Tweak compare_exchange_weak(...) in spin-lock

Mutex was removed in favor of the custom SharedSpinLock.

src/UDPC.h

@@ -6,9 +6,6 @@
 /*!
  * \file UDPC.h
  * \brief Public API for UDPConnection
- *
- * Note that all functions are thread-safe unless mentioned otherwise in the
- * function's documentation.
  */
 
 #ifndef UDPC_CONNECTION_H
@@ -864,6 +861,8 @@ UDPC_EXPORT const char *UDPC_atostr(UDPC_HContext ctx, UDPC_IPV6_ADDR_TYPE addr)
  * \warning The returned pointer must be freed with free(), or
  * UDPC_atostr_unsafe_free(), or UDPC_atostr_unsafe_free_ptr().
  *
+ * This function is thread-safe.
+ *
  * UDPC internally uses UDPC_atostr() for logging. This means that while UDPC
  * is running, a string created with UDPC_atostr() may be overwritten
  * eventually by UDPC. To avoid this situation, UDPC_atostr_unsafe() or
@@ -880,6 +879,8 @@ UDPC_EXPORT const char *UDPC_atostr_unsafe(UDPC_IPV6_ADDR_TYPE addr);
  * \warning The returned pointer must be freed with free(), or
  * UDPC_atostr_unsafe_free(), or UDPC_atostr_unsafe_free_ptr().
  *
+ * This function is thread-safe.
+ *
  * UDPC internally uses UDPC_atostr() for logging. This means that while UDPC
  * is running, a string created with UDPC_atostr() may be overwritten
  * eventually by UDPC. To avoid this situation, UDPC_atostr_unsafe() or
@@ -890,6 +891,8 @@ UDPC_EXPORT const char *UDPC_atostr_unsafe_cid(UDPC_ConnectionId cid);
 
 /*!
  * \brief Free an addr string created with UDPC_atostr_unsafe().
+ *
+ * This function is thread-safe.
  */
 UDPC_EXPORT void UDPC_atostr_unsafe_free(const char *addrBuf);
 
@@ -897,6 +900,8 @@ UDPC_EXPORT void UDPC_atostr_unsafe_free(const char *addrBuf);
  * \brief Free an addr string created with UDPC_atostr_unsafe() and zeroes the
  * pointer.
  *
+ * This function is thread-safe.
+ *
  * \code{.c}
  * UDPC_ConnectionId aConnectionId = ...;
  * const char *addrString = UDPC_atostr_unsafe_cid(aConnectionId);