hello everyone i am looking into asynchronous file writing
(appending).
what the program is doing:
i am running a loop and when the condition is met (basically a timer)
a buffer gets appended to a file. every so often (another timer) the
filename is changed so the next write must create a new file and start
appending into that. it is really a timed Binary log.

i have managed to do that 'saving' with stream to file operations
(where file
is of type fstream), and i have also managed to do it with fopen().
but it is a requirement that the execution is not halted so i looked
into threads... and then i came across asynchronous write.

now looking into aio_write and the struct aiocb that it takes as input
argument, i see that i must provide a file descriptor instead of ther
usual FILE *, that fopen returns.

and i am wondering if i should be opening the file prior to
aio_write(), or just opening the file once for evey new filename (*ie
when the file doesnt exist), getting the file descriptor, and closing
the file, so that when the time for aio_write() comes , aio_write()
will open, write and close the file on its own.

any ideas?

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nass wrote:
> and i am wondering if i should be opening the file prior to
> aio_write(), or just opening the file once for evey new filename (*ie
> when the file doesnt exist), getting the file descriptor, and closing
> the file, so that when the time for aio_write() comes , aio_write()
> will open, write and close the file on its own.

aio_write() expects the filedescriptor (passed down to it
in the aiocb structure) to be opened. Therefore, you
shouldn't call close() unless you have either cancelled
your requests with aio_cancel(), or you are sure
that your aio_write() has finished (by calling aio_return()).

aio_write() will not open and close itself.

Rainer

[ Post a follow-up to this message ]

On Feb 15, 5:15 pm, Rainer Temme <Rainer.Te...@NoSpam.Siemens.Com>
wrote:
> nass wrote: 
>
> aio_write() expects the filedescriptor (passed down to it
> in the aiocb structure) to be opened. Therefore, you
> shouldn't call close() unless you have either cancelled
> your requests with aio_cancel(), or you are sure
> that your aio_write() has finished (by calling aio_return()).
>
> aio_write() will not open and close itself.
>
> Rainer


thank you very much for clarifing that.
may i go ahead and ask why do i get a linker error 'undefined
reference to aio_write'
since i have #include <aio.h> in my class's header file ?

[ Post a follow-up to this message ]

nass wrote:

> may i go ahead and ask why do i get a linker error 'undefined
> reference to aio_write'
> since i have #include <aio.h> in my class's header file ?

#include directives are for the preprocessor and compiler.

You need to tell your linker where to find aio_write.

http://sourceware.org/cgi-bin/cvswe.../?cvsroot=glibc

Add -lrt

[ Post a follow-up to this message ]

On Feb 15, 5:59 pm, Spoon <devn...@localhost.com> wrote:
> nass wrote: 
>
> #include directives are for the preprocessor and compiler.
>
> You need to tell your linker where to find aio_write.
>
> http://sourceware.org/cgi-bin/cvswe.../?cvsroot=glibc
>
> Add -lrt

thank you for the pointer.
the thing is i located aio.h under /usr/include and i figured that it
is in the standard path.
could you tell me where this rt library is located? and how can i know
when a header file needs additional flags in its compiler/linker?
thank you once again, the code finally compiles and links! now time to
debug
nass

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In article <1171558676.030654.185810@h3g2000cwc.googlegroups.com>,
"nass" <athanasios.silis@gmail.com> wrote:

> On Feb 15, 5:59 pm, Spoon <devn...@localhost.com> wrote: 
>
> thank you for the pointer.
> the thing is i located aio.h under /usr/include and i figured that it
> is in the standard path.
> could you tell me where this rt library is located?

It should be in /usr/lib, like all the other system libraries.

> and how can i know
> when a header file needs additional flags in its compiler/linker?

The man page tells you what header files to include and what linker
flags to use.

--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***

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