/* * Copyright (c) 1997, 2015, 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/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 "gc/shared/collectedHeap.hpp" #include "gc/shared/gcLocker.inline.hpp" #include "interpreter/interpreter.hpp" #include "logging/log.hpp" #include "memory/resourceArea.hpp" #include "memory/universe.inline.hpp" #include "oops/oop.inline.hpp" #include "oops/symbol.hpp" #include "runtime/atomic.inline.hpp" #include "runtime/compilationPolicy.hpp" #include "runtime/deoptimization.hpp" #include "runtime/frame.inline.hpp" #include "runtime/interfaceSupport.hpp" #include "runtime/mutexLocker.hpp" #include "runtime/orderAccess.inline.hpp" #include "runtime/osThread.hpp" #include "runtime/safepoint.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 "services/runtimeService.hpp" #include "trace/tracing.hpp" #include "trace/traceMacros.hpp" #include "utilities/events.hpp" #include "utilities/macros.hpp" #if INCLUDE_ALL_GCS #include "gc/cms/concurrentMarkSweepThread.hpp" #include "gc/g1/suspendibleThreadSet.hpp" #endif // INCLUDE_ALL_GCS #ifdef COMPILER1 #include "c1/c1_globals.hpp" #endif // -------------------------------------------------------------------------------------------------- // Implementation of Safepoint begin/end SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized; volatile int SafepointSynchronize::_waiting_to_block = 0; volatile int SafepointSynchronize::_safepoint_counter = 0; int SafepointSynchronize::_current_jni_active_count = 0; long SafepointSynchronize::_end_of_last_safepoint = 0; static volatile int PageArmed = 0 ; // safepoint polling page is RO|RW vs PROT_NONE static volatile int TryingToBlock = 0 ; // proximate value -- for advisory use only static bool timeout_error_printed = false; // Roll all threads forward to a safepoint and suspend them all void SafepointSynchronize::begin() { EventSafepointBegin begin_event; Thread* myThread = Thread::current(); assert(myThread->is_VM_thread(), "Only VM thread may execute a safepoint"); if (PrintSafepointStatistics || PrintSafepointStatisticsTimeout > 0) { _safepoint_begin_time = os::javaTimeNanos(); _ts_of_current_safepoint = tty->time_stamp().seconds(); } #if INCLUDE_ALL_GCS if (UseConcMarkSweepGC) { // In the future we should investigate whether CMS can use the // more-general mechanism below. DLD (01/05). ConcurrentMarkSweepThread::synchronize(false); } else if (UseG1GC) { SuspendibleThreadSet::synchronize(); } #endif // INCLUDE_ALL_GCS // 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(); log_debug(safepoint)("Safepoint synchronization initiated. (%d)", nof_threads); RuntimeService::record_safepoint_begin(); MutexLocker mu(Safepoint_lock); // Reset the count of active JNI critical threads _current_jni_active_count = 0; // Set number of threads to wait for, before we initiate the callbacks _waiting_to_block = nof_threads; TryingToBlock = 0 ; int still_running = nof_threads; // Save the starting time, so that it can be compared to see if this has taken // too long to complete. jlong safepoint_limit_time = 0; timeout_error_printed = false; // PrintSafepointStatisticsTimeout can be specified separately. When // specified, PrintSafepointStatistics will be set to true in // deferred_initialize_stat method. The initialization has to be done // early enough to avoid any races. See bug 6880029 for details. if (PrintSafepointStatistics || PrintSafepointStatisticsTimeout > 0) { deferred_initialize_stat(); } // 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 // 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 // (on MP systems). In order to avoid the overhead of issuing // a memory barrier for each Java thread making native calls, each Java // thread performs a write to a single memory page after changing // the thread state. The VM thread performs a sequence of // mprotect OS calls which forces all previous writes from all // Java threads to be serialized. This is done in the // os::serialize_thread_states() call. This has proven to be // much more efficient than executing a membar instruction // on every call to native code. // 3. Running compiled Code // Compiled code reads a global (Safepoint 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 wait for the thread to // block itself when it attempts transitions to a new state. // { EventSafepointStateSync sync_event; int initial_running = 0; _state = _synchronizing; OrderAccess::fence(); // Flush all thread states to memory if (!UseMembar) { os::serialize_thread_states(); } // Make interpreter safepoint aware Interpreter::notice_safepoints(); if (DeferPollingPageLoopCount < 0) { // Make polling safepoint aware guarantee (PageArmed == 0, "invariant") ; PageArmed = 1 ; os::make_polling_page_unreadable(); } // Consider using active_processor_count() ... but that call is expensive. int ncpus = os::processor_count() ; #ifdef ASSERT for (JavaThread *cur = Threads::first(); cur != NULL; cur = cur->next()) { assert(cur->safepoint_state()->is_running(), "Illegal initial state"); // Clear the visited flag to ensure that the critical counts are collected properly. cur->set_visited_for_critical_count(false); } #endif // ASSERT if (SafepointTimeout) safepoint_limit_time = os::javaTimeNanos() + (jlong)SafepointTimeoutDelay * MICROUNITS; // Iterate through all threads until it have been determined how to stop them all at a safepoint unsigned int iterations = 0; int steps = 0 ; while(still_running > 0) { for (JavaThread *cur = Threads::first(); cur != NULL; cur = cur->next()) { assert(!cur->is_ConcurrentGC_thread(), "A concurrent GC thread is unexpectly being suspended"); ThreadSafepointState *cur_state = cur->safepoint_state(); if (cur_state->is_running()) { cur_state->examine_state_of_thread(); if (!cur_state->is_running()) { still_running--; // consider adjusting steps downward: // steps = 0 // steps -= NNN // steps >>= 1 // steps = MIN(steps, 2000-100) // if (iterations != 0) steps -= NNN } if (log_is_enabled(Trace, safepoint)) { ResourceMark rm; cur_state->print_on(LogHandle(safepoint)::debug_stream()); } } } if (iterations == 0) { initial_running = still_running; if (PrintSafepointStatistics) { begin_statistics(nof_threads, still_running); } } if (still_running > 0) { // Check for if it takes to long if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) { print_safepoint_timeout(_spinning_timeout); } // Spin to avoid context switching. // There's a tension between allowing the mutators to run (and rendezvous) // vs spinning. As the VM thread spins, wasting cycles, it consumes CPU that // a mutator might otherwise use profitably to reach a safepoint. Excessive // spinning by the VM thread on a saturated system can increase rendezvous latency. // Blocking or yielding incur their own penalties in the form of context switching // and the resultant loss of $ residency. // // Further complicating matters is that yield() does not work as naively expected // on many platforms -- yield() does not guarantee that any other ready threads // will run. As such we revert to naked_short_sleep() after some number of iterations. // nakes_short_sleep() is implemented as a short unconditional sleep. // Typical operating systems round a "short" sleep period up to 10 msecs, so sleeping // can actually increase the time it takes the VM thread to detect that a system-wide // stop-the-world safepoint has been reached. In a pathological scenario such as that // described in CR6415670 the VMthread may sleep just before the mutator(s) become safe. // In that case the mutators will be stalled waiting for the safepoint to complete and the // the VMthread will be sleeping, waiting for the mutators to rendezvous. The VMthread // will eventually wake up and detect that all mutators are safe, at which point // we'll again make progress. // // Beware too that that the VMThread typically runs at elevated priority. // Its default priority is higher than the default mutator priority. // Obviously, this complicates spinning. // // Note too that on Windows XP SwitchThreadTo() has quite different behavior than Sleep(0). // Sleep(0) will _not yield to lower priority threads, while SwitchThreadTo() will. // // See the comments in synchronizer.cpp for additional remarks on spinning. // // In the future we might: // 1. Modify the safepoint scheme to avoid potentially unbounded spinning. // This is tricky as the path used by a thread exiting the JVM (say on // on JNI call-out) simply stores into its state field. The burden // is placed on the VM thread, which must poll (spin). // 2. Find something useful to do while spinning. If the safepoint is GC-related // we might aggressively scan the stacks of threads that are already safe. // 3. Use Solaris schedctl to examine the state of the still-running mutators. // If all the mutators are ONPROC there's no reason to sleep or yield. // 4. YieldTo() any still-running mutators that are ready but OFFPROC. // 5. Check system saturation. If the system is not fully saturated then // simply spin and avoid sleep/yield. // 6. As still-running mutators rendezvous they could unpark the sleeping // VMthread. This works well for still-running mutators that become // safe. The