Sample usages: * - *
A Phaser may be used instead of a {@code CountDownLatch} to control - * a one-shot action serving a variable number of parties. The typical - * idiom is for the method setting this up to first register, then - * start the actions, then deregister, as in: + *
A {@code Phaser} may be used instead of a {@code CountDownLatch} + * to control a one-shot action serving a variable number of + * parties. The typical idiom is for the method setting this up to + * first register, then start the actions, then deregister, as in: * *
{@code
* void runTasks(List list) {
* final Phaser phaser = new Phaser(1); // "1" to register self
+ * // create and start threads
* for (Runnable r : list) {
* phaser.register();
* new Thread() {
* public void run() {
* phaser.arriveAndAwaitAdvance(); // await all creation
* r.run();
- * phaser.arriveAndDeregister(); // signal completion
* }
* }.start();
* }
*
- * doSomethingOnBehalfOfWorkers();
- * phaser.arrive(); // allow threads to start
- * int p = phaser.arriveAndDeregister(); // deregister self ...
- * p = phaser.awaitAdvance(p); // ... and await arrival
- * otherActions(); // do other things while tasks execute
- * phaser.awaitAdvance(p); // await final completion
+ * // allow threads to start and deregister self
+ * phaser.arriveAndDeregister();
* }}
*
* One way to cause a set of threads to repeatedly perform actions @@ -139,9 +137,9 @@ import java.util.concurrent.locks.LockSu * phaser.arriveAndDeregister(); // deregister self, don't wait * }} * - *
To create a set of tasks using a tree of Phasers, + *
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 + * 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) {
@@ -249,7 +247,7 @@ public class Phaser {
private final Phaser parent;
/**
- * The root of Phaser tree. Equals this if not in a tree. Used to
+ * The root of phaser tree. Equals this if not in a tree. Used to
* support faster state push-down.
*/
private final Phaser root;
@@ -300,16 +298,16 @@ public class Phaser {
}
/**
- * Creates a new Phaser without any initially registered parties,
+ * Creates a new phaser without any initially registered parties,
* initial phase number 0, and no parent. Any thread using this
- * Phaser will need to first register for it.
+ * phaser will need to first register for it.
*/
public Phaser() {
this(null);
}
/**
- * Creates a new Phaser with the given numbers of registered
+ * Creates a new phaser with the given numbers of registered
* unarrived parties, initial phase number 0, and no parent.
*
* @param parties the number of parties required to trip barrier
@@ -321,7 +319,7 @@ public class Phaser {
}
/**
- * Creates a new Phaser with the given parent, without any
+ * Creates a new phaser with the given parent, without any
* initially registered parties. If parent is non-null this phaser
* is registered with the parent and its initial phase number is
* the same as that of parent phaser.
@@ -341,7 +339,7 @@ public class Phaser {
}
/**
- * Creates a new Phaser with the given parent and numbers of
+ * Creates a new phaser with the given parent and numbers of
* registered unarrived parties. If parent is non-null, this phaser
* is registered with the parent and its initial phase number is
* the same as that of parent phaser.
@@ -463,11 +461,12 @@ public class Phaser {
}
/**
- * Arrives at the barrier, and deregisters from it, without
- * waiting for others. Deregistration reduces number of parties
+ * Arrives at the barrier and deregisters from it without waiting
+ * for others. Deregistration reduces the number of parties
* required to trip the barrier in future phases. If this phaser
* has a parent, and deregistration causes this phaser to have
- * zero parties, this phaser is also deregistered from its parent.
+ * zero parties, this phaser also arrives at and is deregistered
+ * from its parent.
*
* @return the current barrier phase number upon entry to
* this method, or a negative value if terminated
@@ -520,9 +519,11 @@ public class Phaser {
/**
* Arrives at the barrier and awaits others. Equivalent in effect
- * to {@code awaitAdvance(arrive())}. If you instead need to
- * await with interruption of timeout, and/or deregister upon
- * arrival, you can arrange them using analogous constructions.
+ * to {@code awaitAdvance(arrive())}. If you need to await with
+ * interruption or timeout, you can arrange this with an analogous
+ * construction using one of the other forms of the awaitAdvance
+ * method. If instead you need to deregister upon arrival use
+ * {@code arriveAndDeregister}.
*
* @return the phase on entry to this method
* @throws IllegalStateException if not terminated and the number
@@ -533,9 +534,10 @@ public class Phaser {
}
/**
- * Awaits the phase of the barrier to advance from the given
- * value, or returns immediately if argument is negative or this
- * barrier is terminated.
