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view src/share/vm/utilities/taskqueue.hpp @ 17106:3d6132d71975
Compiler warning removed (unused import)
author | Stefan Anzinger <stefan.anzinger@oracle.com> |
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date | Fri, 12 Sep 2014 15:24:00 -0700 |
parents | 4ca6dc0799b6 |
children | 52b4284cb496 |
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/* * Copyright (c) 2001, 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_UTILITIES_TASKQUEUE_HPP #define SHARE_VM_UTILITIES_TASKQUEUE_HPP #include "memory/allocation.hpp" #include "memory/allocation.inline.hpp" #include "runtime/mutex.hpp" #include "utilities/stack.hpp" #ifdef TARGET_OS_ARCH_linux_x86 # include "orderAccess_linux_x86.inline.hpp" #endif #ifdef TARGET_OS_ARCH_linux_sparc # include "orderAccess_linux_sparc.inline.hpp" #endif #ifdef TARGET_OS_ARCH_linux_zero # include "orderAccess_linux_zero.inline.hpp" #endif #ifdef TARGET_OS_ARCH_solaris_x86 # include "orderAccess_solaris_x86.inline.hpp" #endif #ifdef TARGET_OS_ARCH_solaris_sparc # include "orderAccess_solaris_sparc.inline.hpp" #endif #ifdef TARGET_OS_ARCH_windows_x86 # include "orderAccess_windows_x86.inline.hpp" #endif #ifdef TARGET_OS_ARCH_linux_arm # include "orderAccess_linux_arm.inline.hpp" #endif #ifdef TARGET_OS_ARCH_linux_ppc # include "orderAccess_linux_ppc.inline.hpp" #endif #ifdef TARGET_OS_ARCH_bsd_x86 # include "orderAccess_bsd_x86.inline.hpp" #endif #ifdef TARGET_OS_ARCH_bsd_zero # include "orderAccess_bsd_zero.inline.hpp" #endif // Simple TaskQueue stats that are collected by default in debug builds. #if !defined(TASKQUEUE_STATS) && defined(ASSERT) #define TASKQUEUE_STATS 1 #elif !defined(TASKQUEUE_STATS) #define TASKQUEUE_STATS 0 #endif #if TASKQUEUE_STATS #define TASKQUEUE_STATS_ONLY(code) code #else #define TASKQUEUE_STATS_ONLY(code) #endif // TASKQUEUE_STATS #if TASKQUEUE_STATS class TaskQueueStats { public: enum StatId { push, // number of taskqueue pushes pop, // number of taskqueue pops pop_slow, // subset of taskqueue pops that were done slow-path steal_attempt, // number of taskqueue steal attempts steal, // number of taskqueue steals overflow, // number of overflow pushes overflow_max_len, // max length of overflow stack last_stat_id }; public: inline TaskQueueStats() { reset(); } inline void record_push() { ++_stats[push]; } inline void record_pop() { ++_stats[pop]; } inline void record_pop_slow() { record_pop(); ++_stats[pop_slow]; } inline void record_steal(bool success); inline void record_overflow(size_t new_length); TaskQueueStats & operator +=(const TaskQueueStats & addend); inline size_t get(StatId id) const { return _stats[id]; } inline const size_t* get() const { return _stats; } inline void reset(); // Print the specified line of the header (does not include a line separator). static void print_header(unsigned int line, outputStream* const stream = tty, unsigned int width = 10); // Print the statistics (does not include a line separator). void print(outputStream* const stream = tty, unsigned int width = 10) const; DEBUG_ONLY(void verify() const;) private: size_t _stats[last_stat_id]; static const char * const _names[last_stat_id]; }; void TaskQueueStats::record_steal(bool success) { ++_stats[steal_attempt]; if (success) ++_stats[steal]; } void TaskQueueStats::record_overflow(size_t new_len) { ++_stats[overflow]; if (new_len > _stats[overflow_max_len]) _stats[overflow_max_len] = new_len; } void TaskQueueStats::reset() { memset(_stats, 0, sizeof(_stats)); } #endif // TASKQUEUE_STATS // TaskQueueSuper collects functionality common to all GenericTaskQueue instances. template <unsigned int N, MEMFLAGS F> class TaskQueueSuper: public CHeapObj<F> { protected: // Internal type for indexing the queue; also used for the tag. typedef NOT_LP64(uint16_t) LP64_ONLY(uint32_t) idx_t; // The first free element after the last one pushed (mod N). volatile uint _bottom; enum { MOD_N_MASK = N - 1 }; class Age { public: Age(size_t data = 0) { _data = data; } Age(const Age& age) { _data = age._data; } Age(idx_t top, idx_t tag) { _fields._top = top; _fields._tag = tag; } Age get() const volatile { return _data; } void set(Age age) volatile { _data = age._data; } idx_t top() const volatile { return _fields._top; } idx_t tag() const volatile { return _fields._tag; } // Increment top; if it wraps, increment tag also. void increment() { _fields._top = increment_index(_fields._top); if (_fields._top == 0) ++_fields._tag; } Age cmpxchg(const Age new_age, const Age old_age) volatile { return (size_t) Atomic::cmpxchg_ptr((intptr_t)new_age._data, (volatile intptr_t *)&_data, (intptr_t)old_age._data); } bool operator ==(const Age& other) const { return _data == other._data; } private: struct fields { idx_t _top; idx_t _tag; }; union { size_t _data; fields _fields; }; }; volatile Age _age; // These both operate mod N. static uint increment_index(uint ind) { return (ind + 1) & MOD_N_MASK; } static uint decrement_index(uint ind) { return (ind - 1) & MOD_N_MASK; } // Returns a number in the range [0..N). If the result is "N-1", it should be // interpreted as 0. uint dirty_size(uint bot, uint top) const { return (bot - top) & MOD_N_MASK; } // Returns the size corresponding to the given "bot" and "top". uint size(uint bot, uint top) const { uint sz = dirty_size(bot, top); // Has the queue "wrapped", so that bottom is less than top? There's a // complicated special case here. A pair of threads could perform pop_local // and pop_global operations concurrently, starting from a state in which // _bottom == _top+1. The pop_local could succeed in decrementing _bottom, // and the pop_global in incrementing _top (in which case the pop_global // will be awarded the contested queue element.) The resulting state must // be interpreted as an empty queue. (We only need to worry about one such // event: only the queue owner performs pop_local's, and several concurrent // threads attempting to perform the pop_global will all perform the same // CAS, and only one can succeed.) Any stealing thread that reads after // either the increment or decrement will see an empty queue, and will not // join the competitors. The "sz == -1 || sz == N-1" state will not be // modified by concurrent queues, so the owner thread can reset the state to // _bottom == top so subsequent pushes will be performed normally. return (sz == N - 1) ? 0 : sz; } public: TaskQueueSuper() : _bottom(0), _age() {} // Return true if the TaskQueue contains/does not contain any tasks. bool peek() const { return _bottom != _age.top(); } bool is_empty() const { return size() == 0; } // Return an estimate of the number of elements in the queue. // The "careful" version admits the possibility of pop_local/pop_global // races. uint size() const { return size(_bottom, _age.top()); } uint dirty_size() const { return dirty_size(_bottom, _age.top()); } void set_empty() { _bottom = 0; _age.set(0); } // Maximum number of elements allowed in the queue. This is two less // than the actual queue size, for somewhat complicated reasons. uint max_elems() const { return N - 2; } // Total size of queue. static const uint total_size() { return N; } TASKQUEUE_STATS_ONLY(TaskQueueStats stats;) }; // // GenericTaskQueue implements an ABP, Aurora-Blumofe-Plaxton, double- // ended-queue (deque), intended for use in work stealing. Queue operations // are non-blocking. // // A queue owner thread performs push() and pop_local() operations on one end // of the queue, while other threads may steal work using the pop_global() // method. // // The main difference to the original algorithm is that this // implementation allows wrap-around at the end of its allocated // storage, which is an array. // // The original paper is: // // Arora, N. S., Blumofe, R. D., and Plaxton, C. G. // Thread scheduling for multiprogrammed multiprocessors. // Theory of Computing Systems 34, 2 (2001), 115-144. // // The following paper provides an correctness proof and an // implementation for weakly ordered memory models including (pseudo-) // code containing memory barriers for a Chase-Lev deque. Chase-Lev is // similar to ABP, with the main difference that it allows resizing of the // underlying storage: // // Le, N. M., Pop, A., Cohen A., and Nardell, F. Z. // Correct and efficient work-stealing for weak memory models // Proceedings of the 18th ACM SIGPLAN symposium on Principles and // practice of parallel programming (PPoPP 2013), 69-80 // template <class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE> class GenericTaskQueue: public