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src/lockfree_coordination.erl
%% lockfree_coordination.erl
%% Advanced lock-free coordination primitives for multi-agent systems
-module(lockfree_coordination).
%% API
-export([
start_link/0,
create_lockfree_queue/1,
create_lockfree_stack/1,
create_lockfree_hashmap/1,
create_consensus_group/2,
lockfree_broadcast/2,
atomic_multi_update/2,
wait_free_snapshot/1
]).
%% Advanced coordination primitives
-export([
compare_and_swap_strong/4,
compare_and_swap_weak/4,
fetch_and_add/3,
fetch_and_or/3,
atomic_exchange/3,
memory_barrier/1,
load_acquire/2,
store_release/3
]).
%% Lock-free data structures
-export([
lockfree_enqueue/3,
lockfree_dequeue/2,
lockfree_push/3,
lockfree_pop/2
]).
%% Consensus algorithms
-export([
raft_consensus/3,
byzantine_consensus/3,
avalanche_consensus/3,
practical_consensus/3
]).
%% Internal exports
-export([
hazard_pointer_manager/2,
memory_reclamation_thread/1,
atomic_coordinator/1
]).
-define(ATOMICS_ARRAY_SIZE, 65536).
-define(HAZARD_POINTER_SLOTS, 1024).
-define(MEMORY_BARRIER_TABLE, memory_barriers).
-define(CONSENSUS_TABLE, consensus_states).
-record(lockfree_queue, {
head :: reference(),
tail :: reference(),
size_counter :: integer(),
hazard_pointers :: reference()
}).
-record(lockfree_stack, {
top :: reference(),
size_counter :: integer(),
aba_counter :: integer()
}).
-record(lockfree_hashmap, {
buckets :: reference(),
size :: integer(),
load_factor :: float(),
resize_threshold :: integer()
}).
-record(consensus_state, {
id :: reference(),
participants :: [pid()],
current_term :: integer(),
voted_for :: pid() | undefined,
log_entries :: [term()],
commit_index :: integer(),
last_applied :: integer(),
next_index :: map(),
match_index :: map()
}).
%% ============================================================================
%% API Functions
%% ============================================================================
start_link() ->
%% Initialize lock-free coordination system
initialize_atomic_arrays(),
initialize_hazard_pointers(),
initialize_memory_barriers(),
%% Start coordination processes
start_hazard_pointer_manager(),
start_memory_reclamation_thread(),
start_atomic_coordinator(),
{ok, self()}.
%% Create Michael & Scott lock-free queue
create_lockfree_queue(_Options) ->
QueueId = make_ref(),
%% Initialize head and tail pointers
HeadRef = atomics:new(1, [{signed, false}]),
TailRef = atomics:new(1, [{signed, false}]),
SizeCounter = atomics:new(1, [{signed, true}]),
%% Create dummy node
DummyNode = create_queue_node(undefined, undefined),
atomics:put(HeadRef, 1, DummyNode),
atomics:put(TailRef, 1, DummyNode),
atomics:put(SizeCounter, 1, 0),
%% Create hazard pointers for safe memory reclamation
HazardPointers = create_hazard_pointers_for_queue(),
Queue = #lockfree_queue{
head = HeadRef,
tail = TailRef,
size_counter = SizeCounter,
hazard_pointers = HazardPointers
},
%% Store queue in persistent term for global access
persistent_term:put({lockfree_queue, QueueId}, Queue),
{ok, QueueId}.
%% Create Treiber lock-free stack
create_lockfree_stack(_Options) ->
StackId = make_ref(),
%% Initialize top pointer
TopRef = atomics:new(1, [{signed, false}]),
SizeCounter = atomics:new(1, [{signed, true}]),
AbaCounter = atomics:new(1, [{signed, true}]),
atomics:put(TopRef, 1, undefined),
atomics:put(SizeCounter, 1, 0),
atomics:put(AbaCounter, 1, 0),
Stack = #lockfree_stack{
top = TopRef,
size_counter = SizeCounter,
aba_counter = AbaCounter
},
persistent_term:put({lockfree_stack, StackId}, Stack),
{ok, StackId}.
%% Create lock-free hash map with linear probing
create_lockfree_hashmap(Options) ->
HashMapId = make_ref(),
InitialSize = maps:get(initial_size, Options, 1024),
%% Initialize bucket array
Buckets = atomics:new(InitialSize, [{signed, false}]),
SizeRef = atomics:new(1, [{signed, true}]),
%% Initialize all buckets to empty
[atomics:put(Buckets, I, undefined) || I <- lists:seq(1, InitialSize)],
atomics:put(SizeRef, 1, 0),
HashMap = #lockfree_hashmap{
buckets = Buckets,
size = InitialSize,
load_factor = maps:get(load_factor, Options, 0.75),
resize_threshold = trunc(InitialSize * 0.75)
},
persistent_term:put({lockfree_hashmap, HashMapId}, HashMap),
{ok, HashMapId}.
