At 4:19 PM -0400 10/22/05, John E. Malmberg wrote: >>>* Bash shell support. This needs lots of work. Pipes need to be fixed. >> In principle, just replacing my_popen() and my_pclose() in vms/vms.c >>with another implementation would be all that's needed. Also, >>Perl_my_waitpid() would need some work. I think the choice of a pipe >>implementation should be a configure-time option, though, as folks on >>older versions of VMS will probably be best served by what we've got >>now, and in fact there's no proof as yet that currently available >>alternatives are better. > >Actually what Perl has is not too bad, and is much better than the pipe >implementation in the C library. I recently used what I had learned about how >perl works to implement a fix to Bash to eliminate the RWMBX hangs while >running configure scripts.
Cool. Chuck Lane gets all the credit for Perl's pipe implementation, and he was driven to it by exactly the types of hangs you describe. >What I need to do is find out where the extra newlines are being added, >because when I recreated the algorithm for bash, I did not end up with extra >new lines. I also do not seem to be having the problem with truncated lines >either. As I understand the problem, there is a fundamental gotcha when implementing a stream-oriented interface using a record-oriented gizmo like a mailbox, or at least there is when the main purpose is inter-process communication. You can emulate streams to some extent by using buffering, so that you accumulate writes until you see a newline character, at which point you do the actual write, creating a record in the mailbox only when you want the reader to see a record boundary. But sometimes you have to flush your buffer or you will end up with hangs while the reader sits around waiting for a write that has been buffered. And of course your buffer will sometimes fill up and you have to go ahead and write it out before you have a complete record. My guess, though I've never pinned it down and watched it happen in the debugger, is that when we see spurious newlines, it's because a flush has taken place or the buffer has filled up. There is lots and lots of flushing in the Perl test suite; you may just not have as much flushing in what you're doing with bash. -- ________________________________________ Craig A. Berry mailto:[EMAIL PROTECTED] "... getting out of a sonnet is much more difficult than getting in." Brad Leithauser
