org.apache.commons.pool2.impl

## Class BaseGenericObjectPool<T>

- java.lang.Object
- - org.apache.commons.pool2.impl.BaseGenericObjectPool<T>

- Type Parameters:
    `T` - Type of element pooled in this pool. This class is intended to be thread-safe.
  Direct Known Subclasses:
    GenericKeyedObjectPool, GenericObjectPool

      public abstract class BaseGenericObjectPool<T>
      extends Object

  Base class that provides common functionality for `GenericObjectPool` and `GenericKeyedObjectPool`. The primary reason this class exists is reduce code duplication between the two pool implementations.
  Since:
    2.0
  Version:
    $Revision: $

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static int` | `MEAN_TIMING_STATS_CACHE_SIZE` The size of the caches used to store historical data for some attributes so that rolling means may be calculated.

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `BaseGenericObjectPool(BaseObjectPoolConfig config, String jmxNameBase, String jmxNamePrefix)` Handles JMX registration (if required) and the initialization required for monitoring.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `abstract void` | `close()` Closes the pool, destroys the remaining idle objects and, if registered in JMX, deregisters it.
    `abstract void` | `evict()` Perform `numTests` idle object eviction tests, evicting examined objects that meet the criteria for eviction.
    `boolean` | `getBlockWhenExhausted()` Returns whether to block when the `borrowObject()` method is invoked when the pool is exhausted (the maximum number of "active" objects has been reached).
    `long` | `getBorrowedCount()` The total number of objects successfully borrowed from this pool over the lifetime of the pool.
    `long` | `getCreatedCount()` The total number of objects created for this pool over the lifetime of the pool.
    `String` | `getCreationStackTrace()` Provides the stack trace for the call that created this pool.
    `long` | `getDestroyedByBorrowValidationCount()` The total number of objects destroyed by this pool as a result of failing validation during `borrowObject()` over the lifetime of the pool.
    `long` | `getDestroyedByEvictorCount()` The total number of objects destroyed by the evictor associated with this pool over the lifetime of the pool.
    `long` | `getDestroyedCount()` The total number of objects destroyed by this pool over the lifetime of the pool.
    `String` | `getEvictionPolicyClassName()` Returns the name of the `EvictionPolicy` implementation that is used by this pool.
    `ObjectName` | `getJmxName()` Provides the name under which the pool has been registered with the platform MBean server or `null` if the pool has not been registered.
    `boolean` | `getLifo()` Returns whether the pool has LIFO (last in, first out) behaviour with respect to idle objects - always returning the most recently used object from the pool, or as a FIFO (first in, first out) queue, where the pool always returns the oldest object in the idle object pool.
    `long` | `getMaxBorrowWaitTimeMillis()` The maximum time a thread has waited to borrow objects from the pool.
    `int` | `getMaxTotal()` Returns the maximum number of objects that can be allocated by the pool (checked out to clients, or idle awaiting checkout) at a given time.
    `long` | `getMaxWaitMillis()` Returns the maximum amount of time (in milliseconds) the `borrowObject()` method should block before throwing an exception when the pool is exhausted and `getBlockWhenExhausted()` is true.
    `long` | `getMeanActiveTimeMillis()` The mean time objects are active for based on the last `MEAN_TIMING_STATS_CACHE_SIZE` objects returned to the pool.
    `long` | `getMeanBorrowWaitTimeMillis()` The mean time threads wait to borrow an object based on the last `MEAN_TIMING_STATS_CACHE_SIZE` objects borrowed from the pool.
    `long` | `getMeanIdleTimeMillis()` The mean time objects are idle for based on the last `MEAN_TIMING_STATS_CACHE_SIZE` objects borrowed from the pool.
    `long` | `getMinEvictableIdleTimeMillis()` Returns the minimum amount of time an object may sit idle in the pool before it is eligible for eviction by the idle object evictor (if any - see `setTimeBetweenEvictionRunsMillis(long)`).
    `abstract int` | `getNumIdle()` The number of instances currently idle in this pool.
    `int` | `getNumTestsPerEvictionRun()` Returns the maximum number of objects to examine during each run (if any) of the idle object evictor thread.
    `long` | `getReturnedCount()` The total number of objects returned to this pool over the lifetime of the pool.