VMthread must still poll for mutators that call-out. // 7. Drive the policy on time-since-begin instead of iterations. // 8. Consider making the spin duration a function of the # of CPUs: // Spin = (((ncpus-1) * M) + K) + F(still_running) // Alternately, instead of counting iterations of the outer loop // we could count the # of threads visited in the inner loop, above. // 9. On windows consider using the return value from SwitchThreadTo() // to drive subsequent spin/SwitchThreadTo()/Sleep(N) decisions. if (int(iterations) == DeferPollingPageLoopCount) { guarantee (PageArmed == 0, "invariant") ; PageArmed = 1 ; os::make_polling_page_unreadable(); } // Instead of (ncpus > 1) consider either (still_running < (ncpus + EPSILON)) or // ((still_running + _waiting_to_block - TryingToBlock)) < ncpus) ++steps ; if (ncpus > 1 && steps < SafepointSpinBeforeYield) { SpinPause() ; // MP-Polite spin } else if (steps < DeferThrSuspendLoopCount) { os::naked_yield() ; } else { os::naked_short_sleep(1); } iterations ++ ; } assert(iterations < (uint)max_jint, "We have been iterating in the safepoint loop too long"); } assert(still_running == 0, "sanity check"); if (PrintSafepointStatistics) { update_statistics_on_spin_end(); } if (sync_event.should_commit()) { sync_event.set_safepointId(safepoint_counter()); sync_event.set_initialThreadCount(initial_running); sync_event.set_runningThreadCount(_waiting_to_block); sync_event.set_iterations(iterations); sync_event.commit(); } } //EventSafepointStateSync // wait until all threads are stopped { EventSafepointWaitBlocked wait_blocked_event; int initial_waiting_to_block = _waiting_to_block; while (_waiting_to_block > 0) { log_debug(safepoint)("Waiting for %d thread(s) to block", _waiting_to_block); if (!SafepointTimeout || timeout_error_printed) { Safepoint_lock->wait(true); // true, means with no safepoint checks } else { // Compute remaining time jlong remaining_time = safepoint_limit_time - os::javaTimeNanos(); // If there is no remaining time, then there is an error if (remaining_time < 0 || Safepoint_lock->wait(true, remaining_time / MICROUNITS)) { print_safepoint_timeout(_blocking_timeout); } } } assert(_waiting_to_block == 0, "sanity check"); #ifndef PRODUCT if (SafepointTimeout) { jlong current_time = os::javaTimeNanos(); if (safepoint_limit_time < current_time) { tty->print_cr("# SafepointSynchronize: Finished after " INT64_FORMAT_W(6) " ms", ((current_time - safepoint_limit_time) / MICROUNITS + (jlong)SafepointTimeoutDelay)); } } #endif assert((_safepoint_counter & 0x1) == 0, "must be even"); assert(Threads_lock->owned_by_self(), "must hold Threads_lock"); _safepoint_counter ++; // Record state _state = _synchronized; OrderAccess::fence(); if (wait_blocked_event.should_commit()) { wait_blocked_event.set_safepointId(safepoint_counter()); wait_blocked_event.set_runningThreadCount(initial_waiting_to_block); wait_blocked_event.commit(); } } // EventSafepointWaitBlocked #ifdef ASSERT for (JavaThread *cur = Threads::first(); cur != NULL; cur = cur->next()) { // make sure all the threads were visited assert(cur->was_visited_for_critical_count(), "missed a thread"); } #endif // ASSERT // Update the count of active JNI critical regions GCLocker::set_jni_lock_count(_current_jni_active_count); if (log_is_enabled(Debug, safepoint)) { VM_Operation *op = VMThread::vm_operation(); log_debug(safepoint)("Entering safepoint region: %s", (op != NULL) ? op->name() : "no vm operation"); } RuntimeService::record_safepoint_synchronized(); if (PrintSafepointStatistics) { update_statistics_on_sync_end(os::javaTimeNanos()); } // Call stuff that needs to be run when a safepoint is just about to be completed { EventSafepointCleanup cleanup_event; do_cleanup_tasks(); if (cleanup_event.should_commit()) { cleanup_event.set_safepointId(safepoint_counter()); cleanup_event.commit(); } } if (PrintSafepointStatistics) { // Record how much time spend on the above cleanup tasks update_statistics_on_cleanup_end(os::javaTimeNanos()); } if (begin_event.should_commit()) { begin_event.set_safepointId(safepoint_counter()); begin_event.set_totalThreadCount(nof_threads); begin_event.set_jniCriticalThreadCount(_current_jni_active_count); begin_event.commit(); } } // Wake up all threads, so they are ready to resume execution after the safepoint // operation has been carried out void SafepointSynchronize::end() { EventSafepointEnd event; int safepoint_id = safepoint_counter(); // Keep the odd counter as "id" assert(Threads_lock->owned_by_self(), "must hold Threads_lock"); assert((_safepoint_counter & 0x1) == 1, "must be odd"); _safepoint_counter ++; // memory fence isn't required here since an odd _safepoint_counter // value can do no harm and a fence is issued below anyway. DEBUG_ONLY(Thread* myThread = Thread::current();) assert(myThread->is_VM_thread(), "Only VM thread can execute a safepoint"); if (PrintSafepointStatistics) { end_statistics(os::javaTimeNanos()); } #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 = Threads::first(); cur; cur = cur->next()) { assert (!