/*
* Copyright (c) 1997, 2019, 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<int>(_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 safepoint if there are many monitors to deflate.
if (ObjectSynchronizer::is_cleanup_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) {
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));
ObjectSynchronizer::deflate_idle_monitors(_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) {
// This function must be called with the Threads_lock held so an externally
// suspended thread cannot be resumed thus it is safe.
assert(Threads_lock->owned_by_self() && Thread::current()->is_VM_thread(),
"Must hold Threads_lock and 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<int>(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 (!ThreadLocalHandshakes) {
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_safepoint_end_time_epoch_ms = 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();
// amount of time since epoch
_last_safepoint_end_time_epoch_ms = os::javaTimeMillis();
}
// 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();
// amount of time since epoch
_last_safepoint_end_time_epoch_ms = os::javaTimeMillis();
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);
}