.. java:import:: java.util.concurrent Semaphore

.. java:import:: java.util.concurrent.atomic AtomicInteger

.. java:import:: java.util.concurrent.locks ReentrantLock

.. java:import:: org.caosdb.server.database.access Access

.. java:import:: org.caosdb.server.database.access AccessControlAccess

.. java:import:: org.caosdb.server.database.access InfoAccess

.. java:import:: org.caosdb.server.database.access InitAccess

.. java:import:: org.caosdb.server.database.access TransactionAccess

.. java:import:: org.caosdb.server.transaction AccessControlTransaction

.. java:import:: org.caosdb.server.transaction TransactionInterface

.. java:import:: org.caosdb.server.transaction WriteTransactionInterface

.. java:import:: org.caosdb.server.utils Info

.. java:import:: org.caosdb.server.utils Initialization

.. java:import:: org.caosdb.server.utils Releasable

WriteAccessLock
===============

.. java:package:: org.caosdb.server.database
   :noindex:

.. java:type::  class WriteAccessLock extends ReentrantLock implements Releasable

   Acquire and release write access. DatabaseAccessManager uses this class for managing access to entities while processing updates, inserts, deletions and retrievals. Write access will be granted to one and only one thread if no other thread already holds read or write access permits. The write access seat has to be reserved before acquiring the lock.

   The flow is as follows:

   .. parsed-literal::

                                             No new read
                                           access possible,
         Read access      Read access    wait for running read
           possible        possible       threads to fininish

           +------+       +----------+       +----------+
      +--> |  no  | ----> | reserved | ----> | acquired | --+
      |    | Lock |       +----------+       +----------+   |
      |    +------+                 \          /            |
      |                           (1 seat together)         |
      +-----------------------------------------------------+
                  release()

   :author: Timm Fitschen

Constructors
------------
WriteAccessLock
^^^^^^^^^^^^^^^

.. java:constructor:: public WriteAccessLock(ReadAccessSemaphore readSem)
   :outertype: WriteAccessLock

Methods
-------
lockInterruptibly
^^^^^^^^^^^^^^^^^

.. java:method:: @Override public void lockInterruptibly() throws InterruptedException
   :outertype: WriteAccessLock

   Lock the write access seat. This method returns once all current read permits have been released.

release
^^^^^^^

.. java:method:: @Override public void release()
   :outertype: WriteAccessLock

reserve
^^^^^^^

.. java:method:: public void reserve() throws InterruptedException
   :outertype: WriteAccessLock

   Reserve the seat for the next write access. While a write access is reserved but not yet acquired, all read access may still be granted. When a write access has been already granted or another reservation is active, the thread waits until the write access has been released.

   :throws InterruptedException:

unlock
^^^^^^

.. java:method:: @Override public void unlock()
   :outertype: WriteAccessLock

whoHasReservedAccess
^^^^^^^^^^^^^^^^^^^^

.. java:method:: public Thread whoHasReservedAccess()
   :outertype: WriteAccessLock