    `long` | `getSoftMinEvictableIdleTimeMillis()` Returns the minimum amount of time an object may sit idle in the pool before it is eligible for eviction by the idle object evictor (if any - see `setTimeBetweenEvictionRunsMillis(long)`), with the extra condition that at least `minIdle` object instances remain in the pool.
    `SwallowedExceptionListener` | `getSwallowedExceptionListener()` The listener used (if any) to receive notifications of exceptions unavoidably swallowed by the pool.
    `boolean` | `getTestOnBorrow()` Returns whether objects borrowed from the pool will be validated before being returned from the `borrowObject()` method.
    `boolean` | `getTestOnReturn()` Returns whether objects borrowed from the pool will be validated when they are returned to the pool via the `returnObject()` method.
    `boolean` | `getTestWhileIdle()` Returns whether objects sitting idle in the pool will be validated by the idle object evictor (if any - see `setTimeBetweenEvictionRunsMillis(long)`).
    `long` | `getTimeBetweenEvictionRunsMillis()` Returns the number of milliseconds to sleep between runs of the idle object evictor thread.
    `boolean` | `isClosed()` Has this pool instance been closed.
    `void` | `setBlockWhenExhausted(boolean blockWhenExhausted)` Sets whether to block when the `borrowObject()` method is invoked when the pool is exhausted (the maximum number of "active" objects has been reached).
    `void` | `setEvictionPolicyClassName(String evictionPolicyClassName)` Sets the name of the `EvictionPolicy` implementation that is used by this pool.
    `void` | `setLifo(boolean lifo)` Sets whether the pool has LIFO (last in, first out) behaviour with respect to idle objects - always returning the most recently used object from the pool, or as a FIFO (first in, first out) queue, where the pool always returns the oldest object in the idle object pool.
    `void` | `setMaxTotal(int maxTotal)` Sets the cap on the number of objects that can be allocated by the pool (checked out to clients, or idle awaiting checkout) at a given time.
    `void` | `setMaxWaitMillis(long maxWaitMillis)` Sets the maximum amount of time (in milliseconds) the `borrowObject()` method should block before throwing an exception when the pool is exhausted and `getBlockWhenExhausted()` is true.
    `void` | `setMinEvictableIdleTimeMillis(long minEvictableIdleTimeMillis)` Sets the minimum amount of time an object may sit idle in the pool before it is eligible for eviction by the idle object evictor (if any - see `setTimeBetweenEvictionRunsMillis(long)`).
    `void` | `setNumTestsPerEvictionRun(int numTestsPerEvictionRun)` Sets the maximum number of objects to examine during each run (if any) of the idle object evictor thread.
    `void` | `setSoftMinEvictableIdleTimeMillis(long softMinEvictableIdleTimeMillis)` Sets the minimum amount of time an object may sit idle in the pool before it is eligible for eviction by the idle object evictor (if any - see `setTimeBetweenEvictionRunsMillis(long)`), with the extra condition that at least `minIdle` object instances remain in the pool.
    `void` | `setSwallowedExceptionListener(SwallowedExceptionListener swallowedExceptionListener)` The listener used (if any) to receive notifications of exceptions unavoidably swallowed by the pool.
    `void` | `setTestOnBorrow(boolean testOnBorrow)` Sets whether objects borrowed from the pool will be validated before being returned from the `borrowObject()` method.
    `void` | `setTestOnReturn(boolean testOnReturn)` Sets whether objects borrowed from the pool will be validated when they are returned to the pool via the `returnObject()` method.
    `void` | `setTestWhileIdle(boolean testWhileIdle)` Returns whether objects sitting idle in the pool will be validated by the idle object evictor (if any - see `setTimeBetweenEvictionRunsMillis(long)`).
    `void` | `setTimeBetweenEvictionRunsMillis(long timeBetweenEvictionRunsMillis)` Sets the number of milliseconds to sleep between runs of the idle object evictor thread.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### MEAN_TIMING_STATS_CACHE_SIZE

          public static final int MEAN_TIMING_STATS_CACHE_SIZE

      The size of the caches used to store historical data for some attributes so that rolling means may be calculated.
      See Also:
        Constant Field Values

  - ### Constructor Detail

    - #### BaseGenericObjectPool

          public BaseGenericObjectPool(BaseObjectPoolConfig config,
                               String jmxNameBase,
                               String jmxNamePrefix)

