1 files changed, 398 insertions, 0 deletions
diff --git a/subversion/libsvn_subr/object_pool.c b/subversion/libsvn_subr/object_pool.c
new file mode 100644
index 0000000..782ffa2
--- /dev/null
+++ b/subversion/libsvn_subr/object_pool.c
@@ -0,0 +1,398 @@
+/*
+ * config_pool.c :  pool of configuration objects
+ *
+ * ====================================================================
+ *    Licensed to the Apache Software Foundation (ASF) under one
+ *    or more contributor license agreements.  See the NOTICE file
+ *    distributed with this work for additional information
+ *    regarding copyright ownership.  The ASF licenses this file
+ *    to you under the Apache License, Version 2.0 (the
+ *    "License"); you may not use this file except in compliance
+ *    with the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing,
+ *    software distributed under the License is distributed on an
+ *    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ *    KIND, either express or implied.  See the License for the
+ *    specific language governing permissions and limitations
+ *    under the License.
+ * ====================================================================
+ */
+
+
+
+
+#include <assert.h>
+
+#include "svn_error.h"
+#include "svn_hash.h"
+#include "svn_pools.h"
+
+#include "private/svn_atomic.h"
+#include "private/svn_object_pool.h"
+#include "private/svn_subr_private.h"
+#include "private/svn_dep_compat.h"
+
+
+
+/* A reference counting wrapper around the user-provided object.
+ */
+typedef struct object_ref_t
+{
+  /* reference to the parent container */
+  svn_object_pool__t *object_pool;
+
+  /* identifies the bucket in OBJECT_POOL->OBJECTS in which this entry
+   * belongs. */
+  svn_membuf_t key;
+
+  /* User provided object. Usually a wrapper. */
+  void *wrapper;
+
+  /* private pool. This instance and its other members got allocated in it.
+   * Will be destroyed when this instance is cleaned up. */
+  apr_pool_t *pool;
+
+  /* Number of references to this data struct */
+  volatile svn_atomic_t ref_count;
+} object_ref_t;
+
+
+/* Core data structure.  All access to it must be serialized using MUTEX.
+ */
+struct svn_object_pool__t
+{
+  /* serialization object for all non-atomic data in this struct */
+  svn_mutex__t *mutex;
+
+  /* object_ref_t.KEY -> object_ref_t* mapping.
+   *
+   * In shared object mode, there is at most one such entry per key and it
+   * may or may not be in use.  In exclusive mode, only unused references
+   * will be put here and they form chains if there are multiple unused
+   * instances for the key. */
+  apr_hash_t *objects;
+
+  /* same as objects->count but allows for non-sync'ed access */
+  volatile svn_atomic_t object_count;
+
+  /* Number of entries in OBJECTS with a reference count 0.
+     Due to races, this may be *temporarily* off by one or more.
+     Hence we must not strictly depend on it. */
+  volatile svn_atomic_t unused_count;
+
+  /* the root pool owning this structure */
+  apr_pool_t *pool;
+
+  /* extractor and updater for the user object wrappers */
+  svn_object_pool__getter_t getter;
+  svn_object_pool__setter_t setter;
+};
+
+
+/* Pool cleanup function for the whole object pool.
+ */
+static apr_status_t
+object_pool_cleanup(void *baton)
+{
+  svn_object_pool__t *object_pool = baton;
+
+  /* all entries must have been released up by now */
+  SVN_ERR_ASSERT_NO_RETURN(   object_pool->object_count
+                           == object_pool->unused_count);
+
+  return APR_SUCCESS;
+}
+
+/* Remove entries from OBJECTS in OBJECT_POOL that have a ref-count of 0.
+ *
+ * Requires external serialization on OBJECT_POOL.
+ */
+static void
+remove_unused_objects(svn_object_pool__t *object_pool)
+{
+  apr_pool_t *subpool = svn_pool_create(object_pool->pool);
+
+  /* process all hash buckets */
+  apr_hash_index_t *hi;
+  for (hi = apr_hash_first(subpool, object_pool->objects);
+       hi != NULL;
+       hi = apr_hash_next(hi))
+    {
+      object_ref_t *object_ref = apr_hash_this_val(hi);
+
+      /* note that we won't hand out new references while access
+         to the hash is serialized */
+      if (svn_atomic_read(&object_ref->ref_count) == 0)
+        {
+          apr_hash_set(object_pool->objects, object_ref->key.data,
+                       object_ref->key.size, NULL);
+          svn_atomic_dec(&object_pool->object_count);
+          svn_atomic_dec(&object_pool->unused_count);
+
+          svn_pool_destroy(object_ref->pool);
+        }
+    }
+
+  svn_pool_destroy(subpool);
+}
+
+/* Cleanup function called when an object_ref_t gets released.
