Java 8以来旧库并发编译失败

Question

数学库colt (版本1.2)依赖于库(gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html). EDU.oswego.cs.dl.util.concurrent并发编译(版本1.3.4)工作在java 7或以前的版本上。但是，编译在java8(javacVersion1.8)上失败。编译器选项-source 1.4 -target 1.4不解决此问题。

原因是，java 8在接口java.util.Map中引入了一种新的“删除”方法：default boolean remove(Object key, Object value)。这个新方法与库类ConcurrentHashMap.java中实现java.util.Map：protected Object remove(Object key, Object value)的方法"remove“冲突。

一旦确定了问题的原因，我就可以通过在库类ConcurrentHashMap.java中重命名方法来解决这个问题。这是可以接受的，因为库方法只受到保护(而不是公共的)。

还有其他确保java 8兼容性的可能性吗？

• 编译器选项？
• 注释("@ForceOverride")？

Answer 1

没有编译器选项或注释可以忽略冲突的方法签名。

如果您(或者，在本例中是colt)不使用新的remove方法，只需在Java7下编译它，在Java8下编译它就不会给您带来任何好处。

但在这种情况下我更喜欢你的解决方案。

Answer 2

考虑到这个类是JRE类(也称为ConcurrentHashMap )的基础，这里不存在名称冲突，因为该方法完全符合预期的语义。会发生冲突，因为这个方法是protected，这个决定很久以前就已经修改过了。也就是说，当您查看这个类的Java5版本时，您将看到它已经有了remove(Object, Object)，并且它是public。它也是接口所要求的，因此必须是public。

因此，最简单的修复方法不是重命名它，而是将修饰符更改为public并调整返回类型。

但是在你的评论中是正确的，从长远来看，最好的解决方案是迁移到那个类根据提交人本人的建议的JRE版本。

注意:在发布J2SE 5.0时，此软件包进入维护模式:只有必要的更正才会发布。J2SE5包java.util.concurrent包括这个包中主要组件的改进、更高效、标准化的版本。请计划转换您的应用程序使用它们。

这是十多年前的…

Answer 3

将colt从java.util.concurrent类迁移到EDU.oswego.cs.dl.util.concurrent类。正如Holger的回答所引用的，并发库作者建议这样做。

Gentoo为colt1.2.0源代码提供了一个补丁：

--- src/cern/colt/matrix/linalg/SmpBlas.java.orig   2015-10-07 22:23:44.969486000 +0000
+++ src/cern/colt/matrix/linalg/SmpBlas.java    2015-10-07 22:29:15.475486000 +0000
@@ -10,7 +10,8 @@

 import cern.colt.matrix.DoubleMatrix1D;
 import cern.colt.matrix.DoubleMatrix2D;
-import EDU.oswego.cs.dl.util.concurrent.FJTask;
+
+import java.util.concurrent.ForkJoinTask;
 /**
 Parallel implementation of the Basic Linear Algebra System for symmetric multi processing boxes.
 Currently only a few algorithms are parallelised; the others are fully functional, but run in sequential mode.
@@ -198,7 +199,7 @@

    // set up concurrent tasks
    int span = width/noOfTasks;
-   final FJTask[] subTasks = new FJTask[noOfTasks];
+   final ForkJoinTask[] subTasks = new ForkJoinTask[noOfTasks];
    for (int i=0; i<noOfTasks; i++) {
        final int offset = i*span;
        if (i==noOfTasks-1) span = width - span*i; // last span may be a bit larger
@@ -217,24 +218,30 @@
            CC = C.viewPart(offset,0,span,p);
        }

-       subTasks[i] = new FJTask() { 
+       subTasks[i] = new ForkJoinTask() { 
            public void run() { 
                seqBlas.dgemm(transposeA,transposeB,alpha,AA,BB,beta,CC); 
                //System.out.println("Hello "+offset); 
            }
+
+      public boolean exec() { return true; }
+      public void setRawResult(Object o) {}
+      public Object getRawResult() {return null;}
        };
    }

    // run tasks and wait for completion
-   try { 
-       this.smp.taskGroup.invoke(
-           new FJTask() {
-               public void run() { 
-                   coInvoke(subTasks); 
-               }
-           }
-       );
-   } catch (InterruptedException exc) {}
+  this.smp.taskGroup.invoke(
+          new ForkJoinTask() {
+              public void run() {  
+                  invokeAll(subTasks); 
+              }
+
+              public boolean exec() { return true; }
+              public void setRawResult(Object o) {}
+              public Object getRawResult() {return null;}
+          }
+          );
 }
 public void dgemv(final boolean transposeA, final double alpha, DoubleMatrix2D A, final DoubleMatrix1D x, final double beta, DoubleMatrix1D y) {
    /*
@@ -271,7 +278,7 @@

    // set up concurrent tasks
    int span = width/noOfTasks;
-   final FJTask[] subTasks = new FJTask[noOfTasks];
+   final ForkJoinTask[] subTasks = new ForkJoinTask[noOfTasks];
    for (int i=0; i<noOfTasks; i++) {
        final int offset = i*span;
        if (i==noOfTasks-1) span = width - span*i; // last span may be a bit larger
@@ -280,24 +287,30 @@
        final DoubleMatrix2D AA = A.viewPart(offset,0,span,n);
        final DoubleMatrix1D yy = y.viewPart(offset,span);

