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newLISP Fan Club

Forum => newLISP in the real world => Topic started by: rrq on March 13, 2015, 04:53:25 PM

Title: -http mode exit doesn't exit
Post by: rrq on March 13, 2015, 04:53:25 PM
When tracking down why my ^C handler
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(signal 2 exit)
made newlisp in -http mode crash rather then exit, I found that p_exit doesn't actually exit in daemonMode, but rather it IOchannel=0 and throws (aka longjmps) an ERR_USER_RESET error. Thus, execution eventually continues at the AFTER_ERROR_ENTRY label, where fileno stubbornly objects to the IOchannel==0 by crashing. On Linux.



I'm not sure about the intention with p_exit not actually exiting in daemonMode.



Assuming there's a good reason for it, one should avoid IOchannel=0 to let the service progress as per normal. Though, then it's seriously hard to make it exit; either import my own exit or, not so gracefully, rely on (/ 0 0).
Title: Re: -http mode exit doesn't exit
Post by: Lutz on March 14, 2015, 06:37:50 AM
Yes, this is how it is supposed to work. The -d demon mode will only exit/close the current connection, reset newLISP by rolling back stacks and set the evaluation level to top, then listen again for a new connection (1). The top level variable environment state is kept, e.g. when setting a global (top level) variable or definition, exiting and reconnecting again, that variable or definition has the same value.



If you want the server exit for real, use -p instead of -d.



See also:

http://www.newlisp.org/downloads/newlisp_manual.html#tcpip_server

and:

http://www.newlisp.org/downloads/newlisp_manual.html#daemon



(1) Setting IOchannel=NULL is just part of the procedure to force a restart of the server after the reset(). setupServer() then reconfigures IOchannel to a valid Unix file descriptor.



ps: you also could do
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(destroy (sys-info -3)) .. if you must.
Title: Re: -http mode exit doesn't exit
Post by: rrq on March 14, 2015, 05:46:16 PM
Fair enough. exit is supposed to mean "exit the session" rather than "exit the program". Maybe I should read the manual sometimes ;-)



Then I suppose something needs to be done about fileno crashing on IOchannel==0, which sometimes exits the program anyhow with core dump or continues after signaling memory corruption error etc.



The destroy option is good. Though it kills via a new signal, so I'll probably go for importing the "raw" exit instead, as it really is far too easy to grumble about.
Title: Re: -http mode exit doesn't exit
Post by: rrq on March 14, 2015, 07:03:41 PM
Actually, crashing only seems to happen without open connection.



Calling exit with a connection open closes the connection and doesn't crash.



But it then also stops invoking the handler (the low level signal_handler is no longer invoked). This would be because signal_handler doesn't return, which leaves the signal in blocked state. Maybe the signal setup should use sigaction rather than signal, and set up the handling with a SA_NODEFER flag, which avoids that blocking?



Thus:

1) signal handling calling exit without open connection leads to crash, and

2) signal handling calling exit with open connection makes the signal subsequently blocked.



Basically, calling exit in a signal handler for a daemon mode script is a bad idea. I suppose calling reset in a signal handler would be a problem regardless of mode.
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