public final class MessageQueue extends Object
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()
.
Modifier and Type | Class and Description |
---|---|
static interface |
MessageQueue.IdleHandler
Callback interface for discovering when a thread is going to block
waiting for more messages.
|
static interface |
MessageQueue.OnFileDescriptorEventListener
A listener which is invoked when file descriptor related events occur.
|
Modifier and Type | Method and Description |
---|---|
void |
addIdleHandler(MessageQueue.IdleHandler handler)
Add a new
MessageQueue.IdleHandler to this message queue. |
void |
addOnFileDescriptorEventListener(FileDescriptor fd,
int events,
MessageQueue.OnFileDescriptorEventListener listener)
Adds a file descriptor listener to receive notification when file descriptor
related events occur.
|
protected void |
finalize()
Called by the garbage collector on an object when garbage collection
determines that there are no more references to the object.
|
boolean |
isIdle()
Returns true if the looper has no pending messages which are due to be processed.
|
boolean |
isPolling()
Returns whether this looper's thread is currently polling for more work to do.
|
int |
postSyncBarrier()
Posts a synchronization barrier to the Looper's message queue.
|
void |
removeIdleHandler(MessageQueue.IdleHandler handler)
Remove an
MessageQueue.IdleHandler from the queue that was previously added
with addIdleHandler(android.os.MessageQueue.IdleHandler) . |
void |
removeOnFileDescriptorEventListener(FileDescriptor fd)
Removes a file descriptor listener.
|
void |
removeSyncBarrier(int token)
Removes a synchronization barrier.
|
protected void finalize() throws Throwable
Object
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 JavaTM 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.
public boolean isIdle()
This method is safe to call from any thread.
public void addIdleHandler(MessageQueue.IdleHandler handler)
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(android.os.MessageQueue.IdleHandler)
.
This method is safe to call from any thread.
handler
- The IdleHandler to be added.public void removeIdleHandler(MessageQueue.IdleHandler handler)
MessageQueue.IdleHandler
from the queue that was previously added
with addIdleHandler(android.os.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.
handler
- The IdleHandler to be removed.public boolean isPolling()
This method is safe to call from any thread.
public void addOnFileDescriptorEventListener(FileDescriptor fd, int events, MessageQueue.OnFileDescriptorEventListener listener)
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.
fd
- The file descriptor for which a listener will be registered.events
- The set of events to receive: a combination of the
MessageQueue.OnFileDescriptorEventListener.EVENT_INPUT
,
MessageQueue.OnFileDescriptorEventListener.EVENT_OUTPUT
, and
MessageQueue.OnFileDescriptorEventListener.EVENT_ERROR
event masks. If the requested
set of events is zero, then the listener is unregistered.listener
- The listener to invoke when file descriptor events occur.MessageQueue.OnFileDescriptorEventListener
,
removeOnFileDescriptorEventListener(java.io.FileDescriptor)
public void removeOnFileDescriptorEventListener(FileDescriptor fd)
This method does nothing if no listener has been registered for the specified file descriptor.
fd
- The file descriptor whose listener will be unregistered.MessageQueue.OnFileDescriptorEventListener
,
addOnFileDescriptorEventListener(java.io.FileDescriptor, int, android.os.MessageQueue.OnFileDescriptorEventListener)
public int postSyncBarrier()
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!removeSyncBarrier(int)
to release the barrier.public void removeSyncBarrier(int token)
token
- The synchronization barrier token that was returned by
postSyncBarrier()
.IllegalStateException
- if the barrier was not found.