Module stormpot
Package stormpot

Class PoolTap<T extends Poolable>

  • Type Parameters:
    T - the type of Poolable contained in the pool, and made
    Direct Known Subclasses:
    Pool
    public abstract class PoolTap<T extends Poolable>
extends java.lang.Object

    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 <mr.chrisvest@gmail.com>
    See Also:
    Pool

    • Method Summary

      All Methods Instance Methods Abstract Methods Concrete Methods 
      Modifier and Type Method Description
      <R> java.util.Optional<R> apply​(Timeout timeout, java.util.function.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.
      abstract T claim​(Timeout timeout)
      Claim the exclusive rights until released, to an object in the pool.
      boolean supply​(Timeout timeout, java.util.function.Consumer<T> consumer)
      Claim an object from the pool and supply it to the given consumer, and then release it back to the pool.

      • Methods inherited from class java.lang.Object

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

    • Method Detail

      • claim

        public abstract T claim​(Timeout timeout)
                 throws PoolException,
                        java.lang.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.
        java.lang.InterruptedException - if the current thread is interrupted upon entry, or becomes interrupted while waiting.
        java.lang.IllegalArgumentException - if the timeout argument is null.

      • apply

        public final <R> java.util.Optional<R> apply​(Timeout timeout,
                                             java.util.function.Function<T,​R> function)
                                      throws java.lang.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:
        java.lang.InterruptedException - if the thread was interrupted.
        See Also:
        The claim method for more details on failure modes and memory effects.

      • supply

        public final boolean supply​(Timeout timeout,
                            java.util.function.Consumer<T> consumer)
                     throws java.lang.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:
        java.lang.InterruptedException - if the thread was interrupted.
        See Also:
        The claim method for more details on failure modes and memory effects.