TaskQueueSuper<N, F> { ArrayAllocator<E, F> _array_allocator; protected: typedef typename TaskQueueSuper<N, F>::Age Age; typedef typename TaskQueueSuper<N, F>::idx_t idx_t; using TaskQueueSuper<N, F>::_bottom; using TaskQueueSuper<N, F>::_age; using TaskQueueSuper<N, F>::increment_index; using TaskQueueSuper<N, F>::decrement_index; using TaskQueueSuper<N, F>::dirty_size; public: using TaskQueueSuper<N, F>::max_elems; using TaskQueueSuper<N, F>::size; #if TASKQUEUE_STATS using TaskQueueSuper<N, F>::stats; #endif private: // Slow paths for push, pop_local. (pop_global has no fast path.) bool push_slow(E t, uint dirty_n_elems); bool pop_local_slow(uint localBot, Age oldAge); public: typedef E element_type; // Initializes the queue to empty. GenericTaskQueue(); void initialize(); // Push the task "t" on the queue. Returns "false" iff the queue is full. inline bool push(E t); // Attempts to claim a task from the "local" end of the queue (the most // recently pushed). If successful, returns true and sets t to the task; // otherwise, returns false (the queue is empty). inline bool pop_local(volatile E& t); // Like pop_local(), but uses the "global" end of the queue (the least // recently pushed). bool pop_global(volatile E& t); // Delete any resource associated with the queue. ~GenericTaskQueue(); // apply the closure to all elements in the task queue void oops_do(OopClosure* f); private: // Element array. volatile E* _elems; }; template<class E, MEMFLAGS F, unsigned int N> GenericTaskQueue<E, F, N>::GenericTaskQueue() { assert(sizeof(Age) == sizeof(size_t), "Depends on this."); } template<class E, MEMFLAGS F, unsigned int N> void GenericTaskQueue<E, F, N>::initialize() { _elems = _array_allocator.allocate(N); } template<class E, MEMFLAGS F, unsigned int N> void GenericTaskQueue<E, F, N>::oops_do(OopClosure* f) { // tty->print_cr("START OopTaskQueue::oops_do"); uint iters = size(); uint index = _bottom; for (uint i = 0; i < iters; ++i) { index = decrement_index(index); // tty->print_cr(" doing entry %d," INTPTR_T " -> " INTPTR_T, // index, &_elems[index], _elems[index]); E* t = (E*)&_elems[index]; // cast away volatility oop* p = (oop*)t; assert((*t)->is_oop_or_null(), "Not an oop or null"); f->do_oop(p); } // tty->print_cr("END OopTaskQueue::oops_do"); } template<class E, MEMFLAGS F, unsigned int N> bool GenericTaskQueue<E, F, N>::push_slow(E t, uint dirty_n_elems) { if (dirty_n_elems == N - 1) { // Actually means 0, so do the push. uint localBot = _bottom; // g++ complains if the volatile result of the assignment is // unused, so we cast the volatile away. We cannot cast directly // to void, because gcc treats that as not using the result of the // assignment. However, casting to E& means that we trigger an // unused-value warning. So, we cast the E& to void. (void)const_cast<E&>(_elems[localBot] = t); OrderAccess::release_store(&_bottom, increment_index(localBot)); TASKQUEUE_STATS_ONLY(stats.record_push()); return true; } return false; } // pop_local_slow() is done by the owning thread and is trying to // get the last task in the queue. It will compete with pop_global() // that will be used by other threads. The tag age is incremented // whenever the queue goes empty which it will do here if this thread // gets the last task or in pop_global() if the queue wraps (top == 0 // and pop_global() succeeds, see pop_global()). template<class E, MEMFLAGS F, unsigned int N> bool GenericTaskQueue<E, F, N>::pop_local_slow(uint localBot, Age oldAge) { // This queue was observed to contain exactly one element; either this // thread will claim it, or a competing "pop_global". In either case, // the queue will be logically empty afterwards. Create a new Age value // that represents the empty queue for the given value of "_bottom". (We // must also increment "tag" because of the case where "bottom == 1", // "top == 0". A pop_global could read the queue element in that case, // then have the owner thread do a pop followed by another push. Without // the incrementing of "tag", the pop_global's CAS could succeed, // allowing it to believe it has claimed the stale element.) Age newAge((idx_t)localBot, oldAge.tag() + 1); // Perhaps a competing pop_global has already incremented "top", in which // case it wins the element. if (localBot == oldAge.top()) { // No competing pop_global has