=head1 NAME

Smokeping::probes::basefork - Yet Another Base Class for implementing SmokePing Probes

=head1 OVERVIEW

Like Smokeping::probes::basevars, but supports the probe-specific property `forks'
to determine how many processes should be run concurrently. The
targets are pinged one at a time, and the number of pings sent can vary
between targets.

=head1 SYNOPSIS

 *** Probes ***

 +basefork

 forks = 5
 offset = 50%
 step = 300
 timeout = 15

 # The following variables can be overridden in each target section
 pings = 5

 # [...]

 *** Targets ***

 probe = basefork # if this should be the default probe

 # [...]

 + mytarget
 # probe = basefork # if the default probe is something else
 host = my.host
 pings = 5

=head1 DESCRIPTION

Not all pinger programs support testing multiple hosts in a single go like
fping(1). If the measurement takes long enough, there may be not enough time 
perform all the tests in the time available. For example, if the test takes
30 seconds, measuring ten hosts already fills up the SmokePing default 
five minute step.

Thus, it may be necessary to do some of the tests concurrently. This module
defines the B<ping> method that forks the requested number of concurrent 
processes and calls the B<pingone> method that derived classes must provide.

The B<pingone> method is called with one argument: a hash containing
the target that is to be measured. The contents of the hash are
described in I<Smokeping::probes::basevars>(3pm).

The number of concurrent processes is determined by the probe-specific 
variable `forks' and is 5 by default. If there are more 
targets than this value, another round of forks is done after the first 
processes are finished. This continues until all the targets have been
tested.

The timeout in which each child has to finish is set to 5 seconds
multiplied by the maximum number of 'pings' of the targets. You can set
the base timeout differently if you want to, using the timeout property
of the probe in the master config file (this again will be multiplied
by the maximum number of pings). The probe itself can also provide
another default value if desired by modifying the _default value of
the timeout variable.

If the child isn't finished when the timeout occurs, it 
will be killed along with any processes it has started.

The number of pings sent can be specified in the target-specific variable
'pings'.

=head1 VARIABLES

Supported probe-specific variables:

=over

=item forks

Run this many concurrent processes at maximum

Example value: 5

Default value: 5

=item offset

If you run many probes concurrently you may want to prevent them from
hitting your network all at the same time. Using the probe-specific
offset parameter you can change the point in time when each probe will
be run. Offset is specified in % of total interval, or alternatively as
'random', and the offset from the 'General' section is used if nothing
is specified here. Note that this does NOT influence the rrds itself,
it is just a matter of when data acqusition is initiated.
(This variable is only applicable if the variable 'concurrentprobes' is set
in the 'General' section.)

Example value: 50%

=item step

Duration of the base interval that this probe should use, if different
from the one specified in the 'Database' section. Note that the step in
the RRD files is fixed when they are originally generated, and if you
change the step parameter afterwards, you'll have to delete the old RRD
files or somehow convert them. (This variable is only applicable if
the variable 'concurrentprobes' is set in the 'General' section.)

Example value: 300

=item timeout

How long a single 'ping' takes at maximum

Example value: 15

Default value: 5

=back

Supported target-specific variables:

=over

=item pings

How many pings should be sent to each target, if different from the global
value specified in the Database section. Note that the number of pings in
the RRD files is fixed when they are originally generated, and if you
change this parameter afterwards, you'll have to delete the old RRD
files or somehow convert them.

Example value: 5

=back


=head1 AUTHORS

Niko Tyni <ntyni@iki.fi>

=head1 SEE ALSO

L<Smokeping::probes::basevars>, L<Smokeping::probes::EchoPing>

=cut