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

B. Bogart ben at ekran.org
Fri Feb 27 19:46:02 CET 2009

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

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
	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.


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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