synchronized void enqueue (VM_Processor p) {
synchronized void enqueue (VM_Processor p) throws VM_PragmaInterruptible {
  synchronized void enqueue (VM_Processor p) {    if (VM.VerifyAssertions) VM_Scheduler.assert(p.next == null); // not currently on any other queue    if (head == null)      head = p;    else      tail.next = p;    tail = p;  }