diff --git a/lib/concurrent-ruby/concurrent/collection/map/atomic_reference_map_backend.rb b/lib/concurrent-ruby/concurrent/collection/map/atomic_reference_map_backend.rb deleted file mode 100644 index dc5189389..000000000 --- a/lib/concurrent-ruby/concurrent/collection/map/atomic_reference_map_backend.rb +++ /dev/null @@ -1,927 +0,0 @@ -require 'concurrent/constants' -require 'concurrent/thread_safe/util' -require 'concurrent/thread_safe/util/adder' -require 'concurrent/thread_safe/util/cheap_lockable' -require 'concurrent/thread_safe/util/power_of_two_tuple' -require 'concurrent/thread_safe/util/volatile' -require 'concurrent/thread_safe/util/xor_shift_random' - -module Concurrent - - # @!visibility private - module Collection - - # A Ruby port of the Doug Lea's jsr166e.ConcurrentHashMapV8 class version 1.59 - # available in public domain. - # - # Original source code available here: - # http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/jsr166e/ConcurrentHashMapV8.java?revision=1.59 - # - # The Ruby port skips out the +TreeBin+ (red-black trees for use in bins whose - # size exceeds a threshold). - # - # A hash table supporting full concurrency of retrievals and high expected - # concurrency for updates. However, even though all operations are - # thread-safe, retrieval operations do _not_ entail locking, and there is - # _not_ any support for locking the entire table in a way that prevents all - # access. - # - # Retrieval operations generally do not block, so may overlap with update - # operations. Retrievals reflect the results of the most recently _completed_ - # update operations holding upon their onset. (More formally, an update - # operation for a given key bears a _happens-before_ relation with any (non - # +nil+) retrieval for that key reporting the updated value.) For aggregate - # operations such as +clear()+, concurrent retrievals may reflect insertion or - # removal of only some entries. Similarly, the +each_pair+ iterator yields - # elements reflecting the state of the hash table at some point at or since - # the start of the +each_pair+. Bear in mind that the results of aggregate - # status methods including +size()+ and +empty?+} are typically useful only - # when a map is not undergoing concurrent updates in other threads. Otherwise - # the results of these methods reflect transient states that may be adequate - # for monitoring or estimation purposes, but not for program control. - # - # The table is dynamically expanded when there are too many collisions (i.e., - # keys that have distinct hash codes but fall into the same slot modulo the - # table size), with the expected average effect of maintaining roughly two - # bins per mapping (corresponding to a 0.75 load factor threshold for - # resizing). There may be much variance around this average as mappings are - # added and removed, but overall, this maintains a commonly accepted - # time/space tradeoff for hash tables. However, resizing this or any other - # kind of hash table may be a relatively slow operation. When possible, it is - # a good idea to provide a size estimate as an optional :initial_capacity - # initializer argument. An additional optional :load_factor constructor - # argument provides a further means of customizing initial table capacity by - # specifying the table density to be used in calculating the amount of space - # to allocate for the given number of elements. Note that using many keys with - # exactly the same +hash+ is a sure way to slow down performance of any hash - # table. - # - # ## Design overview - # - # The primary design goal of this hash table is to maintain concurrent - # readability (typically method +[]+, but also iteration and related methods) - # while minimizing update contention. Secondary goals are to keep space - # consumption about the same or better than plain +Hash+, and to support high - # initial insertion rates on an empty table by many threads. - # - # Each key-value mapping is held in a +Node+. The validation-based approach - # explained below leads to a lot of code sprawl because retry-control - # precludes factoring into smaller methods. - # - # The table is lazily initialized to a power-of-two size upon the first - # insertion. Each bin in the table normally contains a list of +Node+s (most - # often, the list has only zero or one +Node+). Table accesses require - # volatile/atomic reads, writes, and CASes. The lists of nodes within bins are - # always accurately traversable under volatile reads, so long as lookups check - # hash code and non-nullness of value before checking key equality. - # - # We use the top two bits of +Node+ hash fields for control purposes -- they - # are available anyway because of addressing constraints. As explained further - # below, these top bits are used as follows: - # - # - 00 - Normal - # - 01 - Locked - # - 11 - Locked and may have a thread waiting for lock - # - 10 - +Node+ is a forwarding node - # - # The lower 28 bits of each +Node+'s hash field contain a the key's hash code, - # except for forwarding nodes, for which the lower bits are zero (and so - # always have hash field == +MOVED+). - # - # Insertion (via +[]=+ or its variants) of the first node in an empty bin is - # performed by just CASing it to the bin. This is by far the most common case - # for put operations under most key/hash distributions. Other update - # operations (insert, delete, and replace) require locks. We do not want to - # waste the space required to associate a distinct lock object with each bin, - # so instead use the first node of a bin list itself as a lock. Blocking - # support for these locks relies +Concurrent::ThreadSafe::Util::CheapLockable. However, we also need a - # +try_lock+ construction, so we overlay these by using bits of the +Node+ - # hash field for lock control (see above), and so normally use builtin - # monitors only for blocking and signalling using - # +cheap_wait+/+cheap_broadcast+ constructions. See +Node#try_await_lock+. - # - # Using the first node of a list as a lock does not by itself suffice though: - # When a node is locked, any update must first validate that it is still the - # first node after locking it, and retry if not. Because new nodes are always - # appended to lists, once a node is first in a bin, it remains first until - # deleted or the bin becomes invalidated (upon resizing). However, operations - # that only conditionally update may inspect nodes until the point of update. - # This is a converse of sorts to the lazy locking technique described by - # Herlihy & Shavit. - # - # The main disadvantage of per-bin locks is that other update operations on - # other nodes in a bin list protected by the same lock can stall, for example - # when user +eql?+ or mapping functions take a long time. However, - # statistically, under random hash codes, this is not a common problem. - # Ideally, the frequency of nodes in bins follows a Poisson distribution - # (http://en.wikipedia.org/wiki/Poisson_distribution) with a parameter of - # about 0.5 on average, given the resizing threshold of 0.75, although with a - # large variance because of resizing granularity. Ignoring variance, the - # expected occurrences of list size k are (exp(-0.5) * pow(0.5, k) / - # factorial(k)). The first values are: - # - # - 0: 0.60653066 - # - 1: 0.30326533 - # - 2: 0.07581633 - # - 3: 0.01263606 - # - 4: 0.00157952 - # - 5: 0.00015795 - # - 6: 0.00001316 - # - 7: 0.00000094 - # - 8: 0.00000006 - # - more: less than 1 in ten million - # - # Lock contention probability for two threads accessing distinct elements is - # roughly 1 / (8 * #elements) under random hashes. - # - # The table is resized when occupancy exceeds a percentage threshold - # (nominally, 0.75, but see below). Only a single thread performs the resize - # (using field +size_control+, to arrange exclusion), but the table otherwise - # remains usable for reads and updates. Resizing proceeds by transferring - # bins, one by one, from the table to the next table. Because we are using - # power-of-two expansion, the elements from each bin must either stay at same - # index, or move with a power of two offset. We eliminate unnecessary node - # creation by catching cases where old nodes can be reused because their next - # fields won't change. On average, only about one-sixth of them need cloning - # when a table doubles. The nodes they replace will be garbage collectable as - # soon as they are no longer referenced by any reader thread that may be in - # the midst of concurrently traversing table. Upon transfer, the old table bin - # contains only a special forwarding node (with hash field +MOVED+) that - # contains