8325872: Make GuaranteedSafepointInterval default 0

Reviewed-by: shade, eosterlund, dcubed

src/hotspot/share/runtime/arguments.cpp

@@ -3646,6 +3646,11 @@ jint Arguments::parse(const JavaVMInitArgs* initial_cmd_args) {
 
   apply_debugger_ergo();
 
+  // The VMThread needs to stop now and then to execute these debug options.
+  if ((HandshakeALot || SafepointALot) && FLAG_IS_DEFAULT(GuaranteedSafepointInterval)) {
+    FLAG_SET_DEFAULT(GuaranteedSafepointInterval, 1000);
+  }
+
   if (log_is_enabled(Info, arguments)) {
     LogStream st(Log(arguments)::info());
     Arguments::print_on(&st);

src/hotspot/share/runtime/globals.hpp

@@ -744,9 +744,8 @@ const int ObjectAlignmentInBytes = 8;
                                                                             \
   product(int, MonitorUsedDeflationThreshold, 90, DIAGNOSTIC,               \
           "Percentage of used monitors before triggering deflation (0 is "  \
-          "off). The check is performed on GuaranteedSafepointInterval, "   \
-          "AsyncDeflationInterval or GuaranteedAsyncDeflationInterval, "    \
-          "whichever is lower.")                                            \
+          "off). The check is performed on AsyncDeflationInterval or "      \
+          "GuaranteedAsyncDeflationInterval, whichever is lower.")          \
           range(0, 100)                                                     \
                                                                             \
   product(uintx, NoAsyncDeflationProgressMax, 3, DIAGNOSTIC,                \
@@ -1277,7 +1276,7 @@ const int ObjectAlignmentInBytes = 8;
                                                                             \
   /* notice: the max range value here is max_jint, not max_intx  */         \
   /* because of overflow issue                                   */         \
-  product(intx, GuaranteedSafepointInterval, 1000, DIAGNOSTIC,              \
+  product(intx, GuaranteedSafepointInterval, 0, DIAGNOSTIC,                 \
           "Guarantee a safepoint (at least) every so many milliseconds "    \
           "(0 means none)")                                                 \
           range(0, max_jint)                                                \

src/hotspot/share/runtime/monitorDeflationThread.cpp

@@ -50,11 +50,7 @@ void MonitorDeflationThread::initialize() {
 
 void MonitorDeflationThread::monitor_deflation_thread_entry(JavaThread* jt, TRAPS) {
 
-  // We wait for the lowest of these three intervals:
-  //  - GuaranteedSafepointInterval
-  //      While deflation is not related to safepoint anymore, this keeps compatibility with
-  //      the old behavior when deflation also happened at safepoints. Users who set this
-  //      option to get more/less frequent deflations would be served with this option.
+  // We wait for the lowest of these two intervals:
   //  - AsyncDeflationInterval
   //      Normal threshold-based deflation heuristic checks the conditions at this interval.
   //      See is_async_deflation_needed().
@@ -63,9 +59,6 @@ void MonitorDeflationThread::monitor_deflation_thread_entry(JavaThread* jt, TRAP
   //      See is_async_deflation_needed().
   //
   intx wait_time = max_intx;
-  if (GuaranteedSafepointInterval > 0) {
-    wait_time = MIN2(wait_time, GuaranteedSafepointInterval);
-  }
   if (AsyncDeflationInterval > 0) {
     wait_time = MIN2(wait_time, AsyncDeflationInterval);
   }

src/hotspot/share/runtime/vmThread.cpp

@@ -308,40 +308,26 @@ class HandshakeALotClosure : public HandshakeClosure {
   }
 };
 
-bool VMThread::handshake_alot() {
+bool VMThread::handshake_or_safepoint_alot() {
   assert(_cur_vm_operation == nullptr, "should not have an op yet");
   assert(_next_vm_operation == nullptr, "should not have an op yet");
-  if (!HandshakeALot) {
+  if (!HandshakeALot && !SafepointALot) {
     return false;
   }
-  static jlong last_halot_ms = 0;
+  static jlong last_alot_ms = 0;
   jlong now_ms = nanos_to_millis(os::javaTimeNanos());
-  // If only HandshakeALot is set, but GuaranteedSafepointInterval is 0,
-  // we emit a handshake if it's been more than a second since the last one.
+  // If HandshakeALot or SafepointALot are set, but GuaranteedSafepointInterval is explicitly
+  // set to 0 on the command line, we emit the operation if it's been more than a second
+  // since the last one.
   jlong interval = GuaranteedSafepointInterval != 0 ? GuaranteedSafepointInterval : 1000;
-  jlong deadline_ms = interval + last_halot_ms;
+  jlong deadline_ms = interval + last_alot_ms;
   if (now_ms > deadline_ms) {
-    last_halot_ms = now_ms;
+    last_alot_ms = now_ms;
     return true;
   }
   return false;
 }
 
-void VMThread::setup_periodic_safepoint_if_needed() {
-  assert(_cur_vm_operation  == nullptr, "Already have an op");
-  assert(_next_vm_operation == nullptr, "Already have an op");
-  // Check for a cleanup before SafepointALot to keep stats correct.
-  jlong interval_ms = SafepointTracing::time_since_last_safepoint_ms();
-  bool max_time_exceeded = GuaranteedSafepointInterval != 0 &&
-                           (interval_ms >= GuaranteedSafepointInterval);
-  if (!max_time_exceeded) {
-    return;
-  }
-  if (SafepointALot) {
-    _next_vm_operation = &safepointALot_op;
-  }
-}
-
 bool VMThread::set_next_operation(VM_Operation *op) {
   if (_next_vm_operation != nullptr) {
     return false;
@@ -465,8 +451,8 @@ void VMThread::wait_for_operation() {
     if (_next_vm_operation != nullptr) {
       return;
     }
-    if (handshake_alot()) {
-      {
+    if (handshake_or_safepoint_alot()) {
+      if (HandshakeALot) {
         MutexUnlocker mul(VMOperation_lock);
         HandshakeALotClosure hal_cl;
         Handshake::execute(&hal_cl);
@@ -475,15 +461,14 @@ void VMThread::wait_for_operation() {
       if (_next_vm_operation != nullptr) {
         return;
       }
+      if (SafepointALot) {
+        _next_vm_operation = &safepointALot_op;
+        return;
+      }
     }
     assert(_next_vm_operation == nullptr, "Must be");
     assert(_cur_vm_operation  == nullptr, "Must be");
 
-    setup_periodic_safepoint_if_needed();
-    if (_next_vm_operation != nullptr) {
-      return;
-    }
-
     // We didn't find anything to execute, notify any waiter so they can install an op.
     ml_op_lock.notify_all();
     ml_op_lock.wait(GuaranteedSafepointInterval);

src/hotspot/share/runtime/vmThread.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1998, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1998, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -70,8 +70,7 @@ class VMThread: public NamedThread {
 
   static VMOperationTimeoutTask* _timeout_task;
 
-  static bool handshake_alot();
-  static void setup_periodic_safepoint_if_needed();
+  static bool handshake_or_safepoint_alot();
 
   void evaluate_operation(VM_Operation* op);
   void inner_execute(VM_Operation* op);