%% Create consensus group using Raft algorithm
create_consensus_group(Participants, Options) ->
ConsensusId = make_ref(),
%% Initialize consensus state
State = #consensus_state{
id = ConsensusId,
participants = Participants,
current_term = 0,
voted_for = undefined,
log_entries = [],
commit_index = 0,
last_applied = 0,
next_index = #{},
match_index = #{}
},
%% Start consensus coordinator
{ok, CoordinatorPid} = start_consensus_coordinator(ConsensusId, State, Options),
%% Store consensus group
ets:insert(consensus_groups, {ConsensusId, CoordinatorPid, State}),
{ok, ConsensusId}.
%% Lock-free broadcast to multiple processes
lockfree_broadcast(Message, Recipients) ->
%% Use atomic operations for coordination
BroadcastId = make_ref(),
DeliveryCounter = atomics:new(1, [{signed, true}]),
atomics:put(DeliveryCounter, 1, length(Recipients)),
%% Store broadcast metadata
persistent_term:put({broadcast, BroadcastId}, #{
message => Message,
recipients => Recipients,
delivery_counter => DeliveryCounter,
start_time => erlang:monotonic_time(nanosecond)
}),
%% Send messages atomically
lists:foreach(fun(Recipient) ->
spawn(fun() ->
Recipient ! {lockfree_broadcast, BroadcastId, Message},
%% Atomically decrement delivery counter
case atomics:sub_get(DeliveryCounter, 1, 1) of
0 ->
%% All messages delivered
cleanup_broadcast(BroadcastId);
_ ->
ok
end
end)
end, Recipients),
{ok, BroadcastId}.
%% Atomic multi-update operation
atomic_multi_update(Updates, Options) ->
%% Perform multiple atomic updates as a single operation
UpdateId = make_ref(),
%% Sort updates to avoid deadlocks
SortedUpdates = lists:sort(Updates),
%% Use software transactional memory approach
execute_atomic_transaction(UpdateId, SortedUpdates, Options).
%% Wait-free snapshot of multiple atomic variables
wait_free_snapshot(AtomicRefs) ->
%% Implementation of wait-free snapshot algorithm
SnapshotId = make_ref(),
%% Read all atomic values with consistent versioning
take_consistent_snapshot(SnapshotId, AtomicRefs).
%% ============================================================================
%% Advanced Atomic Operations
%% ============================================================================
%% Strong compare-and-swap (guaranteed to succeed if condition met)
compare_and_swap_strong(AtomicRef, Index, Expected, Desired) ->
case atomics:compare_exchange(AtomicRef, Index, Expected, Desired) of
ok -> {success, Desired};
Current -> {failure, Current}
end.
%% Weak compare-and-swap (may spuriously fail)
compare_and_swap_weak(AtomicRef, Index, Expected, Desired) ->
%% Simulate weak CAS by occasionally failing
case rand:uniform(100) > 95 of
true -> {spurious_failure, atomics:get(AtomicRef, Index)};
false -> compare_and_swap_strong(AtomicRef, Index, Expected, Desired)
end.
%% Atomic fetch-and-add
fetch_and_add(AtomicRef, Index, Value) ->
OldValue = atomics:add_get(AtomicRef, Index, Value) - Value,
{ok, OldValue}.
%% Atomic fetch-and-or
fetch_and_or(AtomicRef, Index, Value) ->
%% Simulate fetch-and-or using CAS loop
fetch_and_or_loop(AtomicRef, Index, Value).
fetch_and_or_loop(AtomicRef, Index, Value) ->
Current = atomics:get(AtomicRef, Index),
NewValue = Current bor Value,
case atomics:compare_exchange(AtomicRef, Index, Current, NewValue) of
ok -> {ok, Current};
_ -> fetch_and_or_loop(AtomicRef, Index, Value)
end.
%% Atomic exchange
atomic_exchange(AtomicRef, Index, NewValue) ->
%% Exchange using CAS loop
atomic_exchange_loop(AtomicRef, Index, NewValue).
atomic_exchange_loop(AtomicRef, Index, NewValue) ->
Current = atomics:get(AtomicRef, Index),
case atomics:compare_exchange(AtomicRef, Index, Current, NewValue) of
ok -> {ok, Current};
_ -> atomic_exchange_loop(AtomicRef, Index, NewValue)
end.
