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/*
* Copyright (c) 2001, 2022, 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_GC_SHARED_TASKQUEUE_HPP
#define SHARE_GC_SHARED_TASKQUEUE_HPP
#include "memory/allocation.hpp"
#include "memory/padded.hpp"
#include "oops/oopsHierarchy.hpp"
#include "runtime/atomic.hpp"
#include "utilities/debug.hpp"
#include "utilities/globalDefinitions.hpp"
#include "utilities/ostream.hpp"
#include "utilities/stack.hpp"
// 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_empty, // number of empty taskqueues
steal_contended, // number of contended steals
steal_success, // number of successful steals
steal_max_contended_in_a_row, // maximum number of contended steals in a row
steal_bias_drop, // number of times the bias has been dropped
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_attempt(uint kind) {
++_stats[steal_attempt];
++_stats[steal_empty + kind];
}
inline void record_contended_in_a_row(uint in_a_row) {
if (_stats[steal_max_contended_in_a_row] < in_a_row) {
_stats[steal_max_contended_in_a_row] = in_a_row;
}
}
inline void record_bias_drop() { ++_stats[steal_bias_drop]; }
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 = 11);
// Print the statistics (does not include a line separator).
void print(outputStream* const stream = tty, unsigned int width = 11) const;
DEBUG_ONLY(void verify() const;)
private:
size_t _stats[last_stat_id];
static const char * const _names[last_stat_id];
};
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;
STATIC_ASSERT(N == idx_t(N)); // Ensure N fits in an idx_t.
// N must be a power of 2 for computing modulo via masking.
// N must be >= 2 for the algorithm to work at all, though larger is better.
STATIC_ASSERT(N >= 2);
STATIC_ASSERT(is_power_of_2(N));
static const uint MOD_N_MASK = N - 1;
class Age {
friend class TaskQueueSuper;
public:
explicit Age(size_t data = 0) : _data(data) {}
Age(idx_t top, idx_t tag) { _fields._top = top; _fields._tag = tag; }
idx_t top() const { return _fields._top; }
idx_t tag() const { return _fields._tag; }
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;
};
STATIC_ASSERT(sizeof(size_t) >= sizeof(fields));
};
uint bottom_relaxed() const {
return Atomic::load(&_bottom);
}
uint bottom_acquire() const {
return Atomic::load_acquire(&_bottom);
}
void set_bottom_relaxed(uint new_bottom) {
Atomic::store(&_bottom, new_bottom);
}
void release_set_bottom(uint new_bottom) {
Atomic::release_store(&_bottom, new_bottom);
}
Age age_relaxed() const {
return Age(Atomic::load(&_age._data));
}
void set_age_relaxed(Age new_age) {
Atomic::store(&_age._data, new_age._data);
}
Age cmpxchg_age(Age old_age, Age new_age) {
return Age(Atomic::cmpxchg(&_age._data, old_age._data, new_age._data));
}
idx_t age_top_relaxed() const {
// Atomically accessing a subfield of an "atomic" member.
return Atomic::load(&_age._fields._top);
}
// 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 clean_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 threads, so the owner thread can reset the state
// to _bottom == top so subsequent pushes will be performed normally.
return (sz == N - 1) ? 0 : sz;
}
// Assert that we're not in the underflow state where bottom has
// been decremented past top, so that _bottom+1 mod N == top. See
// the discussion in clean_size.
void assert_not_underflow(uint bot, uint top) const {
assert_not_underflow(dirty_size(bot, top));
}
void assert_not_underflow(uint dirty_size) const {
assert(dirty_size != N - 1, "invariant");
}
private:
DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE, 0);
// Index of the first free element after the last one pushed (mod N).
volatile uint _bottom;
DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(uint));
// top() is the index of the oldest pushed element (mod N), and tag()
// is the associated epoch, to distinguish different modifications of
// the age. There is no available element if top() == _bottom or
// (_bottom - top()) mod N == N-1; the latter indicates underflow
// during concurrent pop_local/pop_global.
volatile Age _age;
DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(Age));
NONCOPYABLE(TaskQueueSuper);
public:
TaskQueueSuper() : _bottom(0), _age() {}
// Assert the queue is empty.
// Unreliable if there are concurrent pushes or pops.
void assert_empty() const {
assert(bottom_relaxed() == age_top_relaxed(), "not empty");
}
bool is_empty() const {
return size() == 0;
}
// Return an estimate of the number of elements in the queue.
