MessageQueue
  public
  
  final
  
  class
  MessageQueue
  
    extends Object
  
  
  
  
  
  
| java.lang.Object | |
| ↳ | android.os.MessageQueue | 
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().
Summary
| Nested classes | |
|---|---|
| 
        
        
        
        
        interface | MessageQueue.IdleHandlerCallback interface for discovering when a thread is going to block waiting for more messages. | 
| 
        
        
        
        
        interface | MessageQueue.OnFileDescriptorEventListenerA listener which is invoked when file descriptor related events occur. | 
| Public methods | |
|---|---|
| 
        
        
        
        
        
        void | 
      addIdleHandler(MessageQueue.IdleHandler handler)
      Add a new  | 
| 
        
        
        
        
        
        void | 
      addOnFileDescriptorEventListener(FileDescriptor fd, int events, MessageQueue.OnFileDescriptorEventListener listener)
      Adds a file descriptor listener to receive notification when file descriptor related events occur. | 
| 
        
        
        
        
        
        boolean | 
      isIdle()
      Returns true if the looper has no pending messages which are due to be processed and is not blocked on a sync barrier. | 
| 
        
        
        
        
        
        void | 
      removeIdleHandler(MessageQueue.IdleHandler handler)
      Remove an  | 
| 
        
        
        
        
        
        void | 
      removeOnFileDescriptorEventListener(FileDescriptor fd)
      Removes a file descriptor listener. | 
| Protected methods | |
|---|---|
| 
        
        
        
        
        
        void | 
      finalize()
      Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. | 
| Inherited methods | |
|---|---|
Public methods
addIdleHandler
public void addIdleHandler (MessageQueue.IdleHandler handler)
Add a new 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(IdleHandler).
 
This method is safe to call from any thread.
| Parameters | |
|---|---|
| handler | MessageQueue.IdleHandler: The IdleHandler to be added.
 This value cannot benull. | 
addOnFileDescriptorEventListener
public void addOnFileDescriptorEventListener (FileDescriptor fd, int events, MessageQueue.OnFileDescriptorEventListener listener)
Adds a file descriptor listener to receive notification when file descriptor related events occur.
If the file descriptor has already been registered, the specified events and listener will replace any that were previously associated with it. It is not possible to set more than one listener per file descriptor.
It is important to always unregister the listener when the file descriptor is no longer of use.
| Parameters | |
|---|---|
| fd | FileDescriptor: The file descriptor for which a listener will be registered.
 This value cannot benull. | 
| events | int: The set of events to receive: a combination of theOnFileDescriptorEventListener.EVENT_INPUT,OnFileDescriptorEventListener.EVENT_OUTPUT, andOnFileDescriptorEventListener.EVENT_ERRORevent masks.  If the requested
 set of events is zero, then the listener is unregistered.
 Value is either0or a combination ofMessageQueue.OnFileDescriptorEventListener.EVENT_INPUT,MessageQueue.OnFileDescriptorEventListener.EVENT_OUTPUT, andMessageQueue.OnFileDescriptorEventListener.EVENT_ERROR | 
| listener | MessageQueue.OnFileDescriptorEventListener: The listener to invoke when file descriptor events occur.
 This value cannot benull. | 
isIdle
public boolean isIdle ()
Returns true if the looper has no pending messages which are due to be processed and is not blocked on a sync barrier.
This method is safe to call from any thread.
| Returns | |
|---|---|
| boolean | True if the looper is idle. | 
removeIdleHandler
public void removeIdleHandler (MessageQueue.IdleHandler handler)
Remove an IdleHandler from the queue that was previously added
 with addIdleHandler(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 | MessageQueue.IdleHandler: The IdleHandler to be removed.
 This value cannot benull. | 
removeOnFileDescriptorEventListener
public void removeOnFileDescriptorEventListener (FileDescriptor fd)
Removes a file descriptor listener.
This method does nothing if no listener has been registered for the specified file descriptor.
| Parameters | |
|---|---|
| fd | FileDescriptor: The file descriptor whose listener will be unregistered.
 This value cannot benull. | 
Protected methods
finalize
protected void finalize ()
Called by the garbage collector on an object when garbage collection
 determines that there are no more references to the object.
 A subclass overrides the finalize method to dispose of
 system resources or to perform other cleanup.
 
 The general contract of finalize is that it is invoked
 if and when the Java virtual
 machine has determined that there is no longer any
 means by which this object can be accessed by any thread that has
 not yet died, except as a result of an action taken by the
 finalization of some other object or class which is ready to be
 finalized. The finalize method may take any action, including
 making this object available again to other threads; the usual purpose
 of finalize, however, is to perform cleanup actions before
 the object is irrevocably discarded. For example, the finalize method
 for an object that represents an input/output connection might perform
 explicit I/O transactions to break the connection before the object is
 permanently discarded.
 
 The finalize method of class Object performs no
 special action; it simply returns normally. Subclasses of
 Object may override this definition.
 
 The Java programming language does not guarantee which thread will
 invoke the finalize method for any given object. It is
 guaranteed, however, that the thread that invokes finalize will not
 be holding any user-visible synchronization locks when finalize is
 invoked. If an uncaught exception is thrown by the finalize method,
 the exception is ignored and finalization of that object terminates.
 
 After the finalize method has been invoked for an object, no
 further action is taken until the Java virtual machine has again
 determined that there is no longer any means by which this object can
 be accessed by any thread that has not yet died, including possible
 actions by other objects or classes which are ready to be finalized,
 at which point the object may be discarded.
 
 The finalize method is never invoked more than once by a Java
 virtual machine for any given object.
 
 Any exception thrown by the finalize method causes
 the finalization of this object to be halted, but is otherwise
 ignored.
| Throws | |
|---|---|
| Throwable | |
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Last updated 2025-09-17 UTC.
