Question

当我运行下面的代码时，似乎只有一个核心被javaw.exe使用。

int cores = Runtime.getRuntime().availableProcessors();
System.out.println("Number of cores: " + cores); //8 cores

int partitionSize = alphabet.length / cores;
ExecutorService service = Executors.newFixedThreadPool(cores);
List<Future> futures = new ArrayList<Future>();

for (int c = 0; c < cores; c++) {

    char[] part = Arrays.copyOfRange(alphabet, c * partitionSize, (c + 1) * partitionSize);
    futures.add(service.submit(new BruteWorker(part) ));

}

for(Future f : futures)
    f.get();

根据ProcessExplorer的这张图片，我认为我的应用只使用1个CPU吗？如果是，我该如何使用我的所有8核？总CPU利用率为12.5，对应于100％/ 8cores

以下是我从某些println获得的信息：

Number of cores: 8
New thread (id = 11)
New thread (id = 12)
New thread (id = 13)
New thread (id = 14)
New thread (id = 16)
New thread (id = 15)
New thread (id = 17)
New thread (id = 18)
10000000 tries on thread id = 12
20000000 tries on thread id = 12
30000000 tries on thread id = 12
40000000 tries on thread id = 12
50000000 tries on thread id = 12
60000000 tries on thread id = 12

为什么其他线程什么都不做？

BruteWorker类：

public class BruteWorker implements Runnable {
    private static final char[] alphabet = "eaistnrulodmpcvqgbfjhzxykw0123456789!@#$%&*".toCharArray();
    private static final int maxLength = 8;
    private static Map<String, String> hashes;
    private static MessageDigest md ;
    private char[] partition;
    private long nbTries = 0;

    BruteWorker(char[] partition, Map<String, String> hashes) {
        this.partition = partition;
        this.hashes = hashes;
    }

    public void run() {
        System.out.println("New thread (id = "+ Thread.currentThread().getId() +")");
        try {
            md = MessageDigest.getInstance("MD5");
            for(char c : this.partition){
                stringPossibilities(String.valueOf(c), maxLength);
            }
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }
        System.out.println("End of thread (id = "+ Thread.currentThread().getId() +")");
    }

    //Recursive class
    private void stringPossibilities(String prefix, int length) {
        nbTries++;
        if((nbTries % 10000000) == 0){
            System.out.println(nbTries + " tries on thread id = "+ Thread.currentThread().getId());
        }
        md.update(prefix.getBytes());
        byte[] bytes = md.digest();
        String md5 = getMd5Hash(prefix);

        if (hashes.containsKey(md5)){
            System.out.println(prefix + " = " + md5);
        }


        if (prefix.length() < length){
            for (int i = 0; i < alphabet.length; i++){
                char c = alphabet[i];
                stringPossibilities(prefix + c, length);
            }
        }
    }

    private String getMd5Hash(String prefix){
        md.update(prefix.getBytes());
        byte[] bytes = md.digest();
        StringBuilder md5 = new StringBuilder();
        for(int j =0; j < bytes.length; j++){
            md5.append(Integer.toString((bytes[j] & 0xff) + 0x100, 16).substring(1));
        }
        return md5.toString();
    }

}

Answer 1

挣扎着看看这里到底发生了什么，并且同时工作和运行就好了：

public class Main {
    private static final char[] alphabet = "eaistnrulodmpcvqgbfjhzxykw0123456789!@#$%&*".toCharArray();
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        int cores = Runtime.getRuntime().availableProcessors();
        System.out.println("Number of cores: " + cores); //8 cores

        int partitionSize = alphabet.length / cores;
        ExecutorService service = Executors.newFixedThreadPool(cores);
        List<Future> futures = new ArrayList<Future>();

        for (int c = 0; c < cores; c++) {

            char[] part = Arrays.copyOfRange(alphabet, c * partitionSize, (c + 1) * partitionSize);
            futures.add(service.submit(new BruteWorker(part)));

        }

        for(Future f : futures)
            f.get();

        service.shutdown();
        System.out.println("Completed normally");
    }
    public static class BruteWorker implements Runnable {
        private char[] partition;


        BruteWorker(char[] partition) {
            this.partition = partition;
        }

        public void run() {
            System.out.println("New thread (id = "+ Thread.currentThread().getId() +")");
            for (long nbTries = 0; nbTries < 1_000_000_000L; nbTries ++ ) {
                if((nbTries % 10_000_000) == 0){
                    System.out.println(nbTries + " tries on thread id = "+ Thread.currentThread().getId());
                }
            }
            System.out.println("End of thread (id = "+ Thread.currentThread().getId() +")");
        }
    }    
}

Also available (with output) as a gist

请注意，这是对您的代码的破解。

我确实注意到您的代码似乎使用了对MessageDigest和Map<String,String>的静态引用。您的任务可能实际上在其他线程上失败，并且您没有发现这是因为您在等待其他长时间运行的任务之一时被阻止。

尝试捕获run方法中的所有Exceptions并转储堆栈跟踪，这可能具有启发性：

public void run() {
    System.out.println("New thread (id = "+ Thread.currentThread().getId() +")");
    try {
        md = MessageDigest.getInstance("MD5");
        for(char c : this.partition){
            stringPossibilities(String.valueOf(c), maxLength);
        }
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        System.out.println("End of thread (id = "+ Thread.currentThread().getId() +")");
    }
}

改进ExecutorService以在超过1个cpu上执行进程

1 个答案: