/* * Copyright (c) 1997, 2020, 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 * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. * */ #include "precompiled.hpp" #include "classfile/classLoaderDataGraph.inline.hpp" #include "classfile/dictionary.hpp" #include "classfile/stringTable.hpp" #include "classfile/symbolTable.hpp" #include "classfile/systemDictionary.hpp" #include "code/codeCache.hpp" #include "code/icBuffer.hpp" #include "code/nmethod.hpp" #include "code/pcDesc.hpp" #include "code/scopeDesc.hpp" #include "compiler/compilationPolicy.hpp" #include "gc/shared/collectedHeap.hpp" #include "gc/shared/gcLocker.hpp" #include "gc/shared/oopStorage.hpp" #include "gc/shared/strongRootsScope.hpp" #include "gc/shared/workgroup.hpp" #include "interpreter/interpreter.hpp" #include "jfr/jfrEvents.hpp" #include "logging/log.hpp" #include "logging/logStream.hpp" #include "memory/resourceArea.hpp" #include "memory/universe.hpp" #include "oops/oop.inline.hpp" #include "oops/symbol.hpp" #include "runtime/atomic.hpp" #include "runtime/deoptimization.hpp" #include "runtime/frame.inline.hpp" #include "runtime/handles.inline.hpp" #include "runtime/interfaceSupport.inline.hpp" #include "runtime/mutexLocker.hpp" #include "runtime/orderAccess.hpp" #include "runtime/osThread.hpp" #include "runtime/safepoint.hpp" #include "runtime/safepointMechanism.inline.hpp" #include "runtime/signature.hpp" #include "runtime/stubCodeGenerator.hpp" #include "runtime/stubRoutines.hpp" #include "runtime/sweeper.hpp" #include "runtime/synchronizer.hpp" #include "runtime/thread.inline.hpp" #include "runtime/threadSMR.hpp" #include "runtime/timerTrace.hpp" #include "services/runtimeService.hpp" #include "utilities/events.hpp" #include "utilities/macros.hpp" static void post_safepoint_begin_event(EventSafepointBegin& event, uint64_t safepoint_id, int thread_count, int critical_thread_count) { if (event.should_commit()) { event.set_safepointId(safepoint_id); event.set_totalThreadCount(thread_count); event.set_jniCriticalThreadCount(critical_thread_count); event.commit(); } } static void post_safepoint_cleanup_event(EventSafepointCleanup& event, uint64_t safepoint_id) { if (event.should_commit()) { event.set_safepointId(safepoint_id); event.commit(); } } static void post_safepoint_synchronize_event(EventSafepointStateSynchronization& event, uint64_t safepoint_id, int initial_number_of_threads, int threads_waiting_to_block, uint64_t iterations) { if (event.should_commit()) { event.set_safepointId(safepoint_id); event.set_initialThreadCount(initial_number_of_threads); event.set_runningThreadCount(threads_waiting_to_block); event.set_iterations(iterations); event.commit(); } } static void post_safepoint_cleanup_task_event(EventSafepointCleanupTask& event, uint64_t safepoint_id, const char* name) { if (event.should_commit()) { event.set_safepointId(safepoint_id); event.set_name(name); event.commit(); } } static void post_safepoint_end_event(EventSafepointEnd& event, uint64_t safepoint_id) { if (event.should_commit()) { event.set_safepointId(safepoint_id); event.commit(); } } // SafepointCheck SafepointStateTracker::SafepointStateTracker(uint64_t safepoint_id, bool at_safepoint) : _safepoint_id(safepoint_id), _at_safepoint(at_safepoint) {} bool SafepointStateTracker::safepoint_state_changed() { return _safepoint_id != SafepointSynchronize::safepoint_id() || _at_safepoint != SafepointSynchronize::is_at_safepoint(); } // -------------------------------------------------------------------------------------------------- // Implementation of Safepoint begin/end SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized; int SafepointSynchronize::_waiting_to_block = 0; volatile uint64_t SafepointSynchronize::_safepoint_counter = 0; uint64_t SafepointSynchronize::_safepoint_id = 0; const uint64_t SafepointSynchronize::InactiveSafepointCounter = 0; int SafepointSynchronize::_current_jni_active_count = 0; WaitBarrier* SafepointSynchronize::_wait_barrier; static volatile bool PageArmed = false; // safepoint polling page is RO|RW vs PROT_NONE static bool timeout_error_printed = false; // Statistic related static jlong _safepoint_begin_time = 0; static volatile int _nof_threads_hit_polling_page = 0; void SafepointSynchronize::init(Thread* vmthread) { // WaitBarrier should never be destroyed since we will have // threads waiting on it while exiting. _wait_barrier = new WaitBarrier(vmthread); SafepointTracing::init(); } void SafepointSynchronize::increment_jni_active_count() { assert(Thread::current()->is_VM_thread(), "Only VM thread may increment"); ++_current_jni_active_count; } void SafepointSynchronize::decrement_waiting_to_block() { assert(_waiting_to_block > 0, "sanity check"); assert(Thread::current()->is_VM_thread(), "Only VM thread may decrement"); --_waiting_to_block; } bool SafepointSynchronize::thread_not_running(ThreadSafepointState *cur_state) { if (!cur_state->is_running()) { return true; } cur_state->examine_state_of_thread(SafepointSynchronize::safepoint_counter()); if (!cur_state->is_running()) { return true; } LogTarget(Trace, safepoint) lt; if (lt.is_enabled()) { ResourceMark rm; LogStream ls(lt); cur_state->print_on(&ls); } return false; } #ifdef ASSERT static void assert_list_is_valid(const ThreadSafepointState* tss_head, int still_running) { int a = 0; const ThreadSafepointState *tmp_tss = tss_head; while (tmp_tss != NULL) { ++a; assert(tmp_tss->is_running(), "Illegal initial state"); tmp_tss = tmp_tss->get_next(); } assert(a == still_running, "Must