RFR (S): CR 8005926: (thread) Merge ThreadLocalRandom state into java.lang.Thread

[Doug Lea]

>> (The only way to serialize a TLR represents a strange abuse to
>> begin with. You'd need to save the result of
>> ThreadLocalRandom.current() in a field of a serialized object.
>> Which would be a terrible idea ...)

And so, anything sensible that we do here will have the
(too nice?) effect of "fixing" the errors of anyone
crazy enough to do this -- rather than deserializing into
a non-thread-local ThreadLocalRandom, it will attach to
the common one.

Given all this, I think Heinz's suggestion below looks suitable.
Chris, do you agree about the serialization incantations?

-Doug

On 01/15/13 03:06, Dr Heinz M. Kabutz wrote:
> Right, which means we should also add a readResolve() method to return
> ThreadLocalRandom.current().  All you need to do is add this to the class and
> the format should be compatible with Java 1.7.  This means that if someone made
> the mistake of writing ThreadLocalRandom instances, they would now still be able
> to read, but would instead get the correct instance back for their thread:
>
>     /**
>      * We keep the same serial persistent format as in Java 1.7.
>      */
>     private static final ObjectStreamField[] serialPersistentFields = {
>             new ObjectStreamField("rnd", long.class),
>             new ObjectStreamField("initialized", boolean.class),
>             new ObjectStreamField("pad0", long.class),
>             new ObjectStreamField("pad1", long.class),
>             new ObjectStreamField("pad2", long.class),
>             new ObjectStreamField("pad3", long.class),
>             new ObjectStreamField("pad4", long.class),
>             new ObjectStreamField("pad5", long.class),
>             new ObjectStreamField("pad6", long.class),
>             new ObjectStreamField("pad7", long.class),
>     };
>
>     /**
>      * Writes the ThreadLocalRandom object to the ObjectOutputStream using the
>      * same format as in the past.
>      */
>     private void writeObject(ObjectOutputStream out) throws IOException {
>         ObjectOutputStream.PutField fields = out.putFields();
>         fields.put("rnd", rnd);
>         fields.put("initialized", true);
>         fields.put("pad0", 0L);
>         fields.put("pad1", 0L);
>         fields.put("pad2", 0L);
>         fields.put("pad3", 0L);
>         fields.put("pad4", 0L);
>         fields.put("pad5", 0L);
>         fields.put("pad6", 0L);
>         fields.put("pad7", 0L);
>         out.writeFields();
>     }
>
>     /**
>      * Reads the ThreadLocalRandom object from the stream in order to keep
>      * the format compatible, but does not use any of the read data.
>      */
>     private void readObject(ObjectInputStream in)
>             throws ClassNotFoundException, IOException {
>         in.readFields();
>         // we can ignore the values, since we will replace them in the
>         // readResolve() method anyway
>     }
>
>     /**
>      * Once the ThreadLocalRandom object has been read from the stream, we
>      * throw it away and instead return the correct instance for our thread.
>      */
>     private Object readResolve() {
>         return current();
>     }
>