From: Jos Backus <jos@...>
Date: 2012-07-06T05:35:31+09:00
Subject: Re: Green threads in 1.9.* ?

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On Thu, Jul 5, 2012 at 1:22 PM, Eric Hodel <drbrain@segment7.net> wrote:

> A more accurate picture of 1.9 is:
>
> The OS schedules threads to run on CPUs.
>
> The ruby VM has a global lock that only allows one thread to run ruby code
> at a time (the GVL).  The GVL is also held for execution inside C
> extensions unless the author releases the GVL (most extensions release the
> GVL for some part of their operation).
>
> Ruby schedules use of the GVL for threads created by the ruby VM.
>
> A Ruby thread may release the GVL to run non-ruby code.  An example would
> be performing a long calculation such as interacting with a DB, processing
> zlib streams, XML parsing with libxml2, etc.  Such tasks don't need to
> communicate with the ruby VM so they can be running on separate CPUs at the
> same time as the ruby VM.
>
> A Ruby thread will release the GVL when it performs a blocking operation
> such as IO or other system calls.
>
> So the OS and the ruby VM cooperate on thread scheduling.  If multiple
> ruby threads do not need the GVL to run the OS does the majority of the
> scheduling.  If multiple ruby threads do need the GVL ruby does the
> majority of the scheduling.
>

This would make a good FAQ entry, I think. Thanks, Eric.

Jos
-- 
Jos Backus
jos at catnook.com

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<div class=3D"gmail_quote">On Thu, Jul 5, 2012 at 1:22 PM, Eric Hodel <span=
 dir=3D"ltr">&lt;<a href=3D"mailto:drbrain@segment7.net" target=3D"_blank">=
drbrain@segment7.net</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_qu=
ote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex=
">

A more accurate picture of 1.9 is:<br>
<br>
The OS schedules threads to run on CPUs.<br>
<br>
The ruby VM has a global lock that only allows one thread to run ruby code =
at a time (the GVL). =A0The GVL is also held for execution inside C extensi=
ons unless the author releases the GVL (most extensions release the GVL for=
 some part of their operation).<br>

<br>
Ruby schedules use of the GVL for threads created by the ruby VM.<br>
<br>
A Ruby thread may release the GVL to run non-ruby code. =A0An example would=
 be performing a long calculation such as interacting with a DB, processing=
 zlib streams, XML parsing with libxml2, etc. =A0Such tasks don&#39;t need =
to communicate with the ruby VM so they can be running on separate CPUs at =
the same time as the ruby VM.<br>

<br>
A Ruby thread will release the GVL when it performs a blocking operation su=
ch as IO or other system calls.<br>
<br>
So the OS and the ruby VM cooperate on thread scheduling. =A0If multiple ru=
by threads do not need the GVL to run the OS does the majority of the sched=
uling. =A0If multiple ruby threads do need the GVL ruby does the majority o=
f the scheduling.<br>

</blockquote></div><br>This would make a good FAQ entry, I think. Thanks, E=
ric.<br><br>Jos<br>-- <br><div><font><font face=3D"arial,helvetica,sans-ser=
if">Jos Backus</font></font></div><div><font><font face=3D"arial,helvetica,=
sans-serif">jos at <a href=3D"http://catnook.com" target=3D"_blank">catnook=
.com</a><br>
</font></font></div><br>

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