RecursiveAction Class
Definition
Important
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A recursive resultless ForkJoinTask.
[Android.Runtime.Register("java/util/concurrent/RecursiveAction", DoNotGenerateAcw=true)]
public abstract class RecursiveAction : Java.Util.Concurrent.ForkJoinTask[<Android.Runtime.Register("java/util/concurrent/RecursiveAction", DoNotGenerateAcw=true)>]
type RecursiveAction = class
inherit ForkJoinTask- Inheritance
- Attributes
Remarks
A recursive resultless ForkJoinTask. This class establishes conventions to parameterize resultless actions as VoidForkJoinTasks. Because null is the only valid value of type Void, methods such as join always return null upon completion.
<b>Sample Usages.</b> Here is a simple but complete ForkJoin sort that sorts a given long[] array:
{@code
static class SortTask extends RecursiveAction {
final long[] array; final int lo, hi;
SortTask(long[] array, int lo, int hi) {
this.array = array; this.lo = lo; this.hi = hi;
}
SortTask(long[] array) { this(array, 0, array.length); }
protected void compute() {
if (hi - lo < THRESHOLD)
sortSequentially(lo, hi);
else {
int mid = (lo + hi) >>> 1;
invokeAll(new SortTask(array, lo, mid),
new SortTask(array, mid, hi));
merge(lo, mid, hi);
}
}
// implementation details follow:
static final int THRESHOLD = 1000;
void sortSequentially(int lo, int hi) {
Arrays.sort(array, lo, hi);
}
void merge(int lo, int mid, int hi) {
long[] buf = Arrays.copyOfRange(array, lo, mid);
for (int i = 0, j = lo, k = mid; i < buf.length; j++)
array[j] = (k == hi || buf[i] < array[k]) ?
buf[i++] : array[k++];
}
}}
You could then sort anArray by creating new SortTask(anArray) and invoking it in a ForkJoinPool. As a more concrete simple example, the following task increments each element of an array:
{@code
class IncrementTask extends RecursiveAction {
final long[] array; final int lo, hi;
IncrementTask(long[] array, int lo, int hi) {
this.array = array; this.lo = lo; this.hi = hi;
}
protected void compute() {
if (hi - lo < THRESHOLD) {
for (int i = lo; i < hi; ++i)
array[i]++;
}
else {
int mid = (lo + hi) >>> 1;
invokeAll(new IncrementTask(array, lo, mid),
new IncrementTask(array, mid, hi));
}
}
}}
The following example illustrates some refinements and idioms that may lead to better performance: RecursiveActions need not be fully recursive, so long as they maintain the basic divide-and-conquer approach. Here is a class that sums the squares of each element of a double array, by subdividing out only the right-hand-sides of repeated divisions by two, and keeping track of them with a chain of next references. It uses a dynamic threshold based on method getSurplusQueuedTaskCount, but counterbalances potential excess partitioning by directly performing leaf actions on unstolen tasks rather than further subdividing.
{@code
double sumOfSquares(ForkJoinPool pool, double[] array) {
int n = array.length;
Applyer a = new Applyer(array, 0, n, null);
pool.invoke(a);
return a.result;
}
class Applyer extends RecursiveAction {
final double[] array;
final int lo, hi;
double result;
Applyer next; // keeps track of right-hand-side tasks
Applyer(double[] array, int lo, int hi, Applyer next) {
this.array = array; this.lo = lo; this.hi = hi;
this.next = next;
}
double atLeaf(int l, int h) {
double sum = 0;
for (int i = l; i < h; ++i) // perform leftmost base step
sum += array[i] * array[i];
return sum;
}
protected void compute() {
int l = lo;
int h = hi;
Applyer right = null;
while (h - l > 1 && getSurplusQueuedTaskCount() <= 3) {
int mid = (l + h) >>> 1;
right = new Applyer(array, mid, h, right);
right.fork();
h = mid;
}
double sum = atLeaf(l, h);
while (right != null) {
if (right.tryUnfork()) // directly calculate if not stolen
sum += right.atLeaf(right.lo, right.hi);
else {
right.join();
sum += right.result;
}
right = right.next;
}
result = sum;
}
}}
Added in 1.7.
Java documentation for java.util.concurrent.RecursiveAction.
Portions of this page are modifications based on work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License.
