/* * Copyright (c) 1997, 2013, 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. * */ #ifndef SHARE_VM_RUNTIME_SWEEPER_HPP #define SHARE_VM_RUNTIME_SWEEPER_HPP #include "utilities/ticks.hpp" // An NmethodSweeper is an incremental cleaner for: // - cleanup inline caches // - reclamation of nmethods // Removing nmethods from the code cache includes two operations // 1) mark active nmethods // Is done in 'mark_active_nmethods()'. This function is called at a // safepoint and marks all nmethods that are active on a thread's stack. // 2) sweep nmethods // Is done in sweep_code_cache(). This function is the only place in the // sweeper where memory is reclaimed. Note that sweep_code_cache() is not // called at a safepoint. However, sweep_code_cache() stops executing if // another thread requests a safepoint. Consequently, 'mark_active_nmethods()' // and sweep_code_cache() cannot execute at the same time. // To reclaim memory, nmethods are first marked as 'not-entrant'. Methods can // be made not-entrant by (i) the sweeper, (ii) deoptimization, (iii) dependency // invalidation, and (iv) being replaced be a different method version (tiered // compilation). Not-entrant nmethod cannot be called by Java threads, but they // can still be active on the stack. To ensure that active nmethod are not reclaimed, // we have to wait until the next marking phase has completed. If a not-entrant // nmethod was NOT marked as active, it can be converted to 'zombie' state. To safely // remove the nmethod, all inline caches (IC) that point to the the nmethod must be // cleared. After that, the nmethod can be evicted from the code cache. Each nmethod's // state change happens during separate sweeps. It may take at least 3 sweeps before an // nmethod's space is freed. Sweeping is currently done by compiler threads between // compilations or at least each 5 sec (NmethodSweepCheckInterval) when the code cache // is full. class NMethodSweeper : public AllStatic { static long _traversals; // Stack scan count, also sweep ID. static nmethod* _current; // Current nmethod static int _seen; // Nof. nmethod we have currently processed in current pass of CodeCache static int _flushed_count; // Nof. nmethods flushed in current sweep static int _zombified_count; // Nof. nmethods made zombie in current sweep static int _marked_count; // Nof. nmethods marked for reclaim in current sweep static volatile int _invocations; // No. of invocations left until we are completed with this pass static volatile int _sweep_started; // Flag to control conc sweeper //The following are reset in mark_active_nmethods and synchronized by the safepoint static bool _request_mark_phase; // Indicates that a change has happend and we need another mark pahse, // always checked and reset at a safepoint so memory will be in sync. static int _locked_seen; // Number of locked nmethods encountered during the scan static int _not_entrant_seen_on_stack; // Number of not entrant nmethod were are still on stack // Stat counters static int _total_nof_methods_reclaimed; // Accumulated nof methods flushed static Tickspan _total_time_sweeping; // Accumulated time sweeping static Tickspan _total_time_this_sweep; // Total time this sweep static Tickspan _peak_sweep_time; // Peak time for a full sweep static Tickspan _peak_sweep_fraction_time; // Peak time sweeping one fraction static int process_nmethod(nmethod *nm); static void release_nmethod(nmethod* nm); static bool sweep_in_progress(); static void sweep_code_cache(); static void request_nmethod_marking() { _request_mark_phase = true; } static void reset_nmethod_marking() { _request_mark_phase = false; } static bool need_marking_phase() { return _request_mark_phase; } static int _hotness_counter_reset_val; public: static long traversal_count() { return _traversals; } static int total_nof_methods_reclaimed() { return _total_nof_methods_reclaimed; } static const Tickspan total_time_sweeping() { return _total_time_sweeping; } static const Tickspan peak_sweep_time() { return _peak_sweep_time; } static const Tickspan peak_sweep_fraction_time() { return _peak_sweep_fraction_time; } static void log_sweep(const char* msg, const char* format = NULL, ...); #ifdef ASSERT static bool is_sweeping(nmethod* which) { return _current == which; } // Keep track of sweeper activity in the ring buffer static void record_sweep(nmethod* nm, int line); static void report_events(int id, address entry); static void report_events(); #endif static void mark_active_nmethods(); // Invoked at the end of each safepoint static void possibly_sweep(); // Compiler threads call this to sweep static int sort_nmethods_by_hotness(nmethod** nm1, nmethod** nm2); static int hotness_counter_reset_val(); static void notify() { // Request a new sweep of the code cache from the beginning. No // need to synchronize the setting of this flag since it only // changes to false at safepoint so we can never overwrite it with false. request_nmethod_marking(); } }; #endif // SHARE_VM_RUNTIME_SWEEPER_HPP