From 7fa0e2cc00d64ee0399740ff20971f5c11517172 Mon Sep 17 00:00:00 2001
Date: Fri, 22 Jan 2021 11:36:20 +0800
Subject: Backport of JDK-8186042 for OopmapCache implementation

Summary: Backport of JDK-8186042 for OopmapCache implementation
LLT:
Bug url: https://bugs.openjdk.java.net/browse/JDK-8186042
---
 .../shared/vmGCOperations.cpp                 |   6 +-
 .../src/share/vm/interpreter/oopMapCache.cpp  | 150 +++++++++++-------
 .../src/share/vm/interpreter/oopMapCache.hpp  |  11 +-
 hotspot/src/share/vm/oops/method.cpp          |  26 +--
 hotspot/src/share/vm/runtime/memprofiler.cpp  |   2 +-
 hotspot/src/share/vm/runtime/vframe.cpp       |   8 +-
 6 files changed, 111 insertions(+), 92 deletions(-)

diff --git a/hotspot/src/share/vm/gc_implementation/shared/vmGCOperations.cpp b/hotspot/src/share/vm/gc_implementation/shared/vmGCOperations.cpp
index d60f751af..85059b82f 100644
--- a/hotspot/src/share/vm/gc_implementation/shared/vmGCOperations.cpp
+++ b/hotspot/src/share/vm/gc_implementation/shared/vmGCOperations.cpp
@@ -40,6 +40,7 @@
 #if INCLUDE_ALL_GCS
 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
 #endif // INCLUDE_ALL_GCS
+#include "interpreter/oopMapCache.hpp"
 
 #ifndef USDT2
 HS_DTRACE_PROBE_DECL1(hotspot, gc__begin, bool);
@@ -134,7 +135,10 @@ bool VM_GC_Operation::doit_prologue() {
 
 void VM_GC_Operation::doit_epilogue() {
   assert(Thread::current()->is_Java_thread(), "just checking");
-  // Release the Heap_lock first.
+  // Clean up old interpreter OopMap entries that were replaced
+  // during the GC thread root traversal.
+  OopMapCache::cleanup_old_entries();
+  // Release the Heap_lock.
   SharedHeap* sh = SharedHeap::heap();
   if (sh != NULL) sh->_thread_holds_heap_lock_for_gc = false;
   Heap_lock->unlock();
diff --git a/hotspot/src/share/vm/interpreter/oopMapCache.cpp b/hotspot/src/share/vm/interpreter/oopMapCache.cpp
index f696bcb25..528906267 100644
--- a/hotspot/src/share/vm/interpreter/oopMapCache.cpp
+++ b/hotspot/src/share/vm/interpreter/oopMapCache.cpp
@@ -30,6 +30,7 @@
 #include "prims/jvmtiRedefineClassesTrace.hpp"
 #include "runtime/handles.inline.hpp"
 #include "runtime/signature.hpp"
+#include "runtime/atomic.inline.hpp"
 
 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
 
@@ -39,6 +40,9 @@ class OopMapCacheEntry: private InterpreterOopMap {
   friend class OopMapCache;
   friend class VerifyClosure;
 
+ private:
+  OopMapCacheEntry* _next;
+
  protected:
   // Initialization
   void fill(methodHandle method, int bci);
@@ -56,8 +60,9 @@ class OopMapCacheEntry: private InterpreterOopMap {
 
  public:
   OopMapCacheEntry() : InterpreterOopMap() {
+    _next = NULL;
 #ifdef ASSERT
-     _resource_allocate_bit_mask = false;
+    _resource_allocate_bit_mask = false;
 #endif
   }
 };
@@ -424,16 +429,6 @@ void OopMapCacheEntry::flush() {
 
 // Implementation of OopMapCache
 
-#ifndef PRODUCT
-
-static size_t _total_memory_usage = 0;
-
-size_t OopMapCache::memory_usage() {
-  return _total_memory_usage;
-}
-
-#endif
-
 void InterpreterOopMap::resource_copy(OopMapCacheEntry* from) {
   assert(_resource_allocate_bit_mask,
     "Should not resource allocate the _bit_mask");
@@ -474,15 +469,11 @@ inline unsigned int OopMapCache::hash_value_for(methodHandle method, int bci) co
          ^ ((unsigned int) method->size_of_parameters() << 6);
 }
 
+OopMapCacheEntry* volatile OopMapCache::_old_entries = NULL;
 
