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php

Monotonic Time

php.internals

Niklas Keller

9 years ago

Morning Internals,

PHP doesn't currently have a way to access a monotonic time. There's a
feature request in the bug tracker: bugs [dot] php [dot] net/
bug.php?id=68029

A monotonic time is required to measure time intervals correctly, e.g. for
implementing event loops based on stream_select. microtime() is affected by
NTP and leap seconds and can therefore not be reliably used for measuring
time intervals.

Event loops based on extensions like libuv can take advantage of libuv's
own API for accessing a monotonic time.

Related: twitter [dot] com/danluu/status/815442765811023872
Related: blog [dot] cloudflare [dot] com/how-and-why-the-leap-secon
d-affected-cloudflare-dns/

Node.js does have a monotonic time and calls the function
process.hrtime: nodejs [dot] org/api/process.html#process_p
rocess_hrtime_time

There's an existing PECL extension named hrtime: php [dot] net/manual/
en/book.hrtime.php

I think we can reuse parts of it to implement a function in core to access
a monotonic time, I don't think we need to merge the extension into core.

What do you think about adding such a function to the PHP core?

Regards, Niklas

PS: No links, because stupid PHP.net spam filter ...

Niklas Keller

9 years ago

Resending previous mail, because mail distribution was broken...

Morning Internals,

PHP doesn't currently have a way to access a monotonic time. There's a
feature request in the bug tracker: bugs [dot] php [dot]
net/bug.php?id=68029

A monotonic time is required to measure time intervals correctly, e.g. for
implementing event loops based on stream_select. microtime() is affected by
NTP and leap seconds and can therefore not be reliably used for measuring
time intervals.

Event loops based on extensions like libuv can take advantage of libuv's
own API for accessing a monotonic time.

Related: twitter [dot] com/danluu/status/815442765811023872
Related: blog [dot] cloudflare [dot] com/how-and-why-the-leap-secon
d-affected-cloudflare-dns/

Node.js does have a monotonic time and calls the function
process.hrtime: nodejs [dot] org/api/process.html#process_p
rocess_hrtime_time

There's an existing PECL extension named hrtime: php [dot]
net/manual/en/book.hrtime.php

I think we can reuse parts of it to implement a function in core to access
a monotonic time, I don't think we need to merge the extension into core.

What do you think about adding such a function to the PHP core?

Regards, Niklas

PS: No links, because stupid PHP.net spam filter ...

Michael Wallner

9 years ago

On 04/01/17 13:58, Niklas Keller wrote:

> Resending previous mail, because mail distribution was broken...
>
> Morning Internals,
>
> PHP doesn't currently have a way to access a monotonic time. There's a
> feature request in the bug tracker: bugs [dot] php [dot]
> net/bug.php?id=68029
>
> A monotonic time is required to measure time intervals correctly, e.g. for
> implementing event loops based on stream_select. microtime() is affected by
> NTP and leap seconds and can therefore not be reliably used for measuring
> time intervals.
>

...

> There's an existing PECL extension named hrtime: php [dot]
> net/manual/en/book.hrtime.php
>
> I think we can reuse parts of it to implement a function in core to access
> a monotonic time, I don't think we need to merge the extension into core.
>
> What do you think about adding such a function to the PHP core?

+1?

Actually, it seems, that hrtime doesn't let you access the current
value, which is, well, quite a major use case, isn't it?

--
Regards,
Mike

Niklas Keller

9 years ago

>
> Actually, it seems, that hrtime doesn't let you access the current
> value, which is, well, quite a major use case, isn't it?

Yes, that seemed weird to me, too. Did we miss anything, Anatol?

Regards, Niklas

Anatol Belski

9 years ago

Hi,

> -----Original Message-----
> From: Niklas Keller [mailto:me@kelunik.com]
> Sent: Thursday, January 5, 2017 2:27 AM
> To: Michael Wallner <mike@php.net>; Anatol Belski <anatol.php@belski.net>
> Cc: PHP Internals <internals@lists.php.net>
> Subject: Re: [PHP-DEV] Fwd: Monotonic Time
>
> >
> > Actually, it seems, that hrtime doesn't let you access the current
> > value, which is, well, quite a major use case, isn't it?
>
>
> Yes, that seemed weird to me, too. Did we miss anything, Anatol?
>

Yeah, I thought I did that already, but well ...  The ext was more about performance testing, at the start at least. I made some refactoring to it yesterday, so it is now possible to implement an arbitrary userspace timer using the HRTime\PerformanceCounter class. Maybe should add also HRTime\Timer, but it should first get a thought about some good API approach.

