jdk-sandbox: comparison hotspot/src/share/vm/oops/instanceKlass.cpp

equal deleted inserted replaced

-:388b0393a042
+:86e9e4b25bdf
 return probe;
 }
 // Lookup or create a jmethodID.
-// This code can be called by the VM thread.  For this reason it is critical that
+// This code is called by the VMThread and JavaThreads so the
-// there are no blocking operations (safepoints) while the lock is held -- or a
+// locking has to be done very carefully to avoid deadlocks
-// deadlock can occur.
+// and/or other cache consistency problems.
-jmethodID instanceKlass::jmethod_id_for_impl(instanceKlassHandle ik_h, methodHandle method_h) {
+//
+jmethodID instanceKlass::get_jmethod_id(instanceKlassHandle ik_h, methodHandle method_h) {
 size_t idnum = (size_t)method_h->method_idnum();
 jmethodID* jmeths = ik_h->methods_jmethod_ids_acquire();
 size_t length = 0;
 jmethodID id = NULL;
-// array length stored in first element, other elements offset by one
-if (jmeths == NULL ||                         // If there is no jmethodID array,
+// We use a double-check locking idiom here because this cache is
-(length = (size_t)jmeths[0]) <= idnum ||  // or if it is too short,
+// performance sensitive. In the normal system, this cache only
-(id = jmeths[idnum+1]) == NULL) {         // or if this jmethodID isn't allocated
+// transitions from NULL to non-NULL which is safe because we use
+// release_set_methods_jmethod_ids() to advertise the new cache.
-// Do all the safepointing things (allocations) before grabbing the lock.
+// A partially constructed cache should never be seen by a racing
-// These allocations will have to be freed if they are unused.
+// thread. We also use release_store_ptr() to save a new jmethodID
+// in the cache so a partially constructed jmethodID should never be
-// Allocate a new array of methods.
+// 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.
+//
+// If the RedefineClasses() API has been used, then this cache can
+// grow and we'll have transitions from non-NULL to bigger non-NULL.
+// 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 != NULL) {
+// the cache already exists
+if (!ik_h->idnum_can_increment()) {
+// the cache can't grow so we can just get the current values
+get_jmethod_id_length_value(jmeths, idnum, &length, &id);
+} else {
+// cache can grow so we have to be more careful
+if (Threads::number_of_threads() == 0 ||
+SafepointSynchronize::is_at_safepoint()) {
+// we're single threaded or at a safepoint - no locking needed
+get_jmethod_id_length_value(jmeths, idnum, &length, &id);
+} else {
+MutexLocker ml(JmethodIdCreation_lock);
+get_jmethod_id_length_value(jmeths, idnum, &length, &id);
+}
+}
+}
+// implied else:
+// we need to allocate a cache so default length and id values are good
+if (jmeths == NULL ||   // no cache yet
+length <= idnum ||  // cache is too short
+id == NULL) {       // cache doesn't contain entry
+// This function can be called by the VMThread so we have to do all
+// things that might block on a safepoint before grabbing the lock.
+// Otherwise, we can deadlock with the VMThread or have a cache
+// consistency issue. These vars keep track of what we might have
+// to free after the lock is dropped.
+jmethodID  to_dealloc_id     = NULL;
+jmethodID* to_dealloc_jmeths = NULL;
+// may not allocate new_jmeths or use it if we allocate it
 jmethodID* new_jmeths = NULL;
 if (length <= idnum) {
-// A new array will be needed (unless some other thread beats us to it)
+// allocate a new cache that might be used
 size_t size = MAX2(idnum+1, (size_t)ik_h->idnum_allocated_count());
 new_jmeths = NEW_C_HEAP_ARRAY(jmethodID, size+1);
 memset(new_jmeths, 0, (size+1)*sizeof(jmethodID));
-new_jmeths[0] =(jmethodID)size;  // array size held in the first element
+// cache size is stored in element[0], other elements offset by one
-}
+new_jmeths[0] = (jmethodID)size;
+}
-// Allocate a new method ID.