-OopMapCache::OopMapCache() :
-  _mut(Mutex::leaf, "An OopMapCache lock", true)
-{
-  _array  = NEW_C_HEAP_ARRAY(OopMapCacheEntry, _size, mtClass);
-  // Cannot call flush for initialization, since flush
-  // will check if memory should be deallocated
-  for(int i = 0; i < _size; i++) _array[i].initialize();
-  NOT_PRODUCT(_total_memory_usage += sizeof(OopMapCache) + (sizeof(OopMapCacheEntry) * _size);)
+OopMapCache::OopMapCache() {
+  _array  = NEW_C_HEAP_ARRAY(OopMapCacheEntry*, _size, mtClass);
+  for(int i = 0; i < _size; i++) _array[i] = NULL;
 }
 
 
@@ -491,44 +482,59 @@ OopMapCache::~OopMapCache() {
   // Deallocate oop maps that are allocated out-of-line
   flush();
   // Deallocate array
-  NOT_PRODUCT(_total_memory_usage -= sizeof(OopMapCache) + (sizeof(OopMapCacheEntry) * _size);)
-  FREE_C_HEAP_ARRAY(OopMapCacheEntry, _array, mtClass);
+  FREE_C_HEAP_ARRAY(OopMapCacheEntry*, _array, mtClass);
 }
 
 OopMapCacheEntry* OopMapCache::entry_at(int i) const {
-  return &_array[i % _size];
+  return (OopMapCacheEntry*)OrderAccess::load_ptr_acquire(&(_array[i % _size]));
 }
 
+bool OopMapCache::put_at(int i, OopMapCacheEntry* entry, OopMapCacheEntry* old) {
+  return Atomic::cmpxchg_ptr(entry, &_array[i % _size], old) == old;
+ }
 void OopMapCache::flush() {
-  for (int i = 0; i < _size; i++) _array[i].flush();
+  for (int i = 0; i < _size; i++) {
+    OopMapCacheEntry* entry = _array[i];
+    if (entry != NULL) {
+      _array[i] = NULL;  // no barrier, only called in OopMapCache destructor
+      entry->flush();
+      FREE_C_HEAP_OBJ(entry, mtClass);
+    }
+  }
 }
 
+
 void OopMapCache::flush_obsolete_entries() {
-  for (int i = 0; i < _size; i++)
-    if (!_array[i].is_empty() && _array[i].method()->is_old()) {
+  assert(SafepointSynchronize::is_at_safepoint(), "called by RedefineClasses in a safepoint");
+  for (int i = 0; i < _size; i++) {
+    OopMapCacheEntry* entry = _array[i];
+    if (entry != NULL && !entry->is_empty() && entry->method()->is_old()) {
       // Cache entry is occupied by an old redefined method and we don't want
       // to pin it down so flush the entry.
+
       RC_TRACE(0x08000000, ("flush: %s(%s): cached entry @%d",
-        _array[i].method()->name()->as_C_string(),
-        _array[i].method()->signature()->as_C_string(), i));
+        entry->method()->name()->as_C_string(),
+        entry->method()->signature()->as_C_string(), i));
 
-      _array[i].flush();
+      _array[i] = NULL;
+      entry->flush();
+      FREE_C_HEAP_OBJ(entry, mtClass);
     }
+  }
 }
 
 void OopMapCache::lookup(methodHandle method,
                          int bci,
-                         InterpreterOopMap* entry_for) const {
-  MutexLocker x(&_mut);
-
-  OopMapCacheEntry* entry = NULL;
+                         InterpreterOopMap* entry_for){
+  assert(SafepointSynchronize::is_at_safepoint(), "called by GC in a safepoint");
   int probe = hash_value_for(method, bci);
+  int i;
+  OopMapCacheEntry* entry = NULL;
 
   // Search hashtable for match
-  int i;
   for(i = 0; i < _probe_depth; i++) {
     entry = entry_at(probe + i);
-    if (entry->match(method, bci)) {
+    if (entry != NULL && !entry->is_empty() && entry->match(method, bci)) {
       entry_for->resource_copy(entry);
       assert(!entry_for->is_empty(), "A non-empty oop map should be returned");
       return;
@@ -543,26 +549,31 @@ void OopMapCache::lookup(methodHandle method,
   }
 
   // Entry is not in hashtable.
-  // Compute entry and return it
+  // Compute entry
+
+  OopMapCacheEntry* tmp = NEW_C_HEAP_OBJ(OopMapCacheEntry, mtClass);
+  tmp->initialize();
+  tmp->fill(method, bci);
+  entry_for->resource_copy(tmp);
 
   if (method->should_not_be_cached()) {
     // It is either not safe or not a good idea to cache this Method*
     // at this time. We give the caller of lookup() a copy of the
     // interesting info via parameter entry_for, but we don't add it to
     // the cache. See the gory details in Method*.cpp.
-    compute_one_oop_map(method, bci, entry_for);
+    FREE_C_HEAP_OBJ(tmp, mtClass);
     return;
   }
 