yet incremented "top"; we'll try to // install new_age, thus claiming the element. Age tempAge = _age.cmpxchg(newAge, oldAge); if (tempAge == oldAge) { // We win. assert(dirty_size(localBot, _age.top()) != N - 1, "sanity"); TASKQUEUE_STATS_ONLY(stats.record_pop_slow()); return true; } } // We lose; a completing pop_global gets the element. But the queue is empty // and top is greater than bottom. Fix this representation of the empty queue // to become the canonical one. _age.set(newAge); assert(dirty_size(localBot, _age.top()) != N - 1, "sanity"); return false; } template<class E, MEMFLAGS F, unsigned int N> bool GenericTaskQueue<E, F, N>::pop_global(volatile E& t) { Age oldAge = _age.get(); // Architectures with weak memory model require a barrier here // to guarantee that bottom is not older than age, // which is crucial for the correctness of the algorithm. #if !(defined SPARC || defined IA32 || defined AMD64) OrderAccess::fence(); #endif uint localBot = OrderAccess::load_acquire((volatile juint*)&_bottom); uint n_elems = size(localBot, oldAge.top()); if (n_elems == 0) { return false; } // g++ complains if the volatile result of the assignment is // unused, so we cast the volatile away. We cannot cast directly // to void, because gcc treats that as not using the result of the // assignment. However, casting to E& means that we trigger an // unused-value warning. So, we cast the E& to void. (void) const_cast<E&>(t = _elems[oldAge.top()]); Age newAge(oldAge); newAge.increment(); Age resAge = _age.cmpxchg(newAge, oldAge); // Note that using "_bottom" here might fail, since a pop_local might // have decremented it. assert(dirty_size(localBot, newAge.top()) != N - 1, "sanity"); return resAge == oldAge; } template<class E, MEMFLAGS F, unsigned int N> GenericTaskQueue<E, F, N>::~GenericTaskQueue() { FREE_C_HEAP_ARRAY(E, _elems, F); } // OverflowTaskQueue is a TaskQueue that also includes an overflow stack for // elements that do not fit in the TaskQueue. // // This class hides two methods from super classes: // // push() - push onto the task queue or, if that fails, onto the overflow stack // is_empty() - return true if both the TaskQueue and overflow stack are empty // // Note that size() is not hidden--it returns the number of elements in the // TaskQueue, and does not include the size of the overflow stack. This // simplifies replacement of GenericTaskQueues with OverflowTaskQueues. template<class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE> class OverflowTaskQueue: public GenericTaskQueue<E, F, N> { public: typedef Stack<E, F> overflow_t; typedef GenericTaskQueue<E, F, N> taskqueue_t; TASKQUEUE_STATS_ONLY(using taskqueue_t::stats;) // Push task t onto the queue or onto the overflow stack. Return true. inline bool push(E t); // Attempt to pop from the overflow stack; return true if anything was popped. inline bool pop_overflow(E& t); inline overflow_t* overflow_stack() { return &_overflow_stack; } inline bool taskqueue_empty() const { return taskqueue_t::is_empty(); } inline bool overflow_empty() const { return _overflow_stack.is_empty(); } inline bool is_empty() const { return taskqueue_empty() && overflow_empty(); } private: overflow_t _overflow_stack; }; template <class E, MEMFLAGS F, unsigned int N> bool OverflowTaskQueue<E, F, N>::push(E t) { if (!taskqueue_t::push(t)) { overflow_stack()->push(t); TASKQUEUE_STATS_ONLY(stats.record_overflow(overflow_stack()->size())); } return true; } template <class E, MEMFLAGS F, unsigned int N> bool OverflowTaskQueue<E, F, N>::pop_overflow(E& t) { if (overflow_empty()) return false; t = overflow_stack()->pop(); return true; } class TaskQueueSetSuper { protected: static int randomParkAndMiller(int* seed0); public: // Returns "true" if some TaskQueue in the set contains a task. virtual bool peek() = 0; }; template <MEMFLAGS F> class TaskQueueSetSuperImpl: public CHeapObj<F>, public TaskQueueSetSuper { }; template<class T, MEMFLAGS F> class GenericTaskQueueSet: public TaskQueueSetSuperImpl<F> { private: uint _n; T** _queues; public: typedef typename T::element_type E; GenericTaskQueueSet(int n) : _n(n) { typedef T* GenericTaskQueuePtr; _queues = NEW_C_HEAP_ARRAY(GenericTaskQueuePtr, n, F); for (int i = 0; i < n; i++) { _queues[i] = NULL; } } bool steal_best_of_2(uint