the next table as its key. On encountering a forwarding node, - # access and update operations restart, using the new table. - # - # Each bin transfer requires its bin lock. However, unlike other cases, a - # transfer can skip a bin if it fails to acquire its lock, and revisit it - # later. Method +rebuild+ maintains a buffer of TRANSFER_BUFFER_SIZE bins that - # have been skipped because of failure to acquire a lock, and blocks only if - # none are available (i.e., only very rarely). The transfer operation must - # also ensure that all accessible bins in both the old and new table are - # usable by any traversal. When there are no lock acquisition failures, this - # is arranged simply by proceeding from the last bin (+table.size - 1+) up - # towards the first. Upon seeing a forwarding node, traversals arrange to move - # to the new table without revisiting nodes. However, when any node is skipped - # during a transfer, all earlier table bins may have become visible, so are - # initialized with a reverse-forwarding node back to the old table until the - # new ones are established. (This sometimes requires transiently locking a - # forwarding node, which is possible under the above encoding.) These more - # expensive mechanics trigger only when necessary. - # - # The traversal scheme also applies to partial traversals of - # ranges of bins (via an alternate Traverser constructor) - # to support partitioned aggregate operations. Also, read-only - # operations give up if ever forwarded to a null table, which - # provides support for shutdown-style clearing, which is also not - # currently implemented. - # - # Lazy table initialization minimizes footprint until first use. - # - # The element count is maintained using a +Concurrent::ThreadSafe::Util::Adder+, - # which avoids contention on updates but can encounter cache thrashing - # if read too frequently during concurrent access. To avoid reading so - # often, resizing is attempted either when a bin lock is - # contended, or upon adding to a bin already holding two or more - # nodes (checked before adding in the +x_if_absent+ methods, after - # adding in others). Under uniform hash distributions, the - # probability of this occurring at threshold is around 13%, - # meaning that only about 1 in 8 puts check threshold (and after - # resizing, many fewer do so). But this approximation has high - # variance for small table sizes, so we check on any collision - # for sizes <= 64. The bulk putAll operation further reduces - # contention by only committing count updates upon these size - # checks. - # - # @!visibility private - class AtomicReferenceMapBackend - - # @!visibility private - class Table < Concurrent::ThreadSafe::Util::PowerOfTwoTuple - def cas_new_node(i, hash, key, value) - cas(i, nil, Node.new(hash, key, value)) - end - - def try_to_cas_in_computed(i, hash, key) - succeeded = false - new_value = nil - new_node = Node.new(locked_hash = hash | LOCKED, key, NULL) - if cas(i, nil, new_node) - begin - if NULL == (new_value = yield(NULL)) - was_null = true - else - new_node.value = new_value - end - succeeded = true - ensure - volatile_set(i, nil) if !succeeded || was_null - new_node.unlock_via_hash(locked_hash, hash) - end - end - return succeeded, new_value - end - - def try_lock_via_hash(i, node, node_hash) - node.try_lock_via_hash(node_hash) do - yield if volatile_get(i) == node - end - end - - def delete_node_at(i, node, predecessor_node) - if predecessor_node - predecessor_node.next = node.next - else - volatile_set(i, node.next) - end - end - end - - # Key-value entry. Nodes with a hash field of +MOVED+ are special, and do - # not contain user keys or values. Otherwise, keys are never +nil+, and - # +NULL+ +value+ fields indicate that a node is in the process of being - # deleted or created. For purposes of read-only access, a key may be read - # before a value, but can only be used after checking value to be +!