Introducing a new persistent connection caching system using "bundles".

A bundle is a list of all persistent connections to the same host.
The connection cache consists of a hash of bundles, with the
hostname as the key.
The benefits may not be obvious, but they are two:

1) Faster search for connections to reuse, since the hash
   lookup only finds connections to the host in question.
2) It lays out the groundworks for an upcoming patch,
   which will introduce multiple HTTP pipelines.

This patch also removes the awkward list of "closure handles",
which were needed to send QUIT commands to the FTP server
when closing a connection.
Now we allocate a separate closure handle and use that
one to close all connections.

This has been tested in a live system for a few weeks, and of
course passes the test suite.

1 files changed, 270 insertions, 0 deletions

diff --git a/lib/conncache.c b/lib/conncache.c
new file mode 100644
index 000000000..b3186037e
--- /dev/null
+++ b/lib/conncache.c
@@ -0,0 +1,270 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 2012, Linus Nielsen Feltzing, <linus@haxx.se>
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at http://curl.haxx.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ***************************************************************************/
+
+#include "setup.h"
+
+#include <curl/curl.h>
+
+#include "urldata.h"
+#include "url.h"
+#include "progress.h"
+#include "multiif.h"
+#include "sendf.h"
+#include "rawstr.h"
+#include "bundles.h"
+#include "conncache.h"
+
+#include "curl_memory.h"
+/* The last #include file should be: */
+#include "memdebug.h"
+
+#define CONNECTION_HASH_SIZE 97
+
+static void free_bundle_hash_entry(void *freethis)
+{
+  struct connectbundle *b = (struct connectbundle *) freethis;
+
+  Curl_bundle_destroy(b);
+}
+
+struct conncache *Curl_conncache_init(int type)
+{
+  struct conncache *connc;
+
+  connc = calloc(1, sizeof(struct conncache));
+  if(!connc)
+    return NULL;
+
+  connc->hash = Curl_hash_alloc(CONNECTION_HASH_SIZE, Curl_hash_str,
+                                Curl_str_key_compare, free_bundle_hash_entry);
+
+  if(!connc->hash) {
+    free(connc);
+    return NULL;
+  }
+
+  connc->type = type;
+  connc->num_connections = 0;
+
+  return connc;
+}
+
+void Curl_conncache_destroy(struct conncache *connc)
+{
+  Curl_hash_destroy(connc->hash);
+  free(connc);
+}
+
+struct connectbundle *Curl_conncache_find_bundle(struct conncache *connc,
+                                                 char *hostname)
+{
+  struct connectbundle *bundle = NULL;
+
+  if(connc)
+    bundle = Curl_hash_pick(connc->hash, hostname, strlen(hostname)+1);
+
+  return bundle;
+}
+
+static bool conncache_add_bundle(struct conncache *connc,
+                                 char *hostname,
+                                 struct connectbundle *bundle)
+{
+  void *p;
+
+  p = Curl_hash_add(connc->hash, hostname, strlen(hostname)+1, bundle);
+
+  return p?TRUE:FALSE;
+}
+
+static void conncache_remove_bundle(struct conncache *connc,
+                                    struct connectbundle *bundle)
+{
+  struct curl_hash_iterator iter;
+  struct curl_hash_element *he;
+
+  if(!connc)
+    return;
+
+  Curl_hash_start_iterate(connc->hash, &iter);
+
+  he = Curl_hash_next_element(&iter);
+  while(he) {
+    if(he->ptr == bundle) {
+      /* The bundle is destroyed by the hash destructor function,
+         free_bundle_hash_entry() */
+      Curl_hash_delete(connc->hash, he->key, he->key_len);
+      return;
+    }
+
+    he = Curl_hash_next_element(&iter);
+  }
+}
+
+CURLcode Curl_conncache_add_conn(struct conncache *connc,
+                                 struct connectdata *conn)
