path: root/debian/patches/0008-libports-lock-less-reference-counting-for-port_info-.patch

From bd48fb2fa898b97fd0a9581b4e549edf7488b26b Mon Sep 17 00:00:00 2001
From: Justus Winter <4winter@informatik.uni-hamburg.de>
Date: Sat, 3 May 2014 01:02:35 +0200
Subject: [PATCH 8/8] libports: lock-less reference counting for port_info
 objects

* libports/ports.h (struct port_info): Use the new type.
* libports/lookup-port.c: No need to lock _ports_lock anymore.
* libports/bucket-iterate.c: Likewise.
* libports/complete-deallocate.c: Check if someone reacquired a
reference through a hash table lookup.
* libports/create-internal.c: Use the new reference counting primitives.
* libports/get-right.c: Likewise.
* libports/import-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.
---
 libports/bucket-iterate.c           |  4 +---
 libports/complete-deallocate.c      | 14 ++++++++++++++
 libports/create-internal.c          |  3 +--
 libports/get-right.c                |  2 +-
 libports/import-port.c              |  3 +--
 libports/lookup-port.c              |  4 +---
 libports/port-deref-weak.c          | 10 +++-------
 libports/port-deref.c               | 34 ++++++++++++++++------------------
 libports/port-ref-weak.c            |  8 +++-----
 libports/port-ref.c                 |  8 +++-----
 libports/ports.h                    |  4 ++--
 libports/reallocate-from-external.c |  2 +-
 libports/transfer-right.c           |  2 +-
 utils/rpctrace.c                    | 10 ++++++++--
 14 files changed, 56 insertions(+), 52 deletions(-)

diff --git a/libports/bucket-iterate.c b/libports/bucket-iterate.c
index 79b6d72..b021b99 100644
--- a/libports/bucket-iterate.c
+++ b/libports/bucket-iterate.c
@@ -35,7 +35,6 @@ _ports_bucket_class_iterate (struct hurd_ihash *ht,
   size_t i, n, nr_items;
   error_t err;
 
-  pthread_mutex_lock (&_ports_lock);
   pthread_rwlock_rdlock (&_ports_htable_lock);
 
   if (ht->nr_items == 0)
@@ -59,13 +58,12 @@ _ports_bucket_class_iterate (struct hurd_ihash *ht,
 
       if (class == 0 || pi->class == class)
 	{
-	  pi->refcnt++;
+	  refcounts_ref (&pi->refcounts, NULL);
 	  p[n] = pi;
 	  n++;
 	}
     }
   pthread_rwlock_unlock (&_ports_htable_lock);
-  pthread_mutex_unlock (&_ports_lock);
 
   if (n != 0 && n != nr_items)
     {
diff --git a/libports/complete-deallocate.c b/libports/complete-deallocate.c
index 4768dab..0d852f5 100644
--- a/libports/complete-deallocate.c
+++ b/libports/complete-deallocate.c
@@ -29,15 +29,29 @@ _ports_complete_deallocate (struct port_info *pi)
 
   if (pi->port_right)
     {
+      struct references result;
+
       pthread_rwlock_wrlock (&_ports_htable_lock);
+      refcounts_references (&pi->refcounts, &result);
+      if (result.hard > 0 || result.weak > 0)
+        {
+          /* A reference was reacquired through a hash table lookup.
+             It's fine, we didn't touch anything yet. */
+          pthread_mutex_unlock (&_ports_htable_lock);
+          return;
+        }
+
       hurd_ihash_locp_remove (&_ports_htable, pi->ports_htable_entry);
       hurd_ihash_locp_remove (&pi->bucket->htable, pi->hentry);
       pthread_rwlock_unlock (&_ports_htable_lock);
+
       mach_port_mod_refs (mach_task_self (), pi->port_right,
 			  MACH_PORT_RIGHT_RECEIVE, -1);
       pi->port_right = MACH_PORT_NULL;
     }
 
