diff -r 000000000000 -r 959103a6100f src/share/classes/com/sun/tools/sjavac/server/CompilerPool.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/share/classes/com/sun/tools/sjavac/server/CompilerPool.java	Wed Apr 27 01:34:52 2016 +0800
@@ -0,0 +1,163 @@
+/*
+ * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package com.sun.tools.sjavac.server;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Semaphore;
+import java.util.Stack;
+import java.util.concurrent.Future;
+
+/** The compiler pool maintains compiler threads.
+ *
+ * <p><b>This is NOT part of any supported API.
+ * If you write code that depends on this, you do so at your own
+ * risk.  This code and its internal interfaces are subject to change
+ * or deletion without notice.</b></p>
+ */
+public class CompilerPool {
+    // The javac server that created this pool.
+    private JavacServer javacServer;
+    // A semaphore protecting the poolsize number of threads.
+    private Semaphore available;
+    // The stack of compiler threads.
+    private Stack<CompilerThread> compilers = new Stack<CompilerThread>();
+    // And the executor server to spawn threads.
+    private final ExecutorService executorPool;
+    // How many requests are active right now?
+    private int concurrentRequests = 0;
+    // When was the last request finished?
+    private long lastRequestFinished = 0;
+    // The total number of requests to this pool.
+    private int numRequests = 0;
+    // Protect access to the three above values.
+    private static final Object conc = new Object();
+
+    /**
+     * Return the javac server that this pool belongs to.
+     */
+    public JavacServer getJavacServer() {
+        return javacServer;
+    }
+
+    /**
+     * Return how many threads are running at this very moment.
+     */
+    public int numActiveRequests()
+    {
+        synchronized (conc) {
+            return concurrentRequests;
+        }
+    }
+
+    /**
+     * Return when the last request was finished.
+     * I.e. the pool has been idle since.
+     */
+    public long lastRequestFinished()
+    {
+        synchronized (conc) {
+            return lastRequestFinished;
+        }
+    }
+
+    /**
+     * Up the number of active requests.
+     */
+    public int startRequest() {
+        int n;
+        synchronized (conc) {
+            concurrentRequests++;
+            numRequests++;
+            n = numRequests;
+        }
+        return n;
+    }
+
+    /**
+     * Down the number of active requests. Return the current time.
+     */
+    public long stopRequest() {
+        synchronized (conc) {
+            concurrentRequests--;
+            lastRequestFinished = System.currentTimeMillis();
+        }
+        return lastRequestFinished;
+    }
+
+    /**
+     * Create a new compiler pool.
+     */
+    CompilerPool(int poolsize, JavacServer server) {
+        available = new Semaphore(poolsize, true);
+        javacServer = server;
+        executorPool = Executors.newFixedThreadPool(poolsize);
+        lastRequestFinished = System.currentTimeMillis();
+    }
+
+    /**
+     * Execute a compiler thread.
+     */
+    public void execute(CompilerThread ct) {
+        executorPool.execute(ct);
+    }
+
+    /**
+     * Execute a minor task, for example generating bytecodes and writing them to disk,
+     * that belong to a major compiler thread task.
+     */
+    public Future<?> executeSubtask(CompilerThread t, Runnable r) {
+        return executorPool.submit(r);
+    }
+
+    /**
+     * Shutdown the pool.
+     */
+    public void shutdown() {
+        executorPool.shutdown();
+    }
+
+    /**
+     * Acquire a compiler thread from the pool, or block until a thread is available.
+     * If the pools is empty, create a new thread, but never more than is "available".
+     */
+    public CompilerThread grabCompilerThread() throws InterruptedException {
+        available.acquire();
+        if (compilers.empty()) {
+            return new CompilerThread(this);
+        }
+        return compilers.pop();
+    }
+
+    /**
+     * Return the specified compiler thread to the pool.
+     */
+    public void returnCompilerThread(CompilerThread h) {
+        compilers.push(h);
+        available.release();
+    }
+}
+