*** old/src/os/solaris/vm/os_solaris.cpp	Fri Aug 18 12:12:44 2017
--- new/src/os/solaris/vm/os_solaris.cpp	Fri Aug 18 12:12:44 2017

*** 3494,3524 ****
--- 3494,3555 ----
  // Void return because it's a hint and can fail.
  void os::hint_no_preempt() {
    schedctl_start(schedctl_init());
  }
  
+ ////////////////////////////////////////////////////////////////////////////////
+ // suspend/resume support
+ 
+ //  The low-level signal-based suspend/resume support is a remnant from the
+ //  old VM-suspension that used to be for java-suspension, safepoints etc,
+ //  within hotspot. Currently used by JFR's OSThreadSampler
+ //
+ //  The remaining code is greatly simplified from the more general suspension
+ //  code that used to be used.
+ //
+ //  The protocol is quite simple:
+ //  - suspend:
+ //      - sends a signal to the target thread
+ //      - polls the suspend state of the osthread using a yield loop
+ //      - target thread signal handler (SR_handler) sets suspend state
+ //        and blocks in sigsuspend until continued
+ //  - resume:
+ //      - sets target osthread state to continue
+ //      - sends signal to end the sigsuspend loop in the SR_handler
+ //
+ //  Note that the SR_lock plays no role in this suspend/resume protocol,
+ //  but is checked for NULL in SR_handler as a thread termination indicator.
+ //  The SR_lock is, however, used by JavaThread::java_suspend()/java_resume() APIs.
+ //
+ //  Note that resume_clear_context() and suspend_save_context() are needed
+ //  by SR_handler(), so that fetch_frame_from_ucontext() works,
+ //  which in part is used by:
+ //    - Forte Analyzer: AsyncGetCallTrace()
+ //    - StackBanging: get_frame_at_stack_banging_point()
+ //    - JFR: get_topframe()-->....-->get_valid_uc_in_signal_handler()
+ 
  static void resume_clear_context(OSThread *osthread) {
    osthread->set_ucontext(NULL);
  }
  
  static void suspend_save_context(OSThread *osthread, ucontext_t* context) {
    osthread->set_ucontext(context);
  }
  
  static PosixSemaphore sr_semaphore;
  
! void os::Solaris::SR_handler(Thread* thread, ucontext_t* uc) {
! void os::Solaris::SR_handler(Thread* thread, ucontext_t* context) {
    // Save and restore errno to avoid confusing native code with EINTR
    // after sigsuspend.
    int old_errno = errno;
  
    OSThread* osthread = thread->osthread();
    assert(thread->is_VM_thread() || thread->is_Java_thread(), "Must be VMThread or JavaThread");
  
    os::SuspendResume::State current = osthread->sr.state();
    if (current == os::SuspendResume::SR_SUSPEND_REQUEST) {
!     suspend_save_context(osthread, uc);
!     suspend_save_context(osthread, context);
  
      // attempt to switch the state, we assume we had a SUSPEND_REQUEST
      os::SuspendResume::State state = osthread->sr.suspended();
      if (state == os::SuspendResume::SR_SUSPENDED) {
        sigset_t suspend_set;  // signals for sigsuspend()

*** 3661,3709 ****
--- 3692,3701 ----
      do_task(context);
      do_resume(_thread->osthread());
    }
  }
  
  class PcFetcher : public os::SuspendedThreadTask {
   public:
    PcFetcher(Thread* thread) : os::SuspendedThreadTask(thread) {}
    ExtendedPC result();
   protected:
    void do_task(const os::SuspendedThreadTaskContext& context);
   private:
    ExtendedPC _epc;
  };
  
  ExtendedPC PcFetcher::result() {
    guarantee(is_done(), "task is not done yet.");
    return _epc;
  }
  
  void PcFetcher::do_task(const os::SuspendedThreadTaskContext& context) {
    Thread* thread = context.thread();
    OSThread* osthread = thread->osthread();
    if (osthread->ucontext() != NULL) {
      _epc = os::Solaris::ucontext_get_pc((const ucontext_t *) context.ucontext());
    } else {
      // NULL context is unexpected, double-check this is the VMThread
      guarantee(thread->is_VM_thread(), "can only be called for VMThread");
    }
  }
  
  // A lightweight implementation that does not suspend the target thread and
  // thus returns only a hint. Used for profiling only!
  ExtendedPC os::get_thread_pc(Thread* thread) {
    // Make sure that it is called by the watcher and the Threads lock is owned.
    assert(Thread::current()->is_Watcher_thread(), "Must be watcher and own Threads_lock");
    // For now, is only used to profile the VM Thread
    assert(thread->is_VM_thread(), "Can only be called for VMThread");
    PcFetcher fetcher(thread);
    fetcher.run();
    return fetcher.result();
  }
  
  
  // This does not do anything on Solaris. This is basically a hook for being
  // able to use structured exception handling (thread-local exception filters) on, e.g., Win32.
  void os::os_exception_wrapper(java_call_t f, JavaValue* value,
                                const methodHandle& method, JavaCallArguments* args,
                                Thread* thread) {