@GwtCompatible(emulated=true) public abstract class AbstractFuture<V> extends InternalFutureFailureAccess implements ListenableFuture<V>
ListenableFuture
, intended for advanced users only. More
common ways to create a ListenableFuture
include instantiating a SettableFuture
,
submitting a task to a ListeningExecutorService
, and deriving a Future
from an
existing one, typically using methods like Futures.transform
and Futures.catching
.
This class implements all methods in ListenableFuture
. Subclasses should provide a way
to set the result of the computation through the protected methods set(Object)
, setFuture(ListenableFuture)
and setException(Throwable)
. Subclasses may also override
afterDone()
, which will be invoked automatically when the future completes. Subclasses
should rarely override other methods.
Modifier and Type | Class and Description |
---|---|
private static class |
AbstractFuture.AtomicHelper |
private static class |
AbstractFuture.Cancellation
A special value to represent cancellation and the 'wasInterrupted' bit.
|
private static class |
AbstractFuture.Failure
A special value to represent failure, when
setException(java.lang.Throwable) is called successfully. |
private static class |
AbstractFuture.Listener
Listeners also form a stack through the
listeners field. |
private static class |
AbstractFuture.SafeAtomicHelper
AbstractFuture.AtomicHelper based on AtomicReferenceFieldUpdater . |
private static class |
AbstractFuture.SetFuture<V>
A special value that encodes the 'setFuture' state.
|
private static class |
AbstractFuture.SynchronizedHelper
AbstractFuture.AtomicHelper based on synchronized and volatile writes. |
(package private) static interface |
AbstractFuture.Trusted<V>
Tag interface marking trusted subclasses.
|
(package private) static class |
AbstractFuture.TrustedFuture<V>
A less abstract subclass of AbstractFuture.
|
private static class |
AbstractFuture.UnsafeAtomicHelper
AbstractFuture.AtomicHelper based on Unsafe . |
private static class |
AbstractFuture.Waiter
Waiter links form a Treiber stack, in the
waiters field. |
Modifier and Type | Field and Description |
---|---|
private static AbstractFuture.AtomicHelper |
ATOMIC_HELPER |
private static boolean |
GENERATE_CANCELLATION_CAUSES |
private AbstractFuture.Listener |
listeners
All listeners.
|
private static java.util.logging.Logger |
log |
private static java.lang.Object |
NULL
A special value to represent
null . |
private static long |
SPIN_THRESHOLD_NANOS |
private java.lang.Object |
value
This field encodes the current state of the future.
|
private AbstractFuture.Waiter |
waiters
All waiting threads.
|
Modifier | Constructor and Description |
---|---|
protected |
AbstractFuture()
Constructor for use by subclasses.
|
Modifier and Type | Method and Description |
---|---|
private void |
addDoneString(java.lang.StringBuilder builder) |
void |
addListener(java.lang.Runnable listener,
java.util.concurrent.Executor executor)
Registers a listener to be run on the given executor.
|
protected void |
afterDone()
Callback method that is called exactly once after the future is completed.
|
boolean |
cancel(boolean mayInterruptIfRunning) |
private static java.util.concurrent.CancellationException |
cancellationExceptionWithCause(java.lang.String message,
java.lang.Throwable cause) |
private AbstractFuture.Listener |
clearListeners(AbstractFuture.Listener onto)
Clears the
listeners list and prepends its contents to onto , least recently
added first. |
private static void |
complete(AbstractFuture<?> future)
Unblocks all threads and runs all listeners.
|
private static void |
executeListener(java.lang.Runnable runnable,
java.util.concurrent.Executor executor)
Submits the given runnable to the given
Executor catching and logging all runtime exceptions thrown by the executor. |
V |
get() |
V |
get(long timeout,
java.util.concurrent.TimeUnit unit) |
private V |
getDoneValue(java.lang.Object obj)
Unboxes
obj . |
private static java.lang.Object |
getFutureValue(ListenableFuture<?> future)
Returns a value that satisfies the contract of the
value field based on the state of
given future. |
private static <V> V |
getUninterruptibly(java.util.concurrent.Future<V> future)
An inlined private copy of
Uninterruptibles.getUninterruptibly(java.util.concurrent.Future<V>) used to break an
internal dependency on other /util/concurrent classes. |
protected void |
interruptTask()
Subclasses can override this method to implement interruption of the future's computation.
|
boolean |
isCancelled() |
boolean |
isDone() |
(package private) void |
maybePropagateCancellationTo(java.util.concurrent.Future<?> related)
If this future has been cancelled (and possibly interrupted), cancels (and possibly interrupts)
the given future (if available).
|
protected java.lang.String |
pendingToString()
Provide a human-readable explanation of why this future has not yet completed.
