NAME¶
POE::Resource::Clock - internal clock used for ordering the queue
SYNOPSIS¶
sub POE::Kernel::USE_POSIXRT { 0 }
use POE;
DESCRIPTION¶
POE::Resource::Clock is a helper module for POE::Kernel. It provides the
features to keep an internal monotonic clock and a wall clock. It also
converts between this monotonic clock and the wall clock.
The monotonic clock is used to keep an ordered queue of events. The wall clock
is used to communicate the time with user code ("alarm_set" in
POE::Kernel, "alarm_remove" in POE::Kernel).
There are 3 possible clock sources in order of preference: POSIX::RT::Clock,
Time::HiRes and "time" in perlfunc. Only
"POSIX::RT::Clock" has a separate monotonic and wall clock; the
other two use the same source for both clocks.
Clock selection and behaviour is controlled with the following:
USE_POSIXRT¶
export POE_USE_POSIXRT=0
or
sub POE::Kernel::USE_POSIXRT { 0 }
Uses the "monotonic" clock source for queue priority and the
"realtime" clock source for wall clock. Not used if POSIX::RT::Clock
is not installed or your system does not have a "monotonic" clock.
Defaults to true. If you want the old POE behaviour, set this to 0.
USE_STATIC_EPOCH¶
export POE_USE_STATIC_EPOCH=0
or
sub POE::Kernel::USE_STATIC_EPOCH { 0 }
The epoch of the POSIX::RT::Clock monotonic is different from that of the
realtime clock. For instance on Linux 2.6.18, the monotonic clock is the
number of seconds since system boot. This epoch is used to convert from
walltime into monotonic time for "alarm" in POE::Kernel,
"alarm_add" in POE::Kernel and "alarm_set" in POE::Kernel.
If "USE_STATIC_EPOCH" is true (the default), then the epoch is
calculated at load time. If false, the epoch is calculated each time it is
needed.
Defaults to true. Only relevant for if using POSIX::RT::Clock. Long-running POE
servers should have this set to false so that system clock skew does mess up
the queue.
It is important to point out that without a static epoch, the ordering of the
following two alarms is undefined.
$poe_kernel->alarm_set( a1 => $time );
$poe_kernel->alarm_set( a2 => $time );
USE_EXACT_EPOCH¶
export POE_USE_EXACT_EPOCH=1
or
sub POE::Kernel::USE_EXACT_EPOCH { 1 }
There currently no way to exactly get the monotonic clock's epoch. Instead the
difference between the current monotonic clock value to the realtime clock's
value is used. This is obviously inexact because there is a slight delay
between the 2 system calls. Setting USE_EXACT_EPOCH to true will calculate an
average of this difference over 250 ms or at least 20 samples. What's more,
the system calls are done in both orders (monotonic then realtime, realtime
then monotonic) to try and get a more exact value.
Defaults to false. Only relevant if "USE_STATIC_EPOCH" is true.
USE_HIRES¶
export POE_USE_HIRES=0
or
sub POE::Kernel::USE_HIRES { 0 }
Use Time::HiRes as both monotonic and wall clock source. This was POE's previous
default clock.
Defaults to true. Only relevant if "USE_POSIXRT" is false. Set this to
false to use "time" in perlfunc.
EXPORTS¶
This module optionally exports a few timekeeping helper functions.
mono2wall¶
mono2wall() converts a monotonic time to an epoch wall time.
my $wall = mono2wall( $monotonic );
monotime¶
monotime() makes a best-effort attempt to return the time from a
monotonic system clock. It may fall back to non-monotonic time if there are no
monotonic clocks available.
my $monotonic = monotime();
sleep¶
sleep() makes a best-effort attempt to sleep a particular amount of
high-resolution time using a monotonic clock. This feature will degrade
gracefully to non-monotonic high-resolution clocks, then low-resolution
clocks, depending on available libraries.
sleep( 3.141 );
time¶
time() is a backwards compatible alias for
walltime(). Please see
walltime()'s documentation for details.
wall2mono¶
wall2mono() makes a best-effort attempt to convert wall time to its
equivalent monotonic-clock time. Its feature degrades gracefully depending on
clock availability.
my $monotonic = wall2mono( $epoch );
walltime¶
time() makes a best-effort attempt to return non-monotonic wall time at
the highest available resolution known.
my $epoch = walltime();
SEE ALSO¶
See POE::Resource for general discussion about resources and the classes that
manage them.
BUGS¶
None known.
AUTHORS & COPYRIGHTS¶
Please see POE for more information about authors and contributors.