8152955: Many safepoints of "no vm operation" kind

Reviewed-by: dholmes, rkennke, shade

hotspot/src/share/vm/runtime/safepoint.cpp

@@ -396,9 +396,7 @@ void SafepointSynchronize::begin() {
   GCLocker::set_jni_lock_count(_current_jni_active_count);
 
   if (log_is_enabled(Debug, safepoint)) {
-    VM_Operation *op = VMThread::vm_operation();
-    log_debug(safepoint)("Entering safepoint region: %s",
-                         (op != NULL) ? op->name() : "no vm operation");
+    log_debug(safepoint)("Entering safepoint region: %s", VMThread::vm_safepoint_description());
   }
 
   RuntimeService::record_safepoint_synchronized();
@@ -845,10 +843,8 @@ void SafepointSynchronize::print_safepoint_timeout(SafepointTimeoutReason reason
   // To debug the long safepoint, specify both DieOnSafepointTimeout &
   // ShowMessageBoxOnError.
   if (DieOnSafepointTimeout) {
-    VM_Operation *op = VMThread::vm_operation();
     fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.",
-          SafepointTimeoutDelay,
-          op != NULL ? op->name() : "no vm operation");
+          SafepointTimeoutDelay, VMThread::vm_safepoint_description());
   }
 }
 

hotspot/src/share/vm/runtime/vmThread.cpp

@@ -204,6 +204,7 @@ VMThread*         VMThread::_vm_thread          = NULL;
 VM_Operation*     VMThread::_cur_vm_operation   = NULL;
 VMOperationQueue* VMThread::_vm_queue           = NULL;
 PerfCounter*      VMThread::_perf_accumulated_vm_operation_time = NULL;
+const char*       VMThread::_no_op_reason       = NULL;
 
 
 void VMThread::create() {
@@ -273,6 +274,7 @@ void VMThread::run() {
   }
 
   // 4526887 let VM thread exit at Safepoint
+  _no_op_reason = "Halt";
   SafepointSynchronize::begin();
 
   if (VerifyBeforeExit) {
@@ -380,6 +382,25 @@ void VMThread::evaluate_operation(VM_Operation* op) {
   }
 }
 
+bool VMThread::no_op_safepoint_needed(bool check_time) {
+  if (SafepointALot) {
+    _no_op_reason = "SafepointALot";
+    return true;
+  }
+  if (!SafepointSynchronize::is_cleanup_needed()) {
+    return false;
+  }
+  if (check_time) {
+    long interval = SafepointSynchronize::last_non_safepoint_interval();
+    bool max_time_exceeded = GuaranteedSafepointInterval != 0 &&
+                             (interval > GuaranteedSafepointInterval);
+    if (!max_time_exceeded) {
+      return false;
+    }
+  }
+  _no_op_reason = "Cleanup";
+  return true;
+}
 
 void VMThread::loop() {
   assert(_cur_vm_operation == NULL, "no current one should be executing");
@@ -418,8 +439,7 @@ void VMThread::loop() {
           exit(-1);
         }
 
-        if (timedout && (SafepointALot ||
-                         SafepointSynchronize::is_cleanup_needed())) {
+        if (timedout && VMThread::no_op_safepoint_needed(false)) {
           MutexUnlockerEx mul(VMOperationQueue_lock,
                               Mutex::_no_safepoint_check_flag);
           // Force a safepoint since we have not had one for at least
@@ -542,14 +562,10 @@ void VMThread::loop() {
     //
     // We want to make sure that we get to a safepoint regularly.
     //
-    if (SafepointALot || SafepointSynchronize::is_cleanup_needed()) {
-      long interval          = SafepointSynchronize::last_non_safepoint_interval();
-      bool max_time_exceeded = GuaranteedSafepointInterval != 0 && (interval > GuaranteedSafepointInterval);
-      if (SafepointALot || max_time_exceeded) {
-        HandleMark hm(VMThread::vm_thread());
-        SafepointSynchronize::begin();
-        SafepointSynchronize::end();
-      }
+    if (VMThread::no_op_safepoint_needed(true)) {
+      HandleMark hm(VMThread::vm_thread());
+      SafepointSynchronize::begin();
+      SafepointSynchronize::end();
     }
   }
 }

hotspot/src/share/vm/runtime/vmThread.hpp

@@ -99,7 +99,12 @@ class VMThread: public NamedThread {
   static Monitor * _terminate_lock;
   static PerfCounter* _perf_accumulated_vm_operation_time;
 
+  static const char* _no_op_reason;
+
+  static bool no_op_safepoint_needed(bool check_time);
+
   void evaluate_operation(VM_Operation* op);
+
  public:
   // Constructor
   VMThread();
@@ -126,7 +131,10 @@ class VMThread: public NamedThread {
   static void execute(VM_Operation* op);
 
   // Returns the current vm operation if any.
-  static VM_Operation* vm_operation()             { return _cur_vm_operation;   }
+  static VM_Operation* vm_operation()             { return _cur_vm_operation; }
+
+  // Returns the current vm operation name or set reason
+  static const char* vm_safepoint_description()   { return _cur_vm_operation != NULL ? _cur_vm_operation->name() : _no_op_reason; };
 
   // Returns the single instance of VMThread.
   static VMThread* vm_thread()                    { return _vm_thread; }