Re: Print inside SIGNALS

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Re^2: Print inside SIGNALS by haukex (Archbishop) on Jul 16, 2018 at 20:18 UTC
I can replicate that the first snippet doesn't seem to output anything. However, it seems that the signal does get triggered, it just has something to do with buffering, as the following two examples work. Are you really just doing `print "Timeout reached";` in your original code, without the newline or anything else that would cause the output to get flushed? See also Suffering from Buffering. `$ perl -wMstrict -e 'alarm 2; $SIG{ALRM}=sub{ print "Timeout reached" }; while(){}' ^C $ perl -wMstrict -e 'alarm 2; $SIG{ALRM}=sub{ print "Timeout reached\n" }; while(){}' Timeout reached $ perl -wMstrict -e '$\|++; alarm 2; $SIG{ALRM}=sub{ print "Timeout reached" }; while(){}' Timeout reached` [download] Elsewhere in this thread you said: My actual perl program is huge to post it here. It does not use threads but it execute many external commands. Well, the trick is to reduce the actual code down to an SSCCE. Delete some code from your program, if the problem persists, that code can stay deleted, but if the problem goes away, then put that code back in. Repeat this over and over until your code is a 10 to 20 line program that demonstrates the issue. Not only will this help you in narrowing down the problem, it'll give us a way to reproduce the actual issue ourselves. Other than the above buffering issue, I wouldn't exclude the possibility that one of the external programs is the culprit, or something else you're doing in your "huge" program. For example, perhaps something questionable is happening to `STDOUT`.	[reply] [d/l] [select]
Re^3: Print inside SIGNALS by ikegami (Patriarch) on Jul 17, 2018 at 11:16 UTC
I can replicate that the first snippet doesn't seem to output anything. Since you killed the process instead of letting it exit cleanly (e.g. using `die` or `exit`), it didn't get to flush its buffers.	[reply] [d/l] [select]
Re^4: Print inside SIGNALS by haukex (Archbishop) on Jul 17, 2018 at 11:51 UTC
I can replicate that the first snippet doesn't seem to output anything. Since you killed the process instead of letting it exit cleanly (e.g. using `die` or `exit`), it didn't get to flush its buffers. Yes, hence my wording, which I've highlighted above. Or am I missing your point?	[reply] [d/l] [select]
Re^5: Print inside SIGNALS by ikegami (Patriarch) on Jul 17, 2018 at 16:15 UTC
Re^3: Print inside SIGNALS by pedrete (Sexton) on Jul 16, 2018 at 21:03 UTC
Fool me... EUREKA! Buffering issue as suggested by haukex !!!! Thank you everybody....	[reply]
Re^2: Print inside SIGNALS by haj (Vicar) on Jul 16, 2018 at 20:34 UTC
This is not so special. If you print to a terminal, you might note that this code does work, in the sense that the output appears after two seconds: `alarm 2; $SIG{ALRM} = \&Finish; while (1==1){}; sub Finish { print "Timeout reached\n"; }` [download] After that, the endless loop continues. The only difference is the line feed: STDOUT is typically line buffered if output is to the terminal. So, you just don't see the output. For output to a file or socket, you might want to set `$\|` to a true value.	[reply] [d/l]