+ */
+static apr_status_t
+object_ref_cleanup(void *baton)
+{
+  object_ref_t *object = baton;
+  svn_object_pool__t *object_pool = object->object_pool;
+
+  /* If we released the last reference to object, there is one more
+     unused entry.
+
+     Note that unused_count does not need to be always exact but only
+     needs to become exact *eventually* (we use it to check whether we
+     should remove unused objects every now and then).  I.e. it must
+     never drift off / get stuck but always reflect the true value once
+     all threads left the racy sections.
+   */
+  if (svn_atomic_dec(&object->ref_count) == 0)
+    svn_atomic_inc(&object_pool->unused_count);
+
+  return APR_SUCCESS;
+}
+
+/* Handle reference counting for the OBJECT_REF that the caller is about
+ * to return.  The reference will be released when POOL gets cleaned up.
+ *
+ * Requires external serialization on OBJECT_REF->OBJECT_POOL.
+ */
+static void
+add_object_ref(object_ref_t *object_ref,
+              apr_pool_t *pool)
+{
+  /* Update ref counter.
+     Note that this is racy with object_ref_cleanup; see comment there. */
+  if (svn_atomic_inc(&object_ref->ref_count) == 0)
+    svn_atomic_dec(&object_ref->object_pool->unused_count);
+
+  /* make sure the reference gets released automatically */
+  apr_pool_cleanup_register(pool, object_ref, object_ref_cleanup,
+                            apr_pool_cleanup_null);
+}
+
+/* Actual implementation of svn_object_pool__lookup.
+ *
+ * Requires external serialization on OBJECT_POOL.
+ */
+static svn_error_t *
+lookup(void **object,
+       svn_object_pool__t *object_pool,
+       svn_membuf_t *key,
+       void *baton,
+       apr_pool_t *result_pool)
+{
+  object_ref_t *object_ref
+    = apr_hash_get(object_pool->objects, key->data, key->size);
+
+  if (object_ref)
+    {
+      *object = object_pool->getter(object_ref->wrapper, baton, result_pool);
+      add_object_ref(object_ref, result_pool);
+    }
+  else
+    {
+      *object = NULL;
+    }
+
+  return SVN_NO_ERROR;
+}
+
+/* Actual implementation of svn_object_pool__insert.
+ *
+ * Requires external serialization on OBJECT_POOL.
+ */
+static svn_error_t *
+insert(void **object,
+       svn_object_pool__t *object_pool,
+       const svn_membuf_t *key,
+       void *wrapper,
+       void *baton,
+       apr_pool_t *wrapper_pool,
+       apr_pool_t *result_pool)
+{
+  object_ref_t *object_ref
+    = apr_hash_get(object_pool->objects, key->data, key->size);
+  if (object_ref)
+    {
+      /* entry already exists (e.g. race condition) */
+      svn_error_t *err = object_pool->setter(&object_ref->wrapper,
+                                             wrapper, baton,
+                                             object_ref->pool);
+      if (err)
+        {
+          /* if we had an issue in the setter, then OBJECT_REF is in an
+           * unknown state now.  Keep it around for the current users
+           * (i.e. don't clean the pool) but remove it from the list of
+           * available ones.
+           */
+          apr_hash_set(object_pool->objects, key->data, key->size, NULL);
+          svn_atomic_dec(&object_pool->object_count);
+
+          /* for the unlikely case that the object got created _and_
+           * already released since we last checked: */
+          if (svn_atomic_read(&object_ref->ref_count) == 0)
+            svn_atomic_dec(&object_pool->unused_count);
+
+          /* cleanup the new data as well because it's not safe to use
+           * either.
+           */
+          svn_pool_destroy(wrapper_pool);
+
+          /* propagate error */
+          return svn_error_trace(err);
+        }
+
+      /* Destroy the new one and return a reference to the existing one
+       * because the existing one may already have references on it.