Constructors
| RecursiveAction() |
Constructor for subclasses to call. |
| RecursiveAction(IntPtr, JniHandleOwnership) |
A constructor used when creating managed representations of JNI objects; called by the runtime. |
Properties
| Class |
Returns the runtime class of this |
| Exception |
Returns the exception thrown by the base computation, or a
|
| ForkJoinTaskTag |
Returns the tag for this task. (Inherited from ForkJoinTask) |
| Handle |
The handle to the underlying Android instance. (Inherited from Object) |
| IsCancelled |
Returns |
| IsCompletedAbnormally |
Returns |
| IsCompletedNormally |
Returns |
| IsDone |
Returns |
| JniIdentityHashCode | (Inherited from Object) |
| JniPeerMembers | |
| PeerReference | (Inherited from Object) |
| RawRawResult |
Returns the result that would be returned by Join(), even
if this task completed abnormally, or |
| ThresholdClass |
This API supports the Mono for Android infrastructure and is not intended to be used directly from your code. |
| ThresholdType |
This API supports the Mono for Android infrastructure and is not intended to be used directly from your code. |
Methods
| Cancel(Boolean) |
Attempts to cancel execution of this task. (Inherited from ForkJoinTask) |
| Clone() |
Creates and returns a copy of this object. (Inherited from Object) |
| CompareAndSetForkJoinTaskTag(Int16, Int16) |
Atomically conditionally sets the tag value for this task. (Inherited from ForkJoinTask) |
| Complete(Object) |
Completes this task, and if not already aborted or cancelled,
returning the given value as the result of subsequent
invocations of |
| CompleteExceptionally(Throwable) |
Completes this task abnormally, and if not already aborted or
cancelled, causes it to throw the given exception upon
|
| Compute() |
The main computation performed by this task. |
| Dispose() | (Inherited from Object) |
| Dispose(Boolean) | (Inherited from Object) |
| Equals(Object) |
Indicates whether some other object is "equal to" this one. (Inherited from Object) |
| Exec() |
Implements execution conventions for RecursiveActions. |
| Fork() |
Arranges to asynchronously execute this task in the pool the
current task is running in, if applicable, or using the |
| Get() |
Waits if necessary for the computation to complete, and then retrieves its result. (Inherited from ForkJoinTask) |
| Get(Int64, TimeUnit) |
Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available. (Inherited from ForkJoinTask) |
| GetHashCode() |
Returns a hash code value for the object. (Inherited from Object) |
| Invoke() |
Commences performing this task, awaits its completion if
necessary, and returns its result, or throws an (unchecked)
|
| JavaFinalize() |
Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. (Inherited from Object) |
| Join() |
Returns the result of the computation when it #isDone is done. (Inherited from ForkJoinTask) |
| Notify() |
Wakes up a single thread that is waiting on this object's monitor. (Inherited from Object) |
| NotifyAll() |
Wakes up all threads that are waiting on this object's monitor. (Inherited from Object) |
| QuietlyComplete() |
Completes this task normally without setting a value. (Inherited from ForkJoinTask) |
| QuietlyInvoke() |
Commences performing this task and awaits its completion if necessary, without returning its result or throwing its exception. (Inherited from ForkJoinTask) |
| QuietlyJoin() |
Joins this task, without returning its result or throwing its exception. (Inherited from ForkJoinTask) |
| Reinitialize() |
Resets the internal bookkeeping state of this task, allowing a
subsequent |
| SetForkJoinTaskTag(Int16) |
Atomically sets the tag value for this task and returns the old value. (Inherited from ForkJoinTask) |
| SetHandle(IntPtr, JniHandleOwnership) |
Sets the Handle property. (Inherited from Object) |
| SetRawResult(Object) |
Forces the given value to be returned as a result. (Inherited from ForkJoinTask) |
| ToArray<T>() | (Inherited from Object) |
| ToString() |
Returns a string representation of the object. (Inherited from Object) |
| TryUnfork() |
Tries to unschedule this task for execution. (Inherited from ForkJoinTask) |
| UnregisterFromRuntime() | (Inherited from Object) |
| Wait() |
Causes the current thread to wait until it is awakened, typically by being <em>notified</em> or <em>interrupted</em>. (Inherited from Object) |
| Wait(Int64, Int32) |
Causes the current thread to wait until it is awakened, typically by being <em>notified</em> or <em>interrupted</em>, or until a certain amount of real time has elapsed. (Inherited from Object) |
| Wait(Int64) |
Causes the current thread to wait until it is awakened, typically by being <em>notified</em> or <em>interrupted</em>, or until a certain amount of real time has elapsed. (Inherited from Object) |
Explicit Interface Implementations
| IJavaPeerable.Disposed() | (Inherited from Object) |
| IJavaPeerable.DisposeUnlessReferenced() | (Inherited from Object) |
| IJavaPeerable.Finalized() | (Inherited from Object) |
| IJavaPeerable.JniManagedPeerState | (Inherited from Object) |
| IJavaPeerable.SetJniIdentityHashCode(Int32) | (Inherited from Object) |
| IJavaPeerable.SetJniManagedPeerState(JniManagedPeerStates) | (Inherited from Object) |
| IJavaPeerable.SetPeerReference(JniObjectReference) | (Inherited from Object) |
Extension Methods
| JavaCast<TResult>(IJavaObject) |
Performs an Android runtime-checked type conversion. |
| JavaCast<TResult>(IJavaObject) | |
| GetJniTypeName(IJavaPeerable) | |
| GetAsync(IFuture, Int64, TimeUnit) | |
| GetAsync(IFuture) | |