+{
+  CURLcode result;
+  struct connectbundle *bundle;
+  struct SessionHandle *data = conn->data;
+
+  bundle = Curl_conncache_find_bundle(data->state.conn_cache,
+                                      conn->host.name);
+  if(!bundle) {
+    result = Curl_bundle_create(data, &bundle);
+    if(result != CURLE_OK)
+      return result;
+
+    if(!conncache_add_bundle(data->state.conn_cache,
+                             conn->host.name, bundle))
+      return CURLE_OUT_OF_MEMORY;
+  }
+
+  result = Curl_bundle_add_conn(bundle, conn);
+  if(result != CURLE_OK)
+    return result;
+
+  connc->num_connections++;
+
+  return CURLE_OK;
+}
+
+void Curl_conncache_remove_conn(struct conncache *connc,
+                                struct connectdata *conn)
+{
+  struct connectbundle *bundle = conn->bundle;
+
+  /* The bundle pointer can be NULL, since this function can be called
+     due to a failed connection attempt, before being added to a bundle */
+  if(bundle) {
+    Curl_bundle_remove_conn(bundle, conn);
+    if(bundle->num_connections == 0) {
+      conncache_remove_bundle(connc, bundle);
+    }
+    connc->num_connections--;
+
+    DEBUGF(infof(conn->data, "The cache now contains %d members\n",
+                 connc->num_connections));
+  }
+}
+
+/* This function iterates the entire connection cache and calls the
+   function func() with the connection pointer as the first argument
+   and the supplied 'param' argument as the other */
+void Curl_conncache_foreach(struct conncache *connc,
+                            void *param,
+                            void (*func)(void *conn, void *param))
+{
+  struct curl_hash_iterator iter;
+  struct curl_llist_element *curr;
+  struct curl_hash_element *he;
+
+  if(!connc)
+    return;
+
+  Curl_hash_start_iterate(connc->hash, &iter);
+
+  he = Curl_hash_next_element(&iter);
+  while(he) {
+    struct connectbundle *bundle;
+    struct connectdata *conn;
+
+    bundle = he->ptr;
+
+    curr = bundle->conn_list->head;
+    while(curr) {
+      /* Yes, we need to update curr before calling func(), because func()
+         might decide to remove the connection */
+      conn = curr->ptr;
+      curr = curr->next;
+
+      func(conn, param);
+    }
+
+    he = Curl_hash_next_element(&iter);
+  }
+}
+
+/* Return the first connection found in the cache. Used when closing all
+   connections */
+struct connectdata *
+Curl_conncache_find_first_connection(struct conncache *connc)
+{
+  struct curl_hash_iterator iter;
+  struct curl_llist_element *curr;
+  struct curl_hash_element *he;
+  struct connectbundle *bundle;
+
+  Curl_hash_start_iterate(connc->hash, &iter);
+
+  he = Curl_hash_next_element(&iter);
+  while(he) {
+    bundle = he->ptr;
+
+    curr = bundle->conn_list->head;
+    if(curr) {
+      return curr->ptr;
+    }
+
+    he = Curl_hash_next_element(&iter);
+  }
+
+  return NULL;
+}
+
+
+#if 0
+/* Useful for debugging the connection cache */
+void Curl_conncache_print(struct conncache *connc)
+{
+  struct curl_hash_iterator iter;
+  struct curl_llist_element *curr;
+  struct curl_hash_element *he;
+
+  if(!connc)
+    return;
+
+  fprintf(stderr, "=Bundle cache=\n");
+
+  Curl_hash_start_iterate(connc->hash, &iter);
+
+  he = Curl_hash_next_element(&iter);
+  while(he) {
+    struct connectbundle *bundle;
+    struct connectdata *conn;
+
+    bundle = he->ptr;
+
+    fprintf(stderr, "%s -", he->key);
+    curr = bundle->conn_list->head;
+    while(curr) {
+      conn = curr->ptr;
+
+      fprintf(stderr, " [%p %d]", (void *)conn, conn->inuse);
+      curr = curr->next;
+    }
+    fprintf(stderr, "\n");
+
+    he = Curl_hash_next_element(&iter);
+  }
+}
+#endif