be the same"); } #endif // ASSERT static void back_off(int64_t start_time) { // We start with fine-grained nanosleeping until a millisecond has // passed, at which point we resort to plain naked_short_sleep. if (os::javaTimeNanos() - start_time < NANOSECS_PER_MILLISEC) { os::naked_short_nanosleep(10 * (NANOUNITS / MICROUNITS)); } else { os::naked_short_sleep(1); } } int SafepointSynchronize::synchronize_threads(jlong safepoint_limit_time, int nof_threads, int* initial_running) { JavaThreadIteratorWithHandle jtiwh; #ifdef ASSERT for (; JavaThread *cur = jtiwh.next(); ) { assert(cur->safepoint_state()->is_running(), "Illegal initial state"); } jtiwh.rewind(); #endif // ASSERT // Iterate through all threads until it has been determined how to stop them all at a safepoint. int still_running = nof_threads; ThreadSafepointState *tss_head = NULL; ThreadSafepointState **p_prev = &tss_head; for (; JavaThread *cur = jtiwh.next(); ) { ThreadSafepointState *cur_tss = cur->safepoint_state(); assert(cur_tss->get_next() == NULL, "Must be NULL"); if (thread_not_running(cur_tss)) { --still_running; } else { *p_prev = cur_tss; p_prev = cur_tss->next_ptr(); } } *p_prev = NULL; DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);) *initial_running = still_running; // If there is no thread still running, we are already done. if (still_running <= 0) { assert(tss_head == NULL, "Must be empty"); return 1; } int iterations = 1; // The first iteration is above. int64_t start_time = os::javaTimeNanos(); do { // Check if this has taken too long: if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) { print_safepoint_timeout(); } if (int(iterations) == -1) { // overflow - something is wrong. // We can only overflow here when we are using global // polling pages. We keep this guarantee in its original // form so that searches of the bug database for this // failure mode find the right bugs. guarantee (!PageArmed, "invariant"); } p_prev = &tss_head; ThreadSafepointState *cur_tss = tss_head; while (cur_tss != NULL) { assert(cur_tss->is_running(), "Illegal initial state"); if (thread_not_running(cur_tss)) { --still_running; *p_prev = NULL; ThreadSafepointState *tmp = cur_tss; cur_tss = cur_tss->get_next(); tmp->set_next(NULL); } else { *p_prev = cur_tss; p_prev = cur_tss->next_ptr(); cur_tss = cur_tss->get_next(); } } DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);) if (still_running > 0) { back_off(start_time); } iterations++; } while (still_running > 0); assert(tss_head == NULL, "Must be empty"); return iterations; } void SafepointSynchronize::arm_safepoint() { // Begin the process of bringing the system to a safepoint. // Java threads can be in several different states and are // stopped by different mechanisms: // // 1. Running interpreted // When executing branching/returning byte codes interpreter // checks if the poll is armed, if so blocks in SS::block(). // When using global polling the interpreter dispatch table // is changed to force it to check for a safepoint condition // between bytecodes. // 2. Running in native code // When returning from the native code, a Java thread must check // the safepoint _state to see if we must block. If the // VM thread sees a Java thread in native, it does // not wait for this thread to block. The order of the memory // writes and reads of both the safepoint state and the Java // threads state is critical. In order to guarantee that the // memory writes are serialized with respect to each other, // the VM thread issues a memory barrier instruction. // 3. Running compiled Code // Compiled code reads the local polling page that // is set to fault if we are trying to get to a safepoint. // 4. Blocked // A thread which is blocked will not be allowed to return from the // block condition until the safepoint operation is complete. // 5. In VM or Transitioning between states // If a Java thread is currently running in the VM or transitioning // between states, the safepointing code will poll the thread state // until the thread blocks itself when it attempts transitions to a // new state or locking a safepoint checked monitor. // We must never miss a thread with correct safepoint id, so we must make sure we arm // the wait barrier for the next safepoint id/counter. // Arming must be done after resetting _current_jni_active_count, _waiting_to_block. _wait_barrier->arm(static_cast(_safepoint_counter + 1)); assert((_safepoint_counter & 0x1) == 0, "must be even"); // The store to _safepoint_counter must happen after any stores in arming. Atomic::release_store(&_safepoint_counter, _safepoint_counter + 1); // We are synchronizing OrderAccess::storestore(); // Ordered with _safepoint_counter _state = _synchronizing; if (SafepointMechanism::uses_thread_local_poll()) { // Arming the per thread poll while having _state != _not_synchronized means safepointing log_trace(safepoint)("Setting thread local yield flag for threads"); OrderAccess::storestore(); // storestore, global state -> local state for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) { // Make sure the threads start polling, it is time to yield. SafepointMechanism::arm_local_poll(cur); } } OrderAccess::fence(); // storestore|storeload, global state -> local state if (SafepointMechanism::uses_global_page_poll()) { // Make interpreter safepoint aware Interpreter::notice_safepoints(); // Make polling safepoint aware guarantee (!PageArmed, "invariant") ; PageArmed = true; os::make_polling_page_unreadable(); } } // Roll all threads forward to a