+       */
+      svn_pool_destroy(wrapper_pool);
+    }
+  else
+    {
+      /* add new index entry */
+      object_ref = apr_pcalloc(wrapper_pool, sizeof(*object_ref));
+      object_ref->object_pool = object_pool;
+      object_ref->wrapper = wrapper;
+      object_ref->pool = wrapper_pool;
+
+      svn_membuf__create(&object_ref->key, key->size, wrapper_pool);
+      object_ref->key.size = key->size;
+      memcpy(object_ref->key.data, key->data, key->size);
+
+      apr_hash_set(object_pool->objects, object_ref->key.data,
+                   object_ref->key.size, object_ref);
+      svn_atomic_inc(&object_pool->object_count);
+
+      /* the new entry is *not* in use yet.
+       * add_object_ref will update counters again.
+       */
+      svn_atomic_inc(&object_ref->object_pool->unused_count);
+    }
+
+  /* return a reference to the object we just added */
+  *object = object_pool->getter(object_ref->wrapper, baton, result_pool);
+  add_object_ref(object_ref, result_pool);
+
+  /* limit memory usage */
+  if (svn_atomic_read(&object_pool->unused_count) * 2
+      > apr_hash_count(object_pool->objects) + 2)
+    remove_unused_objects(object_pool);
+
+  return SVN_NO_ERROR;
+}
+
+/* Implement svn_object_pool__getter_t as no-op.
+ */
+static void *
+default_getter(void *object,
+               void *baton,
+               apr_pool_t *pool)
+{
+  return object;
+}
+
+/* Implement svn_object_pool__setter_t as no-op.
+ */
+static svn_error_t *
+default_setter(void **target,
+               void *source,
+               void *baton,
+               apr_pool_t *pool)
+{
+  return SVN_NO_ERROR;
+}
+
+
+/* API implementation */
+
+svn_error_t *
+svn_object_pool__create(svn_object_pool__t **object_pool,
+                        svn_object_pool__getter_t getter,
+                        svn_object_pool__setter_t setter,
+                        svn_boolean_t thread_safe,
+                        apr_pool_t *pool)
+{
+  svn_object_pool__t *result;
+
+  /* construct the object pool in our private ROOT_POOL to survive POOL
+   * cleanup and to prevent threading issues with the allocator
+   */
+  result = apr_pcalloc(pool, sizeof(*result));
+  SVN_ERR(svn_mutex__init(&result->mutex, thread_safe, pool));
+
+  result->pool = pool;
+  result->objects = svn_hash__make(result->pool);
+  result->getter = getter ? getter : default_getter;
+  result->setter = setter ? setter : default_setter;
+
+  /* make sure we clean up nicely.
+   * We need two cleanup functions of which exactly one will be run
+   * (disabling the respective other as the first step).  If the owning
+   * pool does not cleaned up / destroyed explicitly, it may live longer
+   * than our allocator.  So, we need do act upon cleanup requests from
+   * either side - owning_pool and root_pool.
+   */
+  apr_pool_cleanup_register(pool, result, object_pool_cleanup,
+                            apr_pool_cleanup_null);
+
+  *object_pool = result;
+  return SVN_NO_ERROR;
+}
+
+apr_pool_t *
+svn_object_pool__new_wrapper_pool(svn_object_pool__t *object_pool)
+{
+  return svn_pool_create(object_pool->pool);
+}
+
+svn_mutex__t *
+svn_object_pool__mutex(svn_object_pool__t *object_pool)
+{
+  return object_pool->mutex;
+}
+
+unsigned
+svn_object_pool__count(svn_object_pool__t *object_pool)
+{
+  return svn_atomic_read(&object_pool->object_count);
+}
+
+svn_error_t *
+svn_object_pool__lookup(void **object,
+                        svn_object_pool__t *object_pool,
+                        svn_membuf_t *key,
+                        void *baton,
+                        apr_pool_t *result_pool)
+{
+  *object = NULL;
+  SVN_MUTEX__WITH_LOCK(object_pool->mutex,
+                       lookup(object, object_pool, key, baton, result_pool));
+  return SVN_NO_ERROR;
+}
+
+svn_error_t *
+svn_object_pool__insert(void **object,
+                        svn_object_pool__t *object_pool,
+                        const svn_membuf_t *key,
+                        void *wrapper,
+                        void *baton,
+                        apr_pool_t *wrapper_pool,
+                        apr_pool_t *result_pool)
+{
+  *object = NULL;
+  SVN_MUTEX__WITH_LOCK(object_pool->mutex,
+                       insert(object, object_pool, key, wrapper, baton,
+                              wrapper_pool, result_pool));
+  return SVN_NO_ERROR;
+}