From b2ae574d39adfe283c61a3ec0c766e8780f345af Mon Sep 17 00:00:00 2001
From: Justus Winter <4winter@informatik.uni-hamburg.de>
Date: Sat, 3 May 2014 03:53:41 +0200
Subject: libports: use a global hash table for the lookups

Previously, libports used a hash table per port bucket.  This makes
looking up a port difficult if one does not know the port bucket, as
one has to iterate over all buckets and do a hash table lookup each.

Having to iterate over the buckets makes it necessary to keep a list
of all buckets, which has to be updated and protected by a lock as
well.

Also, the current code in _ports_bucket_class_iterate iterates over
the hash table associated with the bucket given.  When
ports_class_iterate calls this common function, it obtains a reference
to the bucket from one of the ports in the given class.  This will not
work if a class contains ports in different port buckets.  This
limitation is not documented as far as I can see.  Again, having to
maintain this list has its cost and requires serialization.

Use a global hash table for lookups instead.  Keep the per-bucket hash
tables for efficient iteration over buckets.  Furthermore, serialize
access to all hash tables using a separate lock.  Remove the linked
lists of all buckets and all ports in a class.

* libports/bucket-iterate.c (ports_bucket_iterate): Acquire
_ports_htable_lock.  Also, generalize ports_bucket_iterate so that it
takes a pointer to a hash table as first argument.
(ports_bucket_iterate): Ajust call to former function accordingly.
* libports/class-iterate.c (ports_class_iterate): Just call the
generalized _ports_bucket_class_iterate with the global hash table as
argument.
* libports/ports.h (struct port_info): Remove the port class links.
(struct port_bucket): Remove the hash table, and the all buckets link.
(_ports_all_buckets): Remove declaration.
(_ports_htable): New global hash table.
(_ports_htable_lock): Protected by this lock.
* libports/claim-right.c: Adjust accordingly.
* libports/complete-deallocate.c: Likewise.
* libports/create-bucket.c: Likewise.
* libports/create-class.c: Likewise.
* libports/create-internal.c: Likewise.
* libports/destroy-right.c: Likewise.
* libports/import-port.c: Likewise.
* libports/lookup-port.c: Likewise.
* libports/reallocate-from-external.c: Likewise.
* libports/reallocate-port.c: Likewise.
* libports/transfer-right.c: Likewise.
* libports/inhibit-all-rpcs.c: Iterate over the hash table.
* libports/inhibit-bucket-rpcs.c: Likewise, but filter using bucket.
* libports/inhibit-class-rpcs.c: Likewise, but filter using class.
* libports/init.c (_ports_htable): Initialize.
(_ports_htable_lock): Likewise.
---
 libports/bucket-iterate.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

(limited to 'libports/bucket-iterate.c')

diff --git a/libports/bucket-iterate.c b/libports/bucket-iterate.c
index 2d1b00d8..b9ef0eb7 100644
--- a/libports/bucket-iterate.c
+++ b/libports/bucket-iterate.c
@@ -25,7 +25,7 @@
 /* Internal entrypoint for both ports_bucket_iterate and ports_class_iterate.
    If CLASS is non-null, call FUN only for ports in that class.  */
 error_t
-_ports_bucket_class_iterate (struct port_bucket *bucket,
+_ports_bucket_class_iterate (struct hurd_ihash *ht,
 			     struct port_class *class,
 			     error_t (*fun)(void *))
 {
@@ -36,23 +36,26 @@ _ports_bucket_class_iterate (struct port_bucket *bucket,
   error_t err;
 
   pthread_mutex_lock (&_ports_lock);
+  pthread_rwlock_rdlock (&_ports_htable_lock);
 
-  if (bucket->htable.nr_items == 0)
+  if (ht->nr_items == 0)
     {
+      pthread_rwlock_unlock (&_ports_htable_lock);
       pthread_mutex_unlock (&_ports_lock);
       return 0;
     }
 
-  nr_items = bucket->htable.nr_items;
+  nr_items = ht->nr_items;
   p = malloc (nr_items * sizeof *p);
   if (p == NULL)
     {
+      pthread_rwlock_unlock (&_ports_htable_lock);
       pthread_mutex_unlock (&_ports_lock);
       return ENOMEM;
     }
 
   n = 0;
-  HURD_IHASH_ITERATE (&bucket->htable, arg)
+  HURD_IHASH_ITERATE (ht, arg)
     {
       struct port_info *const pi = arg;
 
@@ -63,6 +66,7 @@ _ports_bucket_class_iterate (struct port_bucket *bucket,
 	  n++;
 	}
     }
+  pthread_rwlock_unlock (&_ports_htable_lock);
   pthread_mutex_unlock (&_ports_lock);
 
   if (n != 0 && n != nr_items)
@@ -89,5 +93,5 @@ error_t
 ports_bucket_iterate (struct port_bucket *bucket,
 		      error_t (*fun)(void *))
 {
-  return _ports_bucket_class_iterate (bucket, 0, fun);
+  return _ports_bucket_class_iterate (&bucket->htable, NULL, fun);
 }
-- 
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