Package icyllis.modernui.core

Class MessageQueue

java.lang.Object
icyllis.modernui.core.MessageQueue
public final class MessageQueue extends Object
Low-level class holding the list of messages to be dispatched by a Looper. Messages are not added directly to a MessageQueue, but rather through Handler objects associated with the Looper.

You can retrieve the MessageQueue for the current thread with Looper.myQueue().

  • Method Details

    • isIdle

      public boolean isIdle()
      Returns true if the looper has no pending messages which are due to be processed.

      This method is safe to call from any thread.

      Returns:
      True if the looper is idle.

    • addIdleHandler

      public void addIdleHandler(@NonNull MessageQueue.IdleHandler handler)
      Add a new MessageQueue.IdleHandler to this message queue. This may be removed automatically for you by returning false from IdleHandler.queueIdle() when it is invoked, or explicitly removing it with removeIdleHandler(icyllis.modernui.core.MessageQueue.IdleHandler).

      This method is safe to call from any thread.

      Parameters:
      handler - The IdleHandler to be added.

    • removeIdleHandler

      public void removeIdleHandler(@NonNull MessageQueue.IdleHandler handler)
      Remove an MessageQueue.IdleHandler from the queue that was previously added with addIdleHandler(icyllis.modernui.core.MessageQueue.IdleHandler). If the given object is not currently in the idle list, nothing is done.

      This method is safe to call from any thread.

      Parameters:
      handler - The IdleHandler to be removed.

    • isPolling

      public boolean isPolling()
      Returns whether this looper's thread is currently polling for more work to do. This is a good signal that the loop is still alive rather than being stuck handling a callback. Note that this method is intrinsically racy, since the state of the loop can change before you get the result back.

      This method is safe to call from any thread.

      Returns:
      True if the looper is currently polling for events.

    • postSyncBarrier

      public int postSyncBarrier()
      Posts a synchronization barrier to the Looper's message queue.

      Message processing occurs as usual until the message queue encounters the synchronization barrier that has been posted. When the barrier is encountered, later synchronous messages in the queue are stalled (prevented from being executed) until the barrier is released by calling removeSyncBarrier(int) and specifying the token that identifies the synchronization barrier.

      This method is used to immediately postpone execution of all subsequently posted synchronous messages until a condition is met that releases the barrier. Asynchronous messages (see Message.isAsynchronous()) are exempt from the barrier and continue to be processed as usual.

      This call must be always matched by a call to removeSyncBarrier(int) with the same token to ensure that the message queue resumes normal operation. Otherwise, the application will probably hang!

      Returns:
      A token that uniquely identifies the barrier. This token must be passed to removeSyncBarrier(int) to release the barrier.

    • removeSyncBarrier

      public void removeSyncBarrier(int token)
      Removes a synchronization barrier.
      Parameters:
      token - The synchronization barrier token that was returned by postSyncBarrier().
      Throws:
      IllegalStateException - if the barrier was not found.