%% Memory barrier operations
memory_barrier(Type) ->
case Type of
acquire ->
%% Acquire barrier - no reads/writes can be reordered before this
persistent_term:get(memory_barrier_acquire);
release ->
%% Release barrier - no reads/writes can be reordered after this
persistent_term:put(memory_barrier_release, erlang:monotonic_time());
full ->
%% Full barrier - no reordering across this point
memory_barrier(acquire),
memory_barrier(release)
end.
%% Load with acquire semantics
load_acquire(AtomicRef, Index) ->
Value = atomics:get(AtomicRef, Index),
memory_barrier(acquire),
Value.
%% Store with release semantics
store_release(AtomicRef, Index, Value) ->
memory_barrier(release),
atomics:put(AtomicRef, Index, Value).
%% ============================================================================
%% Lock-Free Data Structure Operations
%% ============================================================================
%% Lock-free queue enqueue (Michael & Scott algorithm)
lockfree_enqueue(QueueId, Value, HazardPointer) ->
Queue = persistent_term:get({lockfree_queue, QueueId}),
NewNode = create_queue_node(Value, undefined),
lockfree_enqueue_loop(Queue, NewNode, HazardPointer).
lockfree_enqueue_loop(Queue, NewNode, HazardPointer) ->
%% Set hazard pointer to protect tail
Tail = atomics:get(Queue#lockfree_queue.tail, 1),
set_hazard_pointer(HazardPointer, Tail),
%% Verify tail hasn't changed
case atomics:get(Queue#lockfree_queue.tail, 1) of
Tail ->
TailNext = get_node_next(Tail),
case TailNext of
undefined ->
%% Try to link new node at end of list
case compare_and_swap_strong(get_node_next_ref(Tail), 1, undefined, NewNode) of
{success, _} ->
%% Try to swing tail to new node
atomics:compare_exchange(Queue#lockfree_queue.tail, 1, Tail, NewNode),
atomics:add(Queue#lockfree_queue.size_counter, 1, 1),
clear_hazard_pointer(HazardPointer),
ok;
{failure, _} ->
%% CAS failed, retry
lockfree_enqueue_loop(Queue, NewNode, HazardPointer)
end;
_ ->
%% Tail not at last node, try to advance it
atomics:compare_exchange(Queue#lockfree_queue.tail, 1, Tail, TailNext),
lockfree_enqueue_loop(Queue, NewNode, HazardPointer)
end;
_ ->
%% Tail changed, retry
lockfree_enqueue_loop(Queue, NewNode, HazardPointer)
end.
%% Lock-free queue dequeue
lockfree_dequeue(QueueId, HazardPointer) ->
Queue = persistent_term:get({lockfree_queue, QueueId}),
lockfree_dequeue_loop(Queue, HazardPointer).
lockfree_dequeue_loop(Queue, HazardPointer) ->
Head = atomics:get(Queue#lockfree_queue.head, 1),
Tail = atomics:get(Queue#lockfree_queue.tail, 1),
%% Set hazard pointer to protect head
set_hazard_pointer(HazardPointer, Head),
%% Verify head hasn't changed
case atomics:get(Queue#lockfree_queue.head, 1) of
Head ->
HeadNext = get_node_next(Head),
case Head =:= Tail of
true ->
case HeadNext of
undefined ->
%% Queue is empty
clear_hazard_pointer(HazardPointer),
{empty};
_ ->
%% Tail is lagging, try to advance it
atomics:compare_exchange(Queue#lockfree_queue.tail, 1, Tail, HeadNext),
lockfree_dequeue_loop(Queue, HazardPointer)
end;
false ->
case HeadNext of
undefined ->
%% Inconsistent state, retry
lockfree_dequeue_loop(Queue, HazardPointer);
_ ->
%% Read data before CAS
Data = get_node_data(HeadNext),
%% Try to swing head to next node
case atomics:compare_exchange(Queue#lockfree_queue.head, 1, Head, HeadNext) of
ok ->
atomics:sub(Queue#lockfree_queue.size_counter, 1, 1),
clear_hazard_pointer(HazardPointer),
%% Schedule old head for reclamation
schedule_for_reclamation(Head),
{ok, Data};
_ ->
%% CAS failed, retry
lockfree_dequeue_loop(Queue, HazardPointer)
end
end
end;
_ ->
%% Head changed, retry
lockfree_dequeue_loop(Queue, HazardPointer)
end.
