8313332: Simplify lazy jmethodID cache in InstanceKlass

Reviewed-by: amenkov, sspitsyn, dcubed

src/hotspot/share/logging/logTag.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 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
@@ -104,6 +104,7 @@ class outputStream;
   LOG_TAG(itables) \
   LOG_TAG(jfr) \
   LOG_TAG(jit) \
+  LOG_TAG(jmethod) \
   LOG_TAG(jni) \
   LOG_TAG(jvmci) \
   LOG_TAG(jvmti) \

src/hotspot/share/oops/instanceKlass.cpp

@@ -2267,16 +2267,26 @@ void InstanceKlass::set_enclosing_method_indices(u2 class_index,
   }
 }
 
+jmethodID InstanceKlass::update_jmethod_id(jmethodID* jmeths, Method* method, int idnum) {
+  if (method->is_old() && !method->is_obsolete()) {
+    // If the method passed in is old (but not obsolete), use the current version.
+    method = method_with_idnum((int)idnum);
+    assert(method != nullptr, "old and but not obsolete, so should exist");
+  }
+  jmethodID new_id = Method::make_jmethod_id(class_loader_data(), method);
+  Atomic::release_store(&jmeths[idnum + 1], new_id);
+  return new_id;
+}
+
 // Lookup or create a jmethodID.
 // This code is called by the VMThread and JavaThreads so the
 // locking has to be done very carefully to avoid deadlocks
 // and/or other cache consistency problems.
 //
 jmethodID InstanceKlass::get_jmethod_id(const methodHandle& method_h) {
-  size_t idnum = (size_t)method_h->method_idnum();
+  Method* method = method_h();
+  int idnum = method->method_idnum();
   jmethodID* jmeths = methods_jmethod_ids_acquire();
-  size_t length = 0;
-  jmethodID id = nullptr;
 
   // We use a double-check locking idiom here because this cache is
   // performance sensitive. In the normal system, this cache only
@@ -2288,82 +2298,65 @@ jmethodID InstanceKlass::get_jmethod_id(const methodHandle& method_h) {
   // seen either. Cache reads of existing jmethodIDs proceed without a
   // lock, but cache writes of a new jmethodID requires uniqueness and
   // creation of the cache itself requires no leaks so a lock is
-  // generally acquired in those two cases.
+  // acquired in those two cases.
   //
-  // If the RedefineClasses() API has been used, then this cache can
+  // If the RedefineClasses() API has been used, then this cache grows
-  // grow and we'll have transitions from non-null to bigger non-null.
+  // in the redefinition safepoint.
-  // Cache creation requires no leaks and we require safety between all
-  // cache accesses and freeing of the old cache so a lock is generally
-  // acquired when the RedefineClasses() API has been used.
 
-  if (jmeths != nullptr) {
+  if (jmeths == nullptr) {
-    // the cache already exists
+    MutexLocker ml(JmethodIdCreation_lock, Mutex::_no_safepoint_check_flag);
-    if (!idnum_can_increment()) {
+    jmeths = methods_jmethod_ids_acquire();
-      // the cache can't grow so we can just get the current values
+    // Still null?
-      get_jmethod_id_length_value(jmeths, idnum, &length, &id);
+    if (jmeths == nullptr) {
-    } else {
+      size_t size = idnum_allocated_count();
-      MutexLocker ml(JmethodIdCreation_lock, Mutex::_no_safepoint_check_flag);
+      assert(size > (size_t)idnum, "should already have space");
-      get_jmethod_id_length_value(jmeths, idnum, &length, &id);
+      jmeths = NEW_C_HEAP_ARRAY(jmethodID, size + 1, mtClass);
+      memset(jmeths, 0, (size + 1) * sizeof(jmethodID));
+      // cache size is stored in element[0], other elements offset by one
+      jmeths[0] = (jmethodID)size;
+      jmethodID new_id = update_jmethod_id(jmeths, method, idnum);
+
+      // publish jmeths
+      release_set_methods_jmethod_ids(jmeths);
+      return new_id;
     }
   }
-  // implied else:
-  // we need to allocate a cache so default length and id values are good
 