= NULL+. - # - # @!visibility private - class Node - extend Concurrent::ThreadSafe::Util::Volatile - attr_volatile :hash, :value, :next - - include Concurrent::ThreadSafe::Util::CheapLockable - - bit_shift = Concurrent::ThreadSafe::Util::FIXNUM_BIT_SIZE - 2 # need 2 bits for ourselves - # Encodings for special uses of Node hash fields. See above for explanation. - MOVED = ('10' << ('0' * bit_shift)).to_i(2) # hash field for forwarding nodes - LOCKED = ('01' << ('0' * bit_shift)).to_i(2) # set/tested only as a bit - WAITING = ('11' << ('0' * bit_shift)).to_i(2) # both bits set/tested together - HASH_BITS = ('00' << ('1' * bit_shift)).to_i(2) # usable bits of normal node hash - - SPIN_LOCK_ATTEMPTS = Concurrent::ThreadSafe::Util::CPU_COUNT > 1 ? Concurrent::ThreadSafe::Util::CPU_COUNT * 2 : 0 - - attr_reader :key - - def initialize(hash, key, value, next_node = nil) - super() - @key = key - self.lazy_set_hash(hash) - self.lazy_set_value(value) - self.next = next_node - end - - # Spins a while if +LOCKED+ bit set and this node is the first of its bin, - # and then sets +WAITING+ bits on hash field and blocks (once) if they are - # still set. It is OK for this method to return even if lock is not - # available upon exit, which enables these simple single-wait mechanics. - # - # The corresponding signalling operation is performed within callers: Upon - # detecting that +WAITING+ has been set when unlocking lock (via a failed - # CAS from non-waiting +LOCKED+ state), unlockers acquire the - # +cheap_synchronize+ lock and perform a +cheap_broadcast+. - def try_await_lock(table, i) - if table && i >= 0 && i < table.size # bounds check, TODO: why are we bounds checking? - spins = SPIN_LOCK_ATTEMPTS - randomizer = base_randomizer = Concurrent::ThreadSafe::Util::XorShiftRandom.get - while equal?(table.volatile_get(i)) && self.class.locked_hash?(my_hash = hash) - if spins >= 0 - if (randomizer = (randomizer >> 1)).even? # spin at random - if (spins -= 1) == 0 - Thread.pass # yield before blocking - else - randomizer = base_randomizer = Concurrent::ThreadSafe::Util::XorShiftRandom.xorshift(base_randomizer) if randomizer.zero? - end - end - elsif cas_hash(my_hash, my_hash | WAITING) - force_acquire_lock(table, i) - break - end - end - end - end - - def key?(key) - @key.eql?(key) - end - - def matches?(key, hash) - pure_hash == hash && key?(key) - end - - def pure_hash - hash & HASH_BITS - end - - def try_lock_via_hash(node_hash = hash) - if cas_hash(node_hash, locked_hash = node_hash | LOCKED) - begin - yield - ensure - unlock_via_hash(locked_hash, node_hash) - end - end - end - - def locked? - self.class.locked_hash?(hash) - end - - def unlock_via_hash(locked_hash, node_hash) - unless cas_hash(locked_hash, node_hash) - self.hash = node_hash - cheap_synchronize { cheap_broadcast } - end - end - - private - def force_acquire_lock(table, i) - cheap_synchronize do - if equal?(table.volatile_get(i)) && (hash & WAITING) == WAITING - cheap_wait - else - cheap_broadcast # possibly won race vs signaller - end - end - end - - class << self - def locked_hash?(hash) - (hash & LOCKED) != 0 - end - end - end - - # shorthands - MOVED = Node::MOVED - LOCKED = Node::LOCKED - WAITING = Node::WAITING - HASH_BITS = Node::HASH_BITS - - NOW_RESIZING = -1 - DEFAULT_CAPACITY = 16 - MAX_CAPACITY = Concurrent::ThreadSafe::Util::MAX_INT - - # The buffer size for skipped bins during transfers. The - # value is arbitrary but should be large enough to avoid - # most locking stalls during resizes. - TRANSFER_BUFFER_SIZE = 32 - - extend Concurrent::ThreadSafe::Util::Volatile - attr_volatile :table, # The array of bins. Lazily initialized upon first insertion. Size is always a power of two. - - # Table initialization and resizing control. When negative, the - # table is being initialized or resized. Otherwise, when table is - # null, holds the initial table size to use upon creation, or 0 - # for default. After initialization, holds the next element count - # value upon which to resize the table. - :size_control - - def initialize(options = nil) - super() - @counter = Concurrent::ThreadSafe::Util::Adder.new - initial_capacity = options && options[:initial_capacity] || DEFAULT_CAPACITY - self.size_control = (capacity = table_size_for(initial_capacity)) > MAX_CAPACITY ? MAX_CAPACITY : capacity - end - - def get_or_default(key, else_value = nil) - hash = key_hash(key) - current_table = table - while current_table - node = current_table.volatile_get_by_hash(hash) - current_table = - while node - if (node_hash = node.hash) == MOVED - break node.key - elsif (node_hash & HASH_BITS) == hash && node.key?(key) && NULL != (value = node.value) - return value - end - node = node.next - end - end - else_value - end - - def [](key) - get_or_default(key) - end - - def key?