LimitLatch (Apache Tomcat 9.0.120 API Documentation)
Description: declaration: package: org.apache.tomcat.util.threads, class: LimitLatch

# Class LimitLatch

java.lang.Object
org.apache.tomcat.util.threads.LimitLatch

public class LimitLatch extends Object
Shared latch that allows the latch to be acquired a limited number of times after which all subsequent requests to acquire the latch will be placed in a FIFO queue until one of the shares is returned.

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `LimitLatch(long limit)`
  Instantiates a LimitLatch object with an initial limit.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `long`
  `countDown()`
  Releases a shared latch, making it available for another thread to use.
  `void`
  `countUpOrAwait()`
  Acquires a shared latch if one is available or waits for one if no shared latch is current available.
  `long`
  `getCount()`
  Returns the current count for the latch
  `long`
  `getLimit()`
  Obtain the current limit.
  `Collection<Thread>`
  `getQueuedThreads()`
  Provide access to the list of threads waiting to acquire this limited shared latch.
  `boolean`
  `hasQueuedThreads()`
  Returns `true` if there is at least one thread waiting to acquire the shared lock, otherwise returns `false`.
  `boolean`
  `releaseAll()`
  Releases all waiting threads and causes the `limit` to be ignored until `reset()` is called.
  `void`
  `reset()`
  Resets the latch and initializes the shared acquisition counter to zero.
  `void`
  `setLimit(long limit)`
  Sets a new limit.

  ### Methods inherited from class Object

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

- ## Constructor Details

  - ### LimitLatch

    public LimitLatch(long limit)
    Instantiates a LimitLatch object with an initial limit.
    Parameters:
      `limit` - - maximum number of concurrent acquisitions of this latch

- ## Method Details

  - ### getCount

    public long getCount()
    Returns the current count for the latch
    Returns:
      the current count for latch

  - ### getLimit

    public long getLimit()
    Obtain the current limit.
    Returns:
      the limit

  - ### setLimit

    public void setLimit(long limit)
    Sets a new limit. If the limit is decreased there may be a period where more shares of the latch are acquired than the limit. In this case no more shares of the latch will be issued until sufficient shares have been returned to reduce the number of acquired shares of the latch to below the new limit. If the limit is increased, threads currently in the queue may not be issued one of the newly available shares until the next request is made for a latch.
    Parameters:
      `limit` - The new limit

  - ### countUpOrAwait

    public void countUpOrAwait() throws InterruptedException
    Acquires a shared latch if one is available or waits for one if no shared latch is current available.
    Throws:
      `InterruptedException` - If the current thread is interrupted

  - ### countDown

    public long countDown()
    Releases a shared latch, making it available for another thread to use.
    Returns:
      the previous counter value

  - ### releaseAll

    public boolean releaseAll()
    Releases all waiting threads and causes the `limit` to be ignored until `reset()` is called.
    Returns:
      `true` if release was done

  - ### reset

    public void reset()
    Resets the latch and initializes the shared acquisition counter to zero.
    See Also:
      - `releaseAll()`

  - ### hasQueuedThreads

    public boolean hasQueuedThreads()
    Returns `true` if there is at least one thread waiting to acquire the shared lock, otherwise returns `false`.
    Returns:
      `true` if threads are waiting

  - ### getQueuedThreads

    public Collection<Thread> getQueuedThreads()
    Provide access to the list of threads waiting to acquire this limited shared latch.
    Returns:
      a collection of threads