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From kot...@apache.org
Subject svn commit: r1655651 - /subversion/trunk/subversion/libsvn_fs_fs/tree.c
Date Thu, 29 Jan 2015 13:32:50 GMT
Author: kotkov
Date: Thu Jan 29 13:32:50 2015
New Revision: 1655651

URL: http://svn.apache.org/r1655651
Log:
Rework the way FSFS L1 DAG cache (fs_fs_dag_cache_t) deals with the lifetime
of the cached nodes.  Drop the existing approach that performs a non-trivial
reference counting for pools in favor of doing a couple of explicit dup()'s.

As a consequence, this patch restores a standard pool usage pattern for the
accessor functions to the cached DAG nodes — now these nodes are always
allocated in the passed-in pool, and this is a good thing to have.

* subversion/libsvn_fs_fs/tree.c
  (dag_node_cache_get): Ensure that the result is always allocated in the
   passed-in pool instead of (maybe) binding its lifetime to that pool.
   Achieve this by using the passed-in pool when getting the node from L2
   cache and by making a dup() into the L1 cache pool.  For the nodes that
   already are in L1, make a dup() before yielding the result.  After that,
   remove the needs_lock_cache argument and tweak the docstring.
  (get_dag): Update the calls to dag_node_cache_get().  After that, remove
   the unused needs_lock_cache argument and tweak the docstring.
  (svn_fs_fs__create_dag_cache): Do not register the unlock_cache() pool
   cleanup handler, as we don't lock the cache anymore.
  (auto_clear_dag_cache): Do not check whether the cache has locks when
   attempting to clear it.
  (cache_lock_t, lock_cache, unlock_cache, unregister_locks): Remove.
  (fs_fs_dag_cache_t): Remove the 'first_lock' field, tweak the docstring.
  (svn_fs_fs__node_id, svn_fs_fs__node_created_rev, fs_node_relation,
   fs_node_created_path, fs_node_prop, fs_node_proplist, fs_props_changed,
   fs_dir_entries, fs_copied_from, fs_file_length, fs_file_checksum,
   fs_file_contents, fs_try_process_file_contents, fs_contents_changed,
   fs_get_file_delta_stream, history_prev, crawl_directory_dag_for_mergeinfo,
   add_descendant_mergeinfo, open_path, get_root, make_path_mutable,
   copy_helper, get_copy_inheritance): Update the calls to get_dag().

Modified:
    subversion/trunk/subversion/libsvn_fs_fs/tree.c

Modified: subversion/trunk/subversion/libsvn_fs_fs/tree.c
URL: http://svn.apache.org/viewvc/subversion/trunk/subversion/libsvn_fs_fs/tree.c?rev=1655651&r1=1655650&r2=1655651&view=diff
==============================================================================
--- subversion/trunk/subversion/libsvn_fs_fs/tree.c (original)
+++ subversion/trunk/subversion/libsvn_fs_fs/tree.c Thu Jan 29 13:32:50 2015
@@ -100,7 +100,6 @@ typedef struct fs_txn_root_data_t
 static svn_error_t * get_dag(dag_node_t **dag_node_p,
                              svn_fs_root_t *root,
                              const char *path,
-                             svn_boolean_t needs_lock_cache,
                              apr_pool_t *pool);
 
 static svn_fs_root_t *make_revision_root(svn_fs_t *fs, svn_revnum_t rev,
@@ -159,34 +158,10 @@ typedef struct cache_entry_t
  */
 enum { BUCKET_COUNT = 256 };
 