safepoint and suspend them all void SafepointSynchronize::begin() { assert(Thread::current()->is_VM_thread(), "Only VM thread may execute a safepoint"); EventSafepointBegin begin_event; SafepointTracing::begin(VMThread::vm_op_type()); Universe::heap()->safepoint_synchronize_begin(); // By getting the Threads_lock, we assure that no threads are about to start or // exit. It is released again in SafepointSynchronize::end(). Threads_lock->lock(); assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state"); int nof_threads = Threads::number_of_threads(); _nof_threads_hit_polling_page = 0; log_debug(safepoint)("Safepoint synchronization initiated using %s wait barrier. (%d threads)", _wait_barrier->description(), nof_threads); // Reset the count of active JNI critical threads _current_jni_active_count = 0; // Set number of threads to wait for _waiting_to_block = nof_threads; jlong safepoint_limit_time = 0; if (SafepointTimeout) { // Set the limit time, so that it can be compared to see if this has taken // too long to complete. safepoint_limit_time = SafepointTracing::start_of_safepoint() + (jlong)SafepointTimeoutDelay * (NANOUNITS / MILLIUNITS); timeout_error_printed = false; } EventSafepointStateSynchronization sync_event; int initial_running = 0; // Arms the safepoint, _current_jni_active_count and _waiting_to_block must be set before. arm_safepoint(); // Will spin until all threads are safe. int iterations = synchronize_threads(safepoint_limit_time, nof_threads, &initial_running); assert(_waiting_to_block == 0, "No thread should be running"); #ifndef PRODUCT if (safepoint_limit_time != 0) { jlong current_time = os::javaTimeNanos(); if (safepoint_limit_time < current_time) { log_warning(safepoint)("# SafepointSynchronize: Finished after " INT64_FORMAT_W(6) " ms", (int64_t)(current_time - SafepointTracing::start_of_safepoint()) / (NANOUNITS / MILLIUNITS)); } } #endif assert(Threads_lock->owned_by_self(), "must hold Threads_lock"); // Record state _state = _synchronized; OrderAccess::fence(); // Set the new id ++_safepoint_id; #ifdef ASSERT // Make sure all the threads were visited. for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) { assert(cur->was_visited_for_critical_count(_safepoint_counter), "missed a thread"); } #endif // ASSERT // Update the count of active JNI critical regions GCLocker::set_jni_lock_count(_current_jni_active_count); post_safepoint_synchronize_event(sync_event, _safepoint_id, initial_running, _waiting_to_block, iterations); SafepointTracing::synchronized(nof_threads, initial_running, _nof_threads_hit_polling_page); // We do the safepoint cleanup first since a GC related safepoint // needs cleanup to be completed before running the GC op. EventSafepointCleanup cleanup_event; do_cleanup_tasks(); post_safepoint_cleanup_event(cleanup_event, _safepoint_id); post_safepoint_begin_event(begin_event, _safepoint_id, nof_threads, _current_jni_active_count); SafepointTracing::cleanup(); } void SafepointSynchronize::disarm_safepoint() { uint64_t active_safepoint_counter = _safepoint_counter; { JavaThreadIteratorWithHandle jtiwh; #ifdef ASSERT // A pending_exception cannot be installed during a safepoint. The threads // may install an async exception after they come back from a safepoint into // pending_exception after they unblock. But that should happen later. for (; JavaThread *cur = jtiwh.next(); ) { assert (!(cur->has_pending_exception() && cur->safepoint_state()->is_at_poll_safepoint()), "safepoint installed a pending exception"); } #endif // ASSERT if (SafepointMechanism::uses_global_page_poll()) { guarantee (PageArmed, "invariant"); // Make polling safepoint aware os::make_polling_page_readable(); PageArmed = false; // Remove safepoint check from interpreter Interpreter::ignore_safepoints(); } OrderAccess::fence(); // keep read and write of _state from floating up assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization"); // Change state first to _not_synchronized. // No threads should see _synchronized when running. _state = _not_synchronized; // Set the next dormant (even) safepoint id. assert((_safepoint_counter & 0x1) == 1, "must be odd"); Atomic::release_store(&_safepoint_counter, _safepoint_counter + 1); OrderAccess::fence(); // Keep the local state from floating up. jtiwh.rewind(); for (; JavaThread *current = jtiwh.next(); ) { // Clear the visited flag to ensure that the critical counts are collected properly. DEBUG_ONLY(current->reset_visited_for_critical_count(active_safepoint_counter);) ThreadSafepointState* cur_state = current->safepoint_state(); assert(!cur_state->is_running(), "Thread not suspended at safepoint"); cur_state->restart(); // TSS _running assert(cur_state->is_running(), "safepoint state has not been reset"); SafepointMechanism::disarm_if_needed(current, false /* NO release */); } } // ~JavaThreadIteratorWithHandle // Release threads lock, so threads can be created/destroyed again. Threads_lock->unlock(); // Wake threads after local state is correctly set. _wait_barrier->disarm(); } // Wake up all threads, so they are ready to resume execution after the safepoint // operation has been carried out void SafepointSynchronize::end() { assert(Threads_lock->owned_by_self(), "must hold Threads_lock"); EventSafepointEnd event; assert(Thread::current()->is_VM_thread(), "Only VM thread can execute a safepoint"); disarm_safepoint(); Universe::heap()->safepoint_synchronize_end(); SafepointTracing::end(); post_safepoint_end_event(event, safepoint_id()); } bool