|
private void |
releaseWaiters()
Releases all threads in the
waiters list, and clears the list. |
private void |
removeWaiter(AbstractFuture.Waiter node)
Marks the given node as 'deleted' (null waiter) and then scans the list to unlink all deleted
nodes.
|
protected boolean |
set(V value)
Sets the result of this
Future unless this Future has already been cancelled or
set (including set asynchronously). |
protected boolean |
setException(java.lang.Throwable throwable)
Sets the failed result of this
Future unless this Future has already been
cancelled or set (including set asynchronously). |
protected boolean |
setFuture(ListenableFuture<? extends V> future)
Sets the result of this
Future to match the supplied input Future once the
supplied Future is done, unless this Future has already been cancelled or set
(including "set asynchronously," defined below). |
java.lang.String |
toString() |
protected java.lang.Throwable |
tryInternalFastPathGetFailure()
Usually returns
null but, if this Future has failed, may optionally
return the cause of the failure. |
private java.lang.String |
userObjectToString(java.lang.Object o)
Helper for printing user supplied objects into our toString method.
|
protected boolean |
wasInterrupted()
Returns true if this future was cancelled with
mayInterruptIfRunning set to true . |
private static final boolean GENERATE_CANCELLATION_CAUSES
private static final java.util.logging.Logger log
private static final long SPIN_THRESHOLD_NANOS
private static final AbstractFuture.AtomicHelper ATOMIC_HELPER
private static final java.lang.Object NULL
null
.private volatile java.lang.Object value
The valid values are:
null
initial state, nothing has happened.
AbstractFuture.Cancellation
terminal state, cancel
was called.
AbstractFuture.Failure
terminal state, setException
was called.
AbstractFuture.SetFuture
intermediate state, setFuture
was called.
NULL
terminal state, set(null)
was called.
set
was called with a non-null
argument.
private volatile AbstractFuture.Listener listeners
private volatile AbstractFuture.Waiter waiters
private void removeWaiter(AbstractFuture.Waiter node)
public V get(long timeout, java.util.concurrent.TimeUnit unit) throws java.lang.InterruptedException, java.util.concurrent.TimeoutException, java.util.concurrent.ExecutionException
The default AbstractFuture
implementation throws InterruptedException
if the
current thread is interrupted during the call, even if the value is already available.
get
in interface java.util.concurrent.Future<V>
java.util.concurrent.CancellationException
java.lang.InterruptedException
java.util.concurrent.TimeoutException
java.util.concurrent.ExecutionException
public V get() throws java.lang.InterruptedException, java.util.concurrent.ExecutionException
The default AbstractFuture
implementation throws InterruptedException
if the
current thread is interrupted during the call, even if the value is already available.
get
in interface java.util.concurrent.Future<V>
java.util.concurrent.CancellationException
java.lang.InterruptedException
java.util.concurrent.ExecutionException
private V getDoneValue(java.lang.Object obj) throws java.util.concurrent.ExecutionException
java.util.concurrent.ExecutionException
public boolean isDone()
isDone
in interface java.util.concurrent.Future<V>
public boolean isCancelled()
isCancelled
in interface java.util.concurrent.Future<V>
public boolean cancel(boolean mayInterruptIfRunning)
If a cancellation attempt succeeds on a Future
that had previously been set asynchronously, then the cancellation will also be propagated to the delegate
Future
that was supplied in the setFuture
call.
Rather than override this method to perform additional cancellation work or cleanup,
subclasses should override afterDone()
, consulting isCancelled()
and wasInterrupted()
as necessary. This ensures that the work is done even if the future is
cancelled without a call to cancel
, such as by calling setFuture(cancelledFuture)
.
cancel
in interface java.util.concurrent.Future<V>
protected void interruptTask()
cancel(true)
.
The default implementation does nothing.
This method is likely to be deprecated. Prefer to override afterDone()
, checking
wasInterrupted()
to decide whether to interrupt your task.
protected final boolean wasInterrupted()
mayInterruptIfRunning
set to true
.public void addListener(java.lang.Runnable listener, java.util.concurrent.Executor executor)
Future
's computation is complete or, if the computation is already complete, immediately.
There is no guaranteed ordering of execution of listeners, but any listener added through this method is guaranteed to be called once the computation is complete.
Exceptions thrown by a listener will be propagated up to the executor. Any exception thrown
during Executor.execute
(e.g., a RejectedExecutionException
or an exception
thrown by direct execution) will be caught and
logged.
Note: For fast, lightweight listeners that would be safe to execute in any thread, consider
MoreExecutors.directExecutor()
. Otherwise, avoid it. Heavyweight directExecutor
listeners can cause problems, and these problems can be difficult to reproduce because they
depend on timing. For example:
addListener
. That caller may be a
UI thread or other latency-sensitive thread. This can harm UI responsiveness.