-  if (jmeths == nullptr ||   // no cache yet
+  jmethodID id = Atomic::load_acquire(&jmeths[idnum + 1]);
-      length <= idnum ||     // cache is too short
+  if (id == nullptr) {
-      id == nullptr) {       // cache doesn't contain entry
+    MutexLocker ml(JmethodIdCreation_lock, Mutex::_no_safepoint_check_flag);
-
+    id = jmeths[idnum + 1];
-    // This function can be called by the VMThread or GC worker threads so we
+    // Still null?
-    // have to do all things that might block on a safepoint before grabbing the lock.
+    if (id == nullptr) {
-    // Otherwise, we can deadlock with the VMThread or have a cache
+      return update_jmethod_id(jmeths, method, idnum);
-    // consistency issue. These vars keep track of what we might have
-    // to free after the lock is dropped.
-    jmethodID  to_dealloc_id     = nullptr;
-    jmethodID* to_dealloc_jmeths = nullptr;
-
-    // may not allocate new_jmeths or use it if we allocate it
-    jmethodID* new_jmeths = nullptr;
-    if (length <= idnum) {
-      // allocate a new cache that might be used
-      size_t size = MAX2(idnum+1, (size_t)idnum_allocated_count());
-      new_jmeths = NEW_C_HEAP_ARRAY(jmethodID, size+1, mtClass);
-      memset(new_jmeths, 0, (size+1)*sizeof(jmethodID));
-      // cache size is stored in element[0], other elements offset by one
-      new_jmeths[0] = (jmethodID)size;
-    }
-
-    // allocate a new jmethodID that might be used
-    {
-      MutexLocker ml(JmethodIdCreation_lock, Mutex::_no_safepoint_check_flag);
-      jmethodID new_id = nullptr;
-      if (method_h->is_old() && !method_h->is_obsolete()) {
-        // The method passed in is old (but not obsolete), we need to use the current version
-        Method* current_method = method_with_idnum((int)idnum);
-        assert(current_method != nullptr, "old and but not obsolete, so should exist");
-        new_id = Method::make_jmethod_id(class_loader_data(), current_method);
-      } else {
-        // It is the current version of the method or an obsolete method,
-        // use the version passed in
-        new_id = Method::make_jmethod_id(class_loader_data(), method_h());
-      }
-
-      id = get_jmethod_id_fetch_or_update(idnum, new_id, new_jmeths,
-                                          &to_dealloc_id, &to_dealloc_jmeths);
-    }
-
-    // The lock has been dropped so we can free resources.
-    // Free up either the old cache or the new cache if we allocated one.
-    if (to_dealloc_jmeths != nullptr) {
-      FreeHeap(to_dealloc_jmeths);
-    }
-    // free up the new ID since it wasn't needed
-    if (to_dealloc_id != nullptr) {
-      Method::destroy_jmethod_id(class_loader_data(), to_dealloc_id);
     }
   }
   return id;
 }
 