SafepointSynchronize::is_cleanup_needed() { // Need a cleanup safepoint if there are too many monitors in use // and the monitor deflation needs to be done at a safepoint. if (ObjectSynchronizer::is_safepoint_deflation_needed()) return true; // Need a safepoint if some inline cache buffers is non-empty if (!InlineCacheBuffer::is_empty()) return true; if (StringTable::needs_rehashing()) return true; if (SymbolTable::needs_rehashing()) return true; return false; } bool SafepointSynchronize::is_forced_cleanup_needed() { return ObjectSynchronizer::needs_monitor_scavenge(); } class ParallelSPCleanupThreadClosure : public ThreadClosure { private: CodeBlobClosure* _nmethod_cl; DeflateMonitorCounters* _counters; public: ParallelSPCleanupThreadClosure(DeflateMonitorCounters* counters) : _nmethod_cl(UseCodeAging ? NMethodSweeper::prepare_reset_hotness_counters() : NULL), _counters(counters) {} void do_thread(Thread* thread) { // deflate_thread_local_monitors() handles or requests deflation of // this thread's idle monitors. If !AsyncDeflateIdleMonitors or if // there is a special cleanup request, deflation is handled now. // Otherwise, async deflation is requested via a flag. ObjectSynchronizer::deflate_thread_local_monitors(thread, _counters); if (_nmethod_cl != NULL && thread->is_Java_thread() && ! thread->is_Code_cache_sweeper_thread()) { JavaThread* jt = (JavaThread*) thread; jt->nmethods_do(_nmethod_cl); } } }; class ParallelSPCleanupTask : public AbstractGangTask { private: SubTasksDone _subtasks; ParallelSPCleanupThreadClosure _cleanup_threads_cl; uint _num_workers; DeflateMonitorCounters* _counters; public: ParallelSPCleanupTask(uint num_workers, DeflateMonitorCounters* counters) : AbstractGangTask("Parallel Safepoint Cleanup"), _subtasks(SubTasksDone(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS)), _cleanup_threads_cl(ParallelSPCleanupThreadClosure(counters)), _num_workers(num_workers), _counters(counters) {} void work(uint worker_id) { uint64_t safepoint_id = SafepointSynchronize::safepoint_id(); // All threads deflate monitors and mark nmethods (if necessary). Threads::possibly_parallel_threads_do(true, &_cleanup_threads_cl); if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_DEFLATE_MONITORS)) { const char* name = "deflating global idle monitors"; EventSafepointCleanupTask event; TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); // AsyncDeflateIdleMonitors only uses DeflateMonitorCounters // when a special cleanup has been requested. // Note: This logging output will include global idle monitor // elapsed times, but not global idle monitor deflation count. ObjectSynchronizer::do_safepoint_work(_counters); post_safepoint_cleanup_task_event(event, safepoint_id, name); } if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) { const char* name = "updating inline caches"; EventSafepointCleanupTask event; TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); InlineCacheBuffer::update_inline_caches(); post_safepoint_cleanup_task_event(event, safepoint_id, name); } if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_COMPILATION_POLICY)) { const char* name = "compilation policy safepoint handler"; EventSafepointCleanupTask event; TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); CompilationPolicy::policy()->do_safepoint_work(); post_safepoint_cleanup_task_event(event, safepoint_id, name); } if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) { if (SymbolTable::needs_rehashing()) { const char* name = "rehashing symbol table"; EventSafepointCleanupTask event; TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); SymbolTable::rehash_table(); post_safepoint_cleanup_task_event(event, safepoint_id, name); } } if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) { if (StringTable::needs_rehashing()) { const char* name = "rehashing string table"; EventSafepointCleanupTask event; TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); StringTable::rehash_table(); post_safepoint_cleanup_task_event(event, safepoint_id, name); } } if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_SYSTEM_DICTIONARY_RESIZE)) { if (Dictionary::does_any_dictionary_needs_resizing()) { const char* name = "resizing system dictionaries"; EventSafepointCleanupTask event; TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); ClassLoaderDataGraph::resize_dictionaries(); post_safepoint_cleanup_task_event(event, safepoint_id, name); } } if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_REQUEST_OOPSTORAGE_CLEANUP)) { // Don't bother reporting event or time for this very short operation. // To have any utility we'd also want to report whether needed. OopStorage::trigger_cleanup_if_needed(); } _subtasks.all_tasks_completed(_num_workers); } }; // Various cleaning tasks that should be done periodically at safepoints. void SafepointSynchronize::do_cleanup_tasks() { TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup)); // Prepare for monitor deflation. DeflateMonitorCounters deflate_counters; ObjectSynchronizer::prepare_deflate_idle_monitors(&deflate_counters); CollectedHeap* heap = Universe::heap(); assert(heap != NULL, "heap not initialized yet?"); WorkGang* cleanup_workers = heap->get_safepoint_workers(); if (cleanup_workers != NULL) { // Parallel cleanup using GC provided thread pool. uint num_cleanup_workers = cleanup_workers->active_workers(); ParallelSPCleanupTask cleanup(num_cleanup_workers, &deflate_counters); StrongRootsScope srs(num_cleanup_workers); cleanup_workers->run_task(&cleanup); } else { // Serial cleanup using