Re: [Boost-users] [iostreams] interrupted reads / writes

From: Jonathan Turkanis (technews_at_[hidden])
Date: 2005-09-27 21:50:55

Sorry I didn't see this message eariler.

Marcus Alanen wrote:
> Hello,
>
> I have been toying with a framework for process management. I have
> opted to catch SIGCHLD in my signal handler to handle child processes.
> However, boost::iostreams does not seem to recognize system calls
> which are interrupted, and throws exceptions.

Right.

> Witness ./libs/iostreams/src/file_descriptor.cpp:
>
>      errno = 0;
>      std::streamsize result = BOOST_RTL(read)(pimpl_->fd_, s, n);
>      if (errno != 0)
>          throw detail::bad_read();
>      return result == 0 ? -1 : result;
>
> if ::read fails with errno == EINTR, a bad_read will result. This is
> unfortunate, as caught SIGCHLD signals will result in spurious errors,
> as the following strace shows:
> ...
> read(9, 0x95d83ac, 4096)                = ? ERESTARTSYS (To be
> restarted) --- SIGCHLD (Child exited) @ 0 (0) ---
> waitpid(-1, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], WNOHANG) = 2407
> sigreturn()                             = ? (mask now [])
> write(2, "terminate called after throwing "..., 48) = 48
> write(2, "std::ios_base::failure", 22)  = 22
> write(2, "\'\n", 2)                     = 2
> write(2, "  what():  ", 11)             = 11
> write(2, "bad read", 8)                 = 8
> write(2, "\n", 1)                       = 1
> ...
>
> As I understand it, boost was going to use ::read(), but the SIGCHLD
> got in between, resulting in a an exception being thrown.

I don't understand this sentence.
>
> I realize that boost::process is not up and running yet, so this might
> be a usage conflict of posix & boost. Can somebody please enlighten me
> what the usage pattern here should be?

I agree with Ian McCulloch's reply. What are you thinking would be a better
aproach?

> Thanks in advance,
> Marcus

-- 
Jonathan Turkanis
www.kangaroologic.com