+void InstanceKlass::update_methods_jmethod_cache() {
+  assert(SafepointSynchronize::is_at_safepoint(), "only called at safepoint");
+  jmethodID* cache = _methods_jmethod_ids;
+  if (cache != nullptr) {
+    size_t size = idnum_allocated_count();
+    size_t old_size = (size_t)cache[0];
+    if (old_size < size + 1) {
+      // Allocate a larger one and copy entries to the new one.
+      // They've already been updated to point to new methods where applicable (i.e., not obsolete).
+      jmethodID* new_cache = NEW_C_HEAP_ARRAY(jmethodID, size + 1, mtClass);
+      memset(new_cache, 0, (size + 1) * sizeof(jmethodID));
+      // The cache size is stored in element[0]; the other elements are offset by one.
+      new_cache[0] = (jmethodID)size;
+
+      for (int i = 1; i <= (int)old_size; i++) {
+        new_cache[i] = cache[i];
+      }
+      _methods_jmethod_ids = new_cache;
+      FREE_C_HEAP_ARRAY(jmethodID, cache);
+    }
+  }
+}
+
 // Figure out how many jmethodIDs haven't been allocated, and make
 // sure space for them is pre-allocated.  This makes getting all
 // method ids much, much faster with classes with more than 8
@@ -2384,88 +2377,11 @@ void InstanceKlass::ensure_space_for_methodids(int start_offset) {
   }
 }
 
-// Common code to fetch the jmethodID from the cache or update the
-// cache with the new jmethodID. This function should never do anything
-// that causes the caller to go to a safepoint or we can deadlock with
-// the VMThread or have cache consistency issues.
-//
-jmethodID InstanceKlass::get_jmethod_id_fetch_or_update(
-            size_t idnum, jmethodID new_id,
-            jmethodID* new_jmeths, jmethodID* to_dealloc_id_p,
-            jmethodID** to_dealloc_jmeths_p) {
-  assert(new_id != nullptr, "sanity check");
-  assert(to_dealloc_id_p != nullptr, "sanity check");
-  assert(to_dealloc_jmeths_p != nullptr, "sanity check");
-  assert(JmethodIdCreation_lock->owned_by_self(), "sanity check");
-
-  // reacquire the cache - we are locked, single threaded or at a safepoint
-  jmethodID* jmeths = methods_jmethod_ids_acquire();
-  jmethodID  id     = nullptr;
-  size_t     length = 0;
-
-  if (jmeths == nullptr ||                      // no cache yet
-      (length = (size_t)jmeths[0]) <= idnum) {  // cache is too short
-    if (jmeths != nullptr) {
-      // copy any existing entries from the old cache
-      for (size_t index = 0; index < length; index++) {
-        new_jmeths[index+1] = jmeths[index+1];
-      }
-      *to_dealloc_jmeths_p = jmeths;  // save old cache for later delete
-    }
-    release_set_methods_jmethod_ids(jmeths = new_jmeths);
-  } else {
-    // fetch jmethodID (if any) from the existing cache
-    id = jmeths[idnum+1];
-    *to_dealloc_jmeths_p = new_jmeths;  // save new cache for later delete
-  }
-  if (id == nullptr) {
-    // No matching jmethodID in the existing cache or we have a new
-    // cache or we just grew the cache. This cache write is done here
-    // by the first thread to win the foot race because a jmethodID
-    // needs to be unique once it is generally available.
-    id = new_id;
-
-    // The jmethodID cache can be read while unlocked so we have to
-    // make sure the new jmethodID is complete before installing it
-    // in the cache.
-    Atomic::release_store(&jmeths[idnum+1], id);
-  } else {
-    *to_dealloc_id_p = new_id; // save new id for later delete
-  }
-  return id;
-}
-
-
-// Common code to get the jmethodID cache length and the jmethodID
-// value at index idnum if there is one.
-//
-void InstanceKlass::get_jmethod_id_length_value(jmethodID* cache,
-       size_t idnum, size_t *length_p, jmethodID* id_p) {
-  assert(cache != nullptr, "sanity check");
-  assert(length_p != nullptr, "sanity check");
-  assert(id_p != nullptr, "sanity check");
-
-  // cache size is stored in element[0], other elements offset by one
-  *length_p = (size_t)cache[0];
-  if (*length_p <= idnum) {  // cache is too short
-    *id_p = nullptr;
-  } else {
-    *id_p = cache[idnum+1];  // fetch jmethodID (if any)
-  }
-}
-
-
 // Lookup a jmethodID, null if not found.  Do no blocking, no allocations, no handles
 jmethodID InstanceKlass::jmethod_id_or_null(Method* method) {
-  size_t idnum = (size_t)method->method_idnum();
+  int idnum = method->method_idnum();
   jmethodID* jmeths = methods_jmethod_ids_acquire();
-  size_t length;                                // length assigned as debugging crumb
+  return (jmeths != nullptr) ? jmeths[idnum + 1] : nullptr;
-  jmethodID id = nullptr;
-  if (jmeths != nullptr &&                      // If there is a cache
-      (length = (size_t)jmeths[0]) > idnum) {   // and if it is long enough,
-    id = jmeths[idnum+1];                       // Look up the id (may be null)
-  }
-  return id;
 }
 
