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.Dd March 11, 2022
.Dt RATECHECK 9
.Os
.Sh NAME
.Nm ratecheck ,
.Nm ppsratecheck
.Nd "event rate limiting"
.Sh SYNOPSIS
.In sys/time.h
.Ft int
.Fn ratecheck "struct timeval *lasttime" "const struct timeval *mininterval"
.Ft int
.Fn ppsratecheck "struct timeval *lasttime" "int *curpps" "int maxpps"
.Sh DESCRIPTION
The
.Nm ratecheck
and
.Nm ppsratecheck
functions facilitate rate-limiting of arbitrary events.
The former enforces a minimum interval between events while the latter
enforces a maximum number of events per second.
.Pp
The
.Nm ratecheck
function compares the current time to the value pointed to by
.Fa lasttime .
If the difference is equal to or greater than
.Fa mininterval ,
it returns a non-zero value and updates
.Fa lasttime
to the current time.
Otherwise, it returns zero.
.Pp
The
.Nm ppsratecheck
function first compares the current time
to
.Fa lasttime .
If at least a full second has passed, the value pointed to by the
.Fa curpps
argument is reset to 1 and
.Fa lasttime
is updated to the current time.
Otherwise,
.Fa curpps
is incremented and
.Fa lasttime
is left untouched.
In either case,
.Nm ppsratecheck
returns a non-zero value if and only if the updated
.Fa curpps
is less than or equal to
.Fa maxpps
or
.Fa maxpps
is negative.
.Sh SEE ALSO
.Xr counter 9
.Sh HISTORY
The
.Nm ratecheck
and
.Nm ppsratecheck
functions first appeared in
.Fx 5.1 .