libxml 0.0.6

/// We are going to handle the global init+cleanup of libxml in tree, for now.
use std::sync::atomic::{AtomicBool, ATOMIC_BOOL_INIT, Ordering};
use c_signatures::*;

static mut LIBXML_OBJECTS: i64 = 0;

/// Initializes the global libxml2 context once, before the first libxml2 object allocation
pub fn _libxml_global_init() {
    with_lock(||
        unsafe {
          if LIBXML_OBJECTS == 0 {
              xmlInitParser();
              xmlInitGlobals();
          }
          LIBXML_OBJECTS += 1;
        }
    );
}

/// Currently a no-op use `force_global_drop` instead.
pub fn _libxml_global_drop() {
    with_lock(||
        unsafe {
          if LIBXML_OBJECTS == 1 { // Far from perfect, more "desperate" than anything...
              // The big issue here is taht calling these deallocations causes segfaults
              // if any thread is still using libxml2 constructs. And Rust doesn't give us a good hook for "end of static scope",
              // hence we're sunk... For now uncommenting here and leaving a "libxml_force_global_drop()" for manual use...
              //  ... very unsatisfying

              //xmlCleanupGlobals();
              //xmlCleanupParser();
          }
          LIBXML_OBJECTS -= 1;
        }
  );
}

/// Forces a drop of global libxml2 context. Only invoke after all threads using libxml2 are finished.
pub fn force_global_drop() {
  unsafe {
    xmlCleanupGlobals();
    xmlCleanupParser();
  }
}

/// Helper lock mechanism, to allow for safe global libxml2 init/drop
fn with_lock<F>(thunk: F) where F: Fn() {
    static LIBXML_LOCK: AtomicBool = ATOMIC_BOOL_INIT;
    while LIBXML_LOCK.compare_and_swap(false, true, Ordering::SeqCst) {}
    thunk();
    LIBXML_LOCK.store(false, Ordering::SeqCst);
}