Sample usages: * @@ -143,14 +142,14 @@ import java.util.concurrent.locks.LockSu * } * }; * phaser.register(); - * for (Runnable task : tasks) { + * for (final Runnable task : tasks) { * phaser.register(); * new Thread() { * public void run() { * do { * task.run(); * phaser.arriveAndAwaitAdvance(); - * } while(!phaser.isTerminated(); + * } while (!phaser.isTerminated()); * } * }.start(); * } @@ -159,49 +158,45 @@ import java.util.concurrent.locks.LockSu * * If the main task must later await termination, it * may re-register and then execute a similar loop: - *
{@code
+ * {@code
* // ...
* phaser.register();
* while (!phaser.isTerminated())
- * phaser.arriveAndAwaitAdvance();
- * }
+ * phaser.arriveAndAwaitAdvance();}
*
- * Related constructions may be used to await particular phase numbers
+ * Related constructions may be used to await particular phase numbers * in contexts where you are sure that the phase will never wrap around * {@code Integer.MAX_VALUE}. For example: * - *
{@code
- * void awaitPhase(Phaser phaser, int phase) {
- * int p = phaser.register(); // assumes caller not already registered
- * while (p < phase) {
- * if (phaser.isTerminated())
- * // ... deal with unexpected termination
- * else
- * p = phaser.arriveAndAwaitAdvance();
- * }
- * phaser.arriveAndDeregister();
+ * {@code
+ * void awaitPhase(Phaser phaser, int phase) {
+ * int p = phaser.register(); // assumes caller not already registered
+ * while (p < phase) {
+ * if (phaser.isTerminated())
+ * // ... deal with unexpected termination
+ * else
+ * p = phaser.arriveAndAwaitAdvance();
* }
- * }
+ * phaser.arriveAndDeregister();
+ * }}
*
*
* To create a set of tasks using a tree of phasers, * you could use code of the following form, assuming a * Task class with a constructor accepting a phaser that * it registers for upon construction: + * *
{@code
- * void build(Task[] actions, int lo, int hi, Phaser b) {
- * int step = (hi - lo) / TASKS_PER_PHASER;
- * if (step > 1) {
- * int i = lo;
- * while (i < hi) {
- * int r = Math.min(i + step, hi);
- * build(actions, i, r, new Phaser(b));
- * i = r;
+ * void build(Task[] actions, int lo, int hi, Phaser ph) {
+ * if (hi - lo > TASKS_PER_PHASER) {
+ * for (int i = lo; i < hi; i += TASKS_PER_PHASER) {
+ * int j = Math.min(i + TASKS_PER_PHASER, hi);
+ * build(actions, i, j, new Phaser(ph));
* }
* } else {
* for (int i = lo; i < hi; ++i)
- * actions[i] = new Task(b);
- * // assumes new Task(b) performs b.register()
+ * actions[i] = new Task(ph);
+ * // assumes new Task(ph) performs ph.register()
* }
* }
* // .. initially called, for n tasks via
@@ -250,7 +245,6 @@ public class Phaser {
*/
private volatile long state;
- private static final int ushortBits = 16;
private static final int ushortMask = 0xffff;
private static final int phaseMask = 0x7fffffff;
@@ -764,13 +758,22 @@ public class Phaser {
}
/**
- * Overridable method to perform an action upon phase advance, and
- * to control termination. This method is invoked whenever the
- * barrier is tripped (and thus all other waiting parties are
- * dormant). If it returns {@code true}, then, rather than advance
- * the phase number, this barrier will be set to a final
- * termination state, and subsequent calls to {@link #isTerminated}
- * will return true.
+ * Overridable method to perform an action upon impending phase
+ * advance, and to control termination. This method is invoked
+ * upon arrival of the party tripping the barrier (when all other
+ * waiting parties are dormant). If this method returns {@code
+ * true}, then, rather than advance the phase number, this barrier
+ * will be set to a final termination state, and subsequent calls
+ * to {@link #isTerminated} will return true. Any (unchecked)
+ * Exception or Error thrown by an invocation of this method is
+ * propagated to the party attempting to trip the barrier, in
+ * which case no advance occurs.
+ *
+ * The arguments to this method provide the state of the phaser
+ * prevailing for the current transition. (When called from within
+ * an implementation of {@code onAdvance} the values returned by
+ * methods such as {@code getPhase} may or may not reliably
+ * indicate the state to which this transition applies.)
*
*
The default version returns {@code true} when the number of
* registered parties is zero. Normally, overrides that arrange
@@ -778,11 +781,12 @@ public class Phaser {
* property.
*
*
You may override this method to perform an action with side
- * effects visible to participating tasks, but it is in general
- * only sensible to do so in designs where all parties register
- * before any arrive, and all {@link #awaitAdvance} at each phase.
- * Otherwise, you cannot ensure lack of interference from other
- * parties during the invocation of this method.
+ * effects visible to participating tasks, but doing so requires
+ * care: Method {@code onAdvance} may be invoked more than once
+ * per transition. Further, unless all parties register before
+ * any arrive, and all {@link #awaitAdvance} at each phase, then
+ * you cannot ensure lack of interference from other parties
+ * during the invocation of this method.
*
* @param phase the phase number on entering the barrier
* @param registeredParties the current number of registered parties