The portable parts are bundled files timer.[h|c] in the hrtime repo, supporting POSIX, Windows and Mac. They can be reused, or taken as an example, for sure.

Regards

Anatol

Niklas Keller

9 years ago

>
> > > Actually, it seems, that hrtime doesn't let you access the current
> > > value, which is, well, quite a major use case, isn't it?
> >
> >
> > Yes, that seemed weird to me, too. Did we miss anything, Anatol?
> >
> Yeah, I thought I did that already, but well ...  The ext was more about
> performance testing, at the start at least. I made some refactoring to it
> yesterday, so it is now possible to implement an arbitrary userspace timer
> using the HRTime\PerformanceCounter class. Maybe should add also
> HRTime\Timer, but it should first get a thought about some good API
> approach.
>
> The portable parts are bundled files timer.[h|c] in the hrtime repo,
> supporting POSIX, Windows and Mac. They can be reused, or taken as an
> example, for sure.

Hi Anatol,

Do you think we should merge hrtime into core or add a simple function just
like microtime() to ext/standard?

Regards, Niklas

Leigh

9 years ago

On Fri, 13 Jan 2017 at 09:35 Niklas Keller <me@kelunik.com> wrote:

> Hi Anatol,
>
> Do you think we should merge hrtime into core or add a simple function just
> like microtime() to ext/standard?
>
> Regards, Niklas
>

It would be great if it could be a simple function, however it is going to
be difficult to produce something cross-platform and meaningful with a
single function. (I know Anatol has written portable code, I haven't looked
at it but I assume it's wrapping the various structs used by i.e.
performance counters, hrtime, etc.)

I don't think we can get away from having an object-based implementation to
wrap those internal structs, but I do think this is a useful addition
regardless of how it's presented.

Niklas Keller

9 years ago

2017-01-13 15:06 GMT+01:00 Leigh <leight@gmail.com>:

> On Fri, 13 Jan 2017 at 09:35 Niklas Keller <me@kelunik.com> wrote:
>
> > Hi Anatol,
> >
> > Do you think we should merge hrtime into core or add a simple function
> just
> > like microtime() to ext/standard?
> >
> > Regards, Niklas
> >
>
> It would be great if it could be a simple function, however it is going to
> be difficult to produce something cross-platform and meaningful with a
> single function. (I know Anatol has written portable code, I haven't looked
> at it but I assume it's wrapping the various structs used by i.e.
> performance counters, hrtime, etc.)
>
> I don't think we can get away from having an object-based implementation to
> wrap those internal structs, but I do think this is a useful addition
> regardless of how it's presented.
>

With timer.c it's very easy to have it as one function, in fact it's a
simple static method currently doing exactly what I think it should
probably do in core as a function.

http://svn.php.net/viewvc/pecl/hrtime/trunk/hrtime.c?revision=341600&view=markup
< Line 416.

Any name suggestions?

Regards, Niklas

Anatol Belski

9 years ago

Hi,

> -----Original Message-----
> From: Niklas Keller [mailto:me@kelunik.com]
> Sent: Friday, January 13, 2017 4:46 PM
> To: Leigh <leight@gmail.com>
> Cc: Anatol Belski <anatol.php@belski.net>; Michael Wallner <mike@php.net>;
> PHP Internals <internals@lists.php.net>; Bob Weinand <bwoebi@php.net>;
> Daniel Lowrey <rdlowrey@php.net>
> Subject: Re: [PHP-DEV] Fwd: Monotonic Time
>
> 2017-01-13 15:06 GMT+01:00 Leigh <leight@gmail.com>:
>
> > On Fri, 13 Jan 2017 at 09:35 Niklas Keller <me@kelunik.com> wrote:
> >
> > > Hi Anatol,
> > >
> > > Do you think we should merge hrtime into core or add a simple
> > > function
> > just
> > > like microtime() to ext/standard?
> > >
> > > Regards, Niklas
> > >
> >
> > It would be great if it could be a simple function, however it is
> > going to be difficult to produce something cross-platform and
> > meaningful with a single function. (I know Anatol has written portable
> > code, I haven't looked at it but I assume it's wrapping the various structs used
> by i.e.
> > performance counters, hrtime, etc.)
> >
> > I don't think we can get away from having an object-based
> > implementation to wrap those internal structs, but I do think this is
> > a useful addition regardless of how it's presented.
> >
>
> With timer.c it's very easy to have it as one function, in fact it's a simple static
> method currently doing exactly what I think it should probably do in core as a
> function.
>
> http://svn.php.net/viewvc/pecl/hrtime/trunk/hrtime.c?revision=341600&view=
> markup
> < Line 416.
>

The PerformanceCounter class from the hrtime ext allows to implement any time measurement directly in PHP. It provides the most low level units used by the system, the ticks. To convert ticks into actual time, the tick frequency is required. The frequency can be actually hidden from the implementation, or could be exposed to PHP. Exposing might be useful for several reasons, fe if one would want to compare different systems. Anyway, these are the base bricks.

