Module stormpot
Package stormpot

Interface PoolTap<T extends Poolable>

Type Parameters:
T - the type of Poolable contained in the pool, and made available via this pool tap, as determined by the configured allocator.
All Known Subinterfaces:
Pool<T>
All Known Implementing Classes:
BlazePool, BlazePoolSingleThreadedTap, BlazePoolThreadSafeTap, BlazePoolVirtualThreadSafeTap
public interface PoolTap<T extends Poolable>
A PoolTap provides the API for accessing objects in a Pool.

PoolTaps are not necessarily thread-safe, but pools, which extend PoolTap, are always thread-safe.

Author:
Chris Vest
See Also:

  • Method Summary

    Modifier and Type
    Method
    Description
    default <R> Optional<R>
    apply(Timeout timeout, Function<T,R> function)
    Claim an object from the pool and apply the given function to it, returning the result and releasing the object back to the pool.
    T
    claim(Timeout timeout)
    Claim the exclusive rights until released, to an object in the pool.
    default boolean
    supply(Timeout timeout, Consumer<T> consumer)
    Claim an object from the pool and supply it to the given consumer, and then release it back to the pool.
    default T
    tryClaim()
    Returns an object from the pool if the pool contains at least one valid object, otherwise returns null.

  • Method Details

    • claim

      T claim(Timeout timeout) throws PoolException, InterruptedException
      Claim the exclusive rights until released, to an object in the pool. Possibly waiting up to the specified amount of time, as given by the provided Timeout instance, for one to become available if the pool has been depleted. If the timeout elapses before an object can be claimed, then null is returned instead. The timeout will be honoured even if the Allocators allocate methods blocks forever. If the given timeout has a zero or negative value, then the method will not wait.

      If the current thread has already one or more objects currently claimed, then a distinct object will be returned, if one is or becomes available. This means that it is possible for a single thread to deplete the pool, if it so desires. However, doing so is inherently deadlock prone, so avoid claiming more than one object at a time per thread, if at all possible.

      This method may throw a PoolException if the pool have trouble allocating objects. That is, if its assigned Allocator throws exceptions from its allocate method, or returns null.

      An InterruptedException will be thrown if the thread has its interrupted flag set upon entry to this method, or is interrupted while waiting. The interrupted flag on the thread will be cleared after this, as per the general contract of interruptible methods.

      If the pool has been shut down, then an IllegalStateException will be thrown when this method is called. Likewise, if we are waiting for an object to become available, and someone shuts the pool down.

      Here's an example code snippet, where an object is claimed, printed to System.out, and then released back to the pool: 

      Poolable obj = pool.claim(TIMEOUT);
if (obj != null) {
  try {
    System.out.println(obj);
  } finally {
    obj.release();
  }
}

      Memory effects:

      • The release of an object happens-before any subsequent claim or deallocation of that object, and,
      • The allocation of an object happens-before any claim of that object.
      Parameters:
      timeout - The timeout of the maximum permitted time-slice to wait for an object to become available. A timeout with a value of zero or less, means that the call will do no waiting, preferring instead to return early if no objects are available.
      Returns:
      An object of the Poolable subtype T to which the exclusive rights have been claimed, or null if the timeout period elapsed before an object became available.
      Throws:
      PoolException - If an object allocation failed because the Allocator threw an exception from its allocate method, or returned null, or the expiration check threw an exception.
      InterruptedException - if the current thread is interrupted upon entry, or becomes interrupted while waiting.
      IllegalArgumentException - if the timeout argument is null.

    • tryClaim

      default T tryClaim() throws PoolException
      Returns an object from the pool if the pool contains at least one valid object, otherwise returns null. This method will first try to return cached object if available. If no locally cached object is found, it will go through objects in the pool and return the first ready to claim object. If all the objects in the pool is drained, then null will be returned.
      Returns:
      an object from the pool if the pool contains at least one valid object, otherwise returns null.
      Throws:
      PoolException - If an object allocation failed because the Allocator threw an exception from its allocate method, or returned null, or the expiration check threw an exception.

    • apply

      default <R> Optional<R> apply(Timeout timeout, Function<T,R> function) throws InterruptedException
      Claim an object from the pool and apply the given function to it, returning the result and releasing the object back to the pool.

      If an object cannot be claimed within the given timeout, then Optional.empty() is returned instead. The empty() value is also returned if the function returns null.

      Type Parameters:
      R - The return type of the given function.
      Parameters:
      timeout - The timeout of the maximum permitted amount of time to wait for an object to become available. A timeout with a value of zero or less, means that the call will do no waiting, preferring instead to return early if no objects are available.
      function - The function to apply to the claimed object, if any. The function should avoid further claims, since having more than one object claimed at a time per thread is inherently deadlock prone.
      Returns:
      an Optional of either the return value of applying the given function to a claimed object, or empty if the timeout elapsed or the function returned null.
      Throws:
      InterruptedException - if the thread was interrupted.
      See Also:

    • supply

      default boolean supply(Timeout timeout, Consumer<T> consumer) throws InterruptedException
      Claim an object from the pool and supply it to the given consumer, and then release it back to the pool.

      If an object cannot be claimed within the given timeout, then this method returns false. Otherwise, if an object was claimed and supplied to the consumer, the method returns true.

      Parameters:
      timeout - The timeout of the maximum permitted amount of time to wait for an object to become available. A timeout with a value of zero or less, means that the call will do no waiting, preferring instead to return early if no objects are available.
      consumer - The consumer to pass the claimed object to, if any. The consumer should avoid further claims, since having more than one object claimed at a time per thread is inherently deadlock prone.
      Returns:
      true if an object could be claimed within the given timeout and passed to the given consumer, or false otherwise.
      Throws:
      InterruptedException - if the thread was interrupted.
      See Also: