Somehow, it appears I'm getting an ECHILD from select(), which makes no sense to me. I'm writing a server that forks child processes to handle requests. They then exit. The server assigns a signal handler to SIGCHLD to reap dead children, per perlipc. 
   $SIG{CHLD}=\&reaper;

   ...

   sub reaper
   {
      1 while waitpid -1,&POSIX::WNOHANG != -1;
      $SIG{CHLD}=\&reaper;
   }

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If anywhere, this is where an ECHILD would make more sense. Instead, it shows up in the server's main loop, which is the following. 
   use Errno;
   ...

   $select=new IO::Select();
   $select->add(...);

   ...

   while (1) {
      $!=undef;

      while (@ready=$select->can_read()) {
         handle($_) foreach @ready;
      }

      die if $select->count() == 0;  #should always have at least one

      last unless $! == EINTR;       #try again; interrupted by signal
   }

   die if $! == ECHILD;

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The weird part is that the die at the end actually executes. How can this be? I thought ECHILD occurred only in wait() and waitpid(). I understand that system, piped opens, etc. do their own waiting and can generate ECHILD, but how can that error code ever show up where I'm seeing it?

For further background, I'm on RedHat Linux 4.5, running Perl 5.8.5. All sockets involved are IO::Sockets set to block.

This is just weird.

Jim

In reply to Inexplicable ECHILD by williams

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