Niklas, about merging into core - not sure it needs the StopWatch class, but maybe. The performance counter class, at the very low level, could have more chance. Taking timer.c as base should be fine, too, even there is a significant improved potential down to the ASM level later, though very platform specific. In first place what would make sense to know - what exact usage would it be? More specific use case info is what is needed to discuss and figure out the required implementation.

Regards

Anatol

Niklas Keller

9 years ago

>
> Hi,
>
> > -----Original Message-----
> > From: Niklas Keller [mailto:me@kelunik.com]
> > Sent: Friday, January 13, 2017 4:46 PM
> > To: Leigh <leight@gmail.com>
> > Cc: Anatol Belski <anatol.php@belski.net>; Michael Wallner <mike@php.net
> >;
> > PHP Internals <internals@lists.php.net>; Bob Weinand <bwoebi@php.net>;
> > Daniel Lowrey <rdlowrey@php.net>
> > Subject: Re: [PHP-DEV] Fwd: Monotonic Time
> >
> > 2017-01-13 15:06 GMT+01:00 Leigh <leight@gmail.com>:
> >
> > > On Fri, 13 Jan 2017 at 09:35 Niklas Keller <me@kelunik.com> wrote:
> > >
> > > > Hi Anatol,
> > > >
> > > > Do you think we should merge hrtime into core or add a simple
> > > > function
> > > just
> > > > like microtime() to ext/standard?
> > > >
> > > > Regards, Niklas
> > > >
> > >
> > > It would be great if it could be a simple function, however it is
> > > going to be difficult to produce something cross-platform and
> > > meaningful with a single function. (I know Anatol has written portable
> > > code, I haven't looked at it but I assume it's wrapping the various
> structs used
> > by i.e.
> > > performance counters, hrtime, etc.)
> > >
> > > I don't think we can get away from having an object-based
> > > implementation to wrap those internal structs, but I do think this is
> > > a useful addition regardless of how it's presented.
> > >
> >
> > With timer.c it's very easy to have it as one function, in fact it's a
> simple static
> > method currently doing exactly what I think it should probably do in
> core as a
> > function.
> >
> > http://svn.php.net/viewvc/pecl/hrtime/trunk/hrtime.c?
> revision=341600&view=
> > markup
> > < Line 416.
> >
> The PerformanceCounter class from the hrtime ext allows to implement any
> time measurement directly in PHP. It provides the most low level units used
> by the system, the ticks. To convert ticks into actual time, the tick
> frequency is required. The frequency can be actually hidden from the
> implementation, or could be exposed to PHP. Exposing might be useful for
> several reasons, fe if one would want to compare different systems. Anyway,
> these are the base bricks.
>
> Niklas, about merging into core - not sure it needs the StopWatch class,
> but maybe. The performance counter class, at the very low level, could have
> more chance. Taking timer.c as base should be fine, too, even there is a
> significant improved potential down to the ASM level later, though very
> platform specific. In first place what would make sense to know - what
> exact usage would it be? More specific use case info is what is needed to
> discuss and figure out the required implementation.

Hi Anatol,

my specific use case is mainly for event loops, replacing the current
microtime calls there, e.g.
https://github.com/amphp/loop/blob/master/lib/NativeLoop.php#L62

Performance measuring is another one, but not that important to me. If
microtime drifts there, it will show wrong results, but it won't impact
applications with failures like executing DNS timeout watchers too early
and making things fail.

Regards, Niklas

Stas Malyshev

9 years ago

Hi!

> I think we can reuse parts of it to implement a function in core to access
> a monotonic time, I don't think we need to merge the extension into core.

What's wrong with just having an extension?

--
Stas Malyshev
smalyshev@gmail.com

Niklas Keller

9 years ago

>
> Hi!
>
> > I think we can reuse parts of it to implement a function in core to
> access
> > a monotonic time, I don't think we need to merge the extension into core.
>
> What's wrong with just having an extension?
>

Do you mean an external (not bundled) extension?

Simply not having it available by default. Measuring time frames is a
pretty fundamental operation, not only for event loops.

Regards, Niklas