Future
. That
thread may be an internal system thread such as an RPC network thread. Blocking that
thread may stall progress of the whole system. It may even cause a deadlock.
directExecutor
listeners.
This is the most general listener interface. For common operations performed using
listeners, see Futures
. For a simplified but general listener interface, see addCallback()
.
Memory consistency effects: Actions in a thread prior to adding a listener happen-before its execution begins, perhaps in another thread.
Guava implementations of ListenableFuture
promptly release references to listeners
after executing them.
addListener
in interface ListenableFuture<V>
listener
- the listener to run when the computation is completeexecutor
- the executor to run the listener inprotected boolean set(V value)
Future
unless this Future
has already been cancelled or
set (including set asynchronously). When a call to this method returns,
the Future
is guaranteed to be done only if the call was
accepted (in which case it returns true
). If it returns false
, the Future
may have previously been set asynchronously, in which case its result may not be known
yet. That result, though not yet known, cannot be overridden by a call to a set*
method, only by a call to cancel(boolean)
.value
- the value to be used as the resultFuture
protected boolean setException(java.lang.Throwable throwable)
Future
unless this Future
has already been
cancelled or set (including set asynchronously). When a call to this
method returns, the Future
is guaranteed to be done only if
the call was accepted (in which case it returns true
). If it returns false
, the
Future
may have previously been set asynchronously, in which case its result may not be
known yet. That result, though not yet known, cannot be overridden by a call to a set*
method, only by a call to cancel(boolean)
.throwable
- the exception to be used as the failed resultFuture
protected boolean setFuture(ListenableFuture<? extends V> future)
Future
to match the supplied input Future
once the
supplied Future
is done, unless this Future
has already been cancelled or set
(including "set asynchronously," defined below).
If the supplied future is done when this method is called and the call
is accepted, then this future is guaranteed to have been completed with the supplied future by
the time this method returns. If the supplied future is not done and the call is accepted, then
the future will be set asynchronously. Note that such a result, though not yet known,
cannot be overridden by a call to a set*
method, only by a call to cancel(boolean)
.
If the call setFuture(delegate)
is accepted and this Future
is later
cancelled, cancellation will be propagated to delegate
. Additionally, any call to
setFuture
after any cancellation will propagate cancellation to the supplied Future
.
Note that, even if the supplied future is cancelled and it causes this future to complete,
it will never trigger interruption behavior. In particular, it will not cause this future to
invoke the interruptTask()
method, and the wasInterrupted()
method will not
return true
.
future
- the future to delegate toFuture
was not previously
cancelled or set.private static java.lang.Object getFutureValue(ListenableFuture<?> future)
value
field based on the state of
given future.
This is approximately the inverse of getDoneValue(Object)
private static <V> V getUninterruptibly(java.util.concurrent.Future<V> future) throws java.util.concurrent.ExecutionException
Uninterruptibles.getUninterruptibly(java.util.concurrent.Future<V>)
used to break an
internal dependency on other /util/concurrent classes.java.util.concurrent.ExecutionException
private static void complete(AbstractFuture<?> future)
@Beta protected void afterDone()
If interruptTask()
is also run during completion, afterDone()
runs after it.
The default implementation of this method in AbstractFuture
does nothing. This is
intended for very lightweight cleanup work, for example, timing statistics or clearing fields.
If your task does anything heavier consider, just using a listener with an executor.
protected final java.lang.Throwable tryInternalFastPathGetFailure()
null
but, if this Future
has failed, may optionally
return the cause of the failure. "Failure" means specifically "completed with an exception"; it
does not include "was cancelled." To be explicit: If this method returns a non-null value,
then:
isDone()
must return true
isCancelled()
must return false
get()
must not block, and it must throw an ExecutionException
with the
return value of this method as its cause
This method is protected
so that classes like com.google.common.util.concurrent.SettableFuture
do not expose it to their users as an
instance method. In the unlikely event that you need to call this method, call InternalFutures.tryInternalFastPathGetFailure(InternalFutureFailureAccess)
.
tryInternalFastPathGetFailure
in class InternalFutureFailureAccess
final void maybePropagateCancellationTo(java.util.concurrent.Future<?> related)
private void releaseWaiters()
waiters
list, and clears the list.private AbstractFuture.Listener clearListeners(AbstractFuture.Listener onto)
listeners
list and prepends its contents to onto
, least recently
added first.public java.lang.String toString()
toString
in class java.lang.Object
protected java.lang.String pendingToString()
private void addDoneString(java.lang.StringBuilder builder)
private java.lang.String userObjectToString(java.lang.Object o)
private static void executeListener(java.lang.Runnable runnable, java.util.concurrent.Executor executor)
Executor
catching and logging all runtime exceptions thrown by the executor.private static java.util.concurrent.CancellationException cancellationExceptionWithCause(java.lang.String message, java.lang.Throwable cause)