-/* Each pool that has received a DAG node, will hold at least on lock on
-   our cache to ensure that the node remains valid despite being allocated
-   in the cache's pool.  This is the structure to represent the lock.
- */
-typedef struct cache_lock_t
-{
-  /* pool holding the lock */
-  apr_pool_t *pool;
-
-  /* cache being locked */
-  fs_fs_dag_cache_t *cache;
-
-  /* next lock. NULL at EOL */
-  struct cache_lock_t *next;
-
-  /* previous lock. NULL at list head. Only then this==cache->first_lock */
-  struct cache_lock_t *prev;
-} cache_lock_t;
-
 /* The actual cache structure.  All nodes will be allocated in POOL.
    When the number of INSERTIONS (i.e. objects created form that pool)
    exceeds a certain threshold, the pool will be cleared and the cache
    with it.
-
-   To ensure that nodes returned from this structure remain valid, the
-   cache will get locked for the lifetime of the _receiving_ pools (i.e.
-   those in which we would allocate the node if there was no cache.).
-   The cache will only be cleared FIRST_LOCK is 0.
  */
 struct fs_fs_dag_cache_t
 {
@@ -209,110 +184,23 @@ struct fs_fs_dag_cache_t
      This value is a mere hint for optimistic lookup and any value is
      valid (as long as it is < BUCKET_COUNT). */
   apr_size_t last_non_empty;
-
-  /* List of receiving pools that are still alive. */
-  cache_lock_t *first_lock;
 };
 
-/* Cleanup function to be called when a receiving pool gets cleared.
-   Unlocks the cache once.
- */
-static apr_status_t
-unlock_cache(void *baton_void)
-{
-  cache_lock_t *lock = baton_void;
-
-  /* remove lock from chain. Update the head */
-  if (lock->next)
-    lock->next->prev = lock->prev;
-  if (lock->prev)
-    lock->prev->next = lock->next;
-  else
-    lock->cache->first_lock = lock->next;
-
-  return APR_SUCCESS;
-}
-
-/* Cleanup function to be called when the cache itself gets destroyed.
-   In that case, we must unregister all unlock requests.
- */
-static apr_status_t
-unregister_locks(void *baton_void)
-{
-  fs_fs_dag_cache_t *cache = baton_void;
-  cache_lock_t *lock;
-
-  for (lock = cache->first_lock; lock; lock = lock->next)
-    apr_pool_cleanup_kill(lock->pool,
-                          lock,
-                          unlock_cache);
-
-  return APR_SUCCESS;
-}
-
 fs_fs_dag_cache_t*
 svn_fs_fs__create_dag_cache(apr_pool_t *pool)
 {
   fs_fs_dag_cache_t *result = apr_pcalloc(pool, sizeof(*result));
   result->pool = svn_pool_create(pool);
 
-  apr_pool_cleanup_register(pool,
-                            result,
-                            unregister_locks,
-                            apr_pool_cleanup_null);
-
   return result;
 }
 
-/* Prevent the entries in CACHE from being destroyed, for as long as the
-   POOL lives.
- */
-static void
-lock_cache(fs_fs_dag_cache_t* cache, apr_pool_t *pool)
-{
-  /* we only need to lock / unlock once per pool.  Since we will often ask
-     for multiple nodes with the same pool, we can reduce the overhead.
-     However, if e.g. pools are being used in an alternating pattern,
-     we may lock the cache more than once for the same pool (and register
-     just as many cleanup actions).
-   */
-  cache_lock_t *lock = cache->first_lock;
-
-  /* try to find an existing lock for POOL.
-     But limit the time spent on chasing pointers.  */
-  int limiter = 8;
-  while (lock && --limiter)
-    {
-      if (lock->pool == pool)
-        return;
-
-      lock = lock->next;
-    }
-
-  /* create a new lock and put it at the beginning of the lock chain */
-  lock = apr_palloc(pool, sizeof(*lock));
-  lock->cache = cache;
-  lock->pool = pool;
-  lock->next = cache->first_lock;
-  lock->prev = NULL;
-
-  if (cache->first_lock)
-    cache->first_lock->prev = lock;
-  cache->first_lock = lock;
-
-  /* instruct POOL to remove the look upon cleanup */
-  apr_pool_cleanup_register(pool,
-                            lock,
-                            unlock_cache,
-                            apr_pool_cleanup_null);
-}
-
 /* Clears the CACHE at regular intervals (destroying all cached nodes)
  */
 static void
 auto_clear_dag_cache(fs_fs_dag_cache_t* cache)
 {
-  if (cache->first_lock == NULL && cache->insertions > BUCKET_COUNT)
+  if (cache->insertions > BUCKET_COUNT)
     {
       svn_pool_clear(cache->pool);
 