queue_num, int* seed, E& t); void register_queue(uint i, T* q); T* queue(uint n); // The thread with queue number "queue_num" (and whose random number seed is // at "seed") is trying to steal a task from some other queue. (It may try // several queues, according to some configuration parameter.) If some steal // succeeds, returns "true" and sets "t" to the stolen task, otherwise returns // false. bool steal(uint queue_num, int* seed, E& t); bool peek(); }; template<class T, MEMFLAGS F> void GenericTaskQueueSet<T, F>::register_queue(uint i, T* q) { assert(i < _n, "index out of range."); _queues[i] = q; } template<class T, MEMFLAGS F> T* GenericTaskQueueSet<T, F>::queue(uint i) { return _queues[i]; } template<class T, MEMFLAGS F> bool GenericTaskQueueSet<T, F>::steal(uint queue_num, int* seed, E& t) { for (uint i = 0; i < 2 * _n; i++) { if (steal_best_of_2(queue_num, seed, t)) { TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(true)); return true; } } TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(false)); return false; } template<class T, MEMFLAGS F> bool GenericTaskQueueSet<T, F>::steal_best_of_2(uint queue_num, int* seed, E& t) { if (_n > 2) { uint k1 = queue_num; while (k1 == queue_num) k1 = TaskQueueSetSuper::randomParkAndMiller(seed) % _n; uint k2 = queue_num; while (k2 == queue_num || k2 == k1) k2 = TaskQueueSetSuper::randomParkAndMiller(seed) % _n; // Sample both and try the larger. uint sz1 = _queues[k1]->size(); uint sz2 = _queues[k2]->size(); if (sz2 > sz1) return _queues[k2]->pop_global(t); else return _queues[k1]->pop_global(t); } else if (_n == 2) { // Just try the other one. uint k = (queue_num + 1) % 2; return _queues[k]->pop_global(t); } else { assert(_n == 1, "can't be zero."); return false; } } template<class T, MEMFLAGS F> bool GenericTaskQueueSet<T, F>::peek() { // Try all the queues. for (uint j = 0; j < _n; j++) { if (_queues[j]->peek()) return true; } return false; } // When to terminate from the termination protocol. class TerminatorTerminator: public CHeapObj<mtInternal> { public: virtual bool should_exit_termination() = 0; }; // A class to aid in the termination of a set of parallel tasks using // TaskQueueSet's for work stealing. #undef TRACESPINNING class ParallelTaskTerminator: public StackObj { private: int _n_threads; TaskQueueSetSuper* _queue_set; int _offered_termination; #ifdef TRACESPINNING static uint _total_yields; static uint _total_spins; static uint _total_peeks; #endif bool peek_in_queue_set(); protected: virtual void yield(); void sleep(uint millis); public: // "n_threads" is the number of threads to be terminated. "queue_set" is a // queue sets of work queues of other threads. ParallelTaskTerminator(int n_threads, TaskQueueSetSuper* queue_set); // The current thread has no work, and is ready to terminate if everyone // else is. If returns "true", all threads are terminated. If returns // "false", available work has been observed in one of the task queues, // so the global task is not complete. bool offer_termination() { return offer_termination(NULL); } // As above, but it also terminates if the should_exit_termination() // method of the terminator parameter returns true. If terminator is // NULL, then it is ignored. bool offer_termination(TerminatorTerminator* terminator); // Reset the terminator, so that it may be reused again. // The caller is responsible for ensuring that this is done // in an MT-safe manner, once the previous round of use of // the terminator is finished. void reset_for_reuse(); // Same as above but the number of parallel threads is set to the // given number. void reset_for_reuse(int n_threads); #ifdef TRACESPINNING static uint total_yields() { return _total_yields; } static uint total_spins() { return _total_spins; } static uint total_peeks() { return _total_peeks; } static void print_termination_counts(); #endif }; template<class E, MEMFLAGS F, unsigned int N> inline bool GenericTaskQueue<E, F, N>::push(E t) { uint localBot = _bottom; assert(localBot < N, "_bottom out of range."); idx_t top = _age.top(); uint dirty_n_elems = dirty_size(localBot, top); assert(dirty_n_elems < N, "n_elems out of range."); if (dirty_n_elems < max_elems()) { // g++ complains if the volatile result of the assignment is // unused, so we cast the volatile away. We cannot cast