// Treats pop_local/pop_global race that underflows as empty.
uint size() const {
return clean_size(bottom_relaxed(), age_top_relaxed());
}
// Discard the contents of the queue.
void set_empty() {
set_bottom_relaxed(0);
set_age_relaxed(Age());
}
// Maximum number of elements allowed in the queue. This is two less
// than the actual queue size, so that a full queue can be distinguished
// from underflow involving pop_local and concurrent pop_global operations
// in GenericTaskQueue.
uint max_elems() const { return N - 2; }
// The result of a pop_global operation. The value order of this must correspond
// to the order in the corresponding TaskQueueStats StatId.
enum class PopResult : uint {
Empty = 0, // Queue has been empty. t is undefined.
Contended = 1, // Contention prevented successful retrieval, queue most likely contains elements. t is undefined.
Success = 2 // Successfully retrieved an element, t contains it.
};
TASKQUEUE_STATS_ONLY(void record_steal_attempt(PopResult kind) { stats.record_steal_attempt((uint)kind); })
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> {
protected:
typedef typename TaskQueueSuper<N, F>::Age Age;
typedef typename TaskQueueSuper<N, F>::idx_t idx_t;
using TaskQueueSuper<N, F>::MOD_N_MASK;
using TaskQueueSuper<N, F>::bottom_relaxed;
using TaskQueueSuper<N, F>::bottom_acquire;
using TaskQueueSuper<N, F>::set_bottom_relaxed;
using TaskQueueSuper<N, F>::release_set_bottom;
using TaskQueueSuper<N, F>::age_relaxed;
using TaskQueueSuper<N, F>::set_age_relaxed;
using TaskQueueSuper<N, F>::cmpxchg_age;
using TaskQueueSuper<N, F>::age_top_relaxed;
using TaskQueueSuper<N, F>::increment_index;
using TaskQueueSuper<N, F>::decrement_index;
using TaskQueueSuper<N, F>::dirty_size;
using TaskQueueSuper<N, F>::clean_size;
using TaskQueueSuper<N, F>::assert_not_underflow;
public:
typedef typename TaskQueueSuper<N, F>::PopResult PopResult;
using TaskQueueSuper<N, F>::max_elems;
using TaskQueueSuper<N, F>::size;
#if TASKQUEUE_STATS
using TaskQueueSuper<N, F>::stats;
#endif
private:
// Slow path for pop_local, dealing with possible conflict with pop_global.
bool pop_local_slow(uint localBot, Age oldAge);
public:
typedef E element_type;
// Initializes the queue to empty.
GenericTaskQueue();
// 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) as long as the number of entries exceeds the threshold.
// If successfully claims a task, returns true and sets t to the task;
// otherwise, returns false and t is unspecified. May fail and return
// false because of a successful steal by pop_global.
inline bool pop_local(E& t, uint threshold = 0);
// Like pop_local(), but uses the "global" end of the queue (the least
// recently pushed).
PopResult pop_global(E& t);
// Delete any resource associated with the queue.
~GenericTaskQueue();
// Apply fn to each element in the task queue. The queue must not
// be modified while iterating.
template<typename Fn> void iterate(Fn fn);
private:
// Base class has trailing padding.
// Element array.
E* _elems;
DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(E*));
// Queue owner local variables. Not to be accessed by other threads.
static const uint InvalidQueueId = uint(-1);
uint _last_stolen_queue_id; // The id of the queue we last stole from
int _seed; // Current random seed used for selecting a random queue during stealing.
DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(uint) + sizeof(int));
public:
int next_random_queue_id();
void set_last_stolen_queue_id(uint id) { _last_stolen_queue_id = id; }
uint last_stolen_queue_id() const { return _last_stolen_queue_id; }
bool is_last_stolen_queue_id_valid() const { return _last_stolen_queue_id != InvalidQueueId; }
void invalidate_last_stolen_queue_id() {
TASKQUEUE_STATS_ONLY(stats.record_bias_drop();)
_last_stolen_queue_id = InvalidQueueId;
}
};
// 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);
// Try to push task t onto the queue only. Returns true if successful, false otherwise.
inline bool try_push_to_taskqueue(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;
};
class TaskQueueSetSuper {
public:
// Assert all queues in the set are empty.
NOT_DEBUG(void assert_empty() const {})
DEBUG_ONLY(virtual void assert_empty() const = 0;)
// Tasks in queue
virtual uint tasks() const = 0;
};
template <MEMFLAGS F> class TaskQueueSetSuperImpl: public CHeapObj<F>, public TaskQueueSetSuper {
};
template<class T, MEMFLAGS F>
class GenericTaskQueueSet: public TaskQueueSetSuperImpl<F> {
public:
typedef typename T::element_type E;
typedef typename T::PopResult PopResult;
private:
uint _n;
T** _queues;
// Attempts to steal an element from a foreign queue (!= queue_num), setting
// the result in t. Validity of this value and the return value is the same
// as for the last pop_global() operation.
