Perhaps this all just illustrates a pile of bad assumptions I've been making, but:
I have a perl app that daemonizes itself. Among it's daemonizing efforts, it closes all file handles. My app currently utilizes a third-party perl module, which in turn makes use of the DATA file handle, as described in perldata(1). (For all my years of using perl, this was the first I ran into this mechanism, so it took a while to track down why this perl module was misbehaving.) My efforts to come up with a workaround were thwarted by a difficulty on my part in determining that the DATA file handle was was compromised. Attached is a simple perl module, and a test program that fires it's various methods; it scribble its output to syslog, if you want to follow along. The upshot is, when I used POSIX::close to close all file descriptors, somehow the DATA descriptor remained alive: - It was defined. - I could retrieve a file descriptor via fileno(). - I could use seek() and tell() to get/set my filepos. Only stat() seemed to report that there was something was amiss. I would have though fileno(), etc, would have also reported problems. Should they have? I admit, I've not pawed though and bug lists or change lists to see if this is different under newer releases... Example output: An initial working pass: Nov 2 21:43:33 10-160-62-45 ./bar.pl[5463]: [info][fileno][4][4] Nov 2 21:43:33 10-160-62-45 ./bar.pl[5463]: [info][tell][1333][1333] Nov 2 21:43:33 10-160-62-45 ./bar.pl[5463]: [info][eof][][] Nov 2 21:43:33 10-160-62-45 ./bar.pl[5463]: [info][stat][2054,32313,33152,1,0,0,0,1364,1288734213,1288734093,1288734093,4096,8][12] Nov 2 21:43:33 10-160-62-45 ./bar.pl[5463]: [print_end_data][Random text; don't mind me... ] Then, I close all descriptors, but can still utilize the file handle, except that I can't read past whatever my filepos was prior to the descriptor closing: Nov 2 21:43:33 10-160-62-45 ./bar.pl[5463]: [close_fds] Nov 2 21:43:33 10-160-62-45 ./bar.pl[5463]: [seek_data][1333] Nov 2 21:43:33 10-160-62-45 ./bar.pl[5463]: [info][fileno][4][4] Nov 2 21:43:33 10-160-62-45 ./bar.pl[5463]: [info][tell][1364][1364] Nov 2 21:43:33 10-160-62-45 ./bar.pl[5463]: [info][eof][1][1] Nov 2 21:43:33 10-160-62-45 ./bar.pl[5463]: [info][stat][][-1] Nov 2 21:43:33 10-160-62-45 ./bar.pl[5463]: [print_end_data][<undefined>] (In this pass the eof() flag is set, because the print_end_data() method was fired.) In my test code, if you comment out my use of seek_data(), and then use _init_DATA, you can see my use of stat() detects this case, and resets everything. My environment: # perl -v This is perl, v5.8.8 built for i386-linux-thread-multi # cat /etc/redhat-release CentOS release 5.4 (Final) -- Brian Reichert <[email protected]> 55 Crystal Ave. #286 Derry NH 03038-1725 USA BSD admin/developer at large
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