      Handles JMX registration (if required) and the initialization required for monitoring.
      Parameters:
        `config` - Pool configuration
        `jmxNameBase` - The default base JMX name for the new pool unless overridden by the config
        `jmxNamePrefix` - Prefix to be used for JMX name for the new pool

  - ### Method Detail

    - #### getMaxTotal

          public final int getMaxTotal()

      Returns the maximum number of objects that can be allocated by the pool (checked out to clients, or idle awaiting checkout) at a given time. When negative, there is no limit to the number of objects that can be managed by the pool at one time.
      Returns:
        the cap on the total number of object instances managed by the pool.
      See Also:
        `setMaxTotal(int)`

    - #### setMaxTotal

          public final void setMaxTotal(int maxTotal)

      Sets the cap on the number of objects that can be allocated by the pool (checked out to clients, or idle awaiting checkout) at a given time. Use a negative value for no limit.
      Parameters:
        `maxTotal` - The cap on the total number of object instances managed by the pool. Negative values mean that there is no limit to the number of objects allocated by the pool.
      See Also:
        `getMaxTotal()`

    - #### getBlockWhenExhausted

          public final boolean getBlockWhenExhausted()

      Returns whether to block when the `borrowObject()` method is invoked when the pool is exhausted (the maximum number of "active" objects has been reached).
      Returns:
        `true` if `borrowObject()` should block when the pool is exhausted
      See Also:
        `setBlockWhenExhausted(boolean)`

    - #### setBlockWhenExhausted

          public final void setBlockWhenExhausted(boolean blockWhenExhausted)

      Sets whether to block when the `borrowObject()` method is invoked when the pool is exhausted (the maximum number of "active" objects has been reached).
      Parameters:
        `blockWhenExhausted` - `true` if `borrowObject()` should block when the pool is exhausted
      See Also:
        `getBlockWhenExhausted()`

    - #### getMaxWaitMillis

          public final long getMaxWaitMillis()

      Returns the maximum amount of time (in milliseconds) the `borrowObject()` method should block before throwing an exception when the pool is exhausted and `getBlockWhenExhausted()` is true. When less than 0, the `borrowObject()` method may block indefinitely.
      Returns:
        the maximum number of milliseconds `borrowObject()` will block.
      See Also:
        `setMaxWaitMillis(long)`, `setBlockWhenExhausted(boolean)`

    - #### setMaxWaitMillis

          public final void setMaxWaitMillis(long maxWaitMillis)

      Sets the maximum amount of time (in milliseconds) the `borrowObject()` method should block before throwing an exception when the pool is exhausted and `getBlockWhenExhausted()` is true. When less than 0, the `borrowObject()` method may block indefinitely.
      Parameters:
        `maxWaitMillis` - the maximum number of milliseconds `borrowObject()` will block or negative for indefinitely.
      See Also:
        `getMaxWaitMillis()`, `setBlockWhenExhausted(boolean)`

    - #### getLifo

          public final boolean getLifo()

      Returns whether the pool has LIFO (last in, first out) behaviour with respect to idle objects - always returning the most recently used object from the pool, or as a FIFO (first in, first out) queue, where the pool always returns the oldest object in the idle object pool.
      Returns:
        `true` if the pool is configured with LIFO behaviour or `false` if the pool is configured with FIFO behaviour
      See Also:
        `setLifo(boolean)`

    - #### setLifo

          public final void setLifo(boolean lifo)

      Sets whether the pool has LIFO (last in, first out) behaviour with respect to idle objects - always returning the most recently used object from the pool, or as a FIFO (first in, first out) queue, where the pool always returns the oldest object in the idle object pool.
      Parameters:
        `lifo` - `true` if the pool is to be configured with LIFO behaviour or `false` if the pool is to be configured with FIFO behaviour
      See Also:
        `getLifo()`

    - #### getTestOnBorrow

          public final boolean getTestOnBorrow()

      Returns whether objects borrowed from the pool will be validated before being returned from the `borrowObject()` method. Validation is performed by the `validateObject()` method of the factory associated with the pool. If the object fails to validate, it will be removed from the pool and destroyed, and a new attempt will be made to borrow an object from the pool.
      Returns:
        `true` if objects are validated before being returned from the `borrowObject()` method
      See Also:
        `setTestOnBorrow(boolean)`