(cur->has_pending_exception() && cur->safepoint_state()->is_at_poll_safepoint()), "safepoint installed a pending exception"); } #endif // ASSERT if (PageArmed) { // Make polling safepoint aware os::make_polling_page_readable(); PageArmed = 0 ; } // Remove safepoint check from interpreter Interpreter::ignore_safepoints(); { MutexLocker mu(Safepoint_lock); assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization"); // Set to not synchronized, so the threads will not go into the signal_thread_blocked method // when they get restarted. _state = _not_synchronized; OrderAccess::fence(); log_debug(safepoint)("Leaving safepoint region"); // Start suspended threads for(JavaThread *current = Threads::first(); current; current = current->next()) { // A problem occurring on Solaris is when attempting to restart threads // the first #cpus - 1 go well, but then the VMThread is preempted when we get // to the next one (since it has been running the longest). We then have // to wait for a cpu to become available before we can continue restarting // threads. // FIXME: This causes the performance of the VM to degrade when active and with // large numbers of threads. Apparently this is due to the synchronous nature // of suspending threads. // // TODO-FIXME: the comments above are vestigial and no longer apply. // Furthermore, using solaris' schedctl in this particular context confers no benefit if (VMThreadHintNoPreempt) { os::hint_no_preempt(); } ThreadSafepointState* cur_state = current->safepoint_state(); assert(cur_state->type() != ThreadSafepointState::_running, "Thread not suspended at safepoint"); cur_state->restart(); assert(cur_state->is_running(), "safepoint state has not been reset"); } RuntimeService::record_safepoint_end(); // Release threads lock, so threads can be created/destroyed again. It will also starts all threads // blocked in signal_thread_blocked Threads_lock->unlock(); } #if INCLUDE_ALL_GCS // If there are any concurrent GC threads resume them. if (UseConcMarkSweepGC) { ConcurrentMarkSweepThread::desynchronize(false); } else if (UseG1GC) { SuspendibleThreadSet::desynchronize(); } #endif // INCLUDE_ALL_GCS // record this time so VMThread can keep track how much time has elapsed // since last safepoint. _end_of_last_safepoint = os::javaTimeMillis(); if (event.should_commit()) { event.set_safepointId(safepoint_id); event.commit(); } } bool SafepointSynchronize::is_cleanup_needed() { // Need a safepoint if some inline cache buffers is non-empty if (!InlineCacheBuffer::is_empty()) return true; return false; } // Various cleaning tasks that should be done periodically at safepoints void SafepointSynchronize::do_cleanup_tasks() { { const char* name = "deflating idle monitors"; EventSafepointCleanupTask event; TraceTime t1(name, TraceSafepointCleanupTime); ObjectSynchronizer::deflate_idle_monitors(); if (event.should_commit()) { event.set_safepointId(safepoint_counter()); event.set_name(name); event.commit(); } } { const char* name = "updating inline caches"; EventSafepointCleanupTask event; TraceTime t2(name, TraceSafepointCleanupTime); InlineCacheBuffer::update_inline_caches(); if (event.should_commit()) { event.set_safepointId(safepoint_counter()); event.set_name(name); event.commit(); } } { const char* name = "compilation policy safepoint handler"; EventSafepointCleanupTask event; TraceTime t3(name, TraceSafepointCleanupTime); CompilationPolicy::policy()->do_safepoint_work(); if (event.should_commit()) { event.set_safepointId(safepoint_counter()); event.set_name(name); event.commit(); } } { const char* name = "mark nmethods"; EventSafepointCleanupTask event; TraceTime t4(name, TraceSafepointCleanupTime); NMethodSweeper::mark_active_nmethods(); if (event.should_commit()) { event.set_safepointId(safepoint_counter()); event.set_name(name); event.commit(); } } if (SymbolTable::needs_rehashing()) { const char* name = "rehashing symbol table"; EventSafepointCleanupTask event; TraceTime t5(name, TraceSafepointCleanupTime); SymbolTable::rehash_table(); if (event.should_commit()) { event.set_safepointId(safepoint_counter()); event.set_name(name); event.commit(); } } if (StringTable::needs_rehashing()) { const char* name = "rehashing string table"; EventSafepointCleanupTask event; TraceTime t6(name, TraceSafepointCleanupTime); StringTable::rehash_table(); if (event.should_commit()) { event.set_safepointId(safepoint_counter()); event.set_name(name); event.commit(); } } { // CMS delays purging the CLDG until the beginning of the next safepoint and to // make sure concurrent sweep is done const char* name = "purging class loader data graph"; EventSafepointCleanupTask event; TraceTime t7(name, TraceSafepointCleanupTime); ClassLoaderDataGraph::purge_if_needed(); if (event.should_commit()) { event.set_safepointId(safepoint_counter()); event.set_name(name); event.commit(); } } } bool SafepointSynchronize::safepoint_safe(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(); // blocked threads should have already have walkable stack case _thread_blocked: assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable"); return true; default: 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. void SafepointSynchronize::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 callback 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); // 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 // We are highly likely to block on the Safepoint_lock. In order to avoid blocking in this case, // we pretend we are still in the VM. thread->set_thread_state(_thread_in_vm); if (is_synchronizing()) { Atomic::inc (&TryingToBlock) ; } // We will always be holding the Safepoint_lock when we are examine the state // of a thread. Hence, the instructions between the Safepoint_lock->lock() and // Safepoint_lock->unlock() are happening atomic with regards to the safepoint code Safepoint_lock->lock_without_safepoint_check(); if (is_synchronizing()) { // Decrement the number of threads to wait for and signal vm thread assert(_waiting_to_block > 0, "sanity check"); _waiting_to_block--; thread->safepoint_state()->set_has_called_back(true); DEBUG_ONLY(thread->set_visited_for_critical_count(true)); if (thread->in_critical()) { // Notice that this thread is in a critical section increment_jni_active_count(); } // Consider (_waiting_to_block < 2) to pipeline the wakeup of the VM thread if (_waiting_to_block == 0) { Safepoint_lock->notify_all(); } } // We transition the thread to state _thread_blocked here, but // we can't do our usual check for external suspension and then // self-suspend after the lock_without_safepoint_check() call // below because we are often called during transitions while // we hold different locks. That would leave us suspended while // holding a resource which results in deadlocks. thread->set_thread_state(_thread_blocked); Safepoint_lock->unlock(); // We now try to acquire the threads lock. Since this lock is hold by the VM thread during // the entire safepoint, the threads will all line up here during the safepoint. Threads_lock->lock_without_safepoint_check(); // restore original state. This is important if the thread comes from compiled code, so it // will continue to execute with the _thread_in_Java state. thread->set_thread_state(state); Threads_lock->unlock(); break; case _thread_in_native_trans: case _thread_blocked_trans: case _thread_new_trans: if (thread->safepoint_state()->type() == ThreadSafepointState::_call_back) { thread->print_thread_state(); fatal("Deadlock in safepoint code. " "Should have called back to the VM before blocking."); } // We transition the thread to state _thread_blocked here, but // we can't do our usual check for external suspension and then // self-suspend after the lock_without_safepoint_check() call // below because we are often called during transitions while // we hold different locks. That would leave us suspended while // holding a resource which results in deadlocks. thread->set_thread_state(_thread_blocked); // It is not safe to suspend a thread if we discover it is in _thread_in_native_trans. Hence, // the safepoint code might still be waiting for it to block. We need to change the state here, // so it can see that it is at a safepoint. // Block until the safepoint operation is completed. Threads_lock->lock_without_safepoint_check(); // Restore state thread->set_thread_state(state); Threads_lock->unlock(); break; default: fatal("Illegal threadstate encountered: %d", state); } // 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)); } } // ------------------------------------------------------------------------------------------------------ // 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"); assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization"); if (ShowSafepointMsgs) { tty->print("handle_polling_page_exception: "); } if (PrintSafepointStatistics) { inc_page_trap_count(); } ThreadSafepointState* state = thread->safepoint_state(); state->handle_polling_page_exception(); } void SafepointSynchronize::print_safepoint_timeout(SafepointTimeoutReason reason) { 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). tty->cr(); tty->print_cr("# SafepointSynchronize::begin: Timeout detected:"); if (reason == _spinning_timeout) { tty->print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint."); } else if (reason == _blocking_timeout) { tty->print_cr("# SafepointSynchronize::begin: Timed out while waiting for threads to stop."); } tty->print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:"); ThreadSafepointState *cur_state; ResourceMark rm; for(JavaThread *cur_thread = Threads::first(); cur_thread; cur_thread = cur_thread->next()) { cur_state = cur_thread->safepoint_state(); if (cur_thread->thread_state() != _thread_blocked && ((reason == _spinning_timeout && cur_state->is_running()) || (reason == _blocking_timeout && !cur_state->has_called_back()))) { tty->print("# "); cur_thread->print(); tty->cr(); } } tty->print_cr("# SafepointSynchronize::begin: (End of list)"); } // To debug the long safepoint, specify both DieOnSafepointTimeout & // ShowMessageBoxOnError. if (DieOnSafepointTimeout) { VM_Operation *op = VMThread::vm_operation(); fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.", SafepointTimeoutDelay, op != NULL ? op->name() : "no vm operation"); } } // ------------------------------------------------------------------------------------------------------- // Implementation of ThreadSafepointState ThreadSafepointState::ThreadSafepointState(JavaThread *thread) { _thread = thread; _type = _running; _has_called_back = false; _at_poll_safepoint = false; } 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); } } void ThreadSafepointState::examine_state_of_thread() { assert(is_running(), "better be running or just have hit safepoint poll"); JavaThreadState state = _thread->thread_state(); // Save the state at the start of safepoint processing. _orig_thread_state = state; // 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) { roll_forward(_at_safepoint); return; } // Some JavaThread states have an initial safepoint state of // running, but are actually at a safepoint. We will happily // agree and update the safepoint state here. if (SafepointSynchronize::safepoint_safe(_thread, state)) { SafepointSynchronize::check_for_lazy_critical_native(_thread, state); roll_forward(_at_safepoint); return; } if (state == _thread_in_vm) { roll_forward(_call_back); 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; } // Returns true is thread could not be rolled forward at present position. void ThreadSafepointState::roll_forward(suspend_type type) { _type = type; switch(_type) { case _at_safepoint: SafepointSynchronize::signal_thread_at_safepoint(); DEBUG_ONLY(_thread->set_visited_for_critical_count(true)); if (_thread->in_critical()) { // Notice that this thread is in a critical section SafepointSynchronize::increment_jni_active_count(); } break; case _call_back: set_has_called_back(false); break; case _running: default: ShouldNotReachHere(); } } void ThreadSafepointState::restart() { switch(type()) { case _at_safepoint: case _call_back: break; case _running: default: tty->print_cr("restart thread " INTPTR_FORMAT " with state %d", p2i(_thread), _type); _thread->print(); ShouldNotReachHere(); } _type = _running; set_has_called_back(false); } void ThreadSafepointState::print_on(outputStream *st) const { const char *s = NULL; switch(_type) { case _running : s = "_running"; break; case _at_safepoint : s = "_at_safepoint"; break; case _call_back : s = "_call_back"; break; default: ShouldNotReachHere(); } st->print_cr("Thread: " INTPTR_FORMAT " [0x%2x] State: %s _has_called_back %d _at_poll_safepoint %d", p2i(_thread), _thread->osthread()->thread_id(), s, _has_called_back, _at_poll_safepoint); _thread->print_thread_state_on(st); } // --------------------------------------------------------------------------------------------------------------------- // Block the thread at the safepoint poll or poll return. void ThreadSafepointState::handle_polling_page_exception() { // Check state. block() will set thread state to thread_in_vm which will // cause the safepoint state _type to become _call_back. assert(type() == ThreadSafepointState::_running, "polling page exception on thread not running state"); // Step 1: Find the nmethod from the return