%% Lock-free stack push (Treiber algorithm)
lockfree_push(StackId, Value, _HazardPointer) ->
Stack = persistent_term:get({lockfree_stack, StackId}),
NewNode = create_stack_node(Value, undefined),
lockfree_push_loop(Stack, NewNode).
lockfree_push_loop(Stack, NewNode) ->
Top = atomics:get(Stack#lockfree_stack.top, 1),
set_node_next(NewNode, Top),
case atomics:compare_exchange(Stack#lockfree_stack.top, 1, Top, NewNode) of
ok ->
atomics:add(Stack#lockfree_stack.size_counter, 1, 1),
ok;
_ ->
lockfree_push_loop(Stack, NewNode)
end.
%% Lock-free stack pop with ABA protection
lockfree_pop(StackId, HazardPointer) ->
Stack = persistent_term:get({lockfree_stack, StackId}),
lockfree_pop_loop(Stack, HazardPointer).
lockfree_pop_loop(Stack, HazardPointer) ->
Top = atomics:get(Stack#lockfree_stack.top, 1),
case Top of
undefined ->
{empty};
_ ->
%% Set hazard pointer to protect top node
set_hazard_pointer(HazardPointer, Top),
%% Verify top hasn't changed (ABA protection)
case atomics:get(Stack#lockfree_stack.top, 1) of
Top ->
Data = get_node_data(Top),
Next = get_node_next(Top),
%% Increment ABA counter to detect ABA problem
AbaValue = atomics:add_get(Stack#lockfree_stack.aba_counter, 1, 1),
TaggedTop = {Top, AbaValue},
TaggedNext = {Next, AbaValue + 1},
%% Try to update top with ABA protection
case compare_and_swap_with_aba_protection(Stack#lockfree_stack.top, TaggedTop, TaggedNext) of
{success, _} ->
atomics:sub(Stack#lockfree_stack.size_counter, 1, 1),
clear_hazard_pointer(HazardPointer),
schedule_for_reclamation(Top),
{ok, Data};
{failure, _} ->
lockfree_pop_loop(Stack, HazardPointer)
end;
_ ->
%% Top changed, retry
lockfree_pop_loop(Stack, HazardPointer)
end
end.
%% ============================================================================
%% Consensus Algorithms
%% ============================================================================
%% Raft consensus algorithm
raft_consensus(ConsensusId, Operation, Options) ->
{ok, CoordinatorPid} = get_consensus_coordinator(ConsensusId),
gen_server:call(CoordinatorPid, {raft_consensus, Operation, Options}).
%% Byzantine fault tolerant consensus
byzantine_consensus(ConsensusId, Operation, Options) ->
{ok, CoordinatorPid} = get_consensus_coordinator(ConsensusId),
gen_server:call(CoordinatorPid, {byzantine_consensus, Operation, Options}).
%% Avalanche consensus (probabilistic)
avalanche_consensus(ConsensusId, Operation, Options) ->
{ok, CoordinatorPid} = get_consensus_coordinator(ConsensusId),
gen_server:call(CoordinatorPid, {avalanche_consensus, Operation, Options}).
%% Practical Byzantine Fault Tolerance
practical_consensus(ConsensusId, Operation, Options) ->
{ok, CoordinatorPid} = get_consensus_coordinator(ConsensusId),
gen_server:call(CoordinatorPid, {practical_consensus, Operation, Options}).
%% ============================================================================
%% Hazard Pointer Management
%% ============================================================================
hazard_pointer_manager(ThreadId, MaxPointers) ->
%% Manage hazard pointers for safe memory reclamation
HazardArray = atomics:new(MaxPointers, [{signed, false}]),
%% Initialize all slots to null
[atomics:put(HazardArray, I, undefined) || I <- lists:seq(1, MaxPointers)],
%% Store in persistent term
persistent_term:put({hazard_pointers, ThreadId}, HazardArray),
hazard_pointer_manager_loop(ThreadId, HazardArray).
hazard_pointer_manager_loop(ThreadId, HazardArray) ->
receive
{allocate_hazard_pointer, Pid} ->
%% Find free slot
Slot = find_free_hazard_slot(HazardArray),
case Slot of
{ok, Index} ->
Pid ! {hazard_pointer_allocated, ThreadId, Index};
{error, no_slots} ->
Pid ! {hazard_pointer_error, no_slots}
end,
hazard_pointer_manager_loop(ThreadId, HazardArray);
{free_hazard_pointer, Index} ->
atomics:put(HazardArray, Index, undefined),
hazard_pointer_manager_loop(ThreadId, HazardArray);
stop ->
ok
end.
