From bb369ec7d901354825a796542db45defb6bd1906 Mon Sep 17 00:00:00 2001 From: Willem Toorop Date: Fri, 13 Jan 2017 21:12:48 +0100 Subject: [PATCH] Document limits of syncronous functions As agreed in conversation with pull request #246 --- README.md | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/README.md b/README.md index 1b5a4807..3903e278 100644 --- a/README.md +++ b/README.md @@ -179,7 +179,18 @@ Stub mode does not support: # Known Issues -* None +* The synchronous lookup functions will not work when new file descriptors + needed for the lookup will be larger than `FD_SETSIZE`. This is because + the synchronous functions use a "default" event loop under the hood + which is based on `select()` and thus inherits the limits that `select()` has. + + If you need only slightly more file descriptors, it is possible to enlarge + the `FD_SETSIZE` with the `--with-fd-setsize=`*`size`* flag to `configure`. + + To resolve, use the asynchronous functions with an event loop extension for + libevent, libev or libuv. Note that the asynchronous functions will have + the same problem when used in combination with `getdns_context_run()`, which + also uses the default event loop. # Supported Platforms