 inline DependencyContext InstanceKlass::dependencies() {
@@ -2884,7 +2800,7 @@ void InstanceKlass::release_C_heap_structures(bool release_sub_metadata) {
   set_jni_ids(nullptr);
 
   jmethodID* jmeths = methods_jmethod_ids_acquire();
-  if (jmeths != (jmethodID*)nullptr) {
+  if (jmeths != nullptr) {
     release_set_methods_jmethod_ids(nullptr);
     FreeHeap(jmeths);
   }

src/hotspot/share/oops/instanceKlass.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 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
@@ -237,9 +237,9 @@ class InstanceKlass: public Klass {
   JavaThread* volatile _init_thread;        // Pointer to current thread doing initialization (to handle recursive initialization)
 
   OopMapCache*    volatile _oop_map_cache;   // OopMapCache for all methods in the klass (allocated lazily)
-  JNIid*          _jni_ids;              // First JNI identifier for static fields in this class
+  JNIid*          _jni_ids;                  // First JNI identifier for static fields in this class
-  jmethodID*      volatile _methods_jmethod_ids;  // jmethodIDs corresponding to method_idnum, or null if none
+  jmethodID* volatile _methods_jmethod_ids;  // jmethodIDs corresponding to method_idnum, or null if none
-  nmethodBucket*  volatile _dep_context;          // packed DependencyContext structure
+  nmethodBucket*  volatile _dep_context;     // packed DependencyContext structure
   uint64_t        volatile _dep_context_last_cleaned;
   nmethod*        _osr_nmethods_head;    // Head of list of on-stack replacement nmethods for this class
 #if INCLUDE_JVMTI
@@ -794,14 +794,9 @@ public:
 
   // jmethodID support
   jmethodID get_jmethod_id(const methodHandle& method_h);
-  jmethodID get_jmethod_id_fetch_or_update(size_t idnum,
-                     jmethodID new_id, jmethodID* new_jmeths,
-                     jmethodID* to_dealloc_id_p,
-                     jmethodID** to_dealloc_jmeths_p);
-  static void get_jmethod_id_length_value(jmethodID* cache, size_t idnum,
-                size_t *length_p, jmethodID* id_p);
   void ensure_space_for_methodids(int start_offset = 0);
   jmethodID jmethod_id_or_null(Method* method);
+  void update_methods_jmethod_cache();
 
   // annotations support
   Annotations* annotations() const          { return _annotations; }
@@ -1073,17 +1068,12 @@ public:
     Atomic::store(&_init_thread, thread);
   }
 
-  // The RedefineClasses() API can cause new method idnums to be needed
-  // which will cause the caches to grow. Safety requires different
-  // cache management logic if the caches can grow instead of just
-  // going from null to non-null.
-  bool idnum_can_increment() const      { return has_been_redefined(); }
   inline jmethodID* methods_jmethod_ids_acquire() const;
   inline void release_set_methods_jmethod_ids(jmethodID* jmeths);
   // This nulls out jmethodIDs for all methods in 'klass'
   static void clear_jmethod_ids(InstanceKlass* klass);
+  jmethodID update_jmethod_id(jmethodID* jmeths, Method* method, int idnum);
 
