Date: Fri, 22 May 1998 02:09:47 -0400 (EDT) From: HighWind Software Information <info@highwind.com> To: freebsd-hackers@FreeBSD.ORG Cc: support@highwind.com Subject: FreeBSD 2.2.6 + pthread == write() bug Message-ID: <199805220609.CAA05884@highwind.com>
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We here at HighWind are trying to port some threaded apps to
FreeBSD-stable (2.2.6). Things seem to be going well, EXCEPT, we
believe we found a BUG:
When using pthreads (with libc_r), sometimes BLOCKING calls to write()
down a connected TCP file descriptor are returning partial writes:
....
ssize_t byte_count = 0;
while ((byte_count = write(fd, data, bytes_to_write)) != bytes_to_write) {
if (errno != EINTR && errno != EAGAIN) {
if (errno != EPIPE) {
// Use the HighWind "syslog" class
Syslog::syslog(LOG_ERR,
"Error write() of Vector Data %d/%d (%m)",
byte_count, bytes_to_write);
}
return false;
}
}
....
This is syslog'ing (sometimes):
May 22 01:57:57 zonda typhoond[1988]: Error write() of Vector Data 2292/4096 (Undefined error: 0)
Clearly, this shows the "write()" returning with less data written then
was requested.
This is a write() on a descriptor marked BLOCKING. It should either
return "bytes_to_write" or an error. It should NEVER return less than
"bytes_to_write".
Please note, the "while()" loop above is strictly to handle EINTR and
EAGAIN. It should NOT have to handle partial write's since this is a
blocking write!
My understanding is that the libc_r makes the fd "non-blocking" and
does a non-blocking write under the covers. However, that should not
matter. Outside the library, that write() call should be a BLOCKING
write.
I suspect (I'm guessing) that libc_r either forgets to remark the fd
blocking, or it simply doesn't loop on a partial write when it does
its non-blocking write. I don't know.
We'd be happy to provide more details. This is VERY VERY bad bug for
us!! We'd appreciate any help as we have a strong desire to see our
products on FreeBSD.
Rob Fleischman
HighWind Software
rmf@highwind.com
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