+// allocate a new jmethodID that might be used
 jmethodID new_id = NULL;
 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
 methodOop current_method = ik_h->method_with_idnum((int)idnum);
 assert(current_method != NULL, "old and but not obsolete, so should exist");
 // It is the current version of the method or an obsolete method,
 // use the version passed in
 new_id = JNIHandles::make_jmethod_id(method_h);
 }
-if (Threads::number_of_threads() == 0 || SafepointSynchronize::is_at_safepoint()) {
+if (Threads::number_of_threads() == 0 ||
-// No need and unsafe to lock the JmethodIdCreation_lock at safepoint.
+SafepointSynchronize::is_at_safepoint()) {
-id = get_jmethod_id(ik_h, idnum, new_id, new_jmeths);
+// we're single threaded or at a safepoint - no locking needed
+id = get_jmethod_id_fetch_or_update(ik_h, idnum, new_id, new_jmeths,
+&to_dealloc_id, &to_dealloc_jmeths);
 } else {
 MutexLocker ml(JmethodIdCreation_lock);
-id = get_jmethod_id(ik_h, idnum, new_id, new_jmeths);
+id = get_jmethod_id_fetch_or_update(ik_h, 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 != NULL) {
+FreeHeap(to_dealloc_jmeths);
+}
+// free up the new ID since it wasn't needed
+if (to_dealloc_id != NULL) {
+JNIHandles::destroy_jmethod_id(to_dealloc_id);
 }
 }
 return id;
 }
-jmethodID instanceKlass::get_jmethod_id(instanceKlassHandle ik_h, size_t idnum,
+// Common code to fetch the jmethodID from the cache or update the
-jmethodID new_id, jmethodID* new_jmeths) {
+// cache with the new jmethodID. This function should never do anything
-// Retry lookup after we got the lock or ensured we are at safepoint
+// 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(
+instanceKlassHandle ik_h, size_t idnum, jmethodID new_id,
+jmethodID* new_jmeths, jmethodID* to_dealloc_id_p,
+jmethodID** to_dealloc_jmeths_p) {
+assert(new_id != NULL, "sanity check");
+assert(to_dealloc_id_p != NULL, "sanity check");
+assert(to_dealloc_jmeths_p != NULL, "sanity check");
+assert(Threads::number_of_threads() == 0 ||
+SafepointSynchronize::is_at_safepoint() ||
+JmethodIdCreation_lock->owned_by_self(), "sanity check");
+// reacquire the cache - we are locked, single threaded or at a safepoint
 jmethodID* jmeths = ik_h->methods_jmethod_ids_acquire();
-jmethodID  id                = NULL;
+jmethodID  id     = NULL;
-jmethodID  to_dealloc_id     = NULL;
+size_t     length = 0;
-jmethodID* to_dealloc_jmeths = NULL;
-size_t     length;
+if (jmeths == NULL ||                         // no cache yet
+(length = (size_t)jmeths[0]) <= idnum) {  // cache is too short
-if (jmeths == NULL || (length = (size_t)jmeths[0]) <= idnum) {
 if (jmeths != NULL) {
-// We have grown the array: copy the existing entries, and delete the old array
+// 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 = jmeths; // using the new jmeths, deallocate the old one
+*to_dealloc_jmeths_p = jmeths;  // save old cache for later delete
 }
 ik_h->release_set_methods_jmethod_ids(jmeths = new_jmeths);
 } else {
+// fetch jmethodID (if any) from the existing cache
 id = jmeths[idnum+1];
-to_dealloc_jmeths = new_jmeths; // using the old jmeths, deallocate the new one
+*to_dealloc_jmeths_p = new_jmeths;  // save new cache for later delete
 }
 if (id == NULL) {
+// 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;
-jmeths[idnum+1] = id;  // install the new method 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.
