commit f5d4ef14bb47294046d98c06478b0b58c97cf521
Author: Justus Winter <4winter@informatik.uni-hamburg.de>
Date:   Sat May 3 01:02:35 2014 +0200

    libports: implement lockless reference counting
    
    * libports/refcount.h: New file with reference counting primitives.
    * libports/ports.h (struct port_info): Use the new type.
    * libports/bucket-iterate.c: Adjust accordingly.
    * libports/complete-deallocate.c: Likewise.
    * libports/create-internal.c: Likewise.
    * libports/get-right.c: Likewise.
    * libports/import-port.c: Likewise.
    * libports/lookup-port.c: Likewise.
    * libports/port-deref-weak.c: Likewise.
    * libports/port-deref.c: Likewise.
    * libports/port-ref-weak.c: Likewise.
    * libports/port-ref.c: Likewise.
    * libports/reallocate-from-external.c: Likewise.
    * libports/transfer-right.c: Likewise.
    * utils/rpctrace.c: Likewise.

diff --git a/libports/bucket-iterate.c b/libports/bucket-iterate.c
index 498cf13..38a9f7a 100644
--- a/libports/bucket-iterate.c
+++ b/libports/bucket-iterate.c
@@ -55,7 +55,7 @@ _ports_bucket_class_iterate (struct port_bucket *bucket,
 
       if (class == 0 || pi->class == class)
 	{
-	  pi->refcnt++;
+	  ports_port_ref (pi);
 	  p[n] = pi;
 	  n++;
 	}
diff --git a/libports/complete-deallocate.c b/libports/complete-deallocate.c
index 8ce095b..7e7d467 100644
--- a/libports/complete-deallocate.c
+++ b/libports/complete-deallocate.c
@@ -35,6 +35,8 @@ _ports_complete_deallocate (struct port_info *pi)
       pi->port_right = MACH_PORT_NULL;
     }
 
+  pthread_mutex_lock (&_ports_lock);
+
   *pi->prevp = pi->next;
   if (pi->next)
     pi->next->prevp = pi->prevp;
diff --git a/libports/create-internal.c b/libports/create-internal.c
index 8551297..d56637c 100644
--- a/libports/create-internal.c
+++ b/libports/create-internal.c
@@ -54,8 +54,7 @@ _ports_create_port_internal (struct port_class *class,
     }
 
   pi->class = class;
-  pi->refcnt = 1;
-  pi->weakrefcnt = 0;
+  refcount_init (&pi->refcounts, 1, 0);
   pi->cancel_threshold = 0;
   pi->mscount = 0;
   pi->flags = 0;
diff --git a/libports/get-right.c b/libports/get-right.c
index 89050c6..42bfa2b 100644
--- a/libports/get-right.c
+++ b/libports/get-right.c
@@ -41,7 +41,7 @@ ports_get_right (void *port)
   if ((pi->flags & PORT_HAS_SENDRIGHTS) == 0)
     {
       pi->flags |= PORT_HAS_SENDRIGHTS;
-      pi->refcnt++;
+      ports_port_ref (pi);
       err = mach_port_request_notification (mach_task_self (),
 					    pi->port_right,
 					    MACH_NOTIFY_NO_SENDERS,
diff --git a/libports/import-port.c b/libports/import-port.c
index 226f47e..5c66685 100644
--- a/libports/import-port.c
+++ b/libports/import-port.c
@@ -48,8 +48,7 @@ ports_import_port (struct port_class *class, struct port_bucket *bucket,
     return ENOMEM;
   
   pi->class = class;
-  pi->refcnt = 1 + !!stat.mps_srights;
-  pi->weakrefcnt = 0;
+  refcount_init (&pi->refcounts, 1 + !!stat.mps_srights, 0);
   pi->cancel_threshold = 0;
   pi->mscount = stat.mps_mscount;
   pi->flags = stat.mps_srights ? PORT_HAS_SENDRIGHTS : 0;
diff --git a/libports/lookup-port.c b/libports/lookup-port.c
index f79f6f0..289369f 100644
--- a/libports/lookup-port.c
+++ b/libports/lookup-port.c
@@ -44,7 +44,7 @@ ports_lookup_port (struct port_bucket *bucket,
     pi = 0;
 
   if (pi)
-    pi->refcnt++;
+    ports_port_ref (pi);
 
   pthread_mutex_unlock (&_ports_lock);
   
