libc: Remove redundant code in thread atexit code

[aokblast]

Also remove the define

[kib]

I am on edge of proposing to count the number of the list members, and still do the walk_cb_nocall if the number of members does not go to zero after e.g. CXA_DTORS_ITERATIONS times initial list length for dtor removals.

BTW, otherwise walk_cb_nocall() is not needed after your patch.

[aokblast]

In D56022#1281611, @kib wrote:

I am on edge of proposing to count the number of the list members, and still do the walk_cb_nocall if the number of members does not go to zero after e.g. CXA_DTORS_ITERATIONS times initial list length for dtor removals.

Do you mean something like

static void                                                                                                                                                                                        
cxa_thread_walk(void (*cb)(struct cxa_thread_dtor *))                                                                                                                                              
{                                                                                                                                                                                                  
    struct cxa_thread_dtor *dtor;                                                                                                                                                                  
    int cnt = 0;                                                                                                                                                                                   
                                                                                                                                                                                                   
    while ((dtor = LIST_FIRST(&dtors)) != NULL && cnt < CXA_DTORS_ITERATIONS) {                                                                                                                    
        LIST_REMOVE(dtor, entry);                                                                                                                                                                  
        cb(dtor);                                                                                                                                                                                  
        free(dtor);                                                                                                                                                                                
        ++cnt;                                                                                                                                                                                     
    }                                                                                                                                                                                              
}

If so, what is the proper value of CXA_DTORS_ITERATIONS do you think? We cannot just allow a thread to register 4 thread local variable.

And also, should we care about somethink like

#include <iostream>

template <unsigned int T>
struct Foo {
    ~Foo() {
        thread_local Foo<T - 1> val;
        std::cout << T << std::endl;
    }
};

template<>
Foo<0>::~Foo() {
}

int main() {
    Foo<100000> f;
}

, which calls dtor many times but has its end.

[kib]

No. Perhaps it is simpler to show code than to try to explain it, See D56053.

The example you provided would not work with my patch, it requires increasing the CXA_DTORS_ITERATIONS. Not sure if we want this.

[aokblast]

In D56022#1281980, @kib wrote:

No. Perhaps it is simpler to show code than to try to explain it, See D56053.

The example you provided would not work with my patch, it requires increasing the CXA_DTORS_ITERATIONS. Not sure if we want this.

If it breaks the valid C++ code, we should rethink about it. The T value can be somehow greater than CXA_DTORS_ITERATIONS if the user wants.

[kib]

In D56022#1282270, @aokblast wrote:

In D56022#1281980, @kib wrote:

No. Perhaps it is simpler to show code than to try to explain it, See D56053.

The example you provided would not work with my patch, it requires increasing the CXA_DTORS_ITERATIONS. Not sure if we want this.

If it breaks the valid C++ code, we should rethink about it. The T value can be somehow greater than CXA_DTORS_ITERATIONS if the user wants.

I do not disagree but there are also some robustness requirements as part of the implementation quality. So I am unsire, this is why I initially said that 'I am on edge' proposing this. Hanging in the system state (thread exiting) due to user bug is not robust.

That said, your patch should remove walk_cb_nocall(). And perhaps cxa_thread_walk() could drop the argument, simply inlining walk_cb_call.