VMThread. ParallelSPCleanupTask cleanup(1, &deflate_counters); StrongRootsScope srs(1); cleanup.work(0); } // Needs to be done single threaded by the VMThread. This walks // the thread stacks looking for references to metadata before // deciding to remove it from the metaspaces. if (ClassLoaderDataGraph::should_clean_metaspaces_and_reset()) { const char* name = "cleanup live ClassLoaderData metaspaces"; TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); ClassLoaderDataGraph::walk_metadata_and_clean_metaspaces(); } // Finish monitor deflation. ObjectSynchronizer::finish_deflate_idle_monitors(&deflate_counters); assert(InlineCacheBuffer::is_empty(), "should have cleaned up ICBuffer"); } // Methods for determining if a JavaThread is safepoint safe. // False means unsafe with undetermined state. // True means a determined state, but it may be an unsafe state. // If called from a non-safepoint context safepoint_count MUST be InactiveSafepointCounter. bool SafepointSynchronize::try_stable_load_state(JavaThreadState *state, JavaThread *thread, uint64_t safepoint_count) { assert((safepoint_count != InactiveSafepointCounter && Thread::current() == (Thread*)VMThread::vm_thread() && SafepointSynchronize::_state != _not_synchronized) || safepoint_count == InactiveSafepointCounter, "Invalid check"); // To handle the thread_blocked state on the backedge of the WaitBarrier from // previous safepoint and reading the reset value (0/InactiveSafepointCounter) we // re-read state after we read thread safepoint id. The JavaThread changes its // thread state from thread_blocked before resetting safepoint id to 0. // This guarantees the second read will be from an updated thread state. It can // either be different state making this an unsafe state or it can see blocked // again. When we see blocked twice with a 0 safepoint id, either: // - It is normally blocked, e.g. on Mutex, TBIVM. // - It was in SS:block(), looped around to SS:block() and is blocked on the WaitBarrier. // - It was in SS:block() but now on a Mutex. // All of these cases are safe. *state = thread->thread_state(); OrderAccess::loadload(); uint64_t sid = thread->safepoint_state()->get_safepoint_id(); // Load acquire if (sid != InactiveSafepointCounter && sid != safepoint_count) { // In an old safepoint, state not relevant. return false; } return *state == thread->thread_state(); } static bool safepoint_safe_with(JavaThread *thread, JavaThreadState state) { switch(state) { case _thread_in_native: // native threads are safe if they have no java stack or have walkable stack return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable(); case _thread_blocked: // On wait_barrier or blocked. // Blocked threads should already have walkable stack. assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable"); return true; default: return false; } } bool SafepointSynchronize::handshake_safe(JavaThread *thread) { assert(Thread::current()->is_VM_thread(), "Must be VMThread"); if (thread->is_ext_suspended() || thread->is_terminated()) { return true; } JavaThreadState stable_state; if (try_stable_load_state(&stable_state, thread, InactiveSafepointCounter)) { return safepoint_safe_with(thread, stable_state); } return false; } // See if the thread is running inside a lazy critical native and // update the thread critical count if so. Also set a suspend flag to // cause the native wrapper to return into the JVM to do the unlock // once the native finishes. static void check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state) { if (state == _thread_in_native && thread->has_last_Java_frame() && thread->frame_anchor()->walkable()) { // This thread might be in a critical native nmethod so look at // the top of the stack and increment the critical count if it // is. frame wrapper_frame = thread->last_frame(); CodeBlob* stub_cb = wrapper_frame.cb(); if (stub_cb != NULL && stub_cb->is_nmethod() && stub_cb->as_nmethod_or_null()->is_lazy_critical_native()) { // A thread could potentially be in a critical native across // more than one safepoint, so only update the critical state on // the first one. When it returns it will perform the unlock. if (!thread->do_critical_native_unlock()) { #ifdef ASSERT if (!thread->in_critical()) { GCLocker::increment_debug_jni_lock_count(); } #endif thread->enter_critical(); // Make sure the native wrapper calls back on return to // perform the needed critical unlock. thread->set_critical_native_unlock(); } } } } // ------------------------------------------------------------------------------------------------------- // Implementation of Safepoint blocking point void SafepointSynchronize::block(JavaThread *thread) { assert(thread != NULL, "thread must be set"); assert(thread->is_Java_thread(), "not a Java thread"); // Threads shouldn't block if they are in the middle of printing, but... ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id()); // Only bail from the block() call if the thread is gone from the // thread list; starting to exit should still block. if (thread->is_terminated()) { // block current thread if we come here from native code when VM is gone thread->block_if_vm_exited(); // otherwise do nothing return; } JavaThreadState state = thread->thread_state(); thread->frame_anchor()->make_walkable(thread); uint64_t safepoint_id = SafepointSynchronize::safepoint_counter(); // Check that we have a valid thread_state at this point switch(state) { case _thread_in_vm_trans: case _thread_in_Java: // From compiled code case _thread_in_native_trans: case _thread_blocked_trans: case _thread_new_trans: // We have no idea where the VMThread is, it might even be at next safepoint. // So we can miss this poll, but stop at next. // Load dependent store, it must not pass loading of safepoint_id. thread->safepoint_state()->set_safepoint_id(safepoint_id); // Release store // This part we can skip if we notice we miss or are in a future safepoint. OrderAccess::storestore(); // Load in wait barrier should not float up thread->set_thread_state_fence(_thread_blocked); _wait_barrier->wait(static_cast(safepoint_id)); assert(_state != _synchronized, "Can't be"); // If barrier is disarmed stop store from floating above loads in barrier. OrderAccess::loadstore(); thread->set_thread_state(state); // Then we reset the safepoint id to inactive. thread->safepoint_state()->reset_safepoint_id(); // Release store OrderAccess::fence(); break; default: fatal("Illegal threadstate encountered: %d", state); } guarantee(thread->safepoint_state()->get_safepoint_id() == InactiveSafepointCounter, "The safepoint id should be set only in block path"); // Check for pending. async. exceptions or suspends - except if the // thread was blocked inside the VM. has_special_runtime_exit_condition() // is called last since it grabs a lock and we only want to do that when // we must. // // Note: we never deliver an async exception at a polling point as the // compiler may not have an exception handler for it. The polling // code will notice the async and deoptimize and the exception will // be delivered. (Polling at a return point is ok though). Sure is // a lot of bother for a deprecated feature... // // We don't deliver an async exception if the thread state is // _thread_in_native_trans so JNI functions won't be called with // a surprising pending exception. If the thread state is going back to java, // async exception is checked in check_special_condition_for_native_trans(). if (state != _thread_blocked_trans && state != _thread_in_vm_trans && thread->has_special_runtime_exit_condition()) { thread->handle_special_runtime_exit_condition( !thread->is_at_poll_safepoint() && (state != _thread_in_native_trans)); } // cross_modify_fence is done by SafepointMechanism::block_if_requested_slow // which is the only caller here. } // ------------------------------------------------------------------------------------------------------ // Exception handlers void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) { assert(thread->is_Java_thread(), "polling reference encountered by VM thread"); assert(thread->thread_state() == _thread_in_Java, "should come from Java code"); if (!SafepointMechanism::uses_thread_local_poll()) { assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization"); } if (log_is_enabled(Info, safepoint, stats)) { Atomic::inc(&_nof_threads_hit_polling_page); } ThreadSafepointState* state = thread->safepoint_state(); state->handle_polling_page_exception(); } void SafepointSynchronize::print_safepoint_timeout() { if (!timeout_error_printed) { timeout_error_printed = true; // Print out the thread info which didn't reach the safepoint for debugging // purposes (useful when there are lots of threads in the debugger). LogTarget(Warning, safepoint) lt; if (lt.is_enabled()) { ResourceMark rm; LogStream ls(lt); ls.cr(); ls.print_cr("# SafepointSynchronize::begin: Timeout detected:"); ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint."); ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:"); for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) { if (cur_thread->safepoint_state()->is_running()) { ls.print("# "); cur_thread->print_on(&ls); ls.cr(); } } ls.print_cr("# SafepointSynchronize::begin: (End of list)"); } } // To debug the long safepoint, specify both AbortVMOnSafepointTimeout & // ShowMessageBoxOnError. if (AbortVMOnSafepointTimeout) { // Send the blocking thread a signal to terminate and write an error file. for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) { if (cur_thread->safepoint_state()->is_running()) { if (!os::signal_thread(cur_thread, SIGILL, "blocking a safepoint")) { break; // Could not send signal. Report fatal error. } // Give cur_thread a chance to report the error and terminate the VM. os::naked_sleep(3000); } } fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.", SafepointTimeoutDelay, VMThread::vm_operation()->name()); } } // ------------------------------------------------------------------------------------------------------- // Implementation of ThreadSafepointState ThreadSafepointState::ThreadSafepointState(JavaThread *thread) : _at_poll_safepoint(false), _thread(thread), _safepoint_safe(false), _safepoint_id(SafepointSynchronize::InactiveSafepointCounter), _next(NULL) { } void ThreadSafepointState::create(JavaThread *thread) { ThreadSafepointState *state = new ThreadSafepointState(thread); thread->set_safepoint_state(state); } void ThreadSafepointState::destroy(JavaThread *thread) { if (thread->safepoint_state()) { delete(thread->safepoint_state()); thread->set_safepoint_state(NULL); } } uint64_t ThreadSafepointState::get_safepoint_id() const { return Atomic::load_acquire(&_safepoint_id); } void ThreadSafepointState::reset_safepoint_id() { Atomic::release_store(&_safepoint_id, SafepointSynchronize::InactiveSafepointCounter); } void ThreadSafepointState::set_safepoint_id(uint64_t safepoint_id) { Atomic::release_store(&_safepoint_id, safepoint_id); } void ThreadSafepointState::examine_state_of_thread(uint64_t safepoint_count) { assert(is_running(), "better