id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
579	boost.iostreams file_descriptor and sharing	nobody	Jonathan Turkanis	"{{{
Hi!

I have couple of questions about the behavior of
boost::iostreams::file_descriptor.

First, I've noticed that it always opens files with
exclusive access. That is, it calls CreateFileA with a
dwShareMode of 0, which means that ""the object cannot
be shared and cannot be opened again until the handle
is closed"". Is this by design? Wouldn't it be
reasonable to use a share mode of FILE_SHARE_READ when
opening a file only for reading?

Second, the function file_descriptor::open has a third
parameter 'base', which appears to be extra open mode
bits that are always on, in addition to those in the
second parameter to stream::open. What is the purpose
of this? Since there is a stream::open function with
three parameters I can specify these extra bits as well
when opening the file, in order to actually get the
file opened only for reading, but I worry that this
will somehow violate the design of the file_descriptor
class.

I've modified my copy of file_descriptor::open to use a
share mode of FILE_SHARE_READ when opening a file only
for reading and am now calling stream::open with three
arguments in order to make this happen. Is this safe?
It appears to work in the very limited cases I've tried
so far.

Yours,
Gunnar Blomberg (Gunnar.Blomberg@iar.se)

PS. Thanks for an excellent library!
DS.

}}}"	Support Requests	closed		iostreams	None	Problem	fixed