+  pthread_mutex_lock (&_ports_lock);
+
   pi->bucket->count--;
   pi->class->count--;
 
diff --git a/libports/create-internal.c b/libports/create-internal.c
index 8543986..2d85931 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;
+  refcounts_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..8681f46 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++;
+      refcounts_ref (&pi->refcounts, NULL);
       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 2660672..c337c85 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;
+  refcounts_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 858ee11..cff0546 100644
--- a/libports/lookup-port.c
+++ b/libports/lookup-port.c
@@ -28,7 +28,6 @@ ports_lookup_port (struct port_bucket *bucket,
 {
   struct port_info *pi;
 
-  pthread_mutex_lock (&_ports_lock);
   pthread_rwlock_rdlock (&_ports_htable_lock);
 
   pi = hurd_ihash_find (&_ports_htable, port);
@@ -38,10 +37,9 @@ ports_lookup_port (struct port_bucket *bucket,
     pi = 0;
 
   if (pi)
-    pi->refcnt++;
+    ports_port_ref (pi);
 
   pthread_rwlock_unlock (&_ports_htable_lock);
-  pthread_mutex_unlock (&_ports_lock);
 
   return pi;
 }
diff --git a/libports/port-deref-weak.c b/libports/port-deref-weak.c
index beb4842..8432660 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 references result;
+  refcounts_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..b97dd13 100644
--- a/libports/port-deref.c
+++ b/libports/port-deref.c
@@ -25,26 +25,24 @@ void
 ports_port_deref (void *portstruct)
 {
   struct port_info *pi = portstruct;
-  int trieddroppingweakrefs = 0;
-
- retry:
-  
-  pthread_mutex_lock (&_ports_lock);
-  
-  if (pi->refcnt == 1 && pi->weakrefcnt
-      && pi->class->dropweak_routine && !trieddroppingweakrefs)
+  struct references result;
+
+  if (pi->class->dropweak_routine)
     {
-      pthread_mutex_unlock (&_ports_lock);
-      (*pi->class->dropweak_routine) (pi);
-      trieddroppingweakrefs = 1;
-      goto retry;
+      /* If we need to call the dropweak routine, we need to hold one
+         reference while doing so.  We use a weak reference for this
+         purpose, which we acquire by demoting our hard reference to a
+         weak one.  */
+      refcounts_demote (&pi->refcounts, &result);
+
+      if (result.hard == 0 && result.weak > 1)
+        (*pi->class->dropweak_routine) (pi);
+
+      refcounts_deref_weak (&pi->refcounts, &result);
     }
-  
-  assert (pi->refcnt);
+  else
+    refcounts_deref (&pi->refcounts, &result);
 
-  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..e4b7fc8 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 references result;
+  refcounts_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..761c50f 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 references result;
+  refcounts_ref (&pi->refcounts, &result);
+  assert (result.hard > 1 || result.weak > 0);
 }
diff --git a/libports/ports.h b/libports/ports.h
index 6922162..40d3b43 100644
--- a/libports/ports.h
+++ b/libports/ports.h
@@ -27,6 +27,7 @@
 #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.  */
@@ -39,8 +40,7 @@
 struct port_info
 {
   struct port_class *class;
-  int refcnt;
-  int weakrefcnt;
+  refcounts_t 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 9944b39..7205bd9 100644
--- a/libports/reallocate-from-external.c
+++ b/libports/reallocate-from-external.c
@@ -56,7 +56,7 @@ 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++;
+      refcounts_ref (&pi->refcounts, NULL);
     }
   
   pi->port_right = receive;
diff --git a/libports/transfer-right.c b/libports/transfer-right.c
index 3f48290..776a8d2 100644
--- a/libports/transfer-right.c
+++ b/libports/transfer-right.c
@@ -72,7 +72,7 @@ ports_transfer_right (void *tostruct,
       else if (((topi->flags & PORT_HAS_SENDRIGHTS) == 0) && hassendrights)
 	{
 	  topi->flags |= PORT_HAS_SENDRIGHTS;
-	  topi->refcnt++;
+	  refcounts_ref (&topi->refcounts, NULL);
 	}
     }
   
diff --git a/utils/rpctrace.c b/utils/rpctrace.c
index fc913e3..b11fea4 100644
--- a/utils/rpctrace.c
+++ b/utils/rpctrace.c
@@ -431,7 +431,9 @@ 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 (
+	refcounts_hard_references (&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 +850,11 @@ 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 (
+	      refcounts_hard_references (
+		&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
-- 
2.0.0