# Why Thread.abort\_on\_exception = yes doesn't show errors? **URL:** \ **Category:** Ruby\ **Created:** [July 20, 2008, 8:26pm UTC](https://www.ruby-forum.com/t/why-thread-abort-on-exception-yes-doesnt-show-errors/143580 "2008-07-20T20:26:18Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![ISSSSaki\_Baz\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/51bf81/32.png) [@ISSSSaki\_Baz\_C](https://www.ruby-forum.com/u/ISSSSaki_Baz_C)\ **Post date:** [July 20, 2008, 8:26pm UTC](https://www.ruby-forum.com/t/why-thread-abort-on-exception-yes-doesnt-show-errors/143580/1 "2008-07-20T20:26:18Z")
Hi, when Thread.abort\_on\_exception = yes I don’t see any error log in the screen. Note those cases: ## case 1) It’s seems correct: t = Thread.new { sleep 1 qwe } t.abort\_on\_exception = true ## puts “hello !!!” sleep 2 puts “END” =\> hello !!! test.rb:3: undefined local variable or method `qwe' for main:Object (NameError) from test.rb:1:in`initialize’ from test.rb:1:in `new’ from test.rb:1 ## case 2) Why the error is not shown??? t = Thread.new { sleep 1 qwe } t.abort\_on\_exception = false ## puts “hello !!!” sleep 2 puts “END” =\> hello !!! END ## case 3) But if I do a t.join then the error is shown and the program exists !!!: t = Thread.new { sleep 1 qwe } t.abort\_on\_exception = false ## puts “hello !!!” t.join puts “END” =\> hello !!! test.rb:3: undefined local variable or method `qwe' for main:Object (NameError) from test.rb:8:in`join’ from test.rb:8 Conclusion: - If a thread is joined then if that threads has a non handled exception the program will exit (except if the main program handles that exception). - If a thread is “abort\_on\_exception = true” then the program will fail in the moment the thread fails (it makes sense). - If a thead is “abort\_on\_exception = false” then nothing will occur if the threads fails, and no error output will occur. WHY ??? Any comment is appreciated. ---
**Author:** ![ISSSSaki\_Baz\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/51bf81/32.png) [@ISSSSaki\_Baz\_C](https://www.ruby-forum.com/u/ISSSSaki_Baz_C)\ **Post date:** [July 20, 2008, 9:13pm UTC](https://www.ruby-forum.com/t/why-thread-abort-on-exception-yes-doesnt-show-errors/143580/2 "2008-07-20T21:13:15Z")
Iñaki Baz C. wrote: > - If a thread is joined then if that threads has a non handled exception the > program will exit (except if the main program handles that exception). > > - If a thread is “abort\_on\_exception = true” then the program will fail in the > moment the thread fails (it makes sense). > > - If a thead is “abort\_on\_exception = false” then nothing will occur if the > threads fails, and no error output will occur. WHY ??? That’s all intended, IIUC. Point #1 above implies point #3: suppose threads _always_ reported exceptions. Then if you wrote a program to take advantage of #1 by harvesting finished threads and handling their exceptions in the main thread (or more generally the joining thread) you would have spurious exception dumping. You have more control this way, but you have to remember to either set abort\_on\_exception or to wrap your thread in a handler or to join the thread later. These are three styles, each of which has its place. ---
**Author:** ![ISSSSaki\_Baz\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/51bf81/32.png) [@ISSSSaki\_Baz\_C](https://www.ruby-forum.com/u/ISSSSaki_Baz_C)\ **Post date:** [July 20, 2008, 11:47pm UTC](https://www.ruby-forum.com/t/why-thread-abort-on-exception-yes-doesnt-show-errors/143580/3 "2008-07-20T23:47:13Z")
El Domingo, 20 de Julio de 2008, Joel VanderWerf escribió: > You have more control this way, > but you have to remember to either set abort\_on\_exception or to wrap > your thread in a handler or to join the thread later. These are three > styles, each of which has its place. Well, thanks for the explanation but I have a doubt. I run a thread “t2” inside thread “t1” but I don’t want “t1” to wait to “t2” to finish, this is: I don’t need “t1” joins “t2”. I also don’t want the main program ends because “t2” produces an exception that nobody handles, but I want to see the error. Is not a way to get this behaviour? The only solution I see is t1 joins t2, is it? Thanks a lot. ---
