Mercurial > hg > graal-compiler
view src/share/vm/gc_implementation/g1/g1StringDedup.hpp @ 19605:15ef24874df7
Add assertion to ObjectValue conversion
author | Tom Rodriguez <tom.rodriguez@oracle.com> |
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date | Wed, 25 Feb 2015 19:13:16 -0800 |
parents | 1772223a25a2 |
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/* * Copyright (c) 2014, 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_GC_IMPLEMENTATION_G1_G1STRINGDEDUP_HPP #define SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUP_HPP // // String Deduplication // // String deduplication aims to reduce the heap live-set by deduplicating identical // instances of String so that they share the same backing character array. // // The deduplication process is divided in two main parts, 1) finding the objects to // deduplicate, and 2) deduplicating those objects. The first part is done as part of // a normal GC cycle when objects are marked or evacuated. At this time a check is // applied on each object to check if it is a candidate for deduplication. If so, the // object is placed on the deduplication queue for later processing. The second part, // processing the objects on the deduplication queue, is a concurrent phase which // starts right after the stop-the-wold marking/evacuation phase. This phase is // executed by the deduplication thread, which pulls deduplication candidates of the // deduplication queue and tries to deduplicate them. // // A deduplication hashtable is used to keep track of all unique character arrays // used by String objects. When deduplicating, a lookup is made in this table to see // if there is already an identical character array somewhere on the heap. If so, the // String object is adjusted to point to that character array, releasing the reference // to the original array allowing it to eventually be garbage collected. If the lookup // fails the character array is instead inserted into the hashtable so that this array // can be shared at some point in the future. // // Candidate selection // // An object is considered a deduplication candidate if all of the following // statements are true: // // - The object is an instance of java.lang.String // // - The object is being evacuated from a young heap region // // - The object is being evacuated to a young/survivor heap region and the // object's age is equal to the deduplication age threshold // // or // // The object is being evacuated to an old heap region and the object's age is // less than the deduplication age threshold // // Once an string object has been promoted to an old region, or its age is higher // than the deduplication age threshold, is will never become a candidate again. // This approach avoids making the same object a candidate more than once. // // Interned strings are a bit special. They are explicitly deduplicated just before // being inserted into the StringTable (to avoid counteracting C2 optimizations done // on string literals), then they also become deduplication candidates if they reach // the deduplication age threshold or are evacuated to an old heap region. The second // attempt to deduplicate such strings will be in vain, but we have no fast way of // filtering them out. This has not shown to be a problem, as the number of interned // strings is usually dwarfed by the number of normal (non-interned) strings. // // For additional information on string deduplication, please see JEP 192, // http://openjdk.java.net/jeps/192 // #include "memory/allocation.hpp" #include "oops/oop.hpp" class OopClosure; class BoolObjectClosure; class ThreadClosure; class outputStream; class G1StringDedupTable; // // Main interface for interacting with string deduplication. // class G1StringDedup : public AllStatic { private: // Single state for checking if both G1 and string deduplication is enabled. static bool _enabled; // Candidate selection policies, returns true if the given object is // candidate for string deduplication. static bool is_candidate_from_mark(oop obj); static bool is_candidate_from_evacuation(bool from_young, bool to_young, oop obj); public: // Returns true if both G1 and string deduplication is enabled. static bool is_enabled() { return _enabled; } // Initialize string deduplication. static void initialize(); // Stop the deduplication thread. static void stop(); // Immediately deduplicates the given String object, bypassing the // the deduplication queue. static void deduplicate(oop java_string); // Enqueues a deduplication candidate for later processing by the deduplication // thread. Before enqueuing, these functions apply the appropriate candidate // selection policy to filters out non-candidates. static void enqueue_from_mark(oop java_string); static void enqueue_from_evacuation(bool from_young, bool to_young, unsigned int queue, oop java_string); static void oops_do(OopClosure* keep_alive); static void unlink(BoolObjectClosure* is_alive); static void unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* keep_alive, bool allow_resize_and_rehash = true); static void threads_do(ThreadClosure* tc); static void print_worker_threads_on(outputStream* st); static void verify(); }; // // This closure encapsulates the state and the closures needed when scanning // the deduplication queue and table during the unlink_or_oops_do() operation. // A single instance of this closure is created and then shared by all worker // threads participating in the scan. The _next_queue and _next_bucket fields // provide a simple mechanism for GC workers to claim exclusive access to a // queue or a table partition. // class G1StringDedupUnlinkOrOopsDoClosure : public StackObj { private: BoolObjectClosure* _is_alive; OopClosure* _keep_alive; G1StringDedupTable* _resized_table; G1StringDedupTable* _rehashed_table; size_t _next_queue; size_t _next_bucket; public: G1StringDedupUnlinkOrOopsDoClosure(BoolObjectClosure* is_alive, OopClosure* keep_alive, bool allow_resize_and_rehash); ~G1StringDedupUnlinkOrOopsDoClosure(); bool is_resizing() { return _resized_table != NULL; } G1StringDedupTable* resized_table() { return _resized_table; } bool is_rehashing() { return _rehashed_table != NULL; } // Atomically claims the next available queue for exclusive access by // the current thread. Returns the queue number of the claimed queue. size_t claim_queue() { return (size_t)Atomic::add_ptr(1, &_next_queue) - 1; } // Atomically claims the next available table partition for exclusive // access by the current thread. Returns the table bucket number where // the claimed partition starts. size_t claim_table_partition(size_t partition_size) { return (size_t)Atomic::add_ptr(partition_size, &_next_bucket) - partition_size; } // Applies and returns the result from the is_alive closure, or // returns true if no such closure was provided. bool is_alive(oop o) { if (_is_alive != NULL) { return _is_alive->do_object_b(o); } return true; } // Applies the keep_alive closure, or does nothing if no such // closure was provided. void keep_alive(oop* p) { if (_keep_alive != NULL) { _keep_alive->do_oop(p); } } }; #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1STRINGDEDUP_HPP