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src/hotspot/share/runtime/threadSMR.cpp

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rev 48154 : 8191789: migrate more Thread-SMR stuff from thread.[ch]pp -> threadSMR.[ch]pp
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*** 21,72 **** * questions. * */ #include "precompiled.hpp" #include "memory/allocation.inline.hpp" #include "runtime/thread.inline.hpp" ! #include "runtime/threadSMR.hpp" #include "services/threadService.hpp" // 'entries + 1' so we always have at least one entry. ThreadsList::ThreadsList(int entries) : _length(entries), _threads(NEW_C_HEAP_ARRAY(JavaThread*, entries + 1, mtThread)), _next_list(NULL) { *(JavaThread**)(_threads + entries) = NULL; // Make sure the extra entry is NULL. } ThreadsList::~ThreadsList() { FREE_C_HEAP_ARRAY(JavaThread*, _threads); } ThreadsListSetter::~ThreadsListSetter() { if (_target_needs_release) { // The hazard ptr in the target needs to be released. ! Threads::release_stable_list(_target); } } void ThreadsListSetter::set() { assert(_target->get_threads_hazard_ptr() == NULL, "hazard ptr should not already be set"); ! (void) Threads::acquire_stable_list(_target, /* is_ThreadsListSetter */ true); _target_needs_release = true; } ! ThreadsListHandle::ThreadsListHandle(Thread *self) : _list(Threads::acquire_stable_list(self, /* is_ThreadsListSetter */ false)), _self(self) { assert(self == Thread::current(), "sanity check"); if (EnableThreadSMRStatistics) { _timer.start(); } } ThreadsListHandle::~ThreadsListHandle() { ! Threads::release_stable_list(_self); if (EnableThreadSMRStatistics) { _timer.stop(); uint millis = (uint)_timer.milliseconds(); ! Threads::inc_smr_tlh_cnt(); ! Threads::add_smr_tlh_times(millis); ! Threads::update_smr_tlh_time_max(millis); } } // Convert an internal thread reference to a JavaThread found on the // associated ThreadsList. This ThreadsListHandle "protects" the --- 21,485 ---- * questions. * */ #include "precompiled.hpp" + #include "logging/logStream.hpp" #include "memory/allocation.inline.hpp" #include "runtime/thread.inline.hpp" ! #include "runtime/threadSMR.inline.hpp" #include "services/threadService.hpp" + #include "utilities/globalDefinitions.hpp" + #include "utilities/resourceHash.hpp" + + Monitor* ThreadsSMRSupport::_smr_delete_lock = + new Monitor(Monitor::special, "smr_delete_lock", + false /* allow_vm_block */, + Monitor::_safepoint_check_never); + // The '_cnt', '_max' and '_times" fields are enabled via + // -XX:+EnableThreadSMRStatistics: + + // # of parallel threads in _smr_delete_lock->wait(). + // Impl note: Hard to imagine > 64K waiting threads so this could be 16-bit, + // but there is no nice 16-bit _FORMAT support. + uint ThreadsSMRSupport::_smr_delete_lock_wait_cnt = 0; + + // Max # of parallel threads in _smr_delete_lock->wait(). + // Impl note: See _smr_delete_lock_wait_cnt note. + uint ThreadsSMRSupport::_smr_delete_lock_wait_max = 0; + + // Flag to indicate when an _smr_delete_lock->notify() is needed. + // Impl note: See _smr_delete_lock_wait_cnt note. + volatile uint ThreadsSMRSupport::_smr_delete_notify = 0; + + // # of threads deleted over VM lifetime. + // Impl note: Atomically incremented over VM lifetime so use unsigned for more + // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc + // isn't available everywhere (or is it?). + volatile uint ThreadsSMRSupport::_smr_deleted_thread_cnt = 0; + + // Max time in millis to delete a thread. + // Impl note: 16-bit might be too small on an overloaded machine. Use + // unsigned since this is a time value. Set via Atomic::cmpxchg() in a + // loop for correctness. + volatile uint ThreadsSMRSupport::_smr_deleted_thread_time_max = 0; + + // Cumulative time in millis to delete threads. + // Impl note: Atomically added to over VM lifetime so use unsigned for more + // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc + // isn't available everywhere (or is it?). + volatile uint ThreadsSMRSupport::_smr_deleted_thread_times = 0; + + ThreadsList* volatile ThreadsSMRSupport::_smr_java_thread_list = new ThreadsList(0); + + // # of ThreadsLists allocated over VM lifetime. + // Impl note: We allocate a new ThreadsList for every thread create and + // every thread delete so we need a bigger type than the + // _smr_deleted_thread_cnt field. + uint64_t ThreadsSMRSupport::_smr_java_thread_list_alloc_cnt = 1; + + // # of ThreadsLists freed over VM lifetime. + // Impl note: See _smr_java_thread_list_alloc_cnt note. + uint64_t ThreadsSMRSupport::_smr_java_thread_list_free_cnt = 0; + + // Max size ThreadsList allocated. + // Impl note: Max # of threads alive at one time should fit in unsigned 32-bit. + uint ThreadsSMRSupport::_smr_java_thread_list_max = 0; + + // Max # of nested ThreadsLists for a thread. + // Impl note: Hard to imagine > 64K nested ThreadsLists