Package org.apache.cassandra.utils.concurrent

Class Ref<T>

  • All Implemented Interfaces:
    RefCounted<T>
    public final class Ref<T>
extends java.lang.Object
implements RefCounted<T>
    An object that needs ref counting does the two following: - defines a Tidy object that will cleanup once it's gone, (this must retain no references to the object we're tracking (only its resources and how to clean up)) Then, one of two options: 1) Construct a Ref directly pointing to it, and always use this Ref; or 2) - implements RefCounted - encapsulates a Ref, we'll call selfRef, to which it proxies all calls to RefCounted behaviours - users must ensure no references to the selfRef leak, or are retained outside of a method scope. (to ensure the selfRef is collected with the object, so that leaks may be detected and corrected)

    This class' functionality is achieved by what may look at first glance like a complex web of references, but boils down to:

    Target --> selfRef --> [Ref.State] <--> Ref.GlobalState --> Tidy ^ | Ref ---------------------------------------- | Global ------------------------------------- So that, if Target is collected, Impl is collected and, hence, so is selfRef.

    Once ref or selfRef are collected, the paired Ref.State's release method is called, which if it had not already been called will update Ref.GlobalState and log an error.

    Once the Ref.GlobalState has been completely released, the Tidy method is called and it removes the global reference to itself so it may also be collected.

    • Field Detail

      • DEBUG_ENABLED

        public static final boolean DEBUG_ENABLED

    • Method Detail

      • release

        public void release()
        Must be called exactly once, when the logical operation for which this Ref was created has terminated. Failure to abide by this contract will result in an error (eventually) being reported, assuming a hard reference to the resource it managed is not leaked.

      • ensureReleased

        public java.lang.Throwable ensureReleased​(java.lang.Throwable accumulate)

      • ensureReleased

        public void ensureReleased()

      • close

        public void close()

      • get

        public T get()

      • tryRef

        public Ref<T> tryRef()
        Specified by:
        tryRef in interface RefCounted<T>
        Returns:
        the a new Ref() to the managed object, incrementing its refcount, or null if it is already released

      • printDebugInfo

        public java.lang.String printDebugInfo()

      • globalCount

        public int globalCount()
        A convenience method for reporting:
        Returns:
        the number of currently extant references globally, including the shared reference

      • getFieldValue

        public static java.lang.Object getFieldValue​(java.lang.Object object,
                                             java.lang.reflect.Field field)

      • setOnLeak

        public static void setOnLeak​(Ref.OnLeak onLeak)

      • shutdownReferenceReaper

        public static void shutdownReferenceReaper​(long timeout,
                                           java.util.concurrent.TimeUnit unit)
                                    throws java.lang.InterruptedException,
                                           java.util.concurrent.TimeoutException
        Throws:
        java.lang.InterruptedException
        java.util.concurrent.TimeoutException