(key) - get_or_default(key, NULL) != NULL - end - - def []=(key, value) - get_and_set(key, value) - value - end - - def compute_if_absent(key) - hash = key_hash(key) - current_table = table || initialize_table - while true - if !(node = current_table.volatile_get(i = current_table.hash_to_index(hash))) - succeeded, new_value = current_table.try_to_cas_in_computed(i, hash, key) { yield } - if succeeded - increment_size - return new_value - end - elsif (node_hash = node.hash) == MOVED - current_table = node.key - elsif NULL != (current_value = find_value_in_node_list(node, key, hash, node_hash & HASH_BITS)) - return current_value - elsif Node.locked_hash?(node_hash) - try_await_lock(current_table, i, node) - else - succeeded, value = attempt_internal_compute_if_absent(key, hash, current_table, i, node, node_hash) { yield } - return value if succeeded - end - end - end - - def compute_if_present(key) - new_value = nil - internal_replace(key) do |old_value| - if (new_value = yield(NULL == old_value ? nil : old_value)).nil? - NULL - else - new_value - end - end - new_value - end - - def compute(key) - internal_compute(key) do |old_value| - if (new_value = yield(NULL == old_value ? nil : old_value)).nil? - NULL - else - new_value - end - end - end - - def merge_pair(key, value) - internal_compute(key) do |old_value| - if NULL == old_value || !(value = yield(old_value)).nil? - value - else - NULL - end - end - end - - def replace_pair(key, old_value, new_value) - NULL != internal_replace(key, old_value) { new_value } - end - - def replace_if_exists(key, new_value) - if (result = internal_replace(key) { new_value }) && NULL != result - result - end - end - - def get_and_set(key, value) # internalPut in the original CHMV8 - hash = key_hash(key) - current_table = table || initialize_table - while true - if !(node = current_table.volatile_get(i = current_table.hash_to_index(hash))) - if current_table.cas_new_node(i, hash, key, value) - increment_size - break - end - elsif (node_hash = node.hash) == MOVED - current_table = node.key - elsif Node.locked_hash?(node_hash) - try_await_lock(current_table, i, node) - else - succeeded, old_value = attempt_get_and_set(key, value, hash, current_table, i, node, node_hash) - break old_value if succeeded - end - end - end - - def delete(key) - replace_if_exists(key, NULL) - end - - def delete_pair(key, value) - result = internal_replace(key, value) { NULL } - if result && NULL != result - !!result - else - false - end - end - - def each_pair - return self unless current_table = table - current_table_size = base_size = current_table.size - i = base_index = 0 - while base_index < base_size - if node = current_table.volatile_get(i) - if node.hash == MOVED - current_table = node.key - current_table_size = current_table.size - else - begin - if NULL != (value = node.value) # skip deleted or special nodes - yield node.key, value - end - end while node = node.next - end - end - - if (i_with_base = i + base_size) < current_table_size - i = i_with_base # visit upper slots if present - else - i = base_index += 1 - end - end - self - end - - def size - (sum = @counter.sum) < 0 ? 0 : sum # ignore transient negative values - end - - def empty? - size == 0 - end - - # Implementation for clear. Steps through each bin, removing all nodes. - def clear - return self unless current_table = table - current_table_size = current_table.size - deleted_count = i = 0 - while i < current_table_size - if !(node = current_table.volatile_get(i)) - i += 1 - elsif (node_hash = node.hash) == MOVED - current_table = node.key - current_table_size = current_table.size - elsif Node.locked_hash?(node_hash) - decrement_size(deleted_count) # opportunistically update count - deleted_count = 0 - node.try_await_lock(current_table, i) - else - current_table.try_lock_via_hash(i, node, node_hash) do - begin - deleted_count += 1 if NULL != node.value # recheck under lock - node.value = nil - end while node = node.next - current_table.volatile_set(i, nil) - i += 1 - end - end - end - decrement_size(deleted_count) - self - end - - private - # Internal versions of the insertion methods, each a - # little more complicated than the last. All have - # the same basic structure: - # 1. If table uninitialized, create - # 2. If bin empty, try to CAS new node - # 3. If bin stale, use new table - # 4. Lock and validate; if valid, scan and add or update - # - # The others interweave other checks and/or alternative actions: - # * Plain +get_and_set+ checks for and performs resize after insertion. - # * compute_if_absent prescans for mapping without lock (and fails to add - # if present), which also makes pre-emptive resize checks worthwhile. - # - # Someday when details settle down a bit more, it might be worth - # some factoring to reduce sprawl. - def internal_replace(key, expected_old_value = NULL, &block) - hash = key_hash(key) - current_table = table - while current_table - if !