From 37739cc6f4a38ef6241abfea42693fa046f80d1b Mon Sep 17 00:00:00 2001
From: Michael Vrable <mvrable@cs.ucsd.edu>
Date: Sat, 18 Sep 2010 21:22:15 -0700
Subject: [PATCH] Allow cloudlog items to be unreferenced in the background.

This is to avoid certain deadlocks, when we don't care if resources are
reclaimed immediately or not.
---
 bluesky/bluesky-private.h |  2 ++
 bluesky/bluesky.h         |  3 +++
 bluesky/cloudlog.c        | 29 ++++++++++++++++++++++++++++-
 bluesky/imap.c            |  2 +-
 bluesky/inode.c           |  2 ++
 bluesky/serialize.c       |  3 +++
 6 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/bluesky/bluesky-private.h b/bluesky/bluesky-private.h
index fccc7a3..7ebd728 100644
--- a/bluesky/bluesky-private.h
+++ b/bluesky/bluesky-private.h
@@ -286,8 +286,10 @@ guint bluesky_cloudlog_hash(gconstpointer a);
 BlueSkyCloudLog *bluesky_cloudlog_new(BlueSkyFS *fs, const BlueSkyCloudID *id);
 gchar *bluesky_cloudlog_id_to_string(BlueSkyCloudID id);
 BlueSkyCloudID bluesky_cloudlog_id_from_string(const gchar *idstr);
+void bluesky_cloudlog_threads_init(BlueSkyFS *fs);
 void bluesky_cloudlog_ref(BlueSkyCloudLog *log);
 void bluesky_cloudlog_unref(BlueSkyCloudLog *log);
+void bluesky_cloudlog_unref_delayed(BlueSkyCloudLog *log);
 void bluesky_cloudlog_erase(BlueSkyCloudLog *log);
 void bluesky_cloudlog_stats_update(BlueSkyCloudLog *log, int type);
 void bluesky_cloudlog_sync(BlueSkyCloudLog *log);
diff --git a/bluesky/bluesky.h b/bluesky/bluesky.h
index 9805086..834097f 100644
--- a/bluesky/bluesky.h
+++ b/bluesky/bluesky.h
@@ -188,6 +188,9 @@ typedef struct {
     /* The inode map, which maps inode numbers to the location of the most
      * recent version. */
     GSequence *inode_map;
+
+    /* Queue for asynchronous cloudlog unrefs, where needed. */
+    GAsyncQueue *unref_queue;
 } BlueSkyFS;
 
 /* Inode number of the root directory. */
diff --git a/bluesky/cloudlog.c b/bluesky/cloudlog.c
index 5d14fc6..e50c269 100644
--- a/bluesky/cloudlog.c
+++ b/bluesky/cloudlog.c
@@ -165,6 +165,33 @@ void bluesky_cloudlog_unref(BlueSkyCloudLog *log)
     }
 }
 
+/* For locking reasons cloudlog unrefs may sometimes need to be performed in
+ * the future.  We launch a thread for handling these delayed unreference
+ * requests. */
+static gpointer cloudlog_unref_thread(gpointer q)
+{
+    GAsyncQueue *queue = (GAsyncQueue *)q;
+
+    while (TRUE) {
+        BlueSkyCloudLog *item = (BlueSkyCloudLog *)g_async_queue_pop(queue);
+        bluesky_cloudlog_unref(item);
+    }
+
+    return NULL;
+}
+
+void bluesky_cloudlog_unref_delayed(BlueSkyCloudLog *log)
+{
+    if (log != NULL)
+        g_async_queue_push(log->fs->unref_queue, log);
+}
+
+void bluesky_cloudlog_threads_init(BlueSkyFS *fs)
+{
+    fs->unref_queue = g_async_queue_new();
+    g_thread_create(cloudlog_unref_thread, fs->unref_queue, FALSE, NULL);
+}
+
 /* Erase the information contained within the in-memory cloud log
  * representation.  This does not free up the item itself, but frees the data
  * and references to other log items and resets the type back to unknown.  If
@@ -206,7 +233,7 @@ void bluesky_cloudlog_insert_locked(BlueSkyCloudLog *log)
 void bluesky_cloudlog_insert(BlueSkyCloudLog *log)
 {
     g_mutex_lock(log->fs->lock);
-    bluesky_cloudlog_insert(log);
+    bluesky_cloudlog_insert_locked(log);
     g_mutex_unlock(log->fs->lock);
 }
 
diff --git a/bluesky/imap.c b/bluesky/imap.c
index 5d5be8a..c496f99 100644
--- a/bluesky/imap.c
+++ b/bluesky/imap.c
@@ -114,7 +114,7 @@ InodeMapEntry *bluesky_inode_map_lookup(GSequence *inode_map, uint64_t inum,
     }
 
     if (action != 0) {
-        bluesky_cloudlog_unref(range->serialized);
+        bluesky_cloudlog_unref_delayed(range->serialized);
         range->serialized = NULL;
     }
 
diff --git a/bluesky/inode.c b/bluesky/inode.c
index 515b72f..0d40da4 100644
--- a/bluesky/inode.c
+++ b/bluesky/inode.c
@@ -94,6 +94,8 @@ BlueSkyFS *bluesky_new_fs(gchar *name)
     fs->log_state = g_new0(BlueSkyCloudLogState, 1);
     fs->log_state->data = g_string_new("");
 
+    bluesky_cloudlog_threads_init(fs);
+
     return fs;
 }
 
diff --git a/bluesky/serialize.c b/bluesky/serialize.c
index dc23cac..b99a35e 100644
--- a/bluesky/serialize.c
+++ b/bluesky/serialize.c
@@ -313,6 +313,9 @@ void bluesky_deserialize_cloudlog(BlueSkyCloudLog *item,
         g_assert(data3 + len3 - data <= len);
         item->type = header->type - '0';
         item->inum = GUINT64_FROM_LE(header->inum);
+    } else {
+        g_warning("Deserializing garbage cloud log item!");
+        return;
     }
 
     BlueSkyFS *fs = item->fs;
-- 
2.20.1