[boost] [Asio] Why does Boost Asio only allow 64 buffers to be sent/recei ved using scatter/gather?

Subject: [boost] [Asio] Why does Boost Asio only allow 64 buffers to be sent/recei ved using scatter/gather?
From: Stephens Patrick (patrick.stephens_at_[hidden])
Date: 2009-10-01 12:58:58

Hi all,

Apologies if this question should be directed at an Asio-specific list but I
could not see one. I originally posted on the users list so trying the
developers list now.

I am curious why the Boost Asio library specifies a maximum of 64 buffers
can be used for scatter/gather operations? I would like to gain a better
understanding as to why this value was used.

The documentation
(http://www.boost.org/doc/libs/1_40_0/doc/html/boost_asio/overview/implement
ation.html), and the code backs it up, seems to specify that the maximum
allowed will be 'min(64, IOV_MAX)' for linux implementations. 

Was this value (64) chosen for some particular reason? 
What would the consequences be of using IOV_MAX if it was greater than 64?

I see that the Windows NT, 2000, XP, 2003 and Vista implementation also has
a limit of 64 so is this something limited by the OS or to keep it
consistent across all the Asio implementations? 

I had a look around to see if there was a restriction under Windows but the
only documentation I could find
(http://msdn.microsoft.com/en-us/library/ms742203%28VS.85%29.aspx) mentions
that it is restricted to a value of 16 under Windows 95, 98 and ME, which
does tally with what the Asio documentation states in the link above.

Thanks for any help,
Pat.

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