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/ports.h | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

(limited to 'libports/ports.h')

diff --git a/libports/ports.h b/libports/ports.h
index 7f131240..8118de9e 100644
--- a/libports/ports.h
+++ b/libports/ports.h
@@ -48,7 +48,7 @@ struct port_info
   struct rpc_info *current_rpcs;
   struct port_bucket *bucket;
   hurd_ihash_locp_t hentry;
-  struct port_info *next, **prevp; /* links on port_class list */
+  hurd_ihash_locp_t ports_htable_entry;
 };
 typedef struct port_info *port_info_t;
 
@@ -61,11 +61,12 @@ typedef struct port_info *port_info_t;
 struct port_bucket
 {
   mach_port_t portset;
+  /* Per-bucket hash table used for fast iteration.  Access must be
+     serialized using _ports_htable_lock.  */
   struct hurd_ihash htable;
   int rpcs;
   int flags;
   int count;
-  struct port_bucket *next;
 };
 /* FLAGS above are the following: */
 #define PORT_BUCKET_INHIBITED	PORTS_INHIBITED
@@ -78,7 +79,6 @@ struct port_class
 {
   int flags;
   int rpcs;
-  struct port_info *ports;
   int count;
   void (*clean_routine) (void *);
   void (*dropweak_routine) (void *);
@@ -277,7 +277,7 @@ error_t ports_class_iterate (struct port_class *class,
 			     error_t (*fun)(void *port));
 
 /* Internal entrypoint for above two.  */
-error_t _ports_bucket_class_iterate (struct port_bucket *bucket,
+error_t _ports_bucket_class_iterate (struct hurd_ihash *ht,
 				     struct port_class *class,
 				     error_t (*fun)(void *port));
 
@@ -402,7 +402,19 @@ extern kern_return_t
 /* Private data */
 extern pthread_mutex_t _ports_lock;
 extern pthread_cond_t _ports_block;
-extern struct port_bucket *_ports_all_buckets;
+
+/* A global hash table mapping port names to port_info objects.  This
+   table is used for port lookups and to iterate over classes.
+
+   A port in this hash table carries an implicit light reference.
+   When the reference counts reach zero, we call
+   _ports_complete_deallocate.  There we reacquire our lock
+   momentarily to check whether someone else reacquired a reference
+   through the hash table.  */
+extern struct hurd_ihash _ports_htable;
+/* Access to all hash tables is protected by this lock.  */
+extern pthread_rwlock_t _ports_htable_lock;
+
 extern int _ports_total_rpcs;
 extern int _ports_flags;
 #define _PORTS_INHIBITED	PORTS_INHIBITED
-- 
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