+/*
+ * Since per-thread-specific-data destructors are not universally
+ * available, i.e. not on Windows, only below CRYPTO_THREAD_LOCAL key
+ * is assumed to have destructor associated. And then an effort is made
+ * to call this single destructor on non-pthread platform[s].
+ *
+ * Initial value is "impossible". It is used as guard value to shortcut
+ * destructor for threads terminating before libcrypto is initialized or
+ * after it's de-initialized. Access to the key doesn't have to be
+ * serialized for the said threads, because they didn't use libcrypto
+ * and it doesn't matter if they pick "impossible" or derefernce real
+ * key value and pull NULL past initialization in the first thread that
+ * intends to use libcrypto.
+ */
+static union {
+ long sane;
+ CRYPTO_THREAD_LOCAL value;
+} destructor_key = { -1 };