--- a/hotspot/src/os/solaris/vm/os_solaris.cpp	Thu Aug 31 17:06:10 2017 +0000
+++ b/hotspot/src/os/solaris/vm/os_solaris.cpp	Thu Aug 31 20:26:53 2017 -0500
@@ -3442,6 +3442,37 @@
   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);
 }
@@ -3452,7 +3483,7 @@
 
 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;
@@ -3462,7 +3493,7 @@
 
   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();
@@ -3609,45 +3640,6 @@
   }
 }
 
-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,