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Re: tee logs no output if stdout is closed


From: Bruno Haible
Subject: Re: tee logs no output if stdout is closed
Date: Sat, 4 Oct 2008 15:09:47 +0200
User-agent: KMail/1.5.4

Jim Meyering wrote:
> > You can distinguish close_stream and close_stdout. close_stream is library 
> > code,
> > close_stdout is not. What about a 'bool ignore_epipe' that influences the
> > behaviour of close_stdout? Whereas the library code that called close_stream
> > has to check against EOF/EPIPE itself if it wants to.
> 
> Indeed.  This sounds workable, perhaps using a new
> close_stdout_ignore_epipe function.

Here's a proposed patch. The function name 'close_stdout_set_ignore_EPIPE'
was chosen for consistency with the already existing function
'close_stdout_set_file_name'.


2008-10-04  Bruno Haible  <address@hidden>
            Jim Meyering  <address@hidden>

        Add an option for ignoring EPIPE during close_stdout.
        * lib/closeout.h: Include <stdbool.h>.
        (close_stdout_set_ignore_EPIPE): New declaration.
        * lib/closeout.c: Include <stdbool.h>.
        (ignore_EPIPE): New variable.
        (close_stdout_set_ignore_EPIPE): New function.
        (close_stdout): Ignore EPIPE error if ignore_EPIPE is set.
        * lib/close-stream.c (close_stream): Mention the possible EPIPE
        failure.
        * modules/closeout (Depends-on): Add stdbool.

--- lib/closeout.h.orig 2008-10-04 15:01:05.000000000 +0200
+++ lib/closeout.h      2008-10-04 15:00:29.000000000 +0200
@@ -1,6 +1,7 @@
 /* Close standard output and standard error.
 
-   Copyright (C) 1998, 2000, 2003, 2004, 2006 Free Software Foundation, Inc.
+   Copyright (C) 1998, 2000, 2003, 2004, 2006, 2008 Free Software Foundation,
+   Inc.
 
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -18,11 +19,14 @@
 #ifndef CLOSEOUT_H
 # define CLOSEOUT_H 1
 
+# include <stdbool.h>
+
 # ifdef __cplusplus
 extern "C" {
 # endif
 
 void close_stdout_set_file_name (const char *file);
+void close_stdout_set_ignore_EPIPE (bool ignore);
 void close_stdout (void);
 
 # ifdef __cplusplus
--- lib/closeout.c.orig 2008-10-04 15:01:05.000000000 +0200
+++ lib/closeout.c      2008-10-04 14:54:01.000000000 +0200
@@ -1,6 +1,6 @@
 /* Close standard output and standard error, exiting with a diagnostic on 
error.
 
-   Copyright (C) 1998, 1999, 2000, 2001, 2002, 2004, 2006 Free
+   Copyright (C) 1998, 1999, 2000, 2001, 2002, 2004, 2006, 2008 Free
    Software Foundation, Inc.
 
    This program is free software: you can redistribute it and/or modify
@@ -21,6 +21,7 @@
 #include "closeout.h"
 
 #include <errno.h>
+#include <stdbool.h>
 #include <stdio.h>
 #include <unistd.h>
 
@@ -42,6 +43,41 @@
   file_name = file;
 }
 
+static bool ignore_EPIPE /* = false */;
+
+/* Specify whether an EPIPE error during the closing of stdout should be
+   ignored (ignore = true) or signaled to the user through an error message
+   (ignore = false).
+
+   This setting matters only if the SIGPIPE signal is ignored (i.e. its
+   handler set to SIG_IGN) or blocked.  Only particular programs need to
+   temporarily ignore SIGPIPE.  If SIGPIPE is ignored or blocked because
+   it was ignored or blocked in the parent process when it created the
+   child process, it usually is a bug in the parent process: It is bad
+   practice to have SIGPIPE ignored or blocked while creating a child
+   process.
+
+   EPIPE occurs when writing to a pipe or socket that has no readers now,
+   when SIGPIPE is ignored or blocked.
+
+   The ignore = false setting is suitable for a scenario where it is normally
+   guaranteed that the pipe writer terminates before the pipe reader.  In
+   this case, an EPIPE is an indication of a premature termination of the
+   pipe reader and should be signaled.
+
+   The ignore = true setting is suitable for a scenario where you don't know
+   ahead of time whether the pipe writer or the pipe reader will terminate
+   first.  In this case, an EPIPE is an indication that the pipe writer can
+   stop doing useless write() calls; this is what close_stdout does anyway.
+   EPIPE is part of the normal pipe/socket shutdown protocol in this case,
+   and should not be signaled.  */
+
+void
+close_stdout_set_ignore_EPIPE (bool ignore)
+{
+  ignore_EPIPE = ignore;
+}
+
 /* Close standard output.  On error, issue a diagnostic and _exit
    with status 'exit_failure'.
 
@@ -68,7 +104,8 @@
 void
 close_stdout (void)
 {
-  if (close_stream (stdout) != 0)
+  if (close_stream (stdout) != 0
+      && !(ignore_EPIPE && errno == EPIPE))
     {
       char const *write_error = _("write error");
       if (file_name)
--- lib/close-stream.c.orig     2008-10-04 15:01:05.000000000 +0200
+++ lib/close-stream.c  2008-10-04 14:58:09.000000000 +0200
@@ -1,6 +1,6 @@
 /* Close a stream, with nicer error checking than fclose's.
 
-   Copyright (C) 1998, 1999, 2000, 2001, 2002, 2004, 2006, 2007 Free
+   Copyright (C) 1998, 1999, 2000, 2001, 2002, 2004, 2006, 2007, 2008 Free
    Software Foundation, Inc.
 
    This program is free software: you can redistribute it and/or modify
@@ -33,6 +33,10 @@
    otherwise.  A failure might set errno to 0 if the error number
    cannot be determined.
 
+   A failure with errno set to EPIPE may or may not indicate an error
+   situation worth signaling to the user.  See the documentation of the
+   close_stdout_set_ignore_EPIPE function for details.
+
    If a program writes *anything* to STREAM, that program should close
    STREAM and make sure that it succeeds before exiting.  Otherwise,
    suppose that you go to the extreme of checking the return status
--- modules/closeout.orig       2008-10-04 15:01:05.000000000 +0200
+++ modules/closeout    2008-10-04 14:18:32.000000000 +0200
@@ -12,6 +12,7 @@
 error
 quotearg
 exitfail
+stdbool
 
 configure.ac:
 gl_CLOSEOUT





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