[PD-dev] How to pass indeterminate args to a thread

[Claude Heiland-Allen]

B. Bogart wrote:
> I figured that doing this with a PD type was unlikely, so I started
> messing with creating a structure for my args and passing a pointer to
> that.
> 
> So I have defined my structure for a single float arg:
> 
> struct floatArgStruct {
> 	gphoto2_struct *gphoto2;
> 	t_symbol *s;
> };
> 
> 
> just under the typedef for the external structure. (Is the external
> struct a better place for its def?)
> 
> Then the function that is executed from the PD selector:
> 
> static void wrapGetConfig(gphoto2_struct *gphoto2, t_symbol *s) {
> 	int ret;
> 	pthread_t thread1;
> 
> 	// instance of structure
> 	struct floatArgStruct threadArgs;
> 
> 	// packaging arguments into structure
> 	threadArgs.gphoto2 = gphoto2;
> 	threadArgs.s = s;
> 
> 	post("I'm about to start the thread.");
> 
> 	// Create thread
> 	ret = pthread_create( &thread1, NULL, mythread, (void *)threadArgs);	
> }
> 
> which populates the structure, and starts the thread. The struct stuff
> appears to work here)
> 
> Above this is the def of the function that is to execute in the thread:
> 
> void *mythread(struct floatArgStruct *threadArgs) {
> 	int i;
> 	post("thread start.");
> 
> 	post("My symbol: %s", threadArgs.s->s_name);    // line 92

threadArgs is a pointer, '.' is only for structs/unions

try '->' instead of '.' to both dereference pointer and access member

> 	outlet_float(threadArgs.gphoto2->x_obj.ob_outlet, 0.00001);
> 
> 	post("thread end.");
> }
> 
> The errors I'm confused about are:
> 
> gphoto2.c:92: error: request for member 's' in something not a structure
> or union
> gphoto2.c:93: error: request for member 'gphoto2' in something not a
> structure or union
> 
> Which means that the structure is not being passed to the thread code
> correctly, as its not recognized as a structure.
> 
> Next gcc complains about the way I'm initiating the thread:
> 
> gphoto2.c:112: error: cannot convert to a pointer type
> gphoto2.c:112: warning: passing argument 3 of 'pthread_create' from
> incompatible pointer type
> 
> In the tutorial the function args were cast as (void *) which does not
> seem to be working in this case.
> 
> Does anyone have any code that does this kind of job I could look at?
> 
> Or is it obvious I'm doing something really wrong?
> 
> This is my first exploration into threads and custom structs (not
> counting the external struct) so I may have it totally wrong.
> 
> Thanks,
> B.
> 
> 
> 
> 
> B. Bogart wrote:
>> Hey all,
>>
>> I've got some simple threading code working, and it looks like that will
>> fix my HUP issues with PD and my gphoto external.
>>
>> Problem I'm having is that I need to pass thread arguments as a pointer
>> to a structure.
>>
>> Are there some PD types I can use to make this work? (A_GIMME?)
>>
>> Or do I need to make struct that holds the *argv argc stuff, pass that
>> structure to the thread, and have it unpack the content?
>>
>> Also my code function that executes the thread does not wait for the
>> threads to complete.
>>
>> What is the best way to make my object output a bang when the thread is
>> complete?
>>
>> Any advice appreciated.
>>
>> Thanks,
>> B.
>>
>>
> 
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