OpenJDK jdk

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When we create a lot of Strings, CoderResult$Cache.get() becomes the bottleneck.

I got a lot of this kind of thread dump during a load test:

"catalina-exec-458" #26857 daemon prio=5 os_prio=0 tid=0x00007f56a01ab800 nid=0x2517 waiting for monitor entry [0x00007f53d38f7000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at java.nio.charset.CoderResult$Cache.get(CoderResult.java:201)
        - waiting to lock <0x00000005c0e89b58> (a java.nio.charset.CoderResult$1)
        at java.nio.charset.CoderResult$Cache.access$200(CoderResult.java:194)
        at java.nio.charset.CoderResult.malformedForLength(CoderResult.java:236)
        at sun.nio.cs.UTF_8$Decoder.malformedN(UTF_8.java:147)
        at sun.nio.cs.UTF_8$Decoder.decode(UTF_8.java:473)
        at java.lang.StringCoding$StringDecoder.decode(StringCoding.java:153)
        at java.lang.StringCoding.decode(StringCoding.java:193)
        at java.lang.StringCoding.decode(StringCoding.java:254)
        at java.lang.String.<init>(String.java:546)
        at java.lang.String.<init>(String.java:566)

The cache has a synchronized method get(int len). Can we optimize this? Replace this with a lock-free cache?


private static abstract class Cache {

        private Map<Integer,WeakReference<CoderResult>> cache = null;

        protected abstract CoderResult create(int len);

        private synchronized CoderResult get(int len) {
            if (len <= 0)
                throw new IllegalArgumentException("Non-positive length");
            Integer k = new Integer(len);
            WeakReference<CoderResult> w;
            CoderResult e = null;
            if (cache == null) {
                cache = new HashMap<Integer,WeakReference<CoderResult>>();
            } else if ((w = cache.get(k)) != null) {
                e = w.get();
            }
            if (e == null) {
                e = create(len);
                cache.put(k, new WeakReference<CoderResult>(e));
            }
            return e;
        }

    }

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