be running or just have hit safepoint poll"); JavaThreadState stable_state; if (!SafepointSynchronize::try_stable_load_state(&stable_state, _thread, safepoint_count)) { // We could not get stable state of the JavaThread. // Consider it running and just return. return; } // Check for a thread that is suspended. Note that thread resume tries // to grab the Threads_lock which we own here, so a thread cannot be // resumed during safepoint synchronization. // We check to see if this thread is suspended without locking to // avoid deadlocking with a third thread that is waiting for this // thread to be suspended. The third thread can notice the safepoint // that we're trying to start at the beginning of its SR_lock->wait() // call. If that happens, then the third thread will block on the // safepoint while still holding the underlying SR_lock. We won't be // able to get the SR_lock and we'll deadlock. // // We don't need to grab the SR_lock here for two reasons: // 1) The suspend flags are both volatile and are set with an // Atomic::cmpxchg() call so we should see the suspended // state right away. // 2) We're being called from the safepoint polling loop; if // we don't see the suspended state on this iteration, then // we'll come around again. // bool is_suspended = _thread->is_ext_suspended(); if (is_suspended) { account_safe_thread(); return; } if (safepoint_safe_with(_thread, stable_state)) { check_for_lazy_critical_native(_thread, stable_state); account_safe_thread(); return; } // All other thread states will continue to run until they // transition and self-block in state _blocked // Safepoint polling in compiled code causes the Java threads to do the same. // Note: new threads may require a malloc so they must be allowed to finish assert(is_running(), "examine_state_of_thread on non-running thread"); return; } void ThreadSafepointState::account_safe_thread() { SafepointSynchronize::decrement_waiting_to_block(); if (_thread->in_critical()) { // Notice that this thread is in a critical section SafepointSynchronize::increment_jni_active_count(); } DEBUG_ONLY(_thread->set_visited_for_critical_count(SafepointSynchronize::safepoint_counter());) assert(!_safepoint_safe, "Must be unsafe before safe"); _safepoint_safe = true; } void ThreadSafepointState::restart() { assert(_safepoint_safe, "Must be safe before unsafe"); _safepoint_safe = false; } void ThreadSafepointState::print_on(outputStream *st) const { const char *s = _safepoint_safe ? "_at_safepoint" : "_running"; st->print_cr("Thread: " INTPTR_FORMAT " [0x%2x] State: %s _at_poll_safepoint %d", p2i(_thread), _thread->osthread()->thread_id(), s, _at_poll_safepoint); _thread->print_thread_state_on(st); } // --------------------------------------------------------------------------------------------------------------------- // Block the thread at poll or poll return for safepoint/handshake. void ThreadSafepointState::handle_polling_page_exception() { // If we're using a global poll, then the thread should not be // marked as safepoint safe yet. assert(!SafepointMechanism::uses_global_page_poll() || !_safepoint_safe, "polling page exception on thread safepoint safe"); // Step 1: Find the nmethod from the return address address real_return_addr = thread()->saved_exception_pc(); CodeBlob *cb = CodeCache::find_blob(real_return_addr); assert(cb != NULL && cb->is_compiled(), "return address should be in nmethod"); CompiledMethod* nm = (CompiledMethod*)cb; // Find frame of caller frame stub_fr = thread()->last_frame(); CodeBlob* stub_cb = stub_fr.cb(); assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub"); RegisterMap map(thread(), true); frame caller_fr = stub_fr.sender(&map); // Should only be poll_return or poll assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" ); // This is a poll immediately before a return. The exception handling code // has already had the effect of causing the return to occur, so the execution // will continue immediately after the call. In addition, the oopmap at the // return point does not mark the return value as an oop (if it is), so // it needs a handle here to be updated. if( nm->is_at_poll_return(real_return_addr) ) { // See if return type is an oop. bool return_oop = nm->method()->is_returning_oop(); Handle return_value; if (return_oop) { // The oop result has been saved on the stack together with all // the other registers. In order to preserve it over GCs we need // to keep it in a handle. oop result = caller_fr.saved_oop_result(&map); assert(oopDesc::is_oop_or_null(result), "must be oop"); return_value = Handle(thread(), result); assert(Universe::heap()->is_in_or_null(result), "must be heap pointer"); } // Block the thread SafepointMechanism::block_if_requested(thread()); // restore oop result, if any if (return_oop) { caller_fr.set_saved_oop_result(&map, return_value()); } } // This is a safepoint poll. Verify the return address and block. else { set_at_poll_safepoint(true); // verify the blob built the "return address" correctly assert(real_return_addr == caller_fr.pc(), "must match"); // Block the thread SafepointMechanism::block_if_requested(thread()); set_at_poll_safepoint(false); // If we have a pending async exception deoptimize the frame // as otherwise we may never deliver it. if (thread()->has_async_condition()) { ThreadInVMfromJavaNoAsyncException __tiv(thread()); Deoptimization::deoptimize_frame(thread(), caller_fr.id()); } // If an exception has been installed we must check for a pending deoptimization // Deoptimize frame if exception has been thrown. if (thread()->has_pending_exception() ) { RegisterMap map(thread(), true); frame caller_fr = stub_fr.sender(&map); if (caller_fr.is_deoptimized_frame()) { // The exception patch will destroy registers that are still // live and will be needed during deoptimization. Defer the // Async exception should have deferred the exception until the // next safepoint which will be detected when we get into // the interpreter so if we have an exception now things // are messed up. fatal("Exception installed and deoptimization is pending"); } } } } // ------------------------------------------------------------------------------------------------------- // Implementation of SafepointTracing jlong SafepointTracing::_last_safepoint_begin_time_ns = 0; jlong SafepointTracing::_last_safepoint_sync_time_ns = 0; jlong SafepointTracing::_last_safepoint_cleanup_time_ns = 0; jlong SafepointTracing::_last_safepoint_end_time_ns = 0; jlong SafepointTracing::_last_app_time_ns = 0; int SafepointTracing::_nof_threads = 0; int SafepointTracing::_nof_running = 0; int SafepointTracing::_page_trap = 0; VM_Operation::VMOp_Type SafepointTracing::_current_type; jlong SafepointTracing::_max_sync_time = 0; jlong SafepointTracing::_max_vmop_time = 0; uint64_t SafepointTracing::_op_count[VM_Operation::VMOp_Terminating] = {0}; void SafepointTracing::init() { // Application start _last_safepoint_end_time_ns = os::javaTimeNanos(); } // Helper method to print the header. static void print_header(outputStream* st) { // The number of spaces is significant here, and should match the format // specifiers in print_statistics(). st->print("VM Operation " "[ threads: total initial_running ]" "[ time: sync cleanup vmop total ]"); st->print_cr(" page_trap_count"); } // This prints a nice table. To get the statistics to not shift due to the logging uptime // decorator, use the option as: -Xlog:safepoint+stats:[outputfile]:none void SafepointTracing::statistics_log() { LogTarget(Info, safepoint, stats) lt; assert (lt.is_enabled(), "should only be called when printing statistics is enabled"); LogStream ls(lt); static int _cur_stat_index = 0; // Print header every 30 entries if ((_cur_stat_index % 30) == 0) { print_header(&ls); _cur_stat_index = 1; // wrap } else { _cur_stat_index++; } ls.print("%-28s [ " INT32_FORMAT_W(8) " " INT32_FORMAT_W(8) " " "]", VM_Operation::name(_current_type), _nof_threads, _nof_running); ls.print("[ " INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " ]", (int64_t)(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns), (int64_t)(_last_safepoint_cleanup_time_ns - _last_safepoint_sync_time_ns), (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_cleanup_time_ns), (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_begin_time_ns)); ls.print_cr(INT32_FORMAT_W(16), _page_trap); } // This method will be called when VM exits. This tries to summarize the sampling. // Current thread may already be deleted, so don't use ResourceMark. void SafepointTracing::statistics_exit_log() { if (!log_is_enabled(Info, safepoint, stats)) { return; } for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) { if (_op_count[index] != 0) { log_info(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index), _op_count[index]); } } log_info(safepoint, stats)("VM operations coalesced during safepoint " INT64_FORMAT, VMThread::get_coalesced_count()); log_info(safepoint, stats)("Maximum sync time " INT64_FORMAT" ns", (int64_t)(_max_sync_time)); log_info(safepoint, stats)("Maximum vm operation time (except for Exit VM operation) " INT64_FORMAT " ns", (int64_t)(_max_vmop_time)); } void SafepointTracing::begin(VM_Operation::VMOp_Type type) { _op_count[type]++; _current_type = type; // update the time stamp to begin recording safepoint time _last_safepoint_begin_time_ns = os::javaTimeNanos(); _last_safepoint_sync_time_ns = 0; _last_safepoint_cleanup_time_ns = 0; _last_app_time_ns = _last_safepoint_begin_time_ns - _last_safepoint_end_time_ns; _last_safepoint_end_time_ns = 0; RuntimeService::record_safepoint_begin(_last_app_time_ns); } void SafepointTracing::synchronized(int nof_threads, int nof_running, int traps) { _last_safepoint_sync_time_ns = os::javaTimeNanos(); _nof_threads = nof_threads; _nof_running = nof_running; _page_trap = traps; RuntimeService::record_safepoint_synchronized(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns); } void SafepointTracing::cleanup() { _last_safepoint_cleanup_time_ns = os::javaTimeNanos(); } void SafepointTracing::end() { _last_safepoint_end_time_ns = os::javaTimeNanos(); if (_max_sync_time < (_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns)) { _max_sync_time = _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns; } if (_max_vmop_time < (_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns)) { _max_vmop_time = _last_safepoint_end_time_ns - _last_safepoint_sync_time_ns; } if (log_is_enabled(Info, safepoint, stats)) { statistics_log(); } log_info(safepoint)( "Safepoint \"%s\", " "Time since last: " JLONG_FORMAT " ns, " "Reaching safepoint: " JLONG_FORMAT " ns, " "At safepoint: " JLONG_FORMAT " ns, " "Total: " JLONG_FORMAT " ns", VM_Operation::name(_current_type), _last_app_time_ns, _last_safepoint_cleanup_time_ns - _last_safepoint_begin_time_ns, _last_safepoint_end_time_ns - _last_safepoint_cleanup_time_ns, _last_safepoint_end_time_ns - _last_safepoint_begin_time_ns ); RuntimeService::record_safepoint_end(_last_safepoint_end_time_ns - _last_safepoint_cleanup_time_ns); }