Why is my C destructor not getting called?

I have two parts of my project: an example.c (which contains our main function) and an api.c (which contains all APIs). They are compiled separately, and the binaries generated by the API are used by the example to successfully make API calls.

I have set up both libraries to contain a constructor and destructor:

example.c

__attribute__((constructor)) static void example_constructor() {
  printf("constructor: example\n");
  api_setup();
}

__attribute__((destructor)) static void example_destructor() {
  printf("destructor: example\n");
  api_teardown();
}

int main() {
  // make API calls
}

api.c

__attribute__((constructor)) static void api_constructor() {
  printf("constructor: api\n");
}

__attribute__((destructor)) static void api_destructor() {
  printf("destructor: api\n");
}

api_setup() {
  // malloc a buffer to be used in the API calls
}

api_teardown() {
  // read + perform task on buffer. send to output file
  // free buffer
}

// other API definitions to manipulate the buffer

When set up like the above, constructors and destructors get called for both the example and API (at the start/end of example's main). Things work great but I'd like to have the api.c constructor/destructor responsible for all setup and teardown work. If I make changes:

api.c

__attribute__((constructor)) static void api_constructor() {
  printf("constructor: api\n");
  api_setup(); // doing setup in api.c constructor instead of example.c constructor
}

__attribute__((destructor)) static void api_destructor() {
  printf("destructor: api\n");
  api_teardown(); // doing teardown in api.c destructor instead of example.c destructor
}

// other API definitions to manipulate the buffer (including setup/teardown)

With the setup moved to the api.c constructor, I find that constructors get called for both example.c and api.c, but the destructor only gets called for example.c.

Why is this? And how could I go about performing all setup/teardown via the api.c constructor/destructor?

Using this attribute in gcc you can control the priority of the constructors/destructors.

• for constructor smaller number means a higher priority
• for destructor smaller number means a lower priority

void __attribute__((constructor(101))) c1(void) { printf("%s\n", __func__);}
void __attribute__((constructor(102))) c2(void) { printf("%s\n", __func__);}
void __attribute__((constructor(103))) c3(void) { printf("%s\n", __func__);}
void __attribute__((constructor(104))) c4(void) { printf("%s\n", __func__);}

void __attribute__((destructor(101))) d1(void) { printf("%s\n", __func__);}
void __attribute__((destructor(102))) d2(void) { printf("%s\n", __func__);}
void __attribute__((destructor(103))) d3(void) { printf("%s\n", __func__);}
void __attribute__((destructor(104))) d4(void) { printf("%s\n", __func__);}

void main(void)
{
}

https://godbolt.org/z/9aGnnW487