CODEWITHSUNDEEP
c++pthreads
leonheess
leonheess

Reputation: 21381

pthread_create without separate function

I have an array of pthread_ts which are started within a for-loop via pthread_create.

I have a ton of variables that are declared beforehand and are important for the inner workings of the thread. I would like to have an anonymous inner function as start-routine of the pthread_create like so:

pthread_create(threads[i], NULL, 

     { inner function here }

, NULL);

I know that C++ doesn't have this in particular so I thought maybe lambdas could be of help or maybe someone has another idea so that I do not have to create a seperate method and hand over all those variables that come before pthread_create.

Upvotes: 1

Views: 1177

Answers (1)

Florian Weimer
Florian Weimer

Reputation: 33719

If a lambda expression does not capture anything, the lambda object can be converted to a C function pointer, so something like this will work:

pthread_t thr;
pthread_create (&thr, NULL,
                [] (void *closure) -> void * {
                  return nullptr;
                }, NULL);

The explicit return type of void * is needed because the inferred one usually will not be correct. Since you cannot use captures, you need to use the closure parameter to pass along a pointer to an object (and use static_cast to cast it to the correct type in the lambda), and for life-time reasons, it is probably necessary to allocate that on the heap.

(Also note that pthreads[i] as the first element to pthread_create does not look right, it's a pointer used to return part of the result, the ID of the new thread.)

Upvotes: 5

Related Questions