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

From: Marcus Alanen (maalanen_at_[hidden])
Date: 2005-09-26 14:45:23

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.

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 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?

Thanks in advance,
Marcus