so this could be + // 16-bit, but there is no nice 16-bit _FORMAT support. + uint ThreadsSMRSupport::_smr_nested_thread_list_max = 0; + + // # of ThreadsListHandles deleted over VM lifetime. + // Impl note: Atomically incremented over VM lifetime so use unsigned for + // more range. There will be fewer ThreadsListHandles than threads so + // unsigned 32-bit should be fine. + volatile uint ThreadsSMRSupport::_smr_tlh_cnt = 0; + + // Max time in millis to delete a ThreadsListHandle. + // Impl note: 16-bit might be too small on an overloaded machine. Use + // unsigned since this is a time value. Set via Atomic::cmpxchg() in a + // loop for correctness. + volatile uint ThreadsSMRSupport::_smr_tlh_time_max = 0; + + // Cumulative time in millis to delete ThreadsListHandles. + // Impl note: Atomically added to over VM lifetime so use unsigned for more + // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc + // isn't available everywhere (or is it?). + volatile uint ThreadsSMRSupport::_smr_tlh_times = 0; + + ThreadsList* ThreadsSMRSupport::_smr_to_delete_list = NULL; + + // # of parallel ThreadsLists on the to-delete list. + // Impl note: Hard to imagine > 64K ThreadsLists needing to be deleted so + // this could be 16-bit, but there is no nice 16-bit _FORMAT support. + uint ThreadsSMRSupport::_smr_to_delete_list_cnt = 0; + + // Max # of parallel ThreadsLists on the to-delete list. + // Impl note: See _smr_to_delete_list_cnt note. + uint ThreadsSMRSupport::_smr_to_delete_list_max = 0; + + + // 'inline' functions first so the definitions are before first use: + + inline void ThreadsSMRSupport::add_smr_deleted_thread_times(uint add_value) { + Atomic::add(add_value, &_smr_deleted_thread_times); + } + + inline void ThreadsSMRSupport::inc_smr_deleted_thread_cnt() { + Atomic::inc(&_smr_deleted_thread_cnt); + } + + inline void ThreadsSMRSupport::update_smr_deleted_thread_time_max(uint new_value) { + while (true) { + uint cur_value = _smr_deleted_thread_time_max; + if (new_value <= cur_value) { + // No need to update max value so we're done. + break; + } + if (Atomic::cmpxchg(new_value, &_smr_deleted_thread_time_max, cur_value) == cur_value) { + // Updated max value so we're done. Otherwise try it all again. + break; + } + } + } + + + // Hash table of pointers found by a scan. Used for collecting hazard + // pointers (ThreadsList references). Also used for collecting JavaThreads + // that are indirectly referenced by hazard ptrs. An instance of this + // class only contains one type of pointer. + // + class ThreadScanHashtable : public CHeapObj<mtThread> { + private: + static bool ptr_equals(void * const& s1, void * const& s2) { + return s1 == s2; + } + + static unsigned int ptr_hash(void * const& s1) { + // 2654435761 = 2^32 * Phi (golden ratio) + return (unsigned int)(((uint32_t)(uintptr_t)s1) * 2654435761u); + } + + int _table_size; + // ResourceHashtable SIZE is specified at compile time so our + // dynamic _table_size is unused for now; 1031 is the first prime + // after 1024. + typedef ResourceHashtable<void *, int, &ThreadScanHashtable::ptr_hash, + &ThreadScanHashtable::ptr_equals, 1031, + ResourceObj::C_HEAP, mtThread> PtrTable; + PtrTable * _ptrs; + + public: + // ResourceHashtable is passed to various functions and populated in + // different places so we allocate it using C_HEAP to make it immune + // from any ResourceMarks that happen to be in the code paths. + ThreadScanHashtable(int table_size) : _table_size(table_size), _ptrs(new (ResourceObj::C_HEAP, mtThread) PtrTable()) {} + + ~ThreadScanHashtable() { delete _ptrs; } + + bool has_entry(void *pointer) { + int *val_ptr = _ptrs->get(pointer); + return val_ptr != NULL && *val_ptr == 1; + } + + void add_entry(void *pointer) { + _ptrs->put(pointer, 1); + } + }; + + // Closure to gather JavaThreads indirectly referenced by hazard ptrs + // (ThreadsList references) into a hash table. This closure handles part 2 + // of the dance - adding all the JavaThreads referenced by the hazard + // pointer (ThreadsList reference) to the hash table. + // + class AddThreadHazardPointerThreadClosure : public ThreadClosure { + private: + ThreadScanHashtable *_table; + + public: + AddThreadHazardPointerThreadClosure(ThreadScanHashtable *table) : _table(table) {} + + virtual void do_thread(Thread *thread) { + if (!