Re: [Xen-devel] [PATCH 00/12] libxl: fork: SIGCHLD flexibility

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Ian Jackson writes ("Re: [Xen-devel] [PATCH 00/12] libxl: fork: SIGCHLD 
flexibility"):
> libxl could (and perhaps should) grow such a thing in its own event
> loop, but thinking about how to write it, it's going to be quite
> tedious![1]
...
> [1] Add a ctx-wide list of pollers, one for every libxl thread in
> poll.  This list has to be covered by its own lock.
> 
> When fd deregistration occurs, we take this lock, wake up all the
> pollers, release the lock, and then wait (perhaps with a condition
> variable) for the pollers to acknowledge that they have left poll().

Something like this (warning, pseudocode).

Ian.

diff --git a/tools/libxl/libxl_event.c b/tools/libxl/libxl_event.c
index 93f8fdc..5e3fe87 100644
--- a/tools/libxl/libxl_event.c
+++ b/tools/libxl/libxl_event.c
@@ -232,6 +232,17 @@ void libxl__ev_fd_deregister(libxl__gc *gc, libxl__ev_fd 
*ev)
     LIBXL_LIST_REMOVE(ev, entry);
     ev->fd = -1;
 
+    with cohort lock{
+        push new cohort, mark it in use;
+
+        loop waiting for acks{
+            signal all pollers in our cohort and all older;
+            if there are none, hooray (exit the loop);
+            condvar wait;
+        }
+        cleanup;
+    }
+
  out:
     CTX_UNLOCK;
 }
@@ -1436,10 +1447,22 @@ static int eventloop_iteration(libxl__egc *egc, 
libxl__poller *poller) {
         poller->fd_polls_allocd = nfds;
     }
 
+    with cohort lock{
+        add poller to list in running cohort;
+    }
+
     CTX_UNLOCK;
     rc = poll(poller->fd_polls, nfds, timeout);
     CTX_LOCK;
 
+    with cohort lock{
+        remove poller from whatever cohort's list it was in #';
+        clean up old running cohorts:
+            while (oldest cohort is empty and unused)
+                delete it;
+        signal cv;
+    }
+
     if (rc < 0) {
         if (errno == EINTR)
             return 0; /* will go round again if caller requires */

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel