Document x509_crt_parse_path() threading behaviour
diff --git a/include/polarssl/x509_crt.h b/include/polarssl/x509_crt.h
index a5ab178..4e7bbb7 100644
--- a/include/polarssl/x509_crt.h
+++ b/include/polarssl/x509_crt.h
@@ -172,6 +172,11 @@
* of failed certificates it encountered. If none complete
* correctly, the first error is returned.
*
+ * \warning This function is NOT thread-safe unless
+ * POLARSSL_THREADING_PTHREADS is defined. If you're using an
+ * alternative threading implementation, you should either use
+ * this function only in the main thread, or mutex it.
+ *
* \param chain points to the start of the chain
* \param path directory / folder to read the certificate files from
*