[Boost-users] general question on sentry in streams

From: Ovanes Markarian (om_boost_at_[hidden])
Date: 2008-08-13 10:27:51

Hello all,

this is probably a wrong place to write this post, but I hope to receive
your thoughts anyway. Writing to moderated c++ group might open my email
address to spammers, so I decided to write my post here.

One of my collegues told me once that C++ streams are slower then Java. We
did some trials (on a Win32 platform with Visual C++ 7.1) and he was able to
prove this. Today when I read the standard on output steams I came accross
the point, that most all stream functions must construct the nested sentry
type. I suddenly remembered the article written by Nathan Myers on locales
available at:
http://www.cantrip.org/locale.html

There he states, that in sentry a locking might be made in a multi-threaded
environment. I looked in the implemenation of my STL distribution (which by
default bundled with VC++ 7.1) and here we go. sentry locks in ctor and
unlocks in dtor. So writing a character by character or integer by integer
will produce the whole bunch of lock/unlock sequences, since standard states
(in §27.6.2.5.4)  that every call to operator << has to create sentry object
instance and that explains to me why the std streams (at least on Windows
are much slower as on Java).

Would be great to hear your thoughts...

Regards,
Ovanes