+OrderAccess::release_store_ptr(&jmeths[idnum+1], id);
 } else {
-to_dealloc_id = new_id; // the new id wasn't used, mark it for deallocation
+*to_dealloc_id_p = new_id; // save new id for later delete
-}
-// Free up unneeded or no longer needed resources
-FreeHeap(to_dealloc_jmeths);
-if (to_dealloc_id != NULL) {
-JNIHandles::destroy_jmethod_id(to_dealloc_id);
 }
 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 != NULL, "sanity check");
+assert(length_p != NULL, "sanity check");
+assert(id_p != NULL, "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 = NULL;
+} 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(methodOop method) {
 size_t idnum = (size_t)method->method_idnum();
 jmethodID* jmeths = methods_jmethod_ids_acquire();
 size_t length;                                // length assigned as debugging crumb
 jmethodID id = NULL;
-if (jmeths != NULL &&                         // If there is a jmethodID array,
+if (jmeths != NULL &&                         // 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;
 }
 // Cache an itable index
 void instanceKlass::set_cached_itable_index(size_t idnum, int index) {
 int* indices = methods_cached_itable_indices_acquire();
-if (indices == NULL ||                         // If there is no index array,
+int* to_dealloc_indices = NULL;
-((size_t)indices[0]) <= idnum) {           // or if it is too short
-// Lock before we allocate the array so we don't leak
+// We use a double-check locking idiom here because this cache is
+// performance sensitive. In the normal system, this cache only
+// transitions from NULL to non-NULL which is safe because we use
+// release_set_methods_cached_itable_indices() to advertise the
+// new cache. A partially constructed cache should never be seen
+// by a racing thread. Cache reads and writes proceed without a
+// lock, but creation of the cache itself requires no leaks so a
+// lock is generally acquired in that case.
+//
+// If the RedefineClasses() API has been used, then this cache can
+// grow and we'll have transitions from non-NULL to bigger non-NULL.
+// 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 (indices == NULL || idnum_can_increment()) {
+// we need a cache or the cache can grow
 MutexLocker ml(JNICachedItableIndex_lock);
-// Retry lookup after we got the lock
+// reacquire the cache to see if another thread already did the work
 indices = methods_cached_itable_indices_acquire();
 size_t length = 0;
-// array length stored in first element, other elements offset by one
+// cache size is stored in element[0], other elements offset by one
 if (indices == NULL || (length = (size_t)indices[0]) <= idnum) {
 size_t size = MAX2(idnum+1, (size_t)idnum_allocated_count());
 int* new_indices = NEW_C_HEAP_ARRAY(int, size+1);
-new_indices[0] =(int)size;  // array size held in the first element
+new_indices[0] = (int)size;
-// Copy the existing entries, if any
+// copy any existing entries
 size_t i;
 for (i = 0; i < length; i++) {
 new_indices[i+1] = indices[i+1];
 }
 // Set all the rest to -1
 for (i = length; i < size; i++) {
 new_indices[i+1] = -1;
 }
 if (indices != NULL) {
-FreeHeap(indices);  // delete any old indices
+// We have an old cache to delete so save it for after we
+// drop the lock.
+to_dealloc_indices = indices;
 }
 release_set_methods_cached_itable_indices(indices = new_indices);
 }
+if (idnum_can_increment()) {
+// this cache can grow so we have to write to it safely
+indices[idnum+1] = index;
+}
 } else {
 CHECK_UNHANDLED_OOPS_ONLY(Thread::current()->clear_unhandled_oops());
 }
-// This is a cache, if there is a race to set it, it doesn't matter
-indices[idnum+1] = index;
+if (!idnum_can_increment()) {
+// The cache cannot grow and this JNI itable index value does not
+// have to be unique like a jmethodID. If there is a race to set it,
+// it doesn't matter.
+indices[idnum+1] = index;
+}
+if (to_dealloc_indices != NULL) {
+// we allocated a new cache so free the old one
+FreeHeap(to_dealloc_indices);
+}
 }
 // Retrieve a cached itable index
 int instanceKlass::cached_itable_index(size_t idnum) {
 // RedefineClasses() support for previous versions:
 // Add an information node that contains weak references to the
 // interesting parts of the previous version of the_class.
+// This is also where we clean out any unused weak references.
+// Note that while we delete nodes from the _previous_versions
+// array, we never delete the array itself until the klass is
+// unloaded. The has_been_redefined() query depends on that fact.
+//
 void instanceKlass::add_previous_version(instanceKlassHandle ikh,
 BitMap* emcp_methods, int emcp_method_count) {
 assert(Thread::current()->is_VM_thread(),
 "only VMThread can add previous versions");

changeset 3824	86e9e4b25bdf
parent 3821	847fddcb639b
child 3916	9acd7f9d4f52