Ralf Wildenhues wrote:
> In the first example using 'read', don't you have to take care of EINTR
> so that './mycat9 < file' doesn't drop forget half the file after being
> suspended and continued again?
Excellent point. I thought that in programs that don't install signal handlers,
EINTR was last seen in SunOS 4, 15 years ago. But no, it also occurs in
MacOS X! Test program:
==========================================================================
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
int
main ()
{
for (;;)
{
char buf[4096];
ssize_t count = read (0, buf, sizeof (buf));
if (count == 0)
break;
if (count < 0)
{
perror ("read");
break;
}
fwrite (buf, 1, count, stdout);
}
return 0;
}
==========================================================================
Run it, type Hello<Return>, then Ctrl-Z and the job control command 'fg'.
Result on all systems except MacOS X:
$ ./a.out
Hello
Hello
^Z
[1]+ Stopped ./a.out
$ fg
./a.out
World
World
Result on MacOS X:
$ ./a.out
Hello
Hello
^Z
[1]+ Stopped ./a.out
$ fg
./a.out
read: Interrupted system call
I have updated the blog / tutorial lesson, and I'm adding this to the gnulib
documentation:
2011-07-03 Bruno Haible <br...@clisp.org>
Comments about EINTR.
* lib/safe-read.h: Explain the purpose of this module.
* lib/safe-write.h: Likewise.
* doc/posix-functions/read.texi: Mention EINTR and the 'safe-read'
module.
* doc/posix-functions/write.texi: Mention EINTR and the 'safe-write'
module.
Reported by Ralf Wildenhues <ralf.wildenh...@gmx.de>.
--- doc/posix-functions/read.texi.orig Sun Jul 3 13:33:13 2011
+++ doc/posix-functions/read.texi Sun Jul 3 12:29:44 2011
@@ -17,4 +17,11 @@
Portability problems not fixed by Gnulib:
@itemize
+@item
+This function may fail with error @code{EINTR}, even in programs that don't
+install any signal handlers, on some platforms:
+MacOS X 10.5.
@end itemize
+
+For handling @code{EINTR}, Gnulib provides a module @samp{safe-read} with a
+function @code{safe_read}.
--- doc/posix-functions/write.texi.orig Sun Jul 3 13:33:13 2011
+++ doc/posix-functions/write.texi Sun Jul 3 12:29:40 2011
@@ -32,4 +32,11 @@
Portability problems not fixed by Gnulib:
@itemize
+@item
+This function may fail with error @code{EINTR}, even in programs that don't
+install any signal handlers, on some platforms:
+MacOS X 10.5.
@end itemize
+
+For handling @code{EINTR}, Gnulib provides a module @samp{safe-write} with a
+function @code{safe_write}.
--- lib/safe-read.h.orig Sun Jul 3 13:33:13 2011
+++ lib/safe-read.h Sun Jul 3 12:57:35 2011
@@ -14,6 +14,19 @@
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
+/* Some system calls may be interrupted and fail with errno = EINTR in the
+ following situations:
+ - The process is stopped and restarted (signal SIGSTOP and SIGCONT, user
+ types Ctrl-Z) on some platforms: MacOS X.
+ - The process receives a signal for which a signal handler was installed
+ with sigaction() with an sa_flags field that does not contain
+ SA_RESTART.
+ - The process receives a signal for which a signal handler was installed
+ with signal() and for which no call to siginterrupt(sig,0) was done,
+ on some platforms: AIX, HP-UX, IRIX, OSF/1, Solaris.
+
+ This module provides a wrapper around read() that handles EINTR. */
+
#include <stddef.h>
#ifdef __cplusplus
--- lib/safe-write.h.orig Sun Jul 3 13:33:13 2011
+++ lib/safe-write.h Sun Jul 3 12:57:36 2011
@@ -14,6 +14,19 @@
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
+/* Some system calls may be interrupted and fail with errno = EINTR in the
+ following situations:
+ - The process is stopped and restarted (signal SIGSTOP and SIGCONT, user
+ types Ctrl-Z) on some platforms: MacOS X.
+ - The process receives a signal for which a signal handler was installed
+ with sigaction() with an sa_flags field that does not contain
+ SA_RESTART.
+ - The process receives a signal for which a signal handler was installed
+ with signal() and for which no call to siginterrupt(sig,0) was done,
+ on some platforms: AIX, HP-UX, IRIX, OSF/1, Solaris.
+
+ This module provides a wrapper around write() that handles EINTR. */
+
#include <stddef.h>
#define SAFE_WRITE_ERROR ((size_t) -1)
--
In memoriam Yuri Shchekochikhin
<http://en.wikipedia.org/wiki/Yuri_Shchekochikhin>