@@ -485,18 +373,12 @@ locate_cache(svn_cache__t **cache,
     }
 }
 
-/* Return NODE for PATH from ROOT's node cache, or NULL if the node
-   isn't cached; read it from the FS. *NODE remains valid until either
-   POOL or the FS gets cleared or destroyed (whichever comes first).
-
-   Since locking can be expensive and POOL may be long-living, for
-   nodes that will not need to survive the next call to this function,
-   set NEEDS_LOCK_CACHE to FALSE. */
+/* Return NODE_P for PATH from ROOT's node cache, or NULL if the node
+   isn't cached; read it from the FS. *NODE_P is allocated in POOL. */
 static svn_error_t *
 dag_node_cache_get(dag_node_t **node_p,
                    svn_fs_root_t *root,
                    const char *path,
-                   svn_boolean_t needs_lock_cache,
                    apr_pool_t *pool)
 {
   svn_boolean_t found;
@@ -518,25 +400,23 @@ dag_node_cache_get(dag_node_t **node_p,
       if (bucket->node == NULL)
         {
           locate_cache(&cache, &key, root, path, pool);
-          SVN_ERR(svn_cache__get((void **)&node, &found, cache, key,
-                                 ffd->dag_node_cache->pool));
+          SVN_ERR(svn_cache__get((void **)&node, &found, cache, key, pool));
           if (found && node)
             {
               /* Patch up the FS, since this might have come from an old FS
               * object. */
               svn_fs_fs__dag_set_fs(node, root->fs);
-              bucket->node = node;
+
+              /* Retain the DAG node in L1 cache. */
+              bucket->node = svn_fs_fs__dag_dup(node,
+                                                ffd->dag_node_cache->pool);
             }
         }
       else
         {
-          node = bucket->node;
+          /* Copy the node from L1 cache into the passed-in POOL. */
+          node = svn_fs_fs__dag_dup(bucket->node, pool);
         }
-
-      /* if we found a node, make sure it remains valid at least as long
-         as it would when allocated in POOL. */
-      if (node && needs_lock_cache)
-        lock_cache(ffd->dag_node_cache, pool);
     }
   else
     {
@@ -887,7 +767,7 @@ get_copy_inheritance(copy_id_inherit_t *
   SVN_ERR(svn_fs_fs__dag_get_copyroot(&copyroot_rev, &copyroot_path,
                                       child->node));
   SVN_ERR(svn_fs_fs__revision_root(&copyroot_root, fs, copyroot_rev, pool));
-  SVN_ERR(get_dag(&copyroot_node, copyroot_root, copyroot_path, FALSE, pool));
+  SVN_ERR(get_dag(&copyroot_node, copyroot_root, copyroot_path, pool));
   copyroot_id = svn_fs_fs__dag_get_id(copyroot_node);
 
   if (svn_fs_fs__id_compare(copyroot_id, child_id) == svn_fs_node_unrelated)
@@ -1094,7 +974,7 @@ open_path(parent_path_t **parent_path_p,
       directory = svn_dirent_dirname(path, pool);
       if (directory[1] != 0) /* root nodes are covered anyway */
         {
-          SVN_ERR(dag_node_cache_get(&here, root, directory, TRUE, pool));
+          SVN_ERR(dag_node_cache_get(&here, root, directory, pool));
 
           /* Did the shortcut work? */
           if (here)
@@ -1161,7 +1041,7 @@ open_path(parent_path_t **parent_path_p,
              complete path. */
           if (next || !(flags & open_path_uncached))
             SVN_ERR(dag_node_cache_get(&cached_node, root, path_so_far->data,
-                                       TRUE, pool));
+                                       pool));
           if (cached_node)
             child = cached_node;
           else
@@ -1300,8 +1180,7 @@ make_path_mutable(svn_fs_root_t *root,
                                           parent_path->node));
       SVN_ERR(svn_fs_fs__revision_root(&copyroot_root, root->fs,
                                        copyroot_rev, pool));
-      SVN_ERR(get_dag(&copyroot_node, copyroot_root, copyroot_path,
-                      FALSE, pool));
+      SVN_ERR(get_dag(&copyroot_node, copyroot_root, copyroot_path, pool));
 
       child_id = svn_fs_fs__dag_get_id(parent_path->node);
       copyroot_id = svn_fs_fs__dag_get_id(copyroot_node);
@@ -1338,16 +1217,11 @@ make_path_mutable(svn_fs_root_t *root,
 
