org.logicalcobwebs.concurrent
Class FutureResult
java.lang.Object
org.logicalcobwebs.concurrent.FutureResult
public class FutureResult
extends java.lang.Object
A class maintaining a single reference variable serving as the result
of an operation. The result cannot be accessed until it has been set.
Sample Usage
class ImageRenderer { Image render(byte[] raw); }
class App {
Executor executor = ...
ImageRenderer renderer = ...
void display(byte[] rawimage) {
try {
FutureResult futureImage = new FutureResult();
Runnable command = futureImage.setter(new Callable() {
public Object call() { return renderer.render(rawImage); }
});
executor.execute(command);
drawBorders(); // do other things while executing
drawCaption();
drawImage((Image)(futureImage.get())); // use future
}
catch (InterruptedException ex) { return; }
catch (InvocationTargetException ex) { cleanup(); return; }
}
}
[
Introduction to this package. ]
protected InvocationTargetException | exception_ - the exception encountered by operation producing result *
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protected boolean | ready_ - Status -- true after first set *
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protected Object | value_ - The result of the operation *
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void | clear() - Clear the value and exception and set to not-ready,
allowing this FutureResult to be reused.
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protected Object | doGet() - internal utility: either get the value or throw the exception *
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Object | get() - Access the reference, waiting if necessary until it is ready.
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InvocationTargetException | getException() - Get the exception, or null if there isn't one (yet).
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boolean | isReady() - Return whether the reference or exception have been set.
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Object | peek() - Access the reference, even if not ready
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void | set(Object newValue) - Set the reference, and signal that it is ready.
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void | setException(Throwable ex) - Set the exception field, also setting ready status.
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Runnable | setter(Callable function) - Return a Runnable object that, when run, will set the result value.
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Object | timedGet(long msecs) - Wait at most msecs to access the reference.
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exception_
protected InvocationTargetException exception_
the exception encountered by operation producing result *
ready_
protected boolean ready_
Status -- true after first set *
value_
protected Object value_
The result of the operation *
FutureResult
public FutureResult()
Create an initially unset FutureResult
clear
public void clear()
Clear the value and exception and set to not-ready,
allowing this FutureResult to be reused. This is not
particularly recommended and must be done only
when you know that no other object is depending on the
properties of this FutureResult.
doGet
protected Object doGet()
throws InvocationTargetException
internal utility: either get the value or throw the exception *
get
public Object get()
throws InterruptedException,
InvocationTargetException
Access the reference, waiting if necessary until it is ready.
getException
public InvocationTargetException getException()
Get the exception, or null if there isn't one (yet).
This does not wait until the future is ready, so should
ordinarily only be called if you know it is.
- the exception encountered by the operation
setting the future, wrapped in an InvocationTargetException
isReady
public boolean isReady()
Return whether the reference or exception have been set.
- true if has been set. else false
peek
public Object peek()
Access the reference, even if not ready
set
public void set(Object newValue)
Set the reference, and signal that it is ready. It is not
considered an error to set the value more than once,
but it is not something you would normally want to do.
newValue
- The value that will be returned by a subsequent get();
setException
public void setException(Throwable ex)
Set the exception field, also setting ready status.
ex
- The exception. It will be reported out wrapped
within an InvocationTargetException
setter
public Runnable setter(Callable function)
Return a Runnable object that, when run, will set the result value.
function
- - a Callable object whose result will be
held by this FutureResult.
- A Runnable object that, when run, will call the
function and (eventually) set the result.
timedGet
public Object timedGet(long msecs)
throws TimeoutException,
InterruptedException,
InvocationTargetException
Wait at most msecs to access the reference.