforces a maximum number of events per second. 47.Pp 48The 49.Nm ratecheck 50function compares the current time to the value pointed to by 51.Fa lasttime . 52If the difference is equal to or greater than 53.Fa mininterval , 54it returns a non-zero value and updates 55.Fa lasttime 56to the current time. 57Otherwise, it returns zero. 58.Pp 59The 60.Nm ppsratecheck 61function first compares the current time 62to 63.Fa lasttime . 64If at least a full second has passed, the value pointed to by the 65.Fa curpps 66argument is reset to 1 and 67.Fa lasttime 68is updated to the current time. 69Otherwise, 70.Fa curpps 71is incremented and 72.Fa lasttime 73is left untouched. 74In either case, 75.Nm ppsratecheck 76returns a non-zero value if and only if the updated 77.Fa curpps 78is less than or equal to 79.Fa maxpps 80or 81.Fa maxpps 82is negative. 83.Sh SEE ALSO 84.Xr counter 9 85.Sh HISTORY 86The 87.Nm ratecheck 88and 89.Nm ppsratecheck 90functions first appeared in 91.Fx 5.1 . 92