 /* Open the node identified by PATH in ROOT.  Set DAG_NODE_P to the
    node we find, allocated in POOL.  Return the error
-   SVN_ERR_FS_NOT_FOUND if this node doesn't exist.
-
-   Since locking can be expensive and POOL may be long-living, for
-   nodes that will not need to survive the next call to this function,
-   set NEEDS_LOCK_CACHE to FALSE. */
+   SVN_ERR_FS_NOT_FOUND if this node doesn't exist. */
 static svn_error_t *
 get_dag(dag_node_t **dag_node_p,
         svn_fs_root_t *root,
         const char *path,
-        svn_boolean_t needs_lock_cache,
         apr_pool_t *pool)
 {
   parent_path_t *parent_path;
@@ -1356,7 +1230,7 @@ get_dag(dag_node_t **dag_node_p,
   /* First we look for the DAG in our cache
      (if the path may be canonical). */
   if (*path == '/')
-    SVN_ERR(dag_node_cache_get(&node, root, path, needs_lock_cache, pool));
+    SVN_ERR(dag_node_cache_get(&node, root, path, pool));
 
   if (! node)
     {
@@ -1366,8 +1240,7 @@ get_dag(dag_node_t **dag_node_p,
        * performance benefit over previously checking path for being
        * canonical. */
       path = svn_fs__canonicalize_abspath(path, pool);
-      SVN_ERR(dag_node_cache_get(&node, root, path, needs_lock_cache,
-                                 pool));
+      SVN_ERR(dag_node_cache_get(&node, root, path, pool));
 
       if (! node)
         {
@@ -1446,7 +1319,7 @@ svn_fs_fs__node_id(const svn_fs_id_t **i
     {
       dag_node_t *node;
 
-      SVN_ERR(get_dag(&node, root, path, FALSE, pool));
+      SVN_ERR(get_dag(&node, root, path, pool));
       *id_p = svn_fs_fs__id_copy(svn_fs_fs__dag_get_id(node), pool);
     }
   return SVN_NO_ERROR;
@@ -1495,12 +1368,12 @@ fs_node_relation(svn_fs_node_relation_t
 
   /* We checked for all separations between ID spaces (repos, txn).
    * Now, we can simply test for the ID values themselves. */
-  SVN_ERR(get_dag(&node, root_a, path_a, FALSE, pool));
+  SVN_ERR(get_dag(&node, root_a, path_a, pool));
   id = svn_fs_fs__dag_get_id(node);
   rev_item_a = *svn_fs_fs__id_rev_item(id);
   node_id_a = *svn_fs_fs__id_node_id(id);
 
-  SVN_ERR(get_dag(&node, root_b, path_b, FALSE, pool));
+  SVN_ERR(get_dag(&node, root_b, path_b, pool));
   id = svn_fs_fs__dag_get_id(node);
   rev_item_b = *svn_fs_fs__id_rev_item(id);
   node_id_b = *svn_fs_fs__id_node_id(id);
@@ -1523,7 +1396,7 @@ svn_fs_fs__node_created_rev(svn_revnum_t
 {
   dag_node_t *node;
 
-  SVN_ERR(get_dag(&node, root, path, FALSE, pool));
+  SVN_ERR(get_dag(&node, root, path, pool));
   return svn_fs_fs__dag_get_revision(revision, node, pool);
 }
 
@@ -1538,7 +1411,7 @@ fs_node_created_path(const char **create
 {
   dag_node_t *node;
 
-  SVN_ERR(get_dag(&node, root, path, TRUE, pool));
+  SVN_ERR(get_dag(&node, root, path, pool));
   *created_path = svn_fs_fs__dag_get_created_path(node);
 
   return SVN_NO_ERROR;
@@ -1602,7 +1475,7 @@ fs_node_prop(svn_string_t **value_p,
   dag_node_t *node;
   apr_hash_t *proplist;
 
-  SVN_ERR(get_dag(&node, root, path, FALSE, pool));
+  SVN_ERR(get_dag(&node, root, path, pool));
   SVN_ERR(svn_fs_fs__dag_get_proplist(&proplist, node, pool));
   *value_p = NULL;
   if (proplist)
@@ -1625,7 +1498,7 @@ fs_node_proplist(apr_hash_t **table_p,
   apr_hash_t *table;
   dag_node_t *node;
 
