超线程 java_如果CPU是超线程,是否可以检查Java？

骑猪看日落 2022-11-09 11:17 124阅读 0赞

我想知道我可以运行的最佳线程数。通常，这等于Runtime.getRuntime()。availableProcessors()。

但是，返回的数字是支持超线程的CPU的两倍。现在，对于一些任务，超线程是好的，但对于别人来说，它什么都不做。在我的情况下，我怀疑它没有什么，所以我想知道是否必须将Runtime.getRuntime()。availableProcessors()返回的数字分成两部分。

为此，我必须推断CPU是否超线程。所以我的问题 – 我如何在Java中做？

谢谢。

编辑

好的，我已经对我的代码进行了基准测试。这是我的环境：

> Lenovo ThinkPad W510(即具有4个内核和超线程的i7 CPU)，16G RAM

> Windows 7

> 84压缩CSV文件，压缩尺寸范围从105M到16M

>所有文件在主线程中逐个读取 – 不需要多线程访问HD。

>每个CSV文件行包含一些数据，这是被解析的，一个快速无上下文的测试确定该行是否相关。

>每个相关行包含两个双精度(代表好奇的经度和纬度)，它们被强制为单个Long，然后存储在共享散列集中。

因此，工作线程不会从HD中读取任何内容，但是它们通过解压缩和解析内容来占用自己(使用opencsv库)。

下面是代码，没有无聊的细节：

public void work(File dir) throws IOException, InterruptedException \{

Set allCoordinates = Collections.newSetFromMap(new ConcurrentHashMap());

int n = 6;

// NO WAITING QUEUE !

ThreadPoolExecutor exec = new ThreadPoolExecutor(n, n, 0L, TimeUnit.MILLISECONDS, new SynchronousQueue());

StopWatch sw1 = new StopWatch();

StopWatch sw2 = new StopWatch();

sw1.start();

sw2.start();

sw2.suspend();

for (WorkItem wi : m\_workItems) \{

for (File file : dir.listFiles(wi.fileNameFilter)) \{

MyTask task;

try \{

sw2.resume();

// The only reading from the HD occurs here:

task = new MyTask(file, m\_coordinateCollector, allCoordinates, wi.headerClass, wi.rowClass);

sw2.suspend();

\} catch (IOException exc) \{

System.err.println(String.format("Failed to read %s - %s", file.getName(), exc.getMessage()));

continue;

boolean retry = true;

while (retry) \{

int count = exec.getActiveCount();

try \{

// Fails if the maximum of the worker threads was created and all are busy.

// This prevents us from loading all the files in memory and getting the OOM exception.

exec.submit(task);

retry = false;

\} catch (RejectedExecutionException exc) \{

// Wait for any worker thread to finish

while (exec.getActiveCount() == count) \{

Thread.sleep(100);

exec.shutdown();

exec.awaitTermination(1, TimeUnit.HOURS);

sw1.stop();

sw2.stop();

System.out.println(String.format("Max concurrent threads = %d", n));

System.out.println(String.format("Total file count = %d", m\_stats.getFileCount()));

System.out.println(String.format("Total lines = %d", m\_stats.getTotalLineCount()));

System.out.println(String.format("Total good lines = %d", m\_stats.getGoodLineCount()));

System.out.println(String.format("Total coordinates = %d", allCoordinates.size()));

System.out.println(String.format("Overall elapsed time = %d sec, excluding I/O = %d sec", sw1.getTime() / 1000, (sw1.getTime() - sw2.getTime()) / 1000));

public class MyTask> implements Runnable \{

private final byte\[\] m\_buffer;

private final String m\_name;

private final CoordinateCollector m\_coordinateCollector;

private final Set m\_allCoordinates;

private final Class m\_headerClass;

private final Class m\_rowClass;

public MyTask(File file, CoordinateCollector coordinateCollector, Set allCoordinates,

Class headerClass, Class rowClass) throws IOException \{

m\_coordinateCollector = coordinateCollector;

m\_allCoordinates = allCoordinates;

m\_headerClass = headerClass;

m\_rowClass = rowClass;

m\_name = file.getName();

m\_buffer = Files.toByteArray(file);

@Override

public void run() \{

try \{

m\_coordinateCollector.collect(m\_name, m\_buffer, m\_allCoordinates, m\_headerClass, m\_rowClass);

\} catch (IOException e) \{

e.printStackTrace(); //To change body of catch statement use File | Settings | File Templates.

请在下面找到结果(稍稍改变输出以省略重复的部分)：

Max concurrent threads = 4

Total file count = 84

Total lines = 56395333

Total good lines = 35119231

Total coordinates = 987045

Overall elapsed time = 274 sec, excluding I/O = 266 sec

Max concurrent threads = 6

Overall elapsed time = 218 sec, excluding I/O = 209 sec

Max concurrent threads = 7

Overall elapsed time = 209 sec, excluding I/O = 199 sec

Max concurrent threads = 8

Overall elapsed time = 201 sec, excluding I/O = 192 sec

Max concurrent threads = 9

Overall elapsed time = 198 sec, excluding I/O = 186 sec

你可以自由地得出自己的结论，但是我的这个超线程确实会改善我在具体情况下的表现。另外，有6个工作线程似乎是这个任务和我的机器的正确选择。

超线程 java_如果CPU是超线程,是否可以检查Java？

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