Class CyclicBarrier
A synchronization aid that allows a set of threads to all wait for each other to reach a common barrier point. CyclicBarriers are useful in programs involving a fixed sized party of threads that must occasionally wait for each other. The barrier is called cyclic because it can be re-used after the waiting threads are released.
A CyclicBarrier supports an optional Runnable command that is run once per barrier point, after the last thread in the party arrives, but before any threads are released. This barrier action is useful for updating shared-state before any of the parties continue.
Sample usage: Here is an example of using 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.await(); >catch (InterruptedException ex) < return; >catch (BrokenBarrierException ex) < return; >> > > public Solver(float[][] matrix) < data = matrix; N = matrix.length; Runnable barrierAction = () ->mergeRows(. ); barrier = new CyclicBarrier(N, barrierAction); List threads = new ArrayList<>(N); for (int i = 0; i < N; i++) < Thread thread = new Thread(new Worker(i)); threads.add(thread); thread.start(); >// wait until done for (Thread thread : threads) try < thread.join(); >catch (InterruptedException ex) < >> > Here, each worker thread processes a row of the matrix, then waits at the barrier until all rows have been processed. When all rows are processed the supplied Runnable barrier action is executed and merges the rows. If the merger determines that a solution has been found then done() will return true and each worker will terminate.
If the barrier action does not rely on the parties being suspended when it is executed, then any of the threads in the party could execute that action when it is released. To facilitate this, each invocation of await() returns the arrival index of that thread at the barrier. You can then choose which thread should execute the barrier action, for example:
The CyclicBarrier uses an all-or-none breakage model for failed synchronization attempts: If a thread leaves a barrier point prematurely because of interruption, failure, or timeout, all other threads waiting at that barrier point will also leave abnormally via BrokenBarrierException (or InterruptedException if they too were interrupted at about the same time).
Memory consistency effects: Actions in a thread prior to calling await() happen-before actions that are part of the barrier action, which in turn happen-before actions following a successful return from the corresponding await() in other threads.
Cycle barrier in java
A synchronization aid that allows a set of threads to all wait for each other to reach a common barrier point. CyclicBarriers are useful in programs involving a fixed sized party of threads that must occasionally wait for each other. The barrier is called cyclic because it can be re-used after the waiting threads are released. A CyclicBarrier supports an optional Runnable command that is run once per barrier point, after the last thread in the party arrives, but before any threads are released. This barrier action is useful for updating shared-state before any of the parties continue. Sample usage: Here is an example of using 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.await(); >catch (InterruptedException ex) < return; >catch (BrokenBarrierException ex) < return; >> > > public Solver(float[][] matrix) < data = matrix; N = matrix.length; Runnable barrierAction = () ->mergeRows(. ); barrier = new CyclicBarrier(N, barrierAction); List threads = new ArrayList<>(N); for (int i = 0; i < N; i++) < Thread thread = new Thread(new Worker(i)); threads.add(thread); thread.start(); >// wait until done for (Thread thread : threads) thread.join(); > > Here, each worker thread processes a row of the matrix then waits at the barrier until all rows have been processed. When all rows are processed the supplied Runnable barrier action is executed and merges the rows. If the merger determines that a solution has been found then done() will return true and each worker will terminate. If the barrier action does not rely on the parties being suspended when it is executed, then any of the threads in the party could execute that action when it is released. To facilitate this, each invocation of await() returns the arrival index of that thread at the barrier. You can then choose which thread should execute the barrier action, for example:
The CyclicBarrier uses an all-or-none breakage model for failed synchronization attempts: If a thread leaves a barrier point prematurely because of interruption, failure, or timeout, all other threads waiting at that barrier point will also leave abnormally via BrokenBarrierException (or InterruptedException if they too were interrupted at about the same time). Memory consistency effects: Actions in a thread prior to calling await() happen-before actions that are part of the barrier action, which in turn happen-before actions following a successful return from the corresponding await() in other threads.
Constructor Summary
Creates a new CyclicBarrier that will trip when the given number of parties (threads) are waiting upon it, and does not perform a predefined action when the barrier is tripped.
Creates a new CyclicBarrier that will trip when the given number of parties (threads) are waiting upon it, and which will execute the given barrier action when the barrier is tripped, performed by the last thread entering the barrier.
Cycle barrier in java
A synchronization aid that allows a set of threads to all wait for each other to reach a common barrier point. CyclicBarriers are useful in programs involving a fixed sized party of threads that must occasionally wait for each other. The barrier is called cyclic because it can be re-used after the waiting threads are released. A CyclicBarrier supports an optional Runnable command that is run once per barrier point, after the last thread in the party arrives, but before any threads are released. This barrier action is useful for updating shared-state before any of the parties continue. Sample usage: Here is an example of using 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.await(); >catch (InterruptedException ex) < return; >catch (BrokenBarrierException ex) < return; >> > > public Solver(float[][] matrix) < data = matrix; N = matrix.length; Runnable barrierAction = new Runnable() < public void run() < mergeRows(. ); >>; barrier = new CyclicBarrier(N, barrierAction); List threads = new ArrayList(N); for (int i = 0; i < N; i++) < Thread thread = new Thread(new Worker(i)); threads.add(thread); thread.start(); >// wait until done for (Thread thread : threads) thread.join(); > > Here, each worker thread processes a row of the matrix then waits at the barrier until all rows have been processed. When all rows are processed the supplied Runnable barrier action is executed and merges the rows. If the merger determines that a solution has been found then done() will return true and each worker will terminate. If the barrier action does not rely on the parties being suspended when it is executed, then any of the threads in the party could execute that action when it is released. To facilitate this, each invocation of await() returns the arrival index of that thread at the barrier. You can then choose which thread should execute the barrier action, for example:
The CyclicBarrier uses an all-or-none breakage model for failed synchronization attempts: If a thread leaves a barrier point prematurely because of interruption, failure, or timeout, all other threads waiting at that barrier point will also leave abnormally via BrokenBarrierException (or InterruptedException if they too were interrupted at about the same time). Memory consistency effects: Actions in a thread prior to calling await() happen-before actions that are part of the barrier action, which in turn happen-before actions following a successful return from the corresponding await() in other threads.