-       subTasks[i] = new FJTask() { 
+       subTasks[i] = new ForkJoinTask() { 
            public void run() { 
                seqBlas.dgemv(transposeA,alpha,AA,x,beta,yy); 
                //System.out.println("Hello "+offset); 
            }
+
+      public boolean exec() { return true; }
+      public void setRawResult(Object o) {}
+      public Object getRawResult() {return null;}
        };
    }

    // run tasks and wait for completion
-   try { 
-       this.smp.taskGroup.invoke(
-           new FJTask() {
-               public void run() { 
-                   coInvoke(subTasks); 
-               }
-           }
-       );
-   } catch (InterruptedException exc) {}
+  this.smp.taskGroup.invoke(
+          new ForkJoinTask() {
+              public void run() {  
+                  invokeAll(subTasks); 
+              }
+
+              public boolean exec() { return true; }
+              public void setRawResult(Object o) {}
+              public Object getRawResult() {return null;}
+          }
+          );
 }
 public void dger(double alpha, DoubleMatrix1D x, DoubleMatrix1D y, DoubleMatrix2D A) {
    seqBlas.dger(alpha,x,y,A);
@@ -369,9 +382,6 @@
 /**
  * Prints various snapshot statistics to System.out; Simply delegates to {@link EDU.oswego.cs.dl.util.concurrent.FJTaskRunnerGroup#stats}.
  */
-public void stats() {
-   if (this.smp!=null) this.smp.stats();
-}
 private double xsum(DoubleMatrix2D A) {
    double[] sums = run(A,true,
        new Matrix2DMatrix2DFunction() {
--- src/cern/colt/matrix/linalg/Smp.java.orig   2015-10-07 21:08:19.443486000 +0000
+++ src/cern/colt/matrix/linalg/Smp.java    2015-10-07 22:28:24.722486000 +0000
@@ -9,12 +9,13 @@
 package cern.colt.matrix.linalg;

 import cern.colt.matrix.DoubleMatrix2D;
-import EDU.oswego.cs.dl.util.concurrent.FJTask;
-import EDU.oswego.cs.dl.util.concurrent.FJTaskRunnerGroup;
+import java.util.concurrent.ForkJoinTask;
+import java.util.concurrent.ForkJoinPool;
+
 /*
 */
 class Smp {
-   protected FJTaskRunnerGroup taskGroup; // a very efficient and light weight thread pool
+   protected ForkJoinPool taskGroup; // a very efficient and light weight thread pool

    protected int maxThreads;   
 /**
@@ -24,41 +25,39 @@
    maxThreads = Math.max(1,maxThreads);
    this.maxThreads = maxThreads;
    if (maxThreads>1) {
-       this.taskGroup = new FJTaskRunnerGroup(maxThreads);
+       this.taskGroup = new ForkJoinPool(maxThreads);
    }
    else { // avoid parallel overhead
        this.taskGroup = null;
    }
 }
-/**
- * Clean up deamon threads, if necessary.
- */
-public void finalize() {
-   if (this.taskGroup!=null) this.taskGroup.interruptAll();
-}
 protected void run(final DoubleMatrix2D[] blocksA, final DoubleMatrix2D[] blocksB, final double[] results, final Matrix2DMatrix2DFunction function) {
-   final FJTask[] subTasks = new FJTask[blocksA.length];
+   final ForkJoinTask[] subTasks = new ForkJoinTask[blocksA.length];
    for (int i=0; i<blocksA.length; i++) {
        final int k = i;
-       subTasks[i] = new FJTask() { 
+       subTasks[i] = new ForkJoinTask() { 
            public void run() {
                double result = function.apply(blocksA[k],blocksB != null ? blocksB[k] : null);
                if (results!=null) results[k] = result; 
                //System.out.print("."); 
            }
+      public boolean exec() { return true; }
+      public void setRawResult(Object o) {}
+      public Object getRawResult() {return null;}
        };
    }

    // run tasks and wait for completion
-   try { 
-       this.taskGroup.invoke(
-           new FJTask() {
-               public void run() { 
-                   coInvoke(subTasks); 
-               }
-           }
-       );
-   } catch (InterruptedException exc) {}
+  this.taskGroup.invoke(
+          new ForkJoinTask() {
+              public void run() {  
+                  invokeAll(subTasks); 
+              }
+              public boolean exec() { return true; }
+              public void setRawResult(Object o) {}
+              public Object getRawResult() {return null;}
+          }
+          );
 }
 protected DoubleMatrix2D[] splitBlockedNN(DoubleMatrix2D A, int threshold, long flops) {
    /*
@@ -186,10 +185,4 @@
    }
    return blocks;
 }
-/**
- * Prints various snapshot statistics to System.out; Simply delegates to {@link EDU.oswego.cs.dl.util.concurrent.FJTaskRunnerGroup#stats}.
- */
-public void stats() {
-   if (this.taskGroup!=null) this.taskGroup.stats();
-}
 }