[Bug c++/34979] New: Atomic line output requested in gcc

[Bug c++/34979] New: Atomic line output requested in gcc

[bkustel at yahoo dot com]

When running gcc in a parallel build or multi-threaded environment, I run into
cases where gcc's error output gets broken in the middle of line or worse,
individual gcc error output lines from different threads/processes get broken
up and mixed together. While I would fully expect interleaving of LINES in a
multithreaded environment with a shared file descriptor (stderr) I would have
hoped that the output of each error LINE would be atomic. I eventually tracked
this down into libcpp/errors.c where I saw that the output of error lines is
often broken up into many output calls to stderr. I believe POSIX dictates that
each individual output call is atomic with respect to other threads or
processes sharing the same file descriptor but of course if a single error line
is output using numerous fputs(), fputc() and *fprintf() calls then POSIX
provides no guarantee that the line will appear unbroken in the final output.

I have filed this as "enhancement" since I'm not prepared to call the lack of
"atomic line output" a bug, but it would sure be a nice feature to have.
Otherwise in parallel build environments one sometimes get fragments of error
message lines intermixed in stderr and it can be quite confusing.
Thanks.


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           Summary: Atomic line output requested in gcc
           Product: gcc
           Version: 4.2.1
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bkustel at yahoo dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34979

[Bug preprocessor/34979] Atomic line output requested in gcc

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2008-01-26 05:43 -------
Really libcpp (the C preprocessor) should be using the normal diagnostic part
of GCC and not its own.


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pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
          Component|c++                         |preprocessor


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34979

[Bug preprocessor/34979] Atomic line output requested in gcc

[rguenth at gcc dot gnu dot org]

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rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2008-01-26 11:35:25
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34979

[Bug other/34979] Atomic line output requested in gcc

[jsm28 at gcc dot gnu dot org]

------- Comment #2 from jsm28 at gcc dot gnu dot org  2009-03-30 00:02 -------
cpplib does now use GCC's diagnostic.c, so if there is a bug here any more it
is not a preprocessor one.  It looks like diagnostic.c (in turn using
pretty-print.c) will write the diagnostic in one fputs call, then the final
newline in an fputc call, then flush the stream, so it's not yet using the
minimal number of stdio calls - though even with the minimal number of such
calls that doesn't and can't guarantee that multiple write() calls aren't used
underneath by libc.


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jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|preprocessor                |other


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34979