(node = current_table.volatile_get(i = current_table.hash_to_index(hash))) - break - elsif (node_hash = node.hash) == MOVED - current_table = node.key - elsif (node_hash & HASH_BITS) != hash && !node.next # precheck - break # rules out possible existence - elsif Node.locked_hash?(node_hash) - try_await_lock(current_table, i, node) - else - succeeded, old_value = attempt_internal_replace(key, expected_old_value, hash, current_table, i, node, node_hash, &block) - return old_value if succeeded - end - end - NULL - end - - def attempt_internal_replace(key, expected_old_value, hash, current_table, i, node, node_hash) - current_table.try_lock_via_hash(i, node, node_hash) do - predecessor_node = nil - old_value = NULL - begin - if node.matches?(key, hash) && NULL != (current_value = node.value) - if NULL == expected_old_value || expected_old_value == current_value # NULL == expected_old_value means whatever value - old_value = current_value - if NULL == (node.value = yield(old_value)) - current_table.delete_node_at(i, node, predecessor_node) - decrement_size - end - end - break - end - - predecessor_node = node - end while node = node.next - - return true, old_value - end - end - - def find_value_in_node_list(node, key, hash, pure_hash) - do_check_for_resize = false - while true - if pure_hash == hash && node.key?(key) && NULL != (value = node.value) - return value - elsif node = node.next - do_check_for_resize = true # at least 2 nodes -> check for resize - pure_hash = node.pure_hash - else - return NULL - end - end - ensure - check_for_resize if do_check_for_resize - end - - def internal_compute(key, &block) - hash = key_hash(key) - current_table = table || initialize_table - while true - if !(node = current_table.volatile_get(i = current_table.hash_to_index(hash))) - succeeded, new_value = current_table.try_to_cas_in_computed(i, hash, key, &block) - if succeeded - if NULL == new_value - break nil - else - increment_size - break new_value - end - end - elsif (node_hash = node.hash) == MOVED - current_table = node.key - elsif Node.locked_hash?(node_hash) - try_await_lock(current_table, i, node) - else - succeeded, new_value = attempt_compute(key, hash, current_table, i, node, node_hash, &block) - break new_value if succeeded - end - end - end - - def attempt_internal_compute_if_absent(key, hash, current_table, i, node, node_hash) - added = false - current_table.try_lock_via_hash(i, node, node_hash) do - while true - if node.matches?(key, hash) && NULL != (value = node.value) - return true, value - end - last = node - unless node = node.next - last.next = Node.new(hash, key, value = yield) - added = true - increment_size - return true, value - end - end - end - ensure - check_for_resize if added - end - - def attempt_compute(key, hash, current_table, i, node, node_hash) - added = false - current_table.try_lock_via_hash(i, node, node_hash) do - predecessor_node = nil - while true - if node.matches?(key, hash) && NULL != (value = node.value) - if NULL == (node.value = value = yield(value)) - current_table.delete_node_at(i, node, predecessor_node) - decrement_size - value = nil - end - return true, value - end - predecessor_node = node - unless node = node.next - if NULL == (value = yield(NULL)) - value = nil - else - predecessor_node.next = Node.new(hash, key, value) - added = true - increment_size - end - return true, value - end - end - end - ensure - check_for_resize if added - end - - def attempt_get_and_set(key, value, hash, current_table, i, node, node_hash) - node_nesting = nil - current_table.try_lock_via_hash(i, node, node_hash) do - node_nesting = 1 - old_value = nil - found_old_value = false - while node - if node.matches?