So what does it mean when the following code:

    $! = 0;
    $res = $sock->read($data, 255);
    # $res: #chars, or 0 for EOF, or undef for error
    $err = $!;
    $iologger->debug("bufrd res " . safe($res) . ": " .
             safe($data) . " err $err");
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Logs this:

2011-10-13 09:21:39,782 DEBUG kcmdproxy.child.io(30674):366 bufrd res 
+<<127>>: <<simkserver<sp>30665<sp>port<sp>2001<sp>client<sp>127.0.0.1
+<sp>command<sp>special<lf>1,8,7,2,13,1,12<lf>13,5,11,10,8,0,13<lf>5,2
+,11,4,5,10,5<lf>3,5,7,10,12,2,12<lf>>> err Resource temporarily unava
+ilable
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The socket call returned 127, which should be a number of characters (and looks about right). And it also set $! (which I had carefully set to 0 before the call). There isn't threading going on, and the signal handling is at the level of setting one variable in the handler, so nothing else should be interrupting to set $!. I suppose I could localize it, just as a test, to see if this still happens, but I don't see how something else can be getting in to set it. Does the $! value mean anything in this case, or is it just garbage?