Constructor Summary
Creates a new CyclicBarrier that will trip when the given number of parties (threads) are waiting upon it, and does not perform a predefined action when the barrier is tripped.
Creates a new CyclicBarrier that will trip when the given number of parties (threads) are waiting upon it, and which will execute the given barrier action when the barrier is tripped, performed by the last thread entering the barrier.
Method Summary
Класс CyclicBarrier, примеры реализации кода в Java
В программировании нередко возникают такие ситуации, когда два или больше потока должны находиться в режиме ожидания в предопределенной точке исполнения до тех пор, пока все эти потоки не достигнут данной точки.
Для этой цели в параллельном API предоставляется класс CyclicBarrier. Он позволяет определить объект синхронизации, который приостанавливается до тех пор, пока определенное количество потоков исполнения не достигнет некоторой барьерной точки.
В классе CyclicBarrier определены следующие конструкторы:
где параметр количество_потоков определяет число потоков, которые должны достигнуть некоторого барьера до того, как их исполнение будет продолжено.
Во второй форме конструктора параметр действие определяет поток, который будет исполняться по достижении барьера.
Общая процедура применения класса CyclicBarrier следующая. Прежде всего нужно создать объект класса CyclicBarrier, указав количество ожидающих потоков исполнения.
А когда каждый поток исполнения достигнет барьера, следует вызвать метод await() для данного объекта. В итоге исполнение потока будет приостановлено до тех пор, пока метод await() не будет вызван во всех остальных потоках исполнения.
Как только указанное количество потоков исполнения достигнет барьера, произойдет возврат из метода await(), и выполнение будет возобновлено. А если дополнительно указать какое-нибудь действие, то будет выполнен соответствующий поток.
У метода await() имеются следующие общие формы:
В первой форме ожидание длится до тех пор, пока каждый поток исполнения не достигнет барьерной точки.
А во второй форме ожидание длится только в течение определенного периода времени, определяемого параметром ожидание. Время ожидания указывается в единицах, обозначаемых параметром единица_времени.
В обеих формах возвращается значение, указывающее порядок, в котором потоки исполнения будут достигать барьерной точки. Первый поток исполнения возвращает значение, равное количеству ожидаемых потоков минус 1, а последний поток возвращает нулевое значение.
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В приведенном ниже примере программы демонстрируется применение класса CyclicBarrier. Эта программа ожидает до тех пор, пока все три потока достигнут барьерной точки. Как только это произойдет, будет выполнен поток, определяемый действием типа BarAction.
Class CyclicBarrier
A synchronization aid that allows a set of threads to all wait for each other to reach a common barrier point. CyclicBarriers are useful in programs involving a fixed sized party of threads that must occasionally wait for each other. The barrier is called cyclic because it can be re-used after the waiting threads are released.
A CyclicBarrier supports an optional Runnable command that is run once per barrier point, after the last thread in the party arrives, but before any threads are released. This barrier action is useful for updating shared-state before any of the parties continue.
Sample usage: Here is an example of using 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.await(); >catch (InterruptedException ex) < return; >catch (BrokenBarrierException ex) < return; >> > > public Solver(float[][] matrix) < data = matrix; N = matrix.length; Runnable barrierAction = () ->mergeRows(. ); barrier = new CyclicBarrier(N, barrierAction); List threads = new ArrayList<>(N); for (int i = 0; i < N; i++) < Thread thread = new Thread(new Worker(i)); threads.add(thread); thread.start(); >// wait until done for (Thread thread : threads) try < thread.join(); >catch (InterruptedException ex) < >> > Here, each worker thread processes a row of the matrix, then waits at the barrier until all rows have been processed. When all rows are processed the supplied Runnable barrier action is executed and merges the rows. If the merger determines that a solution has been found then done() will return true and each worker will terminate.
If the barrier action does not rely on the parties being suspended when it is executed, then any of the threads in the party could execute that action when it is released. To facilitate this, each invocation of await() returns the arrival index of that thread at the barrier. You can then choose which thread should execute the barrier action, for example:
The CyclicBarrier uses an all-or-none breakage model for failed synchronization attempts: If a thread leaves a barrier point prematurely because of interruption, failure, or timeout, all other threads waiting at that barrier point will also leave abnormally via BrokenBarrierException (or InterruptedException if they too were interrupted at about the same time).
Memory consistency effects: Actions in a thread prior to calling await() happen-before actions that are part of the barrier action, which in turn happen-before actions following a successful return from the corresponding await() in other threads.