Add release barriers when allocating objects with concurrent collection

Andrew Haley aph at redhat.com
Thu Aug 27 09:59:18 UTC 2020


8165808 (Add release barriers when allocating objects with concurrent
collection) added release barriers to object allocation paths. But it
only added them in shared code, not in the fast-path code.

I find a comment I added to AArch64 in 2013:

 void MacroAssembler::store_klass(Register dst, Register src) {
+  // FIXME: Should this be a store release?  concurrent gcs assumes
+  // klass length is valid if klass field is not null.

PPC doesn't have release barriers here either:

void MacroAssembler::store_klass(Register dst_oop, Register klass, Register ck) {
  if (UseCompressedClassPointers) {
    encode_klass_not_null(ck, klass);
    stw(ck, oopDesc::klass_offset_in_bytes(), dst_oop);
  } else {
    std(klass, oopDesc::klass_offset_in_bytes(), dst_oop);
  }
}

So what's up? What should we be doing here? Surely if the slow path
code needs the barriers, the fast path does too.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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