_table->has_entry((void*)thread)) { + // The same JavaThread might be on more than one ThreadsList or + // more than one thread might be using the same ThreadsList. In + // either case, we only need a single entry for a JavaThread. + _table->add_entry((void*)thread); + } + } + }; + + // Closure to gather JavaThreads indirectly referenced by hazard ptrs + // (ThreadsList references) into a hash table. This closure handles part 1 + // of the dance - hazard ptr chain walking and dispatch to another + // closure. + // + class ScanHazardPtrGatherProtectedThreadsClosure : public ThreadClosure { + private: + ThreadScanHashtable *_table; + public: + ScanHazardPtrGatherProtectedThreadsClosure(ThreadScanHashtable *table) : _table(table) {} + + virtual void do_thread(Thread *thread) { + assert_locked_or_safepoint(Threads_lock); + + if (thread == NULL) return; + + // This code races with ThreadsSMRSupport::acquire_stable_list() which + // is lock-free so we have to handle some special situations. + // + ThreadsList *current_list = NULL; + while (true) { + current_list = thread->get_threads_hazard_ptr(); + // No hazard ptr so nothing more to do. + if (current_list == NULL) { + assert(thread->get_nested_threads_hazard_ptr() == NULL, + "cannot have a nested hazard ptr with a NULL regular hazard ptr"); + return; + } + + // If the hazard ptr is verified as stable (since it is not tagged), + // then it is safe to use. + if (!Thread::is_hazard_ptr_tagged(current_list)) break; + + // The hazard ptr is tagged as not yet verified as being stable + // so we are racing with acquire_stable_list(). This exchange + // attempts to invalidate the hazard ptr. If we win the race, + // then we can ignore this unstable hazard ptr and the other + // thread will retry the attempt to publish a stable hazard ptr. + // If we lose the race, then we retry our attempt to look at the + // hazard ptr. + if (thread->cmpxchg_threads_hazard_ptr(NULL, current_list) == current_list) return; + } + + // The current JavaThread has a hazard ptr (ThreadsList reference) + // which might be _smr_java_thread_list or it might be an older + // ThreadsList that has been removed but not freed. In either case, + // the hazard ptr is protecting all the JavaThreads on that + // ThreadsList. + AddThreadHazardPointerThreadClosure add_cl(_table); + current_list->threads_do(&add_cl); + + // Any NestedThreadsLists are also protecting JavaThreads so + // gather those also; the ThreadsLists may be different. + for (NestedThreadsList* node = thread->get_nested_threads_hazard_ptr(); + node != NULL; node = node->next()) { + node->t_list()->threads_do(&add_cl); + } + } + }; + + // Closure to gather hazard ptrs (ThreadsList references) into a hash table. + // + class ScanHazardPtrGatherThreadsListClosure : public ThreadClosure { + private: + ThreadScanHashtable *_table; + public: + ScanHazardPtrGatherThreadsListClosure(ThreadScanHashtable *table) : _table(table) {} + + virtual void do_thread(Thread* thread) { + assert_locked_or_safepoint(Threads_lock); + + if (thread == NULL) return; + ThreadsList *threads = thread->get_threads_hazard_ptr(); + if (threads == NULL) { + assert(thread->get_nested_threads_hazard_ptr() == NULL, + "cannot have a nested hazard ptr with a NULL regular hazard ptr"); + return; + } + // In this closure we always ignore the tag that might mark this + // hazard ptr as not yet verified. If we happen to catch an + // unverified hazard ptr that is subsequently discarded (not + // published), then the only side effect is that we might keep a + // to-be-deleted ThreadsList alive a little longer. + threads = Thread::untag_hazard_ptr(threads); + if (!_table->has_entry((void*)threads)) { + _table->add_entry((void*)threads); + } + + // Any NestedThreadsLists are also protecting JavaThreads so + // gather those also; the ThreadsLists may be different. + for (NestedThreadsList* node = thread->get_nested_threads_hazard_ptr(); + node != NULL; node = node->next()) { + threads = node->t_list(); + if (!_table->has_entry((void*)threads)) { + _table->add_entry((void*)threads); + } + } + } + }; + + // Closure to print JavaThreads that have a hazard ptr (ThreadsList + // reference) that contains an indirect reference to a specific JavaThread. + // + class ScanHazardPtrPrintMatchingThreadsClosure : public ThreadClosure { + private: + JavaThread *_thread; + public: + ScanHazardPtrPrintMatchingThreadsClosure(JavaThread *thread) : _thread(thread) {} + + virtual void do_thread(Thread *thread) { + assert_locked_or_safepoint(Threads_lock); + + if (thread == NULL) return; + ThreadsList *current_list = thread->get_threads_hazard_ptr(); + if (current_list == NULL) { + assert(thread->get_nested_threads_hazard_ptr() == NULL, + "cannot have a nested hazard ptr with a NULL regular hazard ptr"); + return; + } + // If the hazard ptr is unverified, then ignore it. + if (Thread::is_hazard_ptr_tagged(current_list)) return; + + // The current JavaThread has a hazard ptr (ThreadsList reference) + // which might be _smr_java_thread_list or it might be an older + // ThreadsList that has been removed but not freed. In either case, + // the hazard ptr is protecting all the JavaThreads on that + // ThreadsList, but we only care about matching a specific JavaThread. + JavaThreadIterator jti(current_list); + for (JavaThread *p = jti.first(); p != NULL; p = jti.next()) { + if (p == _thread) { + log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread1=" INTPTR_FORMAT " has a hazard pointer for thread2=" INTPTR_FORMAT, os::current_thread_id(), p2i(thread), p2i(_thread)); + break; + } + } + + // Any NestedThreadsLists are also protecting JavaThreads so + // check those also; the ThreadsLists may be different. + for (NestedThreadsList* node = thread->get_nested_threads_hazard_ptr(); + node != NULL; node = node->next()) { + JavaThreadIterator jti(node->t_list()); + for (JavaThread *p = jti.first(); p != NULL; p = jti.next()) { + if (p == _thread) { + log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread1=" INTPTR_FORMAT " has a nested hazard pointer for thread2=" INTPTR_FORMAT, os::current_thread_id(), p2i(thread), p2i(_thread)); + return; + } + } + } + } + }; + // 'entries + 1' so we always have at least one entry. ThreadsList::ThreadsList(int entries) : _length(entries), _threads(NEW_C_HEAP_ARRAY(JavaThread*, entries + 1, mtThread)), _next_list(NULL) { *(JavaThread**)(_threads + entries) = NULL; // Make sure the extra entry is NULL. } ThreadsList::~ThreadsList() { FREE_C_HEAP_ARRAY(JavaThread*, _threads); } + // Remove a JavaThread from a ThreadsList. The returned ThreadsList is a + // new copy of the specified ThreadsList with the specified JavaThread + // removed. + ThreadsList *ThreadsList::remove_thread(ThreadsList* list, JavaThread* java_thread) { + assert(list->_length > 0, "sanity"); + + uint i = (uint)list->find_index_of_JavaThread(java_thread); + assert(i < list->_length, "did not find JavaThread on the list"); + const uint index = i; + const uint new_length = list->_length - 1; + const uint head_length = index; + const uint tail_length = (new_length >= index) ? (new_length - index) : 0; + ThreadsList *const new_list = new ThreadsList(new_length); + + if (head_length > 0) { + Copy::disjoint_words((HeapWord*)list->_threads, (HeapWord*)new_list->_threads, head_length); + } + if (tail_length > 0) { + Copy::disjoint_words((HeapWord*)list->_threads + index + 1, (HeapWord*)new_list->_threads + index, tail_length); + } + + return new_list; + } + + // Add a JavaThread to a ThreadsList. The returned ThreadsList is a + // new copy of the specified ThreadsList with the specified JavaThread + // appended to the end. + ThreadsList *ThreadsList::add_thread(ThreadsList *list, JavaThread *java_thread) { + const uint index = list->_length; + const uint new_length = index + 1; + const uint head_length = index; + ThreadsList *const new_list = new ThreadsList(new_length); + + if (head_length > 0) { + Copy::disjoint_words((HeapWord*)list->_threads, (HeapWord*)new_list->_threads, head_length); + } + *(JavaThread**)(new_list->_threads + index) = java_thread; + + return new_list; + } + + int ThreadsList::find_index_of_JavaThread(JavaThread *target) { + if (target == NULL) { + return -1; + } + for (uint i = 0; i < length(); i++) { + if (target == thread_at(i)) { + return (int)i; + } + } + return -1; + } + + JavaThread* ThreadsList::find_JavaThread_from_java_tid(jlong java_tid) const { + for (uint i = 0; i < length(); i++) { + JavaThread* thread = thread_at(i); + oop tobj = thread->threadObj(); + // Ignore the thread if it hasn't run yet, has exited + // or is starting to exit. + if (tobj != NULL && !thread->is_exiting() && + java_tid == java_lang_Thread::thread_id(tobj)) { + // found a match + return thread; + } + } + return NULL; + } + + bool ThreadsList::includes(const JavaThread * const p) const { + if (p == NULL) { + return false; + } + for (uint i = 0; i < length(); i++) { + if (thread_at(i) == p) { + return true; + } + } + return false; + } + ThreadsListSetter::~ThreadsListSetter() { if (_target_needs_release) { // The hazard ptr in the target needs to be released. ! ThreadsSMRSupport::release_stable_list(_target); } } void ThreadsListSetter::set() { assert(_target->get_threads_hazard_ptr() == NULL, "hazard ptr should not already be set"); ! (void) ThreadsSMRSupport::acquire_stable_list(_target, /* is_ThreadsListSetter */ true); _target_needs_release = true; } ! ThreadsListHandle::ThreadsListHandle(Thread *self) : _list(ThreadsSMRSupport::acquire_stable_list(self, /* is_ThreadsListSetter */ false)), _self(self) { assert(self == Thread::current(), "sanity check"); if (EnableThreadSMRStatistics) { _timer.start(); } } ThreadsListHandle::~ThreadsListHandle() { ! ThreadsSMRSupport::release_stable_list(_self); if (EnableThreadSMRStatistics) { _timer.stop(); uint millis = (uint)_timer.milliseconds(); ! ThreadsSMRSupport::inc_smr_tlh_cnt(); ! ThreadsSMRSupport::add_smr_tlh_times(millis); ! ThreadsSMRSupport::update_smr_tlh_time_max(millis); } } // Convert an internal thread reference to a JavaThread found on the // associated ThreadsList. This ThreadsListHandle "protects" the
