src/hotspot/share/runtime/handshake.cpp

rev 47863 : imported patch 10.08.open.rebase_20171114.rehn
rev 47865 : dholmes CR: Fix indents, trailing spaces and various typos. Add descriptions for the '_cnt', '_max' and '_times" fields, add impl notes to document the type choices.

*** 135,160 ****
        if (handshake_has_timed_out(start_time)) {
          handle_timeout();
        }
  
        // We need to re-think this with SMR ThreadsList.
!       // There is assumption in code that Threads_lock should be lock
!       // during certain phases.
        MutexLockerEx ml(Threads_lock, Mutex::_no_safepoint_check_flag);
        ThreadsListHandle tlh;
        if (tlh.includes(_target)) { 
!         // Warning threads address might be re-used.
!         // handshake_process_by_vmthread will check the semaphore for us again
!         // Since we can't have more then one handshake in flight a reuse of thread address
!         // should be okey since the new thread will not have an operation.
          _target->handshake_process_by_vmthread();
        } else {
!         // We can't warn here is since the thread do cancel_handshake after it have been removed
!         // from ThreadsList. So we should just keep looping here until while below return negative
!         // If we have a bug, then we deadlock here, which is good for debugging.
        }
- 
      } while (!poll_for_completed_thread());
    }
  
    VMOp_Type type() const { return VMOp_HandshakeOneThread; }
  
--- 135,161 ----
        if (handshake_has_timed_out(start_time)) {
          handle_timeout();
        }
  
        // We need to re-think this with SMR ThreadsList.
!       // There is an assumption in the code that the Threads_lock should be
!       // locked during certain phases.
        MutexLockerEx ml(Threads_lock, Mutex::_no_safepoint_check_flag);
        ThreadsListHandle tlh;
        if (tlh.includes(_target)) {
!         // Warning _target's address might be re-used.
!         // handshake_process_by_vmthread will check the semaphore for us again.
!         // Since we can't have more then one handshake in flight a reuse of
!         // _target's address should be okay since the new thread will not have
!         // an operation.
          _target->handshake_process_by_vmthread();
        } else {
!         // We can't warn here since the thread does cancel_handshake after
!         // it has been removed from the ThreadsList. So we should just keep
!         // looping here until while below returns false. If we have a bug,
!         // then we hang here, which is good for debugging.
        }
      } while (!poll_for_completed_thread());
    }
  
    VMOp_Type type() const { return VMOp_HandshakeOneThread; }
  
*** 195,210 ****
        // Have VM thread perform the handshake operation for blocked threads.
        // Observing a blocked state may of course be transient but the processing is guarded
        // by semaphores and we optimistically begin by working on the blocked threads
        {
            // We need to re-think this with SMR ThreadsList.
!           // There is assumption in code that Threads_lock should be lock
!           // during certain phases.
            MutexLockerEx ml(Threads_lock, Mutex::_no_safepoint_check_flag);
            for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
!             // A new thread on the ThreadsList will not have an operation.
!             // Hence is skipped in handshake_process_by_vmthread.
              thr->handshake_process_by_vmthread();
            }
        }
  
        while (poll_for_completed_thread()) {
--- 196,211 ----
        // Have VM thread perform the handshake operation for blocked threads.
        // Observing a blocked state may of course be transient but the processing is guarded
        // by semaphores and we optimistically begin by working on the blocked threads
        {
            // We need to re-think this with SMR ThreadsList.
!           // There is an assumption in the code that the Threads_lock should
!           // be locked during certain phases.
            MutexLockerEx ml(Threads_lock, Mutex::_no_safepoint_check_flag);
            for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
!             // A new thread on the ThreadsList will not have an operation,
!             // hence it is skipped in handshake_process_by_vmthread.
              thr->handshake_process_by_vmthread();
            }
        }
  
        while (poll_for_completed_thread()) {