I am confused by the documentation of GSourceFuncs. The documentation indicates that dispatch is only called if either prepare or check returns TRUE. It also indicates that if prepare or check is NULL, then it is treated as if that function returned FALSE. So if both prepare and check are NULL, then dispatch should never be called. However, the GSocketSource implementation until recently used NULL for both prepare and check. So I am missing something. Clearly, in practice, both functions can be NULL, and the source will actually be dispatched, contrary to the documentation.

Looking at the implementation of g_main_context_prepare(), I see that g_source_set_ready_time() effectively overrides the result of prepare, ensuring that dispatch is called. This is sort of documented in the description of g_source_set_ready_time(), but the interaction between the ready time and prepare/check is not mentioned.