Forcing fsync() using an ouput stream in C++

Forcing fsync() using an ouput stream in C++

[Hareesh Nagarajan]

Hi,

I am aware this is a C-programming mailing list. I just thought I
might get some useful inputs from this ML.

My problem is that I haven't figured out how I must fsync an output
stream (in C++) even after reading the contents of this link:
http://gcc.gnu.org/ml/gcc-help/2004-02/msg00285.html

How must I modify this method (this method doesn't work; it prints the
error message and exits!) ?

void logRecovery::syncToDisk(fstream& f)
{
    unix_filebuf_t* buf;
    buf = dynamic_cast<unix_filebuf_t*>(f.rdbuf());
    if (buf == NULL) {
	cerr << "Fatal: Don't know fd of stream" << endl;
	exit(-1);
    }

    fsync(buf->fd());
}

I am using GCC 3.3.4.

Thanks,

Hareesh

Re: Forcing fsync() using an ouput stream in C++

[Steve Graegert]

On Thu, 3 Mar 2005 00:38:10 -0600, Hareesh Nagarajan
<hareesh.nagarajan@gmail.com> wrote:
> Hi,
> 
> I am aware this is a C-programming mailing list. I just thought I
> might get some useful inputs from this ML.
> 
> My problem is that I haven't figured out how I must fsync an output
> stream (in C++) even after reading the contents of this link:
> http://gcc.gnu.org/ml/gcc-help/2004-02/msg00285.html
> 
> How must I modify this method (this method doesn't work; it prints the
> error message and exits!) ?
> 
> void logRecovery::syncToDisk(fstream& f)
> {
>    unix_filebuf_t* buf;
>    buf = dynamic_cast<unix_filebuf_t*>(f.rdbuf());
>    if (buf == NULL) {
>        cerr << "Fatal: Don't know fd of stream" << endl;
>        exit(-1);
>    }
> 
>    fsync(buf->fd());
> }
> 
> I am using GCC 3.3.4.
> 
> Thanks,
> 
> Hareesh
> -
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> 

I have actually now idea why you are using unix_filebuf_t. Why not
simply call f.flush()? If you need to obtain a reference to the
streambuf object associated with a stream you can call f.readbuf() and
then do a sync, like this:

streambuf *buf;
buf = f.readbuf();
buf->sync();

May be I get you wrong, but hope this helps.

-- 
Kind Regards

    \Steve