   // First search for an empty slot
   for(i = 0; i < _probe_depth; i++) {
-    entry  = entry_at(probe + i);
-    if (entry->is_empty()) {
-      entry->fill(method, bci);
-      entry_for->resource_copy(entry);
-      assert(!entry_for->is_empty(), "A non-empty oop map should be returned");
-      return;
-    }
+    entry = entry_at(probe + i);
+    if (entry == NULL) {
+      if(put_at(probe + i, tmp, NULL)) {
+        assert(!entry_for->is_empty(), "A non-empty oop map should be returned");
+        return;
+       }
+     }
   }
 
   if (TraceOopMapGeneration) {
@@ -571,30 +582,51 @@ void OopMapCache::lookup(methodHandle method,
   }
 
   // No empty slot (uncommon case). Use (some approximation of a) LRU algorithm
-  //entry_at(probe + _probe_depth - 1)->flush();
-  //for(i = _probe_depth - 1; i > 0; i--) {
-  //  // Coping entry[i] = entry[i-1];
-  //  OopMapCacheEntry *to   = entry_at(probe + i);
-  //  OopMapCacheEntry *from = entry_at(probe + i - 1);
-  //  to->copy(from);
-  // }
+  // where the first entry in the collision array is replaced with the new one.
+  OopMapCacheEntry* old = entry_at(probe + 0);
+  if (put_at(probe + 0, tmp, old)) {
+    enqueue_for_cleanup(old);
+  } else {
+    enqueue_for_cleanup(tmp);
+  }
 
-  assert(method->is_method(), "gaga");
+  assert(!entry_for->is_empty(), "A non-empty oop map should be returned");
 
-  entry = entry_at(probe + 0);
-  entry->fill(method, bci);
+  return;
+}
 
-  // Copy the  newly cached entry to input parameter
-  entry_for->resource_copy(entry);
+void OopMapCache::enqueue_for_cleanup(OopMapCacheEntry* entry) {
+  bool success = false;
+  OopMapCacheEntry* head;
+  do {
+    head = _old_entries;
+    entry->_next = head;
+    success = Atomic::cmpxchg_ptr((intptr_t*)entry, (intptr_t*)&_old_entries, (intptr_t*)head) == (intptr_t*)head;
+  } while (!success);
 
   if (TraceOopMapGeneration) {
     ResourceMark rm;
-    tty->print("Done with ");
-    method->print_value(); tty->cr();
+    tty->print_cr("enqueue %s at bci %d for cleanup",
+                          entry->method()->name_and_sig_as_C_string(), entry->bci());
   }
-  assert(!entry_for->is_empty(), "A non-empty oop map should be returned");
+}
 
-  return;
+// This is called after GC threads are done and nothing is accessing the old_entries
+// list, so no synchronization needed.
+void OopMapCache::cleanup_old_entries() {
+  OopMapCacheEntry* entry = _old_entries;
+  _old_entries = NULL;
+  while (entry != NULL) {
+    if (TraceOopMapGeneration) {
+      ResourceMark rm;
+      tty->print_cr("cleanup entry %s at bci %d",
+                          entry->method()->name_and_sig_as_C_string(), entry->bci());
+    }
+    OopMapCacheEntry* next = entry->_next;
+    entry->flush();
+    FREE_C_HEAP_OBJ(entry, mtClass);
+    entry = next;
+  }
 }
 
 void OopMapCache::compute_one_oop_map(methodHandle method, int bci, InterpreterOopMap* entry) {
diff --git a/hotspot/src/share/vm/interpreter/oopMapCache.hpp b/hotspot/src/share/vm/interpreter/oopMapCache.hpp
index 99fbe8168..ecbe4340a 100644
--- a/hotspot/src/share/vm/interpreter/oopMapCache.hpp
+++ b/hotspot/src/share/vm/interpreter/oopMapCache.hpp
@@ -147,17 +147,19 @@ class InterpreterOopMap: ResourceObj {
 };
 
 class OopMapCache : public CHeapObj<mtClass> {
+  static OopMapCacheEntry* volatile _old_entries;
  private:
   enum { _size        = 32,     // Use fixed size for now
          _probe_depth = 3       // probe depth in case of collisions
   };
 
-  OopMapCacheEntry* _array;
+  OopMapCacheEntry* volatile * _array;
 
   unsigned int hash_value_for(methodHandle method, int bci) const;
   OopMapCacheEntry* entry_at(int i) const;
 