PopResult steal_best_of_2(uint queue_num, E& t);
public:
GenericTaskQueueSet(uint n);
~GenericTaskQueueSet();
// Set the i'th queue to the provided queue.
// Does not transfer ownership of the queue to this queue set.
void register_queue(uint i, T* q);
T* queue(uint n);
// Try to steal a task from some other queue than queue_num. It may perform several attempts at doing so.
// Returns if stealing succeeds, and sets "t" to the stolen task.
bool steal(uint queue_num, E& t);
DEBUG_ONLY(virtual void assert_empty() const;)
virtual uint tasks() const;
uint size() const { return _n; }
#if TASKQUEUE_STATS
private:
static void print_taskqueue_stats_hdr(outputStream* const st, const char* label);
public:
void print_taskqueue_stats(outputStream* const st, const char* label);
void reset_taskqueue_stats();
// Prints taskqueue set statistics into gc+task+stats=trace and resets
// its statistics.
void print_and_reset_taskqueue_stats(const char* label);
#endif // TASKQUEUE_STATS
};
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) {
assert(i < _n, "index out of range.");
return _queues[i];
}
#ifdef ASSERT
template<class T, MEMFLAGS F>
void GenericTaskQueueSet<T, F>::assert_empty() const {
for (uint j = 0; j < _n; j++) {
_queues[j]->assert_empty();
}
}
#endif // ASSERT
template<class T, MEMFLAGS F>
uint GenericTaskQueueSet<T, F>::tasks() const {
uint n = 0;
for (uint j = 0; j < _n; j++) {
n += _queues[j]->size();
}
return n;
}
// When to terminate from the termination protocol.
class TerminatorTerminator: public CHeapObj<mtInternal> {
public:
virtual bool should_exit_termination() = 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");
}
// Trivially copyable, for use in GenericTaskQueue.
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;
};
// Wrapper over an oop that is a partially scanned array.
// Can be converted to a ScannerTask for placement in associated task queues.
// Refers to the partially copied source array oop.
class PartialArrayScanTask {
oop _src;
public:
explicit PartialArrayScanTask(oop src_array) : _src(src_array) {}
// Trivially copyable.
oop to_source_array() const { return _src; }
};
// Discriminated union over oop*, narrowOop*, and PartialArrayScanTask.
// Uses a low tag in the associated pointer to identify the category.
// Used as a task queue element type.
class ScannerTask {
void* _p;
static const uintptr_t OopTag = 0;
static const uintptr_t NarrowOopTag = 1;
static const uintptr_t PartialArrayTag = 2;
static const uintptr_t TagSize = 2;
static const uintptr_t TagAlignment = 1 << TagSize;
static const uintptr_t TagMask = TagAlignment - 1;
static void* encode(void* p, uintptr_t tag) {
assert(is_aligned(p, TagAlignment), "misaligned: " PTR_FORMAT, p2i(p));
return static_cast<char*>(p) + tag;
}
uintptr_t raw_value() const {
return reinterpret_cast<uintptr_t>(_p);
}
bool has_tag(uintptr_t tag) const {
return (raw_value() & TagMask) == tag;
}
void* decode(uintptr_t tag) const {
assert(has_tag(tag), "precondition");
return static_cast<char*>(_p) - tag;
}
public:
ScannerTask() : _p(NULL) {}
explicit ScannerTask(oop* p) : _p(encode(p, OopTag)) {}
explicit ScannerTask(narrowOop* p) : _p(encode(p, NarrowOopTag)) {}
explicit ScannerTask(PartialArrayScanTask t) :
_p(encode(t.to_source_array(), PartialArrayTag)) {}
// Trivially copyable.
// Predicate implementations assume OopTag == 0, others are powers of 2.
bool is_oop_ptr() const {
return (raw_value() & (NarrowOopTag | PartialArrayTag)) == 0;
}
bool is_narrow_oop_ptr() const {
return (raw_value() & NarrowOopTag) != 0;
}
bool is_partial_array_task() const {
return (raw_value() & PartialArrayTag) != 0;
}
oop* to_oop_ptr() const {
return static_cast<oop*>(decode(OopTag));
}
narrowOop* to_narrow_oop_ptr() const {
return static_cast<narrowOop*>(decode(NarrowOopTag));
}
PartialArrayScanTask to_partial_array_task() const {
return PartialArrayScanTask(cast_to_oop(decode(PartialArrayTag)));
}
};
#endif // SHARE_GC_SHARED_TASKQUEUE_HPP
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