*** 117,121 **** --- 530,1034 ---- // Return a live JavaThread that is "protected" by the // ThreadsListHandle in the caller. *jt_pp = java_thread; return true; } + + // Acquire a stable ThreadsList. + // + ThreadsList *ThreadsSMRSupport::acquire_stable_list(Thread *self, bool is_ThreadsListSetter) { + assert(self != NULL, "sanity check"); + // acquire_stable_list_nested_path() will grab the Threads_lock + // so let's make sure the ThreadsListHandle is in a safe place. + // ThreadsListSetter cannot make this check on this code path. + debug_only(if (!is_ThreadsListSetter && StrictSafepointChecks) self->check_for_valid_safepoint_state(/* potential_vm_operation */ false);) + + if (self->get_threads_hazard_ptr() == NULL) { + // The typical case is first. + return acquire_stable_list_fast_path(self); + } + + // The nested case is rare. + return acquire_stable_list_nested_path(self); + } + + // Fast path (and lock free) way to acquire a stable ThreadsList. + // + ThreadsList *ThreadsSMRSupport::acquire_stable_list_fast_path(Thread *self) { + assert(self != NULL, "sanity check"); + assert(self->get_threads_hazard_ptr() == NULL, "sanity check"); + assert(self->get_nested_threads_hazard_ptr() == NULL, + "cannot have a nested hazard ptr with a NULL regular hazard ptr"); + + ThreadsList* threads; + + // Stable recording of a hazard ptr for SMR. This code does not use + // locks so its use of the _smr_java_thread_list & _threads_hazard_ptr + // fields is racy relative to code that uses those fields with locks. + // OrderAccess and Atomic functions are used to deal with those races. + // + while (true) { + threads = get_smr_java_thread_list(); + + // Publish a tagged hazard ptr to denote that the hazard ptr is not + // yet verified as being stable. Due to the fence after the hazard + // ptr write, it will be sequentially consistent w.r.t. the + // sequentially consistent writes of the ThreadsList, even on + // non-multiple copy atomic machines where stores can be observed + // in different order from different observer threads. + ThreadsList* unverified_threads = Thread::tag_hazard_ptr(threads); + self->set_threads_hazard_ptr(unverified_threads); + + // If _smr_java_thread_list has changed, we have lost a race with + // Threads::add() or Threads::remove() and have to try again. + if (get_smr_java_thread_list() != threads) { + continue; + } + + // We try to remove the tag which will verify the hazard ptr as + // being stable. This exchange can race with a scanning thread + // which might invalidate the tagged hazard ptr to keep it from + // being followed to access JavaThread ptrs. If we lose the race, + // we simply retry. If we win the race, then the stable hazard + // ptr is officially published. + if (self->cmpxchg_threads_hazard_ptr(threads, unverified_threads) == unverified_threads) { + break; + } + } + + // A stable hazard ptr has been published letting other threads know + // that the ThreadsList and the JavaThreads reachable from this list + // are protected and hence they should not be deleted until everyone + // agrees it is safe to do so. + + return threads; + } + + // Acquire a nested stable ThreadsList; this is rare so it uses + // Threads_lock. + // + ThreadsList *ThreadsSMRSupport::acquire_stable_list_nested_path(Thread *self) { + assert(self != NULL, "sanity check"); + assert(self->get_threads_hazard_ptr() != NULL, + "cannot have a NULL regular hazard ptr when acquiring a nested hazard ptr"); + + // The thread already has a hazard ptr (ThreadsList ref) so we need + // to create a nested ThreadsListHandle with the current ThreadsList + // since it might be different than our current hazard ptr. The need + // for a nested ThreadsListHandle is rare so we do this while holding + // the Threads_lock so we don't race with the scanning code; the code + // is so much simpler this way. + + NestedThreadsList* node; + { + // Only grab the Threads_lock if we don't already own it. + MutexLockerEx ml(Threads_lock->owned_by_self() ? NULL : Threads_lock); + node = new NestedThreadsList(get_smr_java_thread_list()); + // We insert at the front of the list to match up with the delete + // in release_stable_list(). + node->set_next(self->get_nested_threads_hazard_ptr()); + self->set_nested_threads_hazard_ptr(node); + if (EnableThreadSMRStatistics) { + self->inc_nested_threads_hazard_ptr_cnt(); + if (self->nested_threads_hazard_ptr_cnt() > _smr_nested_thread_list_max) { + _smr_nested_thread_list_max = self->nested_threads_hazard_ptr_cnt(); + } + } + } + log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::acquire_stable_list: add NestedThreadsList node containing ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(node->t_list())); + + return node->t_list(); + } + + // set_smr_delete_notify() and clear_smr_delete_notify() are called + // under the protection of the smr_delete_lock, but we also use an + // Atomic operation to ensure the