1. 04 Mar, 2008 5 commits
    • Guido Trotter's avatar
      Make LockSet.__names() return a list, not a set · 0cf257c5
      Guido Trotter authored
      Previously the private version of the __names function returned directly a set.
      We'll keep this in the public interface but change the private version to a
      list in order to be able to sort() its result and then loop on it, even though
      we'll need to do this with the usual care that some keys may disappear in
      between.
      
      Reviewed-by: imsnah
      
      0cf257c5
    • Guido Trotter's avatar
      LockSet: improve remove() api · 3f404fc5
      Guido Trotter authored
      Lockset's remove() function used to return a list of locks we failed to remove.
      Rather than doing this we'll return a list of removed locks, so it's more
      similar to how acquire() behaves. This patch also fixes the relevant unit tests.
      
      Reviewed-by: imsnah
      
      3f404fc5
    • Guido Trotter's avatar
      LockSet: make acquire() return the set of names · 0cc00929
      Guido Trotter authored
      In a LockSet acquire() returned True on success. This code changes that to
      return a set containing the names of the elements acquired. This is still a
      true value if we acquired any lock but is slightly more useful (because if
      needed one has access to this data without querying for it). The only change
      happens if acquiring no locks, which though is a usage which should not
      normally happen because it has no practical use.
      
      The patch also changes a some tests to check that the new format is respected.
      
      Reviewed-by: imsnah
      
      0cc00929
    • Guido Trotter's avatar
      LockSet: invert try/for nesting in acquire() · 8b68f394
      Guido Trotter authored
      This patch changes nothing to the functionality of a LockSet. Rather than
      trying to do the whole for loop we try each of its steps. This opens the way to
      handle differently a single failure.
      
      Reviewed-by: imsnah
      8b68f394
    • Guido Trotter's avatar
      Initial GanetiLockManager implementation · 7ee7c0c7
      Guido Trotter authored
      Includes some locking-related constants and explanations on how the
      LockManager should be used, the class itself and its test cases.
      
      The class includes:
        - a basic constructor
        - functions to acquire and release lists of locks at the same level
        - functions to add and remove list of locks at modifiable levels
        - dynamic checks against out-of-order acquisitions and other illegal ops
      
      Its testing library checks that the LockManager behaves correctly and that the
      external assumptions it relies on are respected.
      
      Reviewed-by: imsnah
      7ee7c0c7
  2. 28 Feb, 2008 2 commits
    • Guido Trotter's avatar
      LockSet: make acquire() fail faster on wrong locks · e6c200d6
      Guido Trotter authored
      This patch makes acquire() first look up all the locks in the dict and then try
      to acquire them later. The advantage is that if a lockname is already wrong
      since the beginning we won't need to first queue and acquire other locks to
      find this out.
      
      Of course since there is no locking between the two steps a delete() could
      still happen in between, but SharedLocks are safe in this regard and will just
      make the .acquire() operation fail if this unfortunate condition happens.
      
      Since the right way to check if an instance/node exists and make sure it won't
      stop existing after that is acquiring its lock this improves the common case
      (checking for an incorrect name) while not penalizing correctness, or
      performance as would happen if we kept a lock for the whole process.
      
      Reviewed-by: iustinp
      e6c200d6
    • Guido Trotter's avatar
      LockSet implementation and unit tests · aaae9bc0
      Guido Trotter authored
      A LockSet represents locking for a set of resources of the same type. A thread
      can acquire multiple resources at the same time, and release some or all of
      them, but cannot acquire more resources incrementally at different times
      without releasing all of them in between.
      
      Internally a LockSet uses a SharedLock for each resource to be able to grant
      both exclusive and shared acquisition. It also supports safe addition and
      removal of resources at runtime. Acquisitions are ordered alphabetically in
      order to grant them to be deadlock-free. A lot of assumptions about how the
      code interacts are made in order to grant both safety and speed; in order to
      document all of them the code features pretty lenghty comments.
      
      The test suit tries to catch most common interactions but cannot really tests
      tight race conditions, for which we still need to rely on human checking.
      
      This is the second basic building block for the Ganeti Lock Manager. Instance
      and Node locks will be put in LockSets to manage their acquisition and release.
      
      Reviewed-by: imsnah
      aaae9bc0
  3. 19 Feb, 2008 1 commit
    • Guido Trotter's avatar
      Add the delete() operation to SharedLock · a95fd5d7
      Guido Trotter authored
      This new operation lets a lock be cleanly deleted. The lock will be exclusively
      held before deletion, and after it pending and future acquires will raise an
      exception. Other SharedLock operations are modify to deal with delete() and to
      avoid code duplication.
      
      This patch also adds unit testing for the new function and its interaction with
      the other lock features. The helper threads are sligtly modified to handle and
      report the condition of a deleted lock. As a bonus a non-related unit test
      about not supporting non-blocking mode yet has been added as well.
      
      This feature will be used by the LockSet in order to support deadlock-free
      delete of resources. This in turn will be useful to gracefully handle the
      removal of instances and nodes from the cluster dealing with the fact that
      other operations may be pending on them.
      
      Reviewed-by: iustinp
      a95fd5d7
  4. 18 Feb, 2008 1 commit
  5. 08 Feb, 2008 1 commit
    • Guido Trotter's avatar
      Shared Lock implementation and unit tests. · 162c1c1f
      Guido Trotter authored
      Adding a locking.py file for the ganeti locking library. Its first component is
      the implementation of a non-recursive blocking shared lock complete with a
      testing library.
      
      Reviewed-by: imsnah, iustinp
      162c1c1f