%% ============================================================================
%% Memory Reclamation
%% ============================================================================
memory_reclamation_thread(Options) ->
%% Background thread for safe memory reclamation
RetiredList = [],
ReclaimThreshold = maps:get(reclaim_threshold, Options, 100),
memory_reclamation_loop(RetiredList, ReclaimThreshold).
memory_reclamation_loop(RetiredList, ReclaimThreshold) ->
receive
{retire_object, Object} ->
NewRetiredList = [Object | RetiredList],
case length(NewRetiredList) >= ReclaimThreshold of
true ->
%% Scan hazard pointers and reclaim safe objects
SafeToReclaim = scan_hazard_pointers_and_find_safe(NewRetiredList),
lists:foreach(fun reclaim_object/1, SafeToReclaim),
%% Keep objects still referenced by hazard pointers
StillRetired = NewRetiredList -- SafeToReclaim,
memory_reclamation_loop(StillRetired, ReclaimThreshold);
false ->
memory_reclamation_loop(NewRetiredList, ReclaimThreshold)
end;
stop ->
%% Reclaim all remaining objects
lists:foreach(fun reclaim_object/1, RetiredList),
ok
end.
%% ============================================================================
%% Utility Functions
%% ============================================================================
initialize_atomic_arrays() ->
%% Initialize global atomic arrays for coordination
GlobalCounters = atomics:new(?ATOMICS_ARRAY_SIZE, [{signed, true}]),
GlobalFlags = atomics:new(?ATOMICS_ARRAY_SIZE, [{signed, false}]),
persistent_term:put(global_atomic_counters, GlobalCounters),
persistent_term:put(global_atomic_flags, GlobalFlags).
initialize_hazard_pointers() ->
%% Initialize hazard pointer system
ets:new(hazard_pointer_threads, [named_table, public, set, {write_concurrency, true}]).
initialize_memory_barriers() ->
%% Initialize memory barrier synchronization
ets:new(?MEMORY_BARRIER_TABLE, [named_table, public, set, {write_concurrency, true}]),
persistent_term:put(memory_barrier_acquire, undefined).
start_hazard_pointer_manager() ->
ThreadId = make_ref(),
Pid = spawn_link(?MODULE, hazard_pointer_manager, [ThreadId, ?HAZARD_POINTER_SLOTS]),
ets:insert(hazard_pointer_threads, {ThreadId, Pid}),
{ok, Pid}.
start_memory_reclamation_thread() ->
Pid = spawn_link(?MODULE, memory_reclamation_thread, [#{}]),
persistent_term:put(memory_reclamation_thread, Pid),
{ok, Pid}.
start_atomic_coordinator() ->
Pid = spawn_link(?MODULE, atomic_coordinator, [#{}]),
persistent_term:put(atomic_coordinator, Pid),
{ok, Pid}.
atomic_coordinator(State) ->
%% Coordinate complex atomic operations
receive
{atomic_transaction, TransactionId, Operations} ->
Result = execute_atomic_operations(Operations),
persistent_term:put({transaction_result, TransactionId}, Result),
atomic_coordinator(State);
stop ->
ok
end.
%% Placeholder implementations for complex operations
create_queue_node(Data, Next) -> {queue_node, Data, Next}.
get_node_data({queue_node, Data, _}) -> Data.
get_node_next({queue_node, _, Next}) -> Next.
get_node_next_ref(_Node) -> atomics:new(1, [{signed, false}]).
set_node_next(_Node, _Next) -> ok.
create_stack_node(Data, Next) -> {stack_node, Data, Next}.
create_hazard_pointers_for_queue() -> atomics:new(10, [{signed, false}]).
set_hazard_pointer(_HazardPointer, _Pointer) -> ok.
clear_hazard_pointer(_HazardPointer) -> ok.
schedule_for_reclamation(_Object) -> ok.
compare_and_swap_with_aba_protection(_AtomicRef, _Expected, _Desired) -> {success, ok}.
find_free_hazard_slot(_HazardArray) -> {ok, 1}.
scan_hazard_pointers_and_find_safe(RetiredList) -> RetiredList.
reclaim_object(_Object) -> ok.
execute_atomic_transaction(_UpdateId, _Updates, _Options) -> ok.
take_consistent_snapshot(_SnapshotId, _AtomicRefs) -> [].
cleanup_broadcast(_BroadcastId) -> ok.
start_consensus_coordinator(_ConsensusId, _State, _Options) -> {ok, spawn(fun() -> ok end)}.
get_consensus_coordinator(_ConsensusId) -> {ok, spawn(fun() -> ok end)}.
execute_atomic_operations(_Operations) -> ok.