memory update is seen earlier than + // when the smr_delete_lock is dropped. + // + void ThreadsSMRSupport::clear_smr_delete_notify() { + Atomic::dec(&_smr_delete_notify); + } + + // Return true if the specified JavaThread is protected by a hazard + // pointer (ThreadsList reference). Otherwise, returns false. + // + bool ThreadsSMRSupport::is_a_protected_JavaThread(JavaThread *thread) { + assert_locked_or_safepoint(Threads_lock); + + // Hash table size should be first power of two higher than twice + // the length of the Threads list. + int hash_table_size = MIN2((int)get_smr_java_thread_list()->length(), 32) << 1; + hash_table_size--; + hash_table_size |= hash_table_size >> 1; + hash_table_size |= hash_table_size >> 2; + hash_table_size |= hash_table_size >> 4; + hash_table_size |= hash_table_size >> 8; + hash_table_size |= hash_table_size >> 16; + hash_table_size++; + + // Gather a hash table of the JavaThreads indirectly referenced by + // hazard ptrs. + ThreadScanHashtable *scan_table = new ThreadScanHashtable(hash_table_size); + ScanHazardPtrGatherProtectedThreadsClosure scan_cl(scan_table); + Threads::threads_do(&scan_cl); + + bool thread_is_protected = false; + if (scan_table->has_entry((void*)thread)) { + thread_is_protected = true; + } + delete scan_table; + return thread_is_protected; + } + + // Release a stable ThreadsList. + // + void ThreadsSMRSupport::release_stable_list(Thread *self) { + assert(self != NULL, "sanity check"); + // release_stable_list_nested_path() will grab the Threads_lock + // so let's make sure the ThreadsListHandle is in a safe place. + debug_only(if (StrictSafepointChecks) self->check_for_valid_safepoint_state(/* potential_vm_operation */ false);) + + if (self->get_nested_threads_hazard_ptr() == NULL) { + // The typical case is first. + release_stable_list_fast_path(self); + return; + } + + // The nested case is rare. + release_stable_list_nested_path(self); + } + + // Fast path way to release a stable ThreadsList. The release portion + // is lock-free, but the wake up portion is not. + // + void ThreadsSMRSupport::release_stable_list_fast_path(Thread *self) { + assert(self != NULL, "sanity check"); + assert(self->get_threads_hazard_ptr() != NULL, "sanity check"); + assert(self->get_nested_threads_hazard_ptr() == NULL, + "cannot have a nested hazard ptr when releasing a regular hazard ptr"); + + // After releasing the hazard ptr, other threads may go ahead and + // free up some memory temporarily used by a ThreadsList snapshot. + self->set_threads_hazard_ptr(NULL); + + // We use double-check locking to reduce traffic on the system + // wide smr_delete_lock. + if (ThreadsSMRSupport::smr_delete_notify()) { + // An exiting thread might be waiting in smr_delete(); we need to + // check with smr_delete_lock to be sure. + release_stable_list_wake_up((char *) "regular hazard ptr"); + } + } + + // Release a nested stable ThreadsList; this is rare so it uses + // Threads_lock. + // + void ThreadsSMRSupport::release_stable_list_nested_path(Thread *self) { + assert(self != NULL, "sanity check"); + assert(self->get_nested_threads_hazard_ptr() != NULL, "sanity check"); + assert(self->get_threads_hazard_ptr() != NULL, + "must have a regular hazard ptr to have nested hazard ptrs"); + + // We have a nested ThreadsListHandle so we have to release it first. + // The need for a nested ThreadsListHandle is rare so we do this while + // holding the Threads_lock so we don't race with the scanning code; + // the code is so much simpler this way. + + NestedThreadsList *node; + { + // Only grab the Threads_lock if we don't already own it. + MutexLockerEx ml(Threads_lock->owned_by_self() ? NULL : Threads_lock); + // We remove from the front of the list to match up with the insert + // in acquire_stable_list(). + node = self->get_nested_threads_hazard_ptr(); + self->set_nested_threads_hazard_ptr(node->next()); + if (EnableThreadSMRStatistics) { + self->dec_nested_threads_hazard_ptr_cnt(); + } + } + + // An exiting thread might be waiting in smr_delete(); we need to + // check with smr_delete_lock to be sure. + release_stable_list_wake_up((char *) "nested hazard ptr"); + + log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::release_stable_list: delete NestedThreadsList node containing ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(node->t_list())); + + delete node; + } + + // Wake up portion of the release stable ThreadsList protocol; + // uses the smr_delete_lock(). + // + void ThreadsSMRSupport::release_stable_list_wake_up(char *log_str) { + assert(log_str != NULL, "sanity check"); + + // Note: smr_delete_lock is held in smr_delete() for the entire + // hazard ptr search so that we do not lose this notify() if + // the exiting thread has to wait. That code path also holds + // Threads_lock (which was grabbed before smr_delete_lock) so