Re: Unable to stop the flow graph after calling stop()

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

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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:

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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

Dear Activecat,

Throw an exception. It will kill the application.

Miklos

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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 .
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 ?

https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

_______________________________________________ Discuss-gnuradio
mailing list [email protected]
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Dear gurus,
I got it, thank you very much !

Regards,
Activecat

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 .
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

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