malcolm (earlier version, helpful suggestions)


r27735 | glasser | 2007-11-08 19:50:29 -0600 (Thu, 08 Nov 2007)

Lock the FSFS 'transaction-current' file under its own
'txn-current-lock' file instead of 'write-lock', so that new
transactions and commits don't block each other.

In order to do so, abstract out the locking code a little more.  While
we're at it, make the locking code do "lock,(error:create,lock)"
instead of "stat,(missing:create),lock", to save a stat in the common

* subversion/libsvn_fs_fs/fs.h
  (PATH_TXN_CURRENT_LOCK): New filename.  (And reflow the block.)
  (fs_fs_shared_data_t): If thready, add a txn_current_lock mutex
   field to protect the transaction-current file from concurrent
   access by multiple threads of one process.

* subversion/libsvn_fs_fs/fs.c
  (fs_serialized_init): Create the txn_current_lock mutex, if thready.

* subversion/libsvn_fs_fs/fs_fs.c
  (path_txn_current): New  helper function for getting the path of the
   transaction-current file.
  (path_txn_current_lock): New  helper function for getting the path of the
   txn-current-lock file.
  (get_lock_on_filesystem): Rename from get_write_lock, and generalize
   to lock a given file instead of 'write-lock'.  (Also move earlier
   in the file.)  Remove the stat (see above).
  (with_some_lock): Extract most of svn_fs_fs__with_write_lock into
   this function, which takes as argument a lock filename and (if
   threading) a mutex, instead of a svn_fs_t.
  (svn_fs_fs__with_write_lock): Now just a wrapper around
   with_some_lock (and moved earlier in the file).
  (with_txn_current_lock): New function which runs its body with the
   txn-current-lock file (and mutex) locked.
  (get_and_increment_txn_key_body): Use new path_txn_current helper
  (create_txn_dir): Call get_and_increment_txn_key_body using
   with_txn_current_lock instead of svn_fs_fs__with_write_lock (this
   change is the whole point of the revision).
  (svn_fs_fs__create): Create the txn-current-lock file when creating
   the repo., and use the path_txn_current helper.

* subversion/libsvn_fs_fs/structure
  (Layout of the FS directory): Document that transaction-current is
   modified under the lock of txn-current-lock.

Review by: malcolm (earlier version, helpful suggestions)