    - #### setTestOnBorrow

          public final void setTestOnBorrow(boolean testOnBorrow)

      Sets whether objects borrowed from the pool will be validated before being returned from the `borrowObject()` method. Validation is performed by the `validateObject()` method of the factory associated with the pool. If the object fails to validate, it will be removed from the pool and destroyed, and a new attempt will be made to borrow an object from the pool.
      Parameters:
        `testOnBorrow` - `true` if objects should be validated before being returned from the `borrowObject()` method
      See Also:
        `getTestOnBorrow()`

    - #### getTestOnReturn

          public final boolean getTestOnReturn()

      Returns whether objects borrowed from the pool will be validated when they are returned to the pool via the `returnObject()` method. Validation is performed by the `validateObject()` method of the factory associated with the pool. Returning objects that fail validation are destroyed rather then being returned the pool.
      Returns:
        `true` if objects are validated on return to the pool via the `returnObject()` method
      See Also:
        `setTestOnReturn(boolean)`

    - #### setTestOnReturn

          public final void setTestOnReturn(boolean testOnReturn)

      Sets whether objects borrowed from the pool will be validated when they are returned to the pool via the `returnObject()` method. Validation is performed by the `validateObject()` method of the factory associated with the pool. Returning objects that fail validation are destroyed rather then being returned the pool.
      Parameters:
        `testOnReturn` - `true` if objects are validated on return to the pool via the `returnObject()` method
      See Also:
        `getTestOnReturn()`

    - #### getTestWhileIdle

          public final boolean getTestWhileIdle()

      Returns whether objects sitting idle in the pool will be validated by the idle object evictor (if any - see `setTimeBetweenEvictionRunsMillis(long)`). Validation is performed by the `validateObject()` method of the factory associated with the pool. If the object fails to validate, it will be removed from the pool and destroyed.
      Returns:
        `true` if objects will be validated by the evictor
      See Also:
        `setTestWhileIdle(boolean)`, `setTimeBetweenEvictionRunsMillis(long)`

    - #### setTestWhileIdle

          public final void setTestWhileIdle(boolean testWhileIdle)

      Returns whether objects sitting idle in the pool will be validated by the idle object evictor (if any - see `setTimeBetweenEvictionRunsMillis(long)`). Validation is performed by the `validateObject()` method of the factory associated with the pool. If the object fails to validate, it will be removed from the pool and destroyed. Note that setting this property has no effect unless the idle object evictor is enabled by setting `timeBetweenEvictionRunsMillis` to a positive value.
      Parameters:
        `testWhileIdle` - `true` so objects will be validated by the evictor
      See Also:
        `getTestWhileIdle()`, `setTimeBetweenEvictionRunsMillis(long)`

    - #### getTimeBetweenEvictionRunsMillis

          public final long getTimeBetweenEvictionRunsMillis()

      Returns the number of milliseconds to sleep between runs of the idle object evictor thread. When non-positive, no idle object evictor thread will be run.
      Returns:
        number of milliseconds to sleep between evictor runs
      See Also:
        `setTimeBetweenEvictionRunsMillis(long)`

    - #### setTimeBetweenEvictionRunsMillis

          public final void setTimeBetweenEvictionRunsMillis(long timeBetweenEvictionRunsMillis)

      Sets the number of milliseconds to sleep between runs of the idle object evictor thread. When non-positive, no idle object evictor thread will be run.
      Parameters:
        `timeBetweenEvictionRunsMillis` - number of milliseconds to sleep between evictor runs
      See Also:
        `getTimeBetweenEvictionRunsMillis()`

    - #### getNumTestsPerEvictionRun

          public final int getNumTestsPerEvictionRun()

      Returns the maximum number of objects to examine during each run (if any) of the idle object evictor thread. When positive, the number of tests performed for a run will be the minimum of the configured value and the number of idle instances in the pool. When negative, the number of tests performed will be `ceil(`getNumIdle()`/ abs(`getNumTestsPerEvictionRun()`)) which means that when the value is `-n` roughly one nth of the idle objects will be tested per run.`
      Returns:
        max number of objects to examine during each evictor run
      See Also:
        `setNumTestsPerEvictionRun(int)`, `setTimeBetweenEvictionRunsMillis(long)`