-  // Lock during initialization
 public:
   // Returns the array class for the n'th dimension
   virtual ArrayKlass* array_klass(int n, TRAPS);

src/hotspot/share/oops/method.cpp

@@ -2143,14 +2143,6 @@ class JNIMethodBlock : public CHeapObj<mtClass> {
     return false;  // not found
   }
 
-  // Doesn't really destroy it, just marks it as free so it can be reused.
-  void destroy_method(Method** m) {
-#ifdef ASSERT
-    assert(contains(m), "should be a methodID");
-#endif // ASSERT
-    *m = _free_method;
-  }
-
   // During class unloading the methods are cleared, which is different
   // than freed.
   void clear_all_methods() {
@@ -2203,6 +2195,9 @@ jmethodID Method::make_jmethod_id(ClassLoaderData* cld, Method* m) {
   // Also have to add the method to the list safely, which the lock
   // protects as well.
   assert(JmethodIdCreation_lock->owned_by_self(), "sanity check");
+
+  ResourceMark rm;
+  log_debug(jmethod)("Creating jmethodID for Method %s", m->external_name());
   if (cld->jmethod_ids() == nullptr) {
     cld->set_jmethod_ids(new JNIMethodBlock());
   }
@@ -2215,14 +2210,6 @@ jmethodID Method::jmethod_id() {
   return method_holder()->get_jmethod_id(mh);
 }
 
-// Mark a jmethodID as free.  This is called when there is a data race in
-// InstanceKlass while creating the jmethodID cache.
-void Method::destroy_jmethod_id(ClassLoaderData* cld, jmethodID m) {
-  Method** ptr = (Method**)m;
-  assert(cld->jmethod_ids() != nullptr, "should have method handles");
-  cld->jmethod_ids()->destroy_method(ptr);
-}
-
 void Method::change_method_associated_with_jmethod_id(jmethodID jmid, Method* new_method) {
   // Can't assert the method_holder is the same because the new method has the
   // scratch method holder.

src/hotspot/share/oops/method.hpp

@@ -700,7 +700,6 @@ public:
   // made obsolete or deleted -- in these cases, the jmethodID
   // refers to null (as is the case for any weak reference).
   static jmethodID make_jmethod_id(ClassLoaderData* cld, Method* mh);
-  static void destroy_jmethod_id(ClassLoaderData* cld, jmethodID mid);
 
   // Ensure there is enough capacity in the internal tracking data
   // structures to hold the number of jmethodIDs you plan to generate.

src/hotspot/share/prims/jvmtiRedefineClasses.cpp

@@ -4350,7 +4350,8 @@ void VM_RedefineClasses::redefine_single_class(Thread* current, jclass the_jclas
   the_class->vtable().initialize_vtable();
   the_class->itable().initialize_itable();
 
-  // Leave arrays of jmethodIDs and itable index cache unchanged
+  // Update jmethodID cache if present.
+  the_class->update_methods_jmethod_cache();
 
   // Copy the "source debug extension" attribute from new class version
   the_class->set_source_debug_extension(

src/hotspot/share/runtime/vmStructs.cpp

@@ -253,7 +253,6 @@
   nonstatic_field(InstanceKlass,               _jni_ids,                                      JNIid*)                                \
   nonstatic_field(InstanceKlass,               _osr_nmethods_head,                            nmethod*)                              \
   JVMTI_ONLY(nonstatic_field(InstanceKlass,    _breakpoints,                                  BreakpointInfo*))                      \
-  volatile_nonstatic_field(InstanceKlass,      _methods_jmethod_ids,                          jmethodID*)                            \
   volatile_nonstatic_field(InstanceKlass,      _idnum_allocated_count,                        u2)                                    \
   nonstatic_field(InstanceKlass,               _annotations,                                  Annotations*)                          \
   nonstatic_field(InstanceKlass,               _method_ordering,                              Array<int>*)                           \