directly // to void, because gcc treats that as not using the result of the // assignment. However, casting to E& means that we trigger an // unused-value warning. So, we cast the E& to void. (void) const_cast<E&>(_elems[localBot] = t); OrderAccess::release_store(&_bottom, increment_index(localBot)); TASKQUEUE_STATS_ONLY(stats.record_push()); return true; } else { return push_slow(t, dirty_n_elems); } } template<class E, MEMFLAGS F, unsigned int N> inline bool GenericTaskQueue<E, F, N>::pop_local(volatile E& t) { uint localBot = _bottom; // This value cannot be N-1. That can only occur as a result of // the assignment to bottom in this method. If it does, this method // resets the size to 0 before the next call (which is sequential, // since this is pop_local.) uint dirty_n_elems = dirty_size(localBot, _age.top()); assert(dirty_n_elems != N - 1, "Shouldn't be possible..."); if (dirty_n_elems == 0) return false; localBot = decrement_index(localBot); _bottom = localBot; // This is necessary to prevent any read below from being reordered // before the store just above. OrderAccess::fence(); // g++ complains if the volatile result of the assignment is // unused, so we cast the volatile away. We cannot cast directly // to void, because gcc treats that as not using the result of the // assignment. However, casting to E& means that we trigger an // unused-value warning. So, we cast the E& to void. (void) const_cast<E&>(t = _elems[localBot]); // This is a second read of "age"; the "size()" above is the first. // If there's still at least one element in the queue, based on the // "_bottom" and "age" we've read, then there can be no interference with // a "pop_global" operation, and we're done. idx_t tp = _age.top(); // XXX if (size(localBot, tp) > 0) { assert(dirty_size(localBot, tp) != N - 1, "sanity"); TASKQUEUE_STATS_ONLY(stats.record_pop()); return true; } else { // Otherwise, the queue contained exactly one element; we take the slow // path. return pop_local_slow(localBot, _age.get()); } } typedef GenericTaskQueue<oop, mtGC> OopTaskQueue; typedef GenericTaskQueueSet<OopTaskQueue, mtGC> OopTaskQueueSet; #ifdef _MSC_VER #pragma warning(push) // warning C4522: multiple assignment operators specified #pragma warning(disable:4522) #endif // This is a container class for either an oop* or a narrowOop*. // Both are pushed onto a task queue and the consumer will test is_narrow() // to determine which should be processed. class StarTask { void* _holder; // either union oop* or narrowOop* enum { COMPRESSED_OOP_MASK = 1 }; public: StarTask(narrowOop* p) { assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!"); _holder = (void *)((uintptr_t)p | COMPRESSED_OOP_MASK); } StarTask(oop* p) { assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!"); _holder = (void*)p; } StarTask() { _holder = NULL; } operator oop*() { return (oop*)_holder; } operator narrowOop*() { return (narrowOop*)((uintptr_t)_holder & ~COMPRESSED_OOP_MASK); } StarTask& operator=(const StarTask& t) { _holder = t._holder; return *this; } volatile StarTask& operator=(const volatile StarTask& t) volatile { _holder = t._holder; return *this; } bool is_narrow() const { return (((uintptr_t)_holder & COMPRESSED_OOP_MASK) != 0); } }; class ObjArrayTask { public: ObjArrayTask(oop o = NULL, int idx = 0): _obj(o), _index(idx) { } ObjArrayTask(oop o, size_t idx): _obj(o), _index(int(idx)) { assert(idx <= size_t(max_jint), "too big"); } ObjArrayTask(const ObjArrayTask& t): _obj(t._obj), _index(t._index) { } ObjArrayTask& operator =(const ObjArrayTask& t) { _obj = t._obj; _index = t._index; return *this; } volatile ObjArrayTask& operator =(const volatile ObjArrayTask& t) volatile { (void)const_cast<oop&>(_obj = t._obj); _index = t._index; return *this; } inline oop obj() const { return _obj; } inline int index() const { return _index; } DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid. private: oop _obj; int _index; }; #ifdef _MSC_VER #pragma warning(pop) #endif typedef OverflowTaskQueue<StarTask, mtClass> OopStarTaskQueue; typedef GenericTaskQueueSet<OopStarTaskQueue, mtClass> OopStarTaskQueueSet; typedef OverflowTaskQueue<size_t, mtInternal> RegionTaskQueue; typedef GenericTaskQueueSet<RegionTaskQueue, mtClass> RegionTaskQueueSet; #endif // SHARE_VM_UTILITIES_TASKQUEUE_HPP