EDU.oswego.cs.dl.util.concurrent
public class CyclicBarrier extends Object implements Barrier
CyclicBarriers use an all-or-none breakage model
for failed synchronization attempts: If threads
leave a barrier point prematurely because of timeout
or interruption, others will also leave abnormally
(via BrokenBarrierException), until
the barrier is restart
ed. This is usually
the simplest and best strategy for sharing knowledge
about failures among cooperating threads in the most
common usages contexts of Barriers.
This implementation has the property that interruptions
among newly arriving threads can cause as-yet-unresumed
threads from a previous barrier cycle to return out
as broken. This transmits breakage
as early as possible, but with the possible byproduct that
only some threads returning out of a barrier will realize
that it is newly broken. (Others will not realize this until a
future cycle.) (The Rendezvous class has a more uniform, but
sometimes less desirable policy.)
Barriers support an optional Runnable command that is run once per barrier point.
Sample usage Here is a code sketch of a barrier in a parallel decomposition design.
class Solver { final int N; final float[][] data; final CyclicBarrier barrier; class Worker implements Runnable { int myRow; Worker(int row) { myRow = row; } public void run() { while (!done()) { processRow(myRow); try { barrier.barrier(); } catch (InterruptedException ex) { return; } catch (BrokenBarrierException ex) { return; } } } } public Solver(float[][] matrix) { data = matrix; N = matrix.length; barrier = new CyclicBarrier(N); barrier.setBarrierCommand(new Runnable() { public void run() { mergeRows(...); } }); for (int i = 0; i < N; ++i) { new Thread(new Worker(i)).start(); waitUntilDone(); } }
Field Summary | |
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protected Runnable | barrierCommand_ |
protected boolean | broken_ |
protected int | count_ |
protected int | parties_ |
protected int | resets_ |
Constructor Summary | |
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CyclicBarrier(int parties)
Create a CyclicBarrier for the indicated number of parties,
and no command to run at each barrier. | |
CyclicBarrier(int parties, Runnable command)
Create a CyclicBarrier for the indicated number of parties.
and the given command to run at each barrier point. |
Method Summary | |
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int | attemptBarrier(long msecs)
Enter barrier and wait at most msecs for the other parties()-1 threads. |
int | barrier()
Enter barrier and wait for the other parties()-1 threads. |
boolean | broken() |
protected int | doBarrier(boolean timed, long msecs) |
int | parties() |
void | restart()
Reset to initial state. |
Runnable | setBarrierCommand(Runnable command)
Set the command to run at the point at which all threads reach the
barrier. |
Throws: IllegalArgumentException if parties less than or equal to zero.
Throws: IllegalArgumentException if parties less than or equal to zero.
Returns: if not timed out, the arrival index: the number of other parties that were still waiting upon entry. This is a unique value from zero to parties()-1. If it is zero, then the current thread was the last party to hit barrier point and so was responsible for releasing the others.
Throws: BrokenBarrierException
if any other thread
in any previous or current barrier
since either creation or the last restart
operation left the barrier
prematurely due to interruption or time-out. (If so,
the broken
status is also set.)
Threads that are noticed to have been
interrupted after being released are not considered
to have broken the barrier.
In all cases, the interruption
status of the current thread is preserved, so can be tested
by checking Thread.interrupted
. InterruptedException if this thread was interrupted
during the barrier. If so, broken
status is also set. TimeoutException if this thread timed out waiting for
the barrier. If the timeout occured while already in the
barrier, broken
status is also set.
Returns: the arrival index: the number of other parties that were still waiting upon entry. This is a unique value from zero to parties()-1. If it is zero, then the current thread was the last party to hit barrier point and so was responsible for releasing the others.
Throws: BrokenBarrierException if any other thread
in any previous or current barrier
since either creation or the last restart
operation left the barrier
prematurely due to interruption or time-out. (If so,
the broken
status is also set.)
Threads that are notified to have been
interrupted after being released are not considered
to have broken the barrier.
In all cases, the interruption
status of the current thread is preserved, so can be tested
by checking Thread.interrupted
. InterruptedException if this thread was interrupted
during the barrier, and was the one causing breakage.
If so, broken
status is also set.
Parameters: command the command to run. If null, no command is run.
Returns: the previous command