poll: Document reentrancy restriction on before()

[secnet.git] / secnet.h

diff --git a/secnet.h b/secnet.h
index 1e1e75c34783cfba6b797e4d9ffb4c6383c41044..2c55a329313c5c8c89c1b87934381455e2422cce 100644 (file)
--- a/secnet.h
+++ b/secnet.h
@@ -198,10 +198,20 @@ int32_t calculate_max_start_pad(void);
 
 /* If nfds_io is insufficient for your needs, set it to the required
    number and return ERANGE. timeout is in milliseconds; if it is too
-   high then lower it. It starts at -1 (==infinite) */
+   high then lower it. It starts at -1 (==infinite). */
+/* Note that beforepoll_fn may NOT do anything which might change the
+   fds or timeouts wanted by other registered poll loop loopers.
+   Callers should make sure of this by not making any calls into other
+   modules from the beforepoll_fn; the easiest way to ensure this is
+   for beforepoll_fn to only retreive information and not take any
+   action.
+ */
 typedef int beforepoll_fn(void *st, struct pollfd *fds, int *nfds_io,
                          int *timeout_io);
 typedef void afterpoll_fn(void *st, struct pollfd *fds, int nfds);
+  /* If beforepoll_fn returned ERANGE, afterpoll_fn gets nfds==0.
+     afterpoll_fn never gets !!(fds[].revents & POLLNVAL) - such
+     a report is detected as a fatal error by the event loop. */
 
 /* void BEFOREPOLL_WANT_FDS(int want);
  *   Expects: int *nfds_io;
@@ -216,8 +226,9 @@ typedef void afterpoll_fn(void *st, struct pollfd *fds, int nfds);
 /* Register interest in the main loop of the program. Before a call
    to poll() your supplied beforepoll function will be called. After
    the call to poll() the supplied afterpoll function will be called. */
-extern void register_for_poll(void *st, beforepoll_fn *before,
+struct poll_interest *register_for_poll(void *st, beforepoll_fn *before,
                              afterpoll_fn *after, cstring_t desc);
+void deregister_for_poll(struct poll_interest *i);
 
 /***** END of scheduling support */