On Dec 6, 2014, at 1:30 PM, Peter Levart <peter.lev...@gmail.com> wrote:
> Now what scares me (might be that I don't have an intimacy with LambdaForm
> class like you do). There is a situation where you publish LambdaForm
> instances via data race.
>
> One form of LambdaForm.transformCache is an array of Transform objects (the
> other two forms are not problematic). Transform class has all fields final
> except the 'referent' field of SoftReference, which holds a LambdaForm
> instance. In the following line:
>
> 377 ta[idx] = key;
>
>
> ...you publish Transform object to an element of array with relaxed write,
> and in the following lines:
>
> 271 } else {
> 272 Transform[] ta = (Transform[])c;
> 273 for (int i = 0; i < ta.length; i++) {
> 274 Transform t = ta[i];
> 275 if (t == null) break;
> 276 if (t.equals(key)) { k = t; break; }
> 277 }
> 278 }
> 279 assert(k == null || key.equals(k));
> 280 return (k != null) ? k.get() : null;
>
>
> ...you obtain the element of the array with no synchronization and a relaxed
> read and might return a non-null referent (the LambdaForm) which is then
> returned as an interned instance.
> Transform still has final fields, thus when constructing a Transform using "key.withResult(form))" i don't think hotspot will reorder the store of the referent, or dependent stores, so that they occur after publication of the key element into the Transform[] array. So i think things are also are ok between putInCache and getInCache. > So can LambdaForm instances be published via data races without fear that > they would appear half-initialized? > AFAICT yes. LambdaForm has final/stable fields and i presume it does not leak in the constructor (even when compiling on construction). See also MethodHandle.updateForm for rare cases where the lambda form of a MethodHandle is updated. Paul. > That's what I didn't know when I used a lazySet coupled with volatile get to > access array elements in my version: > > http://cr.openjdk.java.net/~plevart/misc/LambdaFormEditor.WeakCache/webrev.01/ > > > Regards, Peter
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