-  mutable Mutex _mut;
+  bool put_at(int i, OopMapCacheEntry* entry, OopMapCacheEntry* old);
+  static void enqueue_for_cleanup(OopMapCacheEntry* entry);
 
   void flush();
 
@@ -170,13 +172,12 @@ class OopMapCache : public CHeapObj<mtClass> {
 
   // Returns the oopMap for (method, bci) in parameter "entry".
   // Returns false if an oop map was not found.
-  void lookup(methodHandle method, int bci, InterpreterOopMap* entry) const;
+  void lookup(methodHandle method, int bci, InterpreterOopMap* entry);
 
   // Compute an oop map without updating the cache or grabbing any locks (for debugging)
   static void compute_one_oop_map(methodHandle method, int bci, InterpreterOopMap* entry);
 
-  // Returns total no. of bytes allocated as part of OopMapCache's
-  static size_t memory_usage()                     PRODUCT_RETURN0;
+  static void cleanup_old_entries();
 };
 
 #endif // SHARE_VM_INTERPRETER_OOPMAPCACHE_HPP
diff --git a/hotspot/src/share/vm/oops/method.cpp b/hotspot/src/share/vm/oops/method.cpp
index 9e58c0126..24fae4d30 100644
--- a/hotspot/src/share/vm/oops/method.cpp
+++ b/hotspot/src/share/vm/oops/method.cpp
@@ -216,26 +216,14 @@ int Method::fast_exception_handler_bci_for(methodHandle mh, KlassHandle ex_klass
 }
 
 void Method::mask_for(int bci, InterpreterOopMap* mask) {
-
-  Thread* myThread    = Thread::current();
-  methodHandle h_this(myThread, this);
-#ifdef ASSERT
-  bool has_capability = myThread->is_VM_thread() ||
-                        myThread->is_ConcurrentGC_thread() ||
-                        myThread->is_GC_task_thread();
-
-  if (!has_capability) {
-    if (!VerifyStack && !VerifyLastFrame) {
-      // verify stack calls this outside VM thread
-      warning("oopmap should only be accessed by the "
-              "VM, GC task or CMS threads (or during debugging)");
-      InterpreterOopMap local_mask;
-      method_holder()->mask_for(h_this, bci, &local_mask);
-      local_mask.print();
-    }
+  methodHandle h_this(Thread::current(), this);
+  // Only GC uses the OopMapCache during thread stack root scanning
+  // any other uses generate an oopmap but do not save it in the cache.
+  if (Universe::heap()->is_gc_active()) {
+    method_holder()->mask_for(h_this, bci, mask);
+  } else {
+    OopMapCache::compute_one_oop_map(h_this, bci, mask);
   }
-#endif
-  method_holder()->mask_for(h_this, bci, mask);
   return;
 }
 
diff --git a/hotspot/src/share/vm/runtime/memprofiler.cpp b/hotspot/src/share/vm/runtime/memprofiler.cpp
index c1cfb60bd..ddb22601f 100644
--- a/hotspot/src/share/vm/runtime/memprofiler.cpp
+++ b/hotspot/src/share/vm/runtime/memprofiler.cpp
@@ -129,7 +129,7 @@ void MemProfiler::do_trace() {
   fprintf(_log_fp, UINTX_FORMAT_W(6) "," UINTX_FORMAT_W(6) "," UINTX_FORMAT_W(6) "\n",
           handles_memory_usage / K,
           resource_memory_usage / K,
-          OopMapCache::memory_usage() / K);
+          0L);
   fflush(_log_fp);
 }
 
diff --git a/hotspot/src/share/vm/runtime/vframe.cpp b/hotspot/src/share/vm/runtime/vframe.cpp
index 0d5524118..b3a6d0770 100644
--- a/hotspot/src/share/vm/runtime/vframe.cpp
+++ b/hotspot/src/share/vm/runtime/vframe.cpp
@@ -365,13 +365,7 @@ StackValueCollection* interpretedVFrame::expressions() const {
 StackValueCollection* interpretedVFrame::stack_data(bool expressions) const {
 
   InterpreterOopMap oop_mask;
-  // oopmap for current bci
-  if (TraceDeoptimization && Verbose) {
-    methodHandle m_h(Thread::current(), method());
-    OopMapCache::compute_one_oop_map(m_h, bci(), &oop_mask);
-  } else {
-    method()->mask_for(bci(), &oop_mask);
-  }
+  method()->mask_for(bci(), &oop_mask);
 
   const int mask_len = oop_mask.number_of_entries();
 
-- 
2.19.0