-  SVN_ERR(get_dag(&node, root, path, FALSE, pool));
+  SVN_ERR(get_dag(&node, root, path, pool));
   SVN_ERR(svn_fs_fs__dag_get_proplist(&table, node, pool));
   *table_p = table ? table : apr_hash_make(pool);
 
@@ -1746,8 +1619,8 @@ fs_props_changed(svn_boolean_t *changed_
       (SVN_ERR_FS_GENERAL, NULL,
        _("Cannot compare property value between two different filesystems"));
 
-  SVN_ERR(get_dag(&node1, root1, path1, TRUE, pool));
-  SVN_ERR(get_dag(&node2, root2, path2, TRUE, pool));
+  SVN_ERR(get_dag(&node1, root1, path1, pool));
+  SVN_ERR(get_dag(&node2, root2, path2, pool));
   return svn_fs_fs__dag_things_different(changed_p, NULL,
                                          node1, node2, strict, pool);
 }
@@ -1760,7 +1633,7 @@ fs_props_changed(svn_boolean_t *changed_
 static svn_error_t *
 get_root(dag_node_t **node, svn_fs_root_t *root, apr_pool_t *pool)
 {
-  return get_dag(node, root, "/", TRUE, pool);
+  return get_dag(node, root, "/", pool);
 }
 
 
@@ -2491,7 +2364,7 @@ fs_dir_entries(apr_hash_t **table_p,
   int i;
 
   /* Get the entries for this path in the caller's pool. */
-  SVN_ERR(get_dag(&node, root, path, FALSE, pool));
+  SVN_ERR(get_dag(&node, root, path, pool));
   SVN_ERR(svn_fs_fs__dag_dir_entries(&table, node, pool));
 
   /* Convert directory array to hash. */
@@ -2691,7 +2564,7 @@ copy_helper(svn_fs_root_t *from_root,
        _("Copy immutable tree not supported"));
 
   /* Get the NODE for FROM_PATH in FROM_ROOT.*/
-  SVN_ERR(get_dag(&from_node, from_root, from_path, TRUE, pool));
+  SVN_ERR(get_dag(&from_node, from_root, from_path, pool));
 
   /* Build up the parent path from TO_PATH in TO_ROOT.  If the last
      component does not exist, it's not that big a deal.  We'll just
@@ -2768,7 +2641,7 @@ copy_helper(svn_fs_root_t *from_root,
                                             pool));
 
       /* Make a record of this modification in the changes table. */
-      SVN_ERR(get_dag(&new_node, to_root, to_path, TRUE, pool));
+      SVN_ERR(get_dag(&new_node, to_root, to_path, pool));
       SVN_ERR(add_change(to_root->fs, txn_id, to_path,
                          svn_fs_fs__dag_get_id(new_node), kind, FALSE,
                          FALSE, FALSE, svn_fs_fs__dag_node_kind(from_node),
@@ -2849,7 +2722,7 @@ fs_copied_from(svn_revnum_t *rev_p,
 
   /* There is no cached entry, look it up the old-fashioned
       way. */
-  SVN_ERR(get_dag(&node, root, path, TRUE, pool));
+  SVN_ERR(get_dag(&node, root, path, pool));
   SVN_ERR(svn_fs_fs__dag_get_copyfrom_rev(rev_p, node));
   SVN_ERR(svn_fs_fs__dag_get_copyfrom_path(path_p, node));
 
@@ -2920,7 +2793,7 @@ fs_file_length(svn_filesize_t *length_p,
   dag_node_t *file;
 
   /* First create a dag_node_t from the root/path pair. */
-  SVN_ERR(get_dag(&file, root, path, FALSE, pool));
+  SVN_ERR(get_dag(&file, root, path, pool));
 
   /* Now fetch its length */
   return svn_fs_fs__dag_file_length(length_p, file, pool);
@@ -2939,7 +2812,7 @@ fs_file_checksum(svn_checksum_t **checks
 {
   dag_node_t *file;
 
