# Re: Unable to stop the flow graph after calling stop() **URL:** \ **Category:** GNU Radio\ **Created:** [March 3, 2014, 6:54am UTC](https://www.ruby-forum.com/t/re-unable-to-stop-the-flow-graph-after-calling-stop/239518 "2014-03-03T06:54:56Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\ **Post date:** [March 3, 2014, 6:54am UTC](https://www.ruby-forum.com/t/re-unable-to-stop-the-flow-graph-after-calling-stop/239518/1 "2014-03-03T06:54:56Z")
Dear Sir, Thank you very much. What if, we want to stop the flow graph in the constructor of a block? In work() we can just return -1. But in constructor, what value should be returned, also -1 ? Regards, Activecat ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [March 3, 2014, 10:27am UTC](https://www.ruby-forum.com/t/re-unable-to-stop-the-flow-graph-after-calling-stop/239518/2 "2014-03-03T10:27:19Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Activecat, the constructor of a block must have been called before the block has been connect()ed; so there’s no way a flowgraph is already running when your block’s constructor is called. Greetings, Marcus On 03.03.2014 06:53, Activecat wrote: > > > > > \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Discuss-gnuradio > mailing list [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 Comment: Using GnuPG with Thunderbird - [http://www.enigmail.net/](http://www.enigmail.net/) iQEcBAEBAgAGBQJTFEqdAAoJEAFxB7BbsDrLv84H/jghxvQXY6VcZPvRXs1BKmxp Odr8p/ICE9rpcz21M6M0ILxqhKaOp5vlaG/n6UMM2fFU+Cf7RQQkFrVsEBcqUcGg sgYjE+PmTuIbn6xg6mupAJdN1iVsztH+5qU/71SPxJjfwpnJjsJrzzGlQC6JhGIr fPHDG5DLAS11Q8USSFAc5Y7vXI57rskCZ3/Qq1j+dTl5pgNLSzsccb4AmVBy2dCB 7mM1PIxAuTJgaeXbk85BEnhkwdI4HQzOS7phg53ChYIWMKs+WCsjk0weUNMj2VZt rXdd137xZjkfPHyGJ73spjhJ7OHUW8NeQaNxauI8Uf45S6jnNFFx/vzD1EEgIV8= =vI+z -----END PGP SIGNATURE----- ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [March 3, 2014, 11:59am UTC](https://www.ruby-forum.com/t/re-unable-to-stop-the-flow-graph-after-calling-stop/239518/3 "2014-03-03T11:59:44Z")
Dear Marcus, Says, the constructor performed some basic checking on the constructor arguments, then had found some fatal error (says, division by zero) and decided to ban the flowgraph from being executed. A workaround is to get the constructor to set a class variable to false, says, d\_valid = false; then in the work() it will check this d\_valid as follows: ``` int work() { if ( ! d_valid ) return -1 ......... ......... (other stuff as usual) } ``` But isn’t there a better way to do this …? (to ban the flowgraph from being executed within the constructor) Please advise, thanks. Regards, Activecat ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [March 3, 2014, 12:03pm UTC](https://www.ruby-forum.com/t/re-unable-to-stop-the-flow-graph-after-calling-stop/239518/4 "2014-03-03T12:03:51Z")
Dear Activecat, Throw an exception. It will kill the application. Miklos ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [March 3, 2014, 12:39pm UTC](https://www.ruby-forum.com/t/re-unable-to-stop-the-flow-graph-after-calling-stop/239518/5 "2014-03-03T12:39:10Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi Activecat, as Miklos wrote: Let your Constructor throw an exception. For a little detail on that, refer to [http://www.parashift.com/c++-faq-lite/ctors-can-throw.html](http://www.parashift.com/c++-faq-lite/ctors-can-throw.html) . You can surround your block construction with a try{}catch-clause, and handle your error, so your application may deal with that gracefully (instead of just dying). Another common method of dealing with stuff like this is, if you really have complex constructor arguments and might need to check if they make sense in multiple places - - let your class have a static method validate\_arguments(…) that returns true or false, - - let your c’tor call that and throw an exception when it’s false, and - - use that unbound method (that is calling activecats\_class::validate\_arguments() rather than calling instance\_of\_that\_class.validate\_arguments()) from wherever you want to calculate arguments. Greetings, Marcus On 03.03.2014 12:02, Miklos M. wrote: > > Says, the constructor performed some basic checking on the > > (other stuff as usual) } > > > > > > > > this-\>d\_complete == true ? > > > > > > [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) > > > > \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Discuss-gnuradio > > mailing list [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > > [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 Comment: Using GnuPG with Thunderbird - [http://www.enigmail.net/](http://www.enigmail.net/) iQEcBAEBAgAGBQJTFGmXAAoJEAFxB7BbsDrLOLAIAJUgbhHeABDD9bDgCjJYRIhu VzbVgZPo0bnPVfNGkojrO5wRTSzjHbCqQFkKbl4JCPLK6+IPq/9mL+iDffPQ9Aic IGZLhq/ep8LwfiDjjh6D6BNQYmHqa6hRLPkHBzETmKqvBK5258b86IgedJNIDJF7 +qfVZWQsi3FDUyGSD6fVRHOUkfKT3naR0FqhipxtMRWFprBRrovMV23IqbVMdDQv WfxeWyNoJMpYjXPT+S/pt7h9kxKUbcZK4aOWwuhnwmTahFcfcx+GCIc54UQHegVR /WvOD1LNiYIXLJg6wEssN783OXbMqzWTaTl0+CFf6NWO4jQQFaAtoiUk3+EjXIQ= =9pRp -----END PGP SIGNATURE----- ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [March 3, 2014, 2:58pm UTC](https://www.ruby-forum.com/t/re-unable-to-stop-the-flow-graph-after-calling-stop/239518/6 "2014-03-03T14:58:41Z")
Dear gurus, I got it, thank you very much ! Regards, Activecat ---
**Author:** ![activecat\_k](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c57346/32.png) [@activecat\_k](https://www.ruby-forum.com/u/activecat_k)\ **Post date:** [March 3, 2014, 2:12pm UTC](https://www.ruby-forum.com/t/re-unable-to-stop-the-flow-graph-after-calling-stop/239518/7 "2014-03-03T14:12:48Z")
On 03/03/2014 12:37 PM, Marcus Müller wrote: > Hi Activecat, > > as Miklos wrote: Let your Constructor throw an exception. > For a little detail on that, refer to > [http://www.parashift.com/c++-faq-lite/ctors-can-throw.html](http://www.parashift.com/c++-faq-lite/ctors-can-throw.html) . > You can surround your block construction with a try{}catch-clause, and > handle your error, so your application may deal with that gracefully > (instead of just dying). Also, grep for throw in the impl files for an example, we do that a lot in GNU Radio. M