X-Git-Url: https://git.distorted.org.uk/~mdw/adns/blobdiff_plain/ae8cc9775a6eb23901a89a2604f73525b0553db8..8de0fa76b3e27b4a96db5c77415962117650afa7:/src/adns.h

diff --git a/src/adns.h b/src/adns.h
index befa0b3..a903934 100644
--- a/src/adns.h
+++ b/src/adns.h
@@ -1,6 +1,6 @@
 /*
  * adns.h
- * - adns user-visible API (single-threaded, without any locking)
+ * - adns user-visible API
  */
 /*
  *
@@ -401,6 +401,18 @@ typedef struct {
  *  requested.
  */
 
+/* Threads:
+ *  adns does not use any static modifiable state, so it
+ *   is safe to call adns_init several times and then use the
+ *   resulting adns_states concurrently.
+ *  However, it is NOT safe to make simultaneous calls into
+ *   adns using the same adns_state; a single adns_state must be used
+ *   only by one thread at a time.  You can solve this problem by
+ *   having one adns_state per thread, or if that isn't feasible, you
+ *   could maintain a pool of adns_states.  Unfortunately neither of
+ *   these approaches has optimal performance.
+ */
+
 int adns_init(adns_state *newstate_r, adns_initflags flags,
 	      FILE *diagfile /*0=>stderr*/);