-  SVN_ERR(get_dag(&file, root, path, FALSE, pool));
+  SVN_ERR(get_dag(&file, root, path, pool));
   return svn_fs_fs__dag_file_checksum(checksum, file, kind, pool);
 }
 
@@ -2958,7 +2831,7 @@ fs_file_contents(svn_stream_t **contents
   svn_stream_t *file_stream;
 
   /* First create a dag_node_t from the root/path pair. */
-  SVN_ERR(get_dag(&node, root, path, FALSE, pool));
+  SVN_ERR(get_dag(&node, root, path, pool));
 
   /* Then create a readable stream from the dag_node_t. */
   SVN_ERR(svn_fs_fs__dag_get_contents(&file_stream, node, pool));
@@ -2981,7 +2854,7 @@ fs_try_process_file_contents(svn_boolean
                              apr_pool_t *pool)
 {
   dag_node_t *node;
-  SVN_ERR(get_dag(&node, root, path, FALSE, pool));
+  SVN_ERR(get_dag(&node, root, path, pool));
 
   return svn_fs_fs__dag_try_process_file_contents(success, node,
                                                   processor, baton, pool);
@@ -3305,8 +3178,8 @@ fs_contents_changed(svn_boolean_t *chang
         (SVN_ERR_FS_GENERAL, NULL, _("'%s' is not a file"), path2);
   }
 
-  SVN_ERR(get_dag(&node1, root1, path1, TRUE, pool));
-  SVN_ERR(get_dag(&node2, root2, path2, TRUE, pool));
+  SVN_ERR(get_dag(&node1, root1, path1, pool));
+  SVN_ERR(get_dag(&node2, root2, path2, pool));
   return svn_fs_fs__dag_things_different(NULL, changed_p,
                                          node1, node2, strict, pool);
 }
@@ -3326,10 +3199,10 @@ fs_get_file_delta_stream(svn_txdelta_str
   dag_node_t *source_node, *target_node;
 
   if (source_root && source_path)
-    SVN_ERR(get_dag(&source_node, source_root, source_path, TRUE, pool));
+    SVN_ERR(get_dag(&source_node, source_root, source_path, pool));
   else
     source_node = NULL;
-  SVN_ERR(get_dag(&target_node, target_root, target_path, TRUE, pool));
+  SVN_ERR(get_dag(&target_node, target_root, target_path, pool));
 
   /* Create a delta stream that turns the source into the target.  */
   return svn_fs_fs__dag_get_file_delta_stream(stream_p, source_node,
@@ -3793,7 +3666,7 @@ history_prev(svn_fs_history_t **prev_his
 
       SVN_ERR(svn_fs_fs__revision_root(&copyroot_root, fs, copyroot_rev,
                                        scratch_pool));
-      SVN_ERR(get_dag(&node, copyroot_root, copyroot_path, FALSE, scratch_pool));
+      SVN_ERR(get_dag(&node, copyroot_root, copyroot_path, scratch_pool));
       copy_dst = svn_fs_fs__dag_get_created_path(node);
 
       /* If our current path was the very destination of the copy,
@@ -3987,7 +3860,7 @@ crawl_directory_dag_for_mergeinfo(svn_fs
       svn_pool_clear(iterpool);
 
       kid_path = svn_fspath__join(this_path, dirent->name, iterpool);
-      SVN_ERR(get_dag(&kid_dag, root, kid_path, TRUE, iterpool));
+      SVN_ERR(get_dag(&kid_dag, root, kid_path, iterpool));
 
       SVN_ERR(svn_fs_fs__dag_has_mergeinfo(&has_mergeinfo, kid_dag));
       SVN_ERR(svn_fs_fs__dag_has_descendants_with_mergeinfo(&go_down, kid_dag));
@@ -4233,7 +4106,7 @@ add_descendant_mergeinfo(svn_mergeinfo_c
   dag_node_t *this_dag;
   svn_boolean_t go_down;
 
-  SVN_ERR(get_dag(&this_dag, root, path, TRUE, scratch_pool));
+  SVN_ERR(get_dag(&this_dag, root, path, scratch_pool));
   SVN_ERR(svn_fs_fs__dag_has_descendants_with_mergeinfo(&go_down,
                                                         this_dag));
   if (go_down)



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