Documentation
¶
Overview ¶
Package pubsub provides a message broker for one-to-many or many-to-many message distribution. In addition pubsub includes a generic deque and queue implementations suited to concurrent use.
Index ¶
- Variables
- func DistributorIterator[T any](dist Distributor[T]) fun.Iterator[T]
- func Populate[T any](ctx context.Context, iter fun.Iterator[T], broker *Broker[T]) error
- type Broker
- func MakeDistributorBroker[T any](ctx context.Context, dist Distributor[T], opts BrokerOptions) *Broker[T]
- func NewBroker[T any](ctx context.Context, opts BrokerOptions) *Broker[T]
- func NewDequeBroker[T any](ctx context.Context, deque *Deque[T], opts BrokerOptions) *Broker[T]
- func NewLIFOBroker[T any](ctx context.Context, opts BrokerOptions, capacity int) *Broker[T]
- func NewQueueBroker[T any](ctx context.Context, queue *Queue[T], opts BrokerOptions) *Broker[T]
- type BrokerOptions
- type Deque
- func (dq *Deque[T]) Close() error
- func (dq *Deque[T]) ForcePushBack(it T) error
- func (dq *Deque[T]) ForcePushFront(it T) error
- func (dq *Deque[T]) Iterator() fun.Iterator[T]
- func (dq *Deque[T]) IteratorBlocking() fun.Iterator[T]
- func (dq *Deque[T]) IteratorBlockingReverse() fun.Iterator[T]
- func (dq *Deque[T]) IteratorReverse() fun.Iterator[T]
- func (dq *Deque[T]) Len() int
- func (dq *Deque[T]) PopBack() (T, bool)
- func (dq *Deque[T]) PopFront() (T, bool)
- func (dq *Deque[T]) PushBack(it T) error
- func (dq *Deque[T]) PushFront(it T) error
- func (dq *Deque[T]) WaitBack(ctx context.Context) (T, error)
- func (dq *Deque[T]) WaitFront(ctx context.Context) (T, error)
- func (dq *Deque[T]) WaitPushBack(ctx context.Context, it T) error
- func (dq *Deque[T]) WaitPushFront(ctx context.Context, it T) error
- type DequeOptions
- type Distributor
- type Queue
- type QueueOptions
Constants ¶
This section is empty.
Variables ¶
var ( // ErrQueueFull is returned by the Add method of a queue when the queue has // reached its hard capacity limit. ErrQueueFull = errors.New("