freeBuckets = freeBuckets.next;
  private VM_LockBucket allocate () {    VM_LockBucket b = freeBuckets;    freeBuckets = freeBuckets.next;    if (b == null) {      VM.sysFail("Out of space for VM_LockNursery; increase ALLOC");    }    if (STATS) lockNumber++;    return b;  }