diff --git a/libports/port-deref-weak.c b/libports/port-deref-weak.c
index beb4842..48e5354 100644
--- a/libports/port-deref-weak.c
+++ b/libports/port-deref-weak.c
@@ -25,12 +25,8 @@ void
 ports_port_deref_weak (void *portstruct)
 {
   struct port_info *pi = portstruct;
-  
-  pthread_mutex_lock (&_ports_lock);
-  assert (pi->weakrefcnt);
-  pi->weakrefcnt--;
-  if (pi->refcnt == 0 && pi->weakrefcnt == 0)
+  struct refs result;
+  refcount_deref_weak (&pi->refcounts, &result);
+  if (result.hard == 0 && result.weak == 0)
     _ports_complete_deallocate (pi);
-  else
-    pthread_mutex_unlock (&_ports_lock);
 }
diff --git a/libports/port-deref.c b/libports/port-deref.c
index cf9b238..056159c 100644
--- a/libports/port-deref.c
+++ b/libports/port-deref.c
@@ -26,25 +26,19 @@ ports_port_deref (void *portstruct)
 {
   struct port_info *pi = portstruct;
   int trieddroppingweakrefs = 0;
+  struct refs result;
 
  retry:
-  
-  pthread_mutex_lock (&_ports_lock);
-  
-  if (pi->refcnt == 1 && pi->weakrefcnt
+  refcount_deref (&pi->refcounts, &result);
+  if (result.hard == 0 && result.weak > 1
       && pi->class->dropweak_routine && !trieddroppingweakrefs)
     {
-      pthread_mutex_unlock (&_ports_lock);
+      refcount_ref (&pi->refcounts, NULL);
       (*pi->class->dropweak_routine) (pi);
       trieddroppingweakrefs = 1;
       goto retry;
     }
-  
-  assert (pi->refcnt);
 
-  pi->refcnt--;
-  if (pi->refcnt == 0 && pi->weakrefcnt == 0)
+  if (result.hard == 0 && result.weak == 0)
     _ports_complete_deallocate (pi);
-  else
-    pthread_mutex_unlock (&_ports_lock);
 }
diff --git a/libports/port-ref-weak.c b/libports/port-ref-weak.c
index c7d3c69..8b75005 100644
--- a/libports/port-ref-weak.c
+++ b/libports/port-ref-weak.c
@@ -25,9 +25,7 @@ void
 ports_port_ref_weak (void *portstruct)
 {
   struct port_info *pi = portstruct;
-  
-  pthread_mutex_lock (&_ports_lock);
-  assert (pi->refcnt || pi->weakrefcnt);
-  pi->weakrefcnt++;
-  pthread_mutex_unlock (&_ports_lock);
+  struct refs result;
+  refcount_ref_weak (&pi->refcounts, &result);
+  assert (result.hard > 0 || result.weak > 1);
 }
diff --git a/libports/port-ref.c b/libports/port-ref.c
index 92b7118..6310902 100644
--- a/libports/port-ref.c
+++ b/libports/port-ref.c
@@ -25,9 +25,7 @@ void
 ports_port_ref (void *portstruct)
 {
   struct port_info *pi = portstruct;
-  
-  pthread_mutex_lock (&_ports_lock);
-  assert (pi->refcnt || pi->weakrefcnt);
-  pi->refcnt++;
-  pthread_mutex_unlock (&_ports_lock);
+  struct refs result;
+  refcount_ref (&pi->refcounts, &result);
+  assert (result.hard > 1 || result.weak > 0);
 }
diff --git a/libports/ports.h b/libports/ports.h
index 7f13124..7088b2d 100644
--- a/libports/ports.h
+++ b/libports/ports.h
@@ -22,12 +22,15 @@
 #define _HURD_PORTS_
 
 #include <mach.h>
+#include <stdint.h>
 #include <stdlib.h>
 #include <hurd.h>
 #include <hurd/ihash.h>
 #include <mach/notify.h>
 #include <pthread.h>
 
+#include "refcount.h"
+
 /* These are global values for common flags used in the various structures.
    Not all of these are meaningful in all flag fields.  */
 #define PORTS_INHIBITED		0x0100 /* block RPC's */
@@ -39,8 +42,7 @@
 struct port_info
 {
   struct port_class *class;
-  int refcnt;
-  int weakrefcnt;
+  reference_counts refcounts;
   mach_port_mscount_t mscount;
   mach_msg_seqno_t cancel_threshold;
   int flags;
diff --git a/libports/reallocate-from-external.c b/libports/reallocate-from-external.c
index 8cccb2a..4dfc59c 100644
--- a/libports/reallocate-from-external.c
+++ b/libports/reallocate-from-external.c
@@ -53,7 +53,7 @@ ports_reallocate_from_external (void *portstruct, mach_port_t receive)
   else if (((pi->flags & PORT_HAS_SENDRIGHTS) == 0) && stat.mps_srights)
     {
       pi->flags |= PORT_HAS_SENDRIGHTS;
-      pi->refcnt++;
+      ports_port_ref (pi);
     }
   