address if (ShowSafepointMsgs && Verbose) { tty->print_cr("Polling page exception at " INTPTR_FORMAT, p2i(thread()->saved_exception_pc())); } address real_return_addr = thread()->saved_exception_pc(); CodeBlob *cb = CodeCache::find_blob(real_return_addr); assert(cb != NULL && cb->is_nmethod(), "return address should be in nmethod"); nmethod* nm = (nmethod*)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(result == NULL || result->is_oop(), "must be oop"); return_value = Handle(thread(), result); assert(Universe::heap()->is_in_or_null(result), "must be heap pointer"); } // Block the thread SafepointSynchronize::block(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 SafepointSynchronize::block(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"); } } } } // // Statistics & Instrumentations // SafepointSynchronize::SafepointStats* SafepointSynchronize::_safepoint_stats = NULL; jlong SafepointSynchronize::_safepoint_begin_time = 0; int SafepointSynchronize::_cur_stat_index = 0; julong SafepointSynchronize::_safepoint_reasons[VM_Operation::VMOp_Terminating]; julong SafepointSynchronize::_coalesced_vmop_count = 0; jlong SafepointSynchronize::_max_sync_time = 0; jlong SafepointSynchronize::_max_vmop_time = 0; float SafepointSynchronize::_ts_of_current_safepoint = 0.0f; static jlong cleanup_end_time = 0; static bool need_to_track_page_armed_status = false; static bool init_done = false; // Helper method to print the header. static void print_header() { tty->print(" vmop " "[threads: total initially_running wait_to_block] "); tty->print("[time: spin block sync cleanup vmop] "); // no page armed status printed out if it is always armed. if (need_to_track_page_armed_status) { tty->print("page_armed "); } tty->print_cr("page_trap_count"); } void SafepointSynchronize::deferred_initialize_stat() { if (init_done) return; // If PrintSafepointStatisticsTimeout is specified, the statistics data will // be printed right away, in which case, _safepoint_stats will regress to // a single element array. Otherwise, it is a circular ring buffer with default // size of PrintSafepointStatisticsCount. int stats_array_size; if (PrintSafepointStatisticsTimeout > 0) { stats_array_size = 1; PrintSafepointStatistics = true; } else { stats_array_size = PrintSafepointStatisticsCount; } _safepoint_stats = (SafepointStats*)os::malloc(stats_array_size * sizeof(SafepointStats), mtInternal); guarantee(_safepoint_stats != NULL, "not enough memory for safepoint instrumentation data"); if (DeferPollingPageLoopCount >= 0) { need_to_track_page_armed_status = true; } init_done = true; } void SafepointSynchronize::begin_statistics(int nof_threads, int nof_running) { assert(init_done, "safepoint statistics array hasn't been initialized"); SafepointStats *spstat = &_safepoint_stats[_cur_stat_index]; spstat->_time_stamp = _ts_of_current_safepoint; VM_Operation *op = VMThread::vm_operation(); spstat->_vmop_type = (op != NULL ? op->type() : -1); if (op != NULL) { _safepoint_reasons[spstat->_vmop_type]++; } spstat->_nof_total_threads = nof_threads; spstat->_nof_initial_running_threads = nof_running; spstat->_nof_threads_hit_page_trap = 0; // Records the start time of spinning. The real time spent on spinning // will be adjusted when spin is done. Same trick is applied for time // spent on waiting for threads to block. if (nof_running != 0) { spstat->_time_to_spin = os::javaTimeNanos(); } else { spstat->_time_to_spin = 0; } } void SafepointSynchronize::update_statistics_on_spin_end() { SafepointStats *spstat = &_safepoint_stats[_cur_stat_index]; jlong cur_time = os::javaTimeNanos(); spstat->_nof_threads_wait_to_block = _waiting_to_block; if (spstat->_nof_initial_running_threads != 0) { spstat->_time_to_spin = cur_time - spstat->_time_to_spin; } if (need_to_track_page_armed_status) { spstat->_page_armed = (PageArmed == 1); } // Records the start time of waiting for to block. Updated when block is done. if (_waiting_to_block != 0) { spstat->_time_to_wait_to_block = cur_time; } else { spstat->_time_to_wait_to_block = 0; } } void SafepointSynchronize::update_statistics_on_sync_end(jlong end_time) { SafepointStats *spstat = &_safepoint_stats[_cur_stat_index]; if (spstat->_nof_threads_wait_to_block != 0) { spstat->_time_to_wait_to_block = end_time - spstat->_time_to_wait_to_block; } // Records the end time of sync which will be used to calculate the total // vm operation time. Again, the real time spending in syncing will be deducted // from the start of the sync time later when end_statistics is called. spstat->_time_to_sync = end_time - _safepoint_begin_time; if (spstat->_time_to_sync > _max_sync_time) { _max_sync_time = spstat->_time_to_sync; } spstat->_time_to_do_cleanups = end_time; } void SafepointSynchronize::update_statistics_on_cleanup_end(jlong end_time) { SafepointStats *spstat = &_safepoint_stats[_cur_stat_index]; // Record how long spent in cleanup tasks. spstat->_time_to_do_cleanups = end_time - spstat->_time_to_do_cleanups; cleanup_end_time = end_time; } void SafepointSynchronize::end_statistics(jlong vmop_end_time) { SafepointStats *spstat = &_safepoint_stats[_cur_stat_index]; // Update the vm operation time. spstat->_time_to_exec_vmop = vmop_end_time - cleanup_end_time; if (spstat->_time_to_exec_vmop > _max_vmop_time) { _max_vmop_time = spstat->_time_to_exec_vmop; } // Only the sync time longer than the specified // PrintSafepointStatisticsTimeout will be printed out right away. // By default, it is -1 meaning all samples will be put into the list. if ( PrintSafepointStatisticsTimeout > 0) { if (spstat->_time_to_sync > (jlong)PrintSafepointStatisticsTimeout * MICROUNITS) { print_statistics(); } } else { // The safepoint statistics will be printed out when the _safepoin_stats // array fills up. if (_cur_stat_index == PrintSafepointStatisticsCount - 1) { print_statistics(); _cur_stat_index = 0; } else { _cur_stat_index++; } } } void SafepointSynchronize::print_statistics() { SafepointStats* sstats = _safepoint_stats; for (int index = 0; index <= _cur_stat_index; index++) { if (index % 30 == 0) { print_header(); } sstats = &_safepoint_stats[index]; tty->print("%.3f: ", sstats->_time_stamp); tty->print("%-26s [" INT32_FORMAT_W(8) INT32_FORMAT_W(11) INT32_FORMAT_W(15) " ] ", sstats->_vmop_type == -1 ? "no vm operation" : VM_Operation::name(sstats->_vmop_type), sstats->_nof_total_threads, sstats->_nof_initial_running_threads, sstats->_nof_threads_wait_to_block); // "/ MICROUNITS " is to convert the unit from nanos to millis. tty->print(" [" INT64_FORMAT_W(6) INT64_FORMAT_W(6) INT64_FORMAT_W(6) INT64_FORMAT_W(6) INT64_FORMAT_W(6) " ] ", sstats->_time_to_spin / MICROUNITS, sstats->_time_to_wait_to_block / MICROUNITS, sstats->_time_to_sync / MICROUNITS, sstats->_time_to_do_cleanups / MICROUNITS, sstats->_time_to_exec_vmop / MICROUNITS); if (need_to_track_page_armed_status) { tty->print(INT32_FORMAT " ", sstats->_page_armed); } tty->print_cr(INT32_FORMAT " ", sstats->_nof_threads_hit_page_trap); } } // This method will be called when VM exits. It will first call // print_statistics to print out the rest of the sampling. Then // it tries to summarize the sampling. void SafepointSynchronize::print_stat_on_exit() { if (_safepoint_stats == NULL) return; SafepointStats *spstat = &_safepoint_stats[_cur_stat_index]; // During VM exit, end_statistics may not get called and in that // case, if the sync time is less than PrintSafepointStatisticsTimeout, // don't print it out. // Approximate the vm op time. _safepoint_stats[_cur_stat_index]._time_to_exec_vmop = os::javaTimeNanos() - cleanup_end_time; if ( PrintSafepointStatisticsTimeout < 0 || spstat->_time_to_sync > (jlong)PrintSafepointStatisticsTimeout * MICROUNITS) { print_statistics(); } tty->cr(); // Print out polling page sampling status. if (!need_to_track_page_armed_status) { tty->print_cr("Polling page always armed"); } else { tty->print_cr("Defer polling page loop count = " INTX_FORMAT "\n", DeferPollingPageLoopCount); } for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) { if (_safepoint_reasons[index] != 0) { tty->print_cr("%-26s" UINT64_FORMAT_W(10), VM_Operation::name(index), _safepoint_reasons[index]); } } tty->print_cr(UINT64_FORMAT_W(5) " VM operations coalesced during safepoint", _coalesced_vmop_count); tty->print_cr("Maximum sync time " INT64_FORMAT_W(5) " ms", _max_sync_time / MICROUNITS); tty->print_cr("Maximum vm operation time (except for Exit VM operation) " INT64_FORMAT_W(5) " ms", _max_vmop_time / MICROUNITS); } // ------------------------------------------------------------------------------------------------ // Non-product code #ifndef PRODUCT void SafepointSynchronize::print_state() { if (_state == _not_synchronized) { tty->print_cr("not synchronized"); } else if (_state == _synchronizing || _state == _synchronized) { tty->print_cr("State: %s", (_state == _synchronizing) ? "synchronizing" : "synchronized"); for(JavaThread *cur = Threads::first(); cur; cur = cur->next()) { cur->safepoint_state()->print(); } } } void SafepointSynchronize::safepoint_msg(const char* format, ...) { if (ShowSafepointMsgs) { va_list ap; va_start(ap, format); tty->vprint_cr(format, ap); va_end(ap); } } #endif // !PRODUCT