    - #### setNumTestsPerEvictionRun

          public final void setNumTestsPerEvictionRun(int numTestsPerEvictionRun)

      Sets the maximum number of objects to examine during each run (if any) of the idle object evictor thread. When positive, the number of tests performed for a run will be the minimum of the configured value and the number of idle instances in the pool. When negative, the number of tests performed will be `ceil(`getNumIdle()`/ abs(`getNumTestsPerEvictionRun()`)) which means that when the value is `-n` roughly one nth of the idle objects will be tested per run.`
      Parameters:
        `numTestsPerEvictionRun` - max number of objects to examine during each evictor run
      See Also:
        `getNumTestsPerEvictionRun()`, `setTimeBetweenEvictionRunsMillis(long)`

    - #### getMinEvictableIdleTimeMillis

          public final long getMinEvictableIdleTimeMillis()

      Returns the minimum amount of time an object may sit idle in the pool before it is eligible for eviction by the idle object evictor (if any - see `setTimeBetweenEvictionRunsMillis(long)`). When non-positive, no objects will be evicted from the pool due to idle time alone.
      Returns:
        minimum amount of time an object may sit idle in the pool before it is eligible for eviction
      See Also:
        `setMinEvictableIdleTimeMillis(long)`, `setTimeBetweenEvictionRunsMillis(long)`

    - #### setMinEvictableIdleTimeMillis

          public final void setMinEvictableIdleTimeMillis(long minEvictableIdleTimeMillis)

      Sets the minimum amount of time an object may sit idle in the pool before it is eligible for eviction by the idle object evictor (if any - see `setTimeBetweenEvictionRunsMillis(long)`). When non-positive, no objects will be evicted from the pool due to idle time alone.
      Parameters:
        `minEvictableIdleTimeMillis` - minimum amount of time an object may sit idle in the pool before it is eligible for eviction
      See Also:
        `getMinEvictableIdleTimeMillis()`, `setTimeBetweenEvictionRunsMillis(long)`

    - #### getSoftMinEvictableIdleTimeMillis

          public final long getSoftMinEvictableIdleTimeMillis()

      Returns the minimum amount of time an object may sit idle in the pool before it is eligible for eviction by the idle object evictor (if any - see `setTimeBetweenEvictionRunsMillis(long)`), with the extra condition that at least `minIdle` object instances remain in the pool. This setting is overridden by `getMinEvictableIdleTimeMillis()` (that is, if `getMinEvictableIdleTimeMillis()` is positive, then `getSoftMinEvictableIdleTimeMillis()` is ignored).
      Returns:
        minimum amount of time an object may sit idle in the pool before it is eligible for eviction if minIdle instances are available
      See Also:
        `setSoftMinEvictableIdleTimeMillis(long)`

    - #### setSoftMinEvictableIdleTimeMillis

          public final void setSoftMinEvictableIdleTimeMillis(long softMinEvictableIdleTimeMillis)

      Sets the minimum amount of time an object may sit idle in the pool before it is eligible for eviction by the idle object evictor (if any - see `setTimeBetweenEvictionRunsMillis(long)`), with the extra condition that at least `minIdle` object instances remain in the pool. This setting is overridden by `getMinEvictableIdleTimeMillis()` (that is, if `getMinEvictableIdleTimeMillis()` is positive, then `getSoftMinEvictableIdleTimeMillis()` is ignored).
      Parameters:
        `softMinEvictableIdleTimeMillis` - minimum amount of time an object may sit idle in the pool before it is eligible for eviction if minIdle instances are available
      See Also:
        `getSoftMinEvictableIdleTimeMillis()`

    - #### getEvictionPolicyClassName

          public final String getEvictionPolicyClassName()

      Returns the name of the `EvictionPolicy` implementation that is used by this pool.
      Returns:
        The fully qualified class name of the `EvictionPolicy`
      See Also:
        `setEvictionPolicyClassName(String)`

    - #### setEvictionPolicyClassName

          public final void setEvictionPolicyClassName(String evictionPolicyClassName)

      Sets the name of the `EvictionPolicy` implementation that is used by this pool.
      Parameters:
        `evictionPolicyClassName` - the fully qualified class name of the new eviction policy
      See Also:
        `getEvictionPolicyClassName()`

    - #### close

          public abstract void close()

      Closes the pool, destroys the remaining idle objects and, if registered in JMX, deregisters it.