   pi->port_right = receive;
diff --git a/libports/refcount.h b/libports/refcount.h
new file mode 100644
index 0000000..43da5b4
--- /dev/null
+++ b/libports/refcount.h
@@ -0,0 +1,72 @@
+#ifndef _PORTS_REFCOUNT_H_
+#define _PORTS_REFCOUNT_H_
+
+typedef uint64_t reference_counts;
+
+struct refs {
+  uint32_t hard;
+  uint32_t weak;
+};
+
+union _refs {
+  struct refs refs;
+  reference_counts rc;
+};
+
+extern inline void
+refcount_init (reference_counts *ref, uint32_t hard, uint32_t weak)
+{
+  ((union _refs *) ref)->refs =
+    (struct refs) { .hard = hard, .weak = weak };
+}
+
+extern inline void
+refcount_ref (reference_counts *ref, struct refs *result)
+{
+  const union _refs op = { .refs = { .hard = 1 } };
+  reference_counts r = __atomic_add_fetch (ref, op.rc, __ATOMIC_RELAXED);
+  if (result)
+    ((union _refs *) result)->rc = r;
+}
+
+extern inline void
+refcount_deref (reference_counts *ref, struct refs *result)
+{
+  const union _refs op = { .refs = { .hard = 1 } };
+  ((union _refs *) result)->rc =
+    __atomic_sub_fetch (ref, op.rc, __ATOMIC_RELAXED);
+}
+
+extern inline void
+refcount_ref_weak (reference_counts *ref, struct refs *result)
+{
+  const union _refs op = { .refs = { .weak = 1 } };
+  ((union _refs *) result)->rc =
+    __atomic_add_fetch (ref, op.rc, __ATOMIC_RELAXED);
+}
+
+extern inline void
+refcount_deref_weak (reference_counts *ref, struct refs *result)
+{
+  const union _refs op = { .refs = { .weak = 1 } };
+  ((union _refs *) result)->rc =
+    __atomic_sub_fetch (ref, op.rc, __ATOMIC_RELAXED);
+}
+
+extern inline uint32_t
+refcount_hard_refs (reference_counts *ref)
+{
+  union _refs result;
+  result.rc = __atomic_load_n (ref, __ATOMIC_RELAXED);
+  return result.refs.hard;
+}
+
+extern inline uint32_t
+refcount_weak_refs (reference_counts *ref)
+{
+  union _refs result;
+  result.rc = __atomic_load_n (ref, __ATOMIC_RELAXED);
+  return result.refs.weak;
+}
+
+#endif /* _PORTS_REFCOUNT_H_ */
diff --git a/libports/transfer-right.c b/libports/transfer-right.c
index 72488a9..f4e0c86 100644
--- a/libports/transfer-right.c
+++ b/libports/transfer-right.c
@@ -66,7 +66,7 @@ ports_transfer_right (void *tostruct,
       else if (((topi->flags & PORT_HAS_SENDRIGHTS) == 0) && hassendrights)
 	{
 	  topi->flags |= PORT_HAS_SENDRIGHTS;
-	  topi->refcnt++;
+	  ports_port_ref (topi);
 	}
     }
   
diff --git a/utils/rpctrace.c b/utils/rpctrace.c
index fc913e3..248d4e2 100644
--- a/utils/rpctrace.c
+++ b/utils/rpctrace.c
@@ -431,7 +431,8 @@ destroy_receiver_info (struct receiver_info *info)
   while (send_wrapper)
     {
       struct sender_info *next = send_wrapper->next;
-      assert (TRACED_INFO (send_wrapper)->pi.refcnt == 1);
+      assert (refcount_hard_refs (&TRACED_INFO (send_wrapper)->pi.refcounts)
+	      == 1);
       /* Reset the receive_right of the send wrapper in advance to avoid
        * destroy_receiver_info is called when the port info is destroyed. */
       send_wrapper->receive_right = NULL;
@@ -848,7 +849,10 @@ rewrite_right (mach_port_t *right, mach_msg_type_name_t *type,
 	    hurd_ihash_locp_remove (&traced_names, receiver_info->locp);
 
 	    send_wrapper2 = get_send_wrapper (receiver_info, dest, &rr);
-	    assert (TRACED_INFO (send_wrapper2)->pi.refcnt == 1);
+	    assert (
+	        refcount_hard_refs (&TRACED_INFO (send_wrapper2)->pi.refcounts)
+		== 1);
+
 	    name = TRACED_INFO (send_wrapper2)->name;
 	    TRACED_INFO (send_wrapper2)->name = NULL;
 	    /* send_wrapper2 isn't destroyed normally, so we need to unlink