+ * Awaits the phase of the barrier to advance from the given phase
+ * value, or returns immediately if the current phase of the barrier
+ * is not equal to the given phase value or this barrier is
+ * terminated.
*
* @param phase the phase on entry to this method
* @return the phase on exit from this method
@@ -636,16 +638,6 @@ public class Phaser {
}
/**
- * Returns {@code true} if the current phase number equals the given phase.
- *
- * @param phase the phase
- * @return {@code true} if the current phase number equals the given phase
- */
- public final boolean hasPhase(int phase) {
- return phaseOf(getReconciledState()) == phase;
- }
-
- /**
* Returns the number of parties registered at this barrier.
*
* @return the number of parties
@@ -675,9 +667,9 @@ public class Phaser {
}
/**
- * Returns the parent of this phaser, or null if none.
+ * Returns the parent of this phaser, or {@code null} if none.
*
- * @return the parent of this phaser, or null if none
+ * @return the parent of this phaser, or {@code null} if none
*/
public Phaser getParent() {
return parent;
@@ -706,26 +698,22 @@ 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 true, then, rather than advance the
- * phase number, this barrier will be set to a final termination
- * state, and subsequent calls to {@code isTerminated} will
- * return true.
+ * 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.
*
- * The default version returns true when the number of
+ *
The default version returns {@code true} when the number of
* registered parties is zero. Normally, overrides that arrange
* termination for other reasons should also preserve this
* property.
*
- *
You may override this method to perform an action with side
+ *
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 {@code awaitAdvance} at each phase.
- * Otherwise, you cannot ensure lack of interference. In
- * particular, this method may be invoked more than once per
- * transition if other parties successfully register while the
- * invocation of this method is in progress, thus postponing the
- * transition until those parties also arrive, re-triggering this
- * method.
+ * 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.
*
* @param phase the phase number on entering the barrier
* @param registeredParties the current number of registered parties
@@ -930,16 +918,47 @@ public class Phaser {
return p;
}
- // Unsafe mechanics for jsr166y 3rd party package.
+ // Unsafe mechanics
+
+ private static final sun.misc.Unsafe UNSAFE = getUnsafe();
+ private static final long stateOffset =
+ objectFieldOffset("state", Phaser.class);
+
+ private final boolean casState(long cmp, long val) {
+ return UNSAFE.compareAndSwapLong(this, stateOffset, cmp, val);
+ }
+
+ private static long objectFieldOffset(String field, Class klazz) {
+ try {
+ return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
+ } catch (NoSuchFieldException e) {
+ // Convert Exception to corresponding Error
+ NoSuchFieldError error = new NoSuchFieldError(field);
+ error.initCause(e);
+ throw error;
+ }
+ }
+
+ /**
+ * Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package.
+ * Replace with a simple call to Unsafe.getUnsafe when integrating
+ * into a jdk.
+ *
+ * @return a sun.misc.Unsafe
+ */
private static sun.misc.Unsafe getUnsafe() {
try {
return sun.misc.Unsafe.getUnsafe();
} catch (SecurityException se) {
try {
return java.security.AccessController.doPrivileged
- (new java.security.PrivilegedExceptionAction() {
+ (new java.security
+ .PrivilegedExceptionAction() {
public sun.misc.Unsafe run() throws Exception {
- return getUnsafeByReflection();
+ java.lang.reflect.Field f = sun.misc
+ .Unsafe.class.getDeclaredField("theUnsafe");
+ f.setAccessible(true);
+ return (sun.misc.Unsafe) f.get(null);
}});
} catch (java.security.PrivilegedActionException e) {
throw new RuntimeException("Could not initialize intrinsics",
@@ -947,31 +966,4 @@ public class Phaser {
}
}
}
-
- private static sun.misc.Unsafe getUnsafeByReflection()
- throws NoSuchFieldException, IllegalAccessException {
- java.lang.reflect.Field f =
- sun.misc.Unsafe.class.getDeclaredField("theUnsafe");
- f.setAccessible(true);
- return (sun.misc.Unsafe) f.get(null);
- }
-
- private static long fieldOffset(String fieldName, Class klazz) {
- try {
- return UNSAFE.objectFieldOffset(klazz.getDeclaredField(fieldName));
- } catch (NoSuchFieldException e) {
- // Convert Exception to Error
- NoSuchFieldError error = new NoSuchFieldError(fieldName);
- error.initCause(e);
- throw error;
- }
- }
-
- private static final sun.misc.Unsafe UNSAFE = getUnsafe();
- static final long stateOffset =
- fieldOffset("state", Phaser.class);
-
- final boolean casState(long cmp, long val) {
- return UNSAFE.compareAndSwapLong(this, stateOffset, cmp, val);
- }
}