**Author:** ![ISSSSaki\_Baz\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/51bf81/32.png) [@ISSSSaki\_Baz\_C](https://www.ruby-forum.com/u/ISSSSaki_Baz_C)\ **Post date:** [July 21, 2008, 12:11am UTC](https://www.ruby-forum.com/t/why-thread-abort-on-exception-yes-doesnt-show-errors/143580/4 "2008-07-21T00:11:14Z")
El Domingo, 20 de Julio de 2008, Iñaki Baz C. escribió: > Thanks a lot for any suggestion. Opss, I think I have the solution 🙂 * * * class GServer ``` # New Thread for a new IO. def serve(io) loop do data = read_IO_incoming_data() Thread.new { begin Logic::process(data) rescue => e puts "#{e.class}: #{$!}" end } end # loop end # def serve ``` ## end # class GServer Is it OK? 🙂 ---
**Author:** ![ISSSSaki\_Baz\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/51bf81/32.png) [@ISSSSaki\_Baz\_C](https://www.ruby-forum.com/u/ISSSSaki_Baz_C)\ **Post date:** [July 21, 2008, 1:18am UTC](https://www.ruby-forum.com/t/why-thread-abort-on-exception-yes-doesnt-show-errors/143580/5 "2008-07-21T01:18:32Z")
Iñaki Baz C. wrote: > ``` > Thread.new { > begin > Logic::process(data) > rescue => e > puts "#{e.class}: #{$!}" > end > } > > ``` Yes, that’s a standard practice. That’s what I meant by “wrap your thread in a handler” (sorry that was a bit unclear). ---
**Author:** ![ISSSSaki\_Baz\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/51bf81/32.png) [@ISSSSaki\_Baz\_C](https://www.ruby-forum.com/u/ISSSSaki_Baz_C)\ **Post date:** [July 21, 2008, 1:23am UTC](https://www.ruby-forum.com/t/why-thread-abort-on-exception-yes-doesnt-show-errors/143580/6 "2008-07-21T01:23:13Z")
El Lunes, 21 de Julio de 2008, Joel VanderWerf escribió: > thread in a handler" (sorry that was a bit unclear). > Yeah, now after reading again you mail I understood it better 🙂 Thanks a lot for your help. ---
**Author:** ![ISSSSaki\_Baz\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/51bf81/32.png) [@ISSSSaki\_Baz\_C](https://www.ruby-forum.com/u/ISSSSaki_Baz_C)\ **Post date:** [July 20, 2008, 11:55pm UTC](https://www.ruby-forum.com/t/why-thread-abort-on-exception-yes-doesnt-show-errors/143580/7 "2008-07-20T23:55:24Z")
El Domingo, 20 de Julio de 2008, Iñaki Baz C. escribió: > I also don’t want the main program ends because “t2” produces an exception > that nobody handles, but I want to see the error. Is not a way to get this > behaviour? > > The only solution I see is t1 joins t2, is it? Humm, but this is not valid for me, I explain why: I’m using GServer, so it creates a Thread for each incoming TCP connection and runs “serve” method for each one. In “serve” method I parse the TCP incoming data and process it, but I need this connection to remain open and accepting new data even if the received data hasn’t be processed yet (it’s a SIP server). So, in resume I do: * * * class GServer # New Thread for a new IO. def serve(io) ``` loop do data = read_IO_incoming_data() Thread.new { Logic::process(data) } end # loop ``` end # def serve ## end # class GServer As you see, I need the TCP connection remains open and available ALL the time, I can wait to process the last received data, so I run a Thread and repeat **inmediately** the loop. Also I need that if an exception occurs in Logic::process(data) it being shown but don’t stop the programm (abort\_on\_exception = false). But in this way I can’t see the error output if it occurs. How could I get showing the error into the Thread without doing a “join”? (I can’t do a join). Thanks a lot for any suggestion.