(key, hash) && NULL != (old_value = node.value) - found_old_value = true - node.value = value - break - end - last = node - unless node = node.next - last.next = Node.new(hash, key, value) - break - end - node_nesting += 1 - end - - return true, old_value if found_old_value - increment_size - true - end - ensure - check_for_resize if node_nesting && (node_nesting > 1 || current_table.size <= 64) - end - - def initialize_copy(other) - super - @counter = Concurrent::ThreadSafe::Util::Adder.new - self.table = nil - self.size_control = (other_table = other.table) ? other_table.size : DEFAULT_CAPACITY - self - end - - def try_await_lock(current_table, i, node) - check_for_resize # try resizing if can't get lock - node.try_await_lock(current_table, i) - end - - def key_hash(key) - key.hash & HASH_BITS - end - - # Returns a power of two table size for the given desired capacity. - def table_size_for(entry_count) - size = 2 - size <<= 1 while size < entry_count - size - end - - # Initializes table, using the size recorded in +size_control+. - def initialize_table - until current_table ||= table - if (size_ctrl = size_control) == NOW_RESIZING - Thread.pass # lost initialization race; just spin - else - try_in_resize_lock(current_table, size_ctrl) do - initial_size = size_ctrl > 0 ? size_ctrl : DEFAULT_CAPACITY - current_table = self.table = Table.new(initial_size) - initial_size - (initial_size >> 2) # 75% load factor - end - end - end - current_table - end - - # If table is too small and not already resizing, creates next table and - # transfers bins. Rechecks occupancy after a transfer to see if another - # resize is already needed because resizings are lagging additions. - def check_for_resize - while (current_table = table) && MAX_CAPACITY > (table_size = current_table.size) && NOW_RESIZING != (size_ctrl = size_control) && size_ctrl < @counter.sum - try_in_resize_lock(current_table, size_ctrl) do - self.table = rebuild(current_table) - (table_size << 1) - (table_size >> 1) # 75% load factor - end - end - end - - def try_in_resize_lock(current_table, size_ctrl) - if cas_size_control(size_ctrl, NOW_RESIZING) - begin - if current_table == table # recheck under lock - size_ctrl = yield # get new size_control - end - ensure - self.size_control = size_ctrl - end - end - end - - # Moves and/or copies the nodes in each bin to new table. See above for explanation. - def rebuild(table) - old_table_size = table.size - new_table = table.next_in_size_table - # puts "#{old_table_size} -> #{new_table.size}" - forwarder = Node.new(MOVED, new_table, NULL) - rev_forwarder = nil - locked_indexes = nil # holds bins to revisit; nil until needed - locked_arr_idx = 0 - bin = old_table_size - 1 - i = bin - while true - if !(node = table.volatile_get(i)) - # no lock needed (or available) if bin >= 0, because we're not popping values from locked_indexes until we've run through the whole table - redo unless (bin >= 0 ? table.cas(i, nil, forwarder) : lock_and_clean_up_reverse_forwarders(table, old_table_size, new_table, i, forwarder)) - elsif Node.locked_hash?(node_hash = node.hash) - locked_indexes ||= ::Array.new - if bin < 0 && locked_arr_idx > 0 - locked_arr_idx -= 1 - i, locked_indexes[locked_arr_idx] = locked_indexes[locked_arr_idx], i # swap with another bin - redo - end - if bin < 0 || locked_indexes.size >= TRANSFER_BUFFER_SIZE - node.try_await_lock(table, i) # no other options -- block - redo - end - rev_forwarder ||= Node.new(MOVED, table, NULL) - redo unless table.volatile_get(i) == node && node.locked? # recheck before adding to list - locked_indexes << i - new_table.volatile_set(i, rev_forwarder) - new_table.volatile_set(i + old_table_size, rev_forwarder) - else - redo unless split_old_bin(table, new_table, i, node, node_hash, forwarder) - end - - if bin > 0 - i = (bin -= 1) - elsif locked_indexes && !locked_indexes.empty? - bin = -1 - i = locked_indexes.pop - locked_arr_idx = locked_indexes.size - 1 - else - return new_table - end - end - end - - def lock_and_clean_up_reverse_forwarders(old_table, old_table_size, new_table, i, forwarder) - # transiently use a locked forwarding node - locked_forwarder = Node.new(moved_locked_hash = MOVED | LOCKED, new_table, NULL) - if old_table.cas(i, nil, locked_forwarder) - new_table.volatile_set(i, nil) # kill the potential reverse forwarders - new_table.volatile_set(i + old_table_size, nil) # kill the potential reverse forwarders - old_table.volatile_set(i, forwarder) - locked_forwarder.unlock_via_hash(moved_locked_hash, MOVED) - true - end - end - - # Splits a normal bin with list headed by e into lo and hi parts; installs in given table. - def split_old_bin(table, new_table, i, node, node_hash, forwarder) - table.try_lock_via_hash(i, node, node_hash) do - split_bin(new_table, i, node, node_hash) - table.volatile_set(i, forwarder) - end - end - - def split_bin(new_table, i, node, node_hash) - bit = new_table.size >> 1 # bit to split on - run_bit = node_hash & bit - last_run = nil - low = nil - high = nil - current_node = node - # this optimises for the lowest amount of volatile writes and objects created - while current_node = current_node.next - unless (b = current_node.hash & bit) == run_bit - run_bit = b - last_run = current_node - end - end - if run_bit == 0 - low = last_run - else - high = last_run - end - current_node = node - until current_node == last_run - pure_hash = current_node.pure_hash - if (pure_hash & bit) == 0 - low = Node.new(pure_hash, current_node.key, current_node.value, low) - else - high = Node.new(pure_hash, current_node.key, current_node.value, high) - end - current_node = current_node.next - end - new_table.volatile_set(i, low) - new_table.volatile_set(i + bit, high) - end - - def increment_size - @counter.increment - end - - def decrement_size(by = 1) - @counter.add(-by) - end - end - end -end diff --git a/lib/concurrent-ruby/concurrent/map.rb b/lib/concurrent-ruby/concurrent/map.rb index 1b2224195..601e36504 100644 --- a/lib/concurrent-ruby/concurrent/map.rb +++ b/lib/concurrent-ruby/concurrent/map.rb @@ -20,8 +20,8 @@ module Collection require 'concurrent/collection/map/truffleruby_map_backend' TruffleRubyMapBackend else - require 'concurrent/collection/map/atomic_reference_map_backend' - AtomicReferenceMapBackend + require 'concurrent/collection/map/synchronized_map_backend' + SynchronizedMapBackend end else warn 'Concurrent::Map: unsupported Ruby engine, using a fully synchronized Concurrent::Map implementation' diff --git a/lib/concurrent-ruby/concurrent/thread_safe/util/cheap_lockable.rb b/lib/concurrent-ruby/concurrent/thread_safe/util/cheap_lockable.rb deleted file mode 100644 index 0d074319b..000000000 --- a/lib/concurrent-ruby/concurrent/thread_safe/util/cheap_lockable.rb +++ /dev/null @@ -1,81 +0,0 @@ -require 'concurrent/thread_safe/util' -require 'concurrent/thread_safe/util/volatile' -require 'concurrent/utility/engine' - -module Concurrent - - # @!visibility private - module ThreadSafe - - # @!visibility private - module Util - - # Provides a cheapest possible (mainly in terms of memory usage) +Mutex+ - # with the +ConditionVariable+ bundled in. - # - # Usage: - # class A - # include CheapLockable - # - # def do_exlusively - # cheap_synchronize { yield } - # end - # - # def wait_for_something - # cheap_synchronize do - # cheap_wait until resource_available? - # do_something - # cheap_broadcast # wake up others - # end - # end - # end - # - # @!visibility private - module CheapLockable - private - if Concurrent.on_jruby? - # Use Java's native synchronized (this) { wait(); notifyAll(); } to avoid the overhead of the extra Mutex objects - require 'jruby' - - def cheap_synchronize - JRuby.reference0(self).synchronized { yield } - end - - def cheap_wait - JRuby.reference0(self).wait - end - - def cheap_broadcast - JRuby.reference0(self).notify_all - end - else - require 'thread' - - extend Volatile - attr_volatile :mutex - - # Non-reentrant Mutex#synchronize - def cheap_synchronize - true until (my_mutex = mutex) || cas_mutex(nil, my_mutex = Mutex.new) - my_mutex.synchronize { yield } - end - - # Releases this object's +cheap_synchronize+ lock and goes to sleep waiting for other threads to +cheap_broadcast+, reacquires the lock on wakeup. - # Must only be called in +cheap_synchronize+'s block. - def cheap_wait - conditional_variable = @conditional_variable ||= ConditionVariable.new - conditional_variable.wait(mutex) - end - - # Wakes up all threads waiting for this object's +cheap_synchronize+ lock. - # Must only be called in +cheap_broadcast+'s block. - def cheap_broadcast - if conditional_variable = @conditional_variable - conditional_variable.broadcast - end - end - end - end - end - end -end