    - #### isClosed

          public final boolean isClosed()

      Has this pool instance been closed.
      Returns:
        `true` when this pool has been closed.

    - #### evict

          public abstract void evict()
                              throws Exception

      Perform `numTests` idle object eviction tests, evicting examined objects that meet the criteria for eviction. If `testWhileIdle` is true, examined objects are validated when visited (and removed if invalid); otherwise only objects that have been idle for more than `minEvicableIdleTimeMillis` are removed.

      Throws:
        `Exception` - when there is a problem evicting idle objects.

    - #### getJmxName

          public final ObjectName getJmxName()

      Provides the name under which the pool has been registered with the platform MBean server or `null` if the pool has not been registered.
      Returns:
        the JMX name

    - #### getCreationStackTrace

          public final String getCreationStackTrace()

      Provides the stack trace for the call that created this pool. JMX registration may trigger a memory leak so it is important that pools are deregistered when no longer used by calling the `close()` method. This method is provided to assist with identifying code that creates but does not close it thereby creating a memory leak.
      Returns:
        pool creation stack trace

    - #### getBorrowedCount

          public final long getBorrowedCount()

      The total number of objects successfully borrowed from this pool over the lifetime of the pool.
      Returns:
        the borrowed object count

    - #### getReturnedCount

          public final long getReturnedCount()

      The total number of objects returned to this pool over the lifetime of the pool. This excludes attempts to return the same object multiple times.
      Returns:
        the returned object count

    - #### getCreatedCount

          public final long getCreatedCount()

      The total number of objects created for this pool over the lifetime of the pool.
      Returns:
        the created object count

    - #### getDestroyedCount

          public final long getDestroyedCount()

      The total number of objects destroyed by this pool over the lifetime of the pool.
      Returns:
        the destroyed object count

    - #### getDestroyedByEvictorCount

          public final long getDestroyedByEvictorCount()

      The total number of objects destroyed by the evictor associated with this pool over the lifetime of the pool.
      Returns:
        the evictor destroyed object count

    - #### getDestroyedByBorrowValidationCount

          public final long getDestroyedByBorrowValidationCount()

      The total number of objects destroyed by this pool as a result of failing validation during `borrowObject()` over the lifetime of the pool.
      Returns:
        validation destroyed object count

    - #### getMeanActiveTimeMillis

          public final long getMeanActiveTimeMillis()

      The mean time objects are active for based on the last `MEAN_TIMING_STATS_CACHE_SIZE` objects returned to the pool.
      Returns:
        mean time an object has been checked out from the pool among recently returned objects

    - #### getMeanIdleTimeMillis

          public final long getMeanIdleTimeMillis()

      The mean time objects are idle for based on the last `MEAN_TIMING_STATS_CACHE_SIZE` objects borrowed from the pool.
      Returns:
        mean time an object has been idle in the pool among recently borrowed objects

    - #### getMeanBorrowWaitTimeMillis

          public final long getMeanBorrowWaitTimeMillis()

      The mean time threads wait to borrow an object based on the last `MEAN_TIMING_STATS_CACHE_SIZE` objects borrowed from the pool.
      Returns:
        mean time in milliseconds that a recently served thread has had to wait to borrow an object from the pool

    - #### getMaxBorrowWaitTimeMillis

          public final long getMaxBorrowWaitTimeMillis()

      The maximum time a thread has waited to borrow objects from the pool.
      Returns:
        maximum wait time in milliseconds since the pool was created

    - #### getNumIdle

          public abstract int getNumIdle()

      The number of instances currently idle in this pool.
      Returns:
        count of instances available for checkout from the pool

    - #### getSwallowedExceptionListener

          public final SwallowedExceptionListener getSwallowedExceptionListener()

      The listener used (if any) to receive notifications of exceptions unavoidably swallowed by the pool.
      Returns:
        The listener or `null` for no listener

    - #### setSwallowedExceptionListener

          public final void setSwallowedExceptionListener(SwallowedExceptionListener swallowedExceptionListener)

      The listener used (if any) to receive notifications of exceptions unavoidably swallowed by the pool.
      Parameters:
        `swallowedExceptionListener` - The listener or `null` for no listener

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