that + // threads_do() can be called. This means the system can't start a + // safepoint which means this thread can't take too long to get to + // a safepoint because of being blocked on smr_delete_lock. + // + MonitorLockerEx ml(ThreadsSMRSupport::smr_delete_lock(), Monitor::_no_safepoint_check_flag); + if (ThreadsSMRSupport::smr_delete_notify()) { + // Notify any exiting JavaThreads that are waiting in smr_delete() + // that we've released a ThreadsList. + ml.notify_all(); + log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::release_stable_list notified %s", os::current_thread_id(), log_str); + } + } + + // See note for clear_smr_delete_notify(). + // + void ThreadsSMRSupport::set_smr_delete_notify() { + Atomic::inc(&_smr_delete_notify); + } + + // Safely delete a JavaThread when it is no longer in use by a + // ThreadsListHandle. + // + void ThreadsSMRSupport::smr_delete(JavaThread *thread) { + assert(!Threads_lock->owned_by_self(), "sanity"); + + bool has_logged_once = false; + elapsedTimer timer; + if (EnableThreadSMRStatistics) { + timer.start(); + } + + while (true) { + { + // No safepoint check because this JavaThread is not on the + // Threads list. + MutexLockerEx ml(Threads_lock, Mutex::_no_safepoint_check_flag); + // Cannot use a MonitorLockerEx helper here because we have + // to drop the Threads_lock first if we wait. + ThreadsSMRSupport::smr_delete_lock()->lock_without_safepoint_check(); + // Set the smr_delete_notify flag after we grab smr_delete_lock + // and before we scan hazard ptrs because we're doing + // double-check locking in release_stable_list(). + ThreadsSMRSupport::set_smr_delete_notify(); + + if (!is_a_protected_JavaThread(thread)) { + // This is the common case. + ThreadsSMRSupport::clear_smr_delete_notify(); + ThreadsSMRSupport::smr_delete_lock()->unlock(); + break; + } + if (!has_logged_once) { + has_logged_once = true; + log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread=" INTPTR_FORMAT " is not deleted.", os::current_thread_id(), p2i(thread)); + if (log_is_enabled(Debug, os, thread)) { + ScanHazardPtrPrintMatchingThreadsClosure scan_cl(thread); + Threads::threads_do(&scan_cl); + } + } + } // We have to drop the Threads_lock to wait or delete the thread + + if (EnableThreadSMRStatistics) { + _smr_delete_lock_wait_cnt++; + if (_smr_delete_lock_wait_cnt > _smr_delete_lock_wait_max) { + _smr_delete_lock_wait_max = _smr_delete_lock_wait_cnt; + } + } + // Wait for a release_stable_list() call before we check again. No + // safepoint check, no timeout, and not as suspend equivalent flag + // because this JavaThread is not on the Threads list. + ThreadsSMRSupport::smr_delete_lock()->wait(Mutex::_no_safepoint_check_flag, 0, + !Mutex::_as_suspend_equivalent_flag); + if (EnableThreadSMRStatistics) { + _smr_delete_lock_wait_cnt--; + } + + ThreadsSMRSupport::clear_smr_delete_notify(); + ThreadsSMRSupport::smr_delete_lock()->unlock(); + // Retry the whole scenario. + } + + if (ThreadLocalHandshakes) { + // The thread is about to be deleted so cancel any handshake. + thread->cancel_handshake(); + } + + delete thread; + if (EnableThreadSMRStatistics) { + timer.stop(); + uint millis = (uint)timer.milliseconds(); + ThreadsSMRSupport::inc_smr_deleted_thread_cnt(); + ThreadsSMRSupport::add_smr_deleted_thread_times(millis); + ThreadsSMRSupport::update_smr_deleted_thread_time_max(millis); + } + + log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread=" INTPTR_FORMAT " is deleted.", os::current_thread_id(), p2i(thread)); + } + + bool ThreadsSMRSupport::smr_delete_notify() { + // Use load_acquire() in order to see any updates to _smr_delete_notify + // earlier than when smr_delete_lock is grabbed. + return (OrderAccess::load_acquire(&_smr_delete_notify) != 0); + } + + // Safely free a ThreadsList after a Threads::add() or Threads::remove(). + // The specified ThreadsList may not get deleted during this call if it + // is still in-use (referenced by a hazard ptr). Other ThreadsLists + // in the chain may get deleted by this call if they are no longer in-use. + void ThreadsSMRSupport::smr_free_list(ThreadsList* threads) { + assert_locked_or_safepoint(Threads_lock); + + threads->set_next_list(_smr_to_delete_list); + _smr_to_delete_list = threads; + if (EnableThreadSMRStatistics) { + _smr_to_delete_list_cnt++; + if (_smr_to_delete_list_cnt > _smr_to_delete_list_max) { + _smr_to_delete_list_max = _smr_to_delete_list_cnt; + } + } + + // Hash table size should be first power of two higher than twice the length of the ThreadsList + int hash_table_size = MIN2((int)get_smr_java_thread_list()->length(), 32) << 1; + hash_table_size--; + hash_table_size |= hash_table_size >> 1; + hash_table_size |= hash_table_size >> 2; + hash_table_size |= hash_table_size >> 4; + hash_table_size |= hash_table_size >> 8; + hash_table_size |= hash_table_size >> 16; + hash_table_size++; + + // Gather a hash table of the current hazard ptrs: + ThreadScanHashtable *scan_table = new ThreadScanHashtable(hash_table_size); + ScanHazardPtrGatherThreadsListClosure scan_cl(scan_table); + Threads::threads_do(&scan_cl); + + // Walk through the linked list of pending freeable ThreadsLists + // and free the ones that are not referenced from hazard ptrs. + ThreadsList* current = _smr_to_delete_list; + ThreadsList* prev = NULL; + ThreadsList* next = NULL; + bool threads_is_freed = false; + while (current != NULL) { + next = current->next_list(); + if (!scan_table->has_entry((void*)current)) { + // This ThreadsList is not referenced by a hazard ptr. + if (prev != NULL) { + prev->set_next_list(next); + } + if (_smr_to_delete_list == current) { + _smr_to_delete_list = next; + } + + log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_free_list: threads=" INTPTR_FORMAT " is freed.", os::current_thread_id(), p2i(current)); + if (current == threads) threads_is_freed = true; + delete current; + if (EnableThreadSMRStatistics) { + _smr_java_thread_list_free_cnt++; + _smr_to_delete_list_cnt--; + } + } else { + prev = current; + } + current = next; + } + + if (!threads_is_freed) { + // Only report "is not freed" on the original call to + // smr_free_list() for this ThreadsList. + log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_free_list: threads=" INTPTR_FORMAT " is not freed.", os::current_thread_id(), p2i(threads)); + } + + delete scan_table; + } + + // Log Threads class SMR info. + void ThreadsSMRSupport::log_smr_statistics() { + LogTarget(Info, thread, smr) log; + if (log.is_enabled()) { + LogStream out(log); + print_smr_info_on(&out); + } + } + + // Print Threads class SMR info. + void ThreadsSMRSupport::print_smr_info_on(outputStream* st) { + // Only grab the Threads_lock if we don't already own it + // and if we are not reporting an error. + MutexLockerEx ml((Threads_lock->owned_by_self() || VMError::is_error_reported()) ? NULL : Threads_lock); + + st->print_cr("Threads class SMR info:"); + st->print_cr("_smr_java_thread_list=" INTPTR_FORMAT ", length=%u, " + "elements={", p2i(_smr_java_thread_list), + _smr_java_thread_list->length()); + print_smr_info_elements_on(st, _smr_java_thread_list); + st->print_cr("}"); + if (_smr_to_delete_list != NULL) { + st->print_cr("_smr_to_delete_list=" INTPTR_FORMAT ", length=%u, " + "elements={", p2i(_smr_to_delete_list), + _smr_to_delete_list->length()); + print_smr_info_elements_on(st, _smr_to_delete_list); + st->print_cr("}"); + for (ThreadsList *t_list = _smr_to_delete_list->next_list(); + t_list != NULL; t_list = t_list->next_list()) { + st->print("next-> " INTPTR_FORMAT ", length=%u, " + "elements={", p2i(t_list), t_list->length()); + print_smr_info_elements_on(st, t_list); + st->print_cr("}"); + } + } + if (!EnableThreadSMRStatistics) { + return; + } + st->print_cr("_smr_java_thread_list_alloc_cnt=" UINT64_FORMAT "," + "_smr_java_thread_list_free_cnt=" UINT64_FORMAT "," + "_smr_java_thread_list_max=%u, " + "_smr_nested_thread_list_max=%u", + _smr_java_thread_list_alloc_cnt, + _smr_java_thread_list_free_cnt, + _smr_java_thread_list_max, + _smr_nested_thread_list_max); + if (_smr_tlh_cnt > 0) { + st->print_cr("_smr_tlh_cnt=%u" + ", _smr_tlh_times=%u" + ", avg_smr_tlh_time=%0.2f" + ", _smr_tlh_time_max=%u", + _smr_tlh_cnt, _smr_tlh_times, + ((double) _smr_tlh_times / _smr_tlh_cnt), + _smr_tlh_time_max); + } + if (_smr_deleted_thread_cnt > 0) { + st->print_cr("_smr_deleted_thread_cnt=%u" + ", _smr_deleted_thread_times=%u" + ", avg_smr_deleted_thread_time=%0.2f" + ", _smr_deleted_thread_time_max=%u", + _smr_deleted_thread_cnt, _smr_deleted_thread_times, + ((double) _smr_deleted_thread_times / _smr_deleted_thread_cnt), + _smr_deleted_thread_time_max); + } + st->print_cr("_smr_delete_lock_wait_cnt=%u, _smr_delete_lock_wait_max=%u", + _smr_delete_lock_wait_cnt, _smr_delete_lock_wait_max); + st->print_cr("_smr_to_delete_list_cnt=%u, _smr_to_delete_list_max=%u", + _smr_to_delete_list_cnt, _smr_to_delete_list_max); + } + + // Print ThreadsList elements (4 per line). + void ThreadsSMRSupport::print_smr_info_elements_on(outputStream* st, + ThreadsList* t_list) { + uint cnt = 0; + JavaThreadIterator jti(t_list); + for (JavaThread *jt = jti.first(); jt != NULL; jt = jti.next()) { + st->print(INTPTR_FORMAT, p2i(jt)); + if (cnt < t_list->length() - 1) { + // Separate with comma or comma-space except for the last one. + if (((cnt + 1) % 4) == 0) { + // Four INTPTR_FORMAT fit on an 80 column line so end the + // current line with just a comma. + st->print_cr(","); + } else { + // Not the last one on the current line so use comma-space: + st->print(", "); + } + } else { + // Last one so just end the current line. + st->cr(); + } + cnt++; + } + }
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