Package org.apache.commons.configuration2.sync

# Interface Synchronizer

All Known Implementing Classes:
  `NoOpSynchronizer`, `ReadWriteSynchronizer`

public interface Synchronizer

An interface controlling synchronization of configuration instances.

Each `Configuration` object derived from `AbstractConfiguration` has an associated `Synchronizer` object. Before an operation on the configuration is performed (e.g. a property read or an update), the `Synchronizer` is invoked. Depending on the concrete implementation of the `Synchronizer` used, the configuration can be made thread-safe.

Whether a configuration has to be thread-safe or not is a matter of a concrete use case. For instance, an application that just reads some configuration settings on startup does need a thread-safe configuration implementation. A configuration in contrast which is shared between multiple components and updated concurrently should better be thread-safe. In order to satisfy both kinds of use cases, the support for thread-safety has been extracted out of the configuration implementation and refactored into this `Synchronizer` interface. By assigning different `Synchronizer` implementations to a configuration instance, the instance's support for concurrent access can be adapted to the concrete use case.

The methods defined by this interface are similar to a read-write lock. The `Synchronizer` is notified when read or write operations start and end. A concrete implementation can then apply a specific policy to decide when threads need to block or when access to the configuration for the desired operation is granted.

Since:
  2.0

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `beginRead()`
  Notifies this `Synchronizer` that the current thread is going to start a read operation on the managed configuration.
  `void`
  `beginWrite()`
  Notifies this `Synchronizer` that the current thread is going to start a write operation on the managed configuration.
  `void`
  `endRead()`
  Notifies this `Synchronizer` that the current thread has finished its read operation.
  `void`
  `endWrite()`
  Notifies this `Synchronizer` that the current thread has finished its write operation.

- ## Method Details

  - ### beginRead

    void beginRead()
    Notifies this `Synchronizer` that the current thread is going to start a read operation on the managed configuration. This call can block if a concrete implementation decides that the thread has to wait until a specific condition is fulfilled.

  - ### beginWrite

    void beginWrite()
    Notifies this `Synchronizer` that the current thread is going to start a write operation on the managed configuration. This call may block. For instance, a concrete implementation may suspend the thread until all read operations currently active are finished,

  - ### endRead

    void endRead()
    Notifies this `Synchronizer` that the current thread has finished its read operation. This may cause other waiting threads to be granted access to the managed configuration.

  - ### endWrite

    void endWrite()
    Notifies this `Synchronizer` that the current thread has finished its write operation. This may cause other waiting threads to be granted access to the managed configuration.