Clears a reference to a variable.
pp must not be NULL.
If the reference is NULL then this function does nothing.
Otherwise, the variable is destroyed using destroy and the
pointer is set to NULL.
This function is threadsafe and modifies the pointer atomically,
using memory barriers where needed.
A macro is also included that allows this function to be used without
pointer casts.
Since 2.34
Clears a reference to a variable. pp must not be NULL. If the reference is NULL then this function does nothing. Otherwise, the variable is destroyed using destroy and the pointer is set to NULL. This function is threadsafe and modifies the pointer atomically, using memory barriers where needed. A macro is also included that allows this function to be used without pointer casts. Since 2.34