Package org.apache.uima.util

Class CasPool

java.lang.Object
org.apache.uima.util.CasPool
public class CasPool extends Object
This class represents a simple pool of CAS instances. This is useful for multithreaded applications, where there is a need for multiple CASes to be processed simultaneously. Because CAS creation is expensive, it is a good idea to create a pool of reusable CAS instances at initialization time, rather than creating a new CAS each time one is needed.

Clients check-out CAS instances from the pool using the getCas() method and check-in CAS instances using the releaseCas(CAS) method.

Design considerations: The pool favors reuse of CASes is some arbitrary preferred priority order. For example if there is a pool of 10 CASes, but only 2 are being check-out at any given time, the same 2 CASes will be used (as opposed to a FIFO approach where all the CASes would be cycled through). If more threads request CASes from the pool than are available, the pool (optionally) puts requesting threads into a wait state. When CASes become available, the longest-waiting thread gets the CAS; this approach prevents starvation behavior (where some threads get all the CASes and others get none).

  • Constructor Details

    • CasPool

      public CasPool(int aNumInstances, Collection<? extends ProcessingResourceMetaData> aCollectionOfProcessingResourceMetaData, Properties aPerformanceTuningSettings, ResourceManager aResourceManager) throws ResourceInitializationException
      Creates a new CasPool
      Parameters:
      aNumInstances - the number of CAS instances in the pool
      aCollectionOfProcessingResourceMetaData - a collection of ProcessingResourceMetaData objects.
      aPerformanceTuningSettings - Properties object containing framework performance tuning settings using key names defined on UIMAFramework interface
      aResourceManager - the resource manager to use to resolve import declarations within the metadata
      Throws:
      ResourceInitializationException - if the CAS instances could not be created

    • CasPool

      public CasPool(int aNumInstances, AnalysisEngine aAnalysisEngine) throws ResourceInitializationException
      Creates a new CasPool
      Parameters:
      aNumInstances - the number of CAS instances in the pool
      aAnalysisEngine - the analysis engine that will create the CAS instances and which will later be used to process them
      Throws:
      ResourceInitializationException - if the CAS instances could not be created

    • CasPool

      public CasPool(int aNumInstances, ProcessingResourceMetaData aMetaData) throws ResourceInitializationException
      Creates a new CasPool
      Parameters:
      aNumInstances - the number of CAS instances in the pool
      aMetaData - metadata that includes the type system for the CAS
      Throws:
      ResourceInitializationException - if the CAS instances could not be created

    • CasPool

      public CasPool(int aNumInstances, ProcessingResourceMetaData aMetaData, ResourceManager aResourceManager) throws ResourceInitializationException
      Creates a new CasPool
      Parameters:
      aNumInstances - the number of CAS instances in the pool
      aMetaData - metadata that includes the type system for the CAS
      aResourceManager - Resource Manager
      Throws:
      ResourceInitializationException - if the CAS instances could not be created

    • CasPool

      public CasPool(int aNumInstances, CasDefinition aCasDefinition, Properties aPerformanceTuningSettings) throws ResourceInitializationException
      Creates a new CasPool. TODO: do we need this method AND the one that takes a CasManager?
      Parameters:
      aNumInstances - the number of CAS instances in the pool
      aCasDefinition - the Cas definition, which includes the type system, type priorities, and indexes for the CASes in the pool.
      aPerformanceTuningSettings - Properties object containing framework performance tuning settings using key names defined on UIMAFramework interface
      Throws:
      ResourceInitializationException - -

    • CasPool

      public CasPool(int aNumInstances, CasManager aCasManager, Properties aPerformanceTuningSettings) throws ResourceInitializationException
      Creates a new CasPool
      Parameters:
      aNumInstances - the number of CAS instances in the pool
      aCasManager - CAS Manager that will be used to create the CAS. The CAS Manager holds the CAS Definition. Also all CASes created from the same CAS Manager will share identical TypeSystem objects.
      aPerformanceTuningSettings - Properties object containing framework performance tuning settings using key names defined on UIMAFramework interface
      Throws:
      ResourceInitializationException - -

  • Method Details

    • getCas

      public CAS getCas()
      Checks out a CAS from the pool.
      Returns:
      a CAS instance. Returns null if none are available (in which case the client may Object.wait() on this object in order to be notified when an instance becomes available).

    • getCas

      public CAS getCas(long aTimeout)
      Checks out a CAS from the pool. If none is currently available, wait for the specified amount of time for one to be checked in.
      Parameters:
      aTimeout - the time to wait in milliseconds. A value of <=0 will wait forever.
      Returns:
      a CAS instance. Returns null if none are available within the specified timeout period.

    • releaseCas

      public void releaseCas(CAS aCas)
      Checks in a CAS to the pool. This automatically calls the CAS.reset() method, to ensure that when the CAS is later retrieved from the pool it will be ready to use. Also notifies other Threads that may be waiting for an instance to become available. Synchronized on the CAS to avoid the unnatural case where multiple threads attempt to return the same CAS to the pool at the same time.
      Parameters:
      aCas - the Cas to release

    • getSize

      public int getSize()
      Gets the size of this pool (the total number of CAS instances that it can hold).
      Returns:
      the size of this pool

    • getNumAvailable

      public int getNumAvailable()
      Gets the number of CASes currently available in this pool.
      Returns:
      the numberof available CASes

    • getAllInstances

      protected Vector<CAS> getAllInstances()

    • getFreeInstances

      protected Vector<CAS> getFreeInstances()