libports: Force threads to wake up periodically

Quiescence support in port-deref-deferred.c assumes that all threads will
sooner or later go through a quiescent state (because it finished processing
a message). But that is not true: proc doesn't set a thread timeout, and
thus some threads can stay indefinitely stuck in receiving messages. And
thus the deferred dereferencing used by ports_destroy_right never gets
achieved. This accumulation can be seen by running:

while true ; do echo $(echo -n $(echo a)) > /dev/null ; done

while running vminfo 4 | wc -l in parallel.

Making threads get out of mach_msg at least periodically allows
unstucking quiescence generations.

1 files changed, 8 insertions, 5 deletions

diff --git a/libports/manage-multithread.c b/libports/manage-multithread.c
index 9c036911..62f5c4e7 100644
--- a/libports/manage-multithread.c
+++ b/libports/manage-multithread.c
@@ -256,11 +256,14 @@ ports_manage_port_operations_multithread (struct port_bucket *bucket,
     startover:
 
       do
-	err = mach_msg_server_timeout (synchronized_demuxer,
-				       0, bucket->portset,
-				       timeout ? MACH_RCV_TIMEOUT : 0,
-				       timeout);
-      while (err != MACH_RCV_TIMED_OUT);
+	{
+	  err = mach_msg_server_timeout (synchronized_demuxer,
+					 0, bucket->portset,
+					 MACH_RCV_TIMEOUT,
+					 timeout ? timeout : 10 * 1000);
+	  _ports_thread_quiescent (&bucket->threadpool, &thread);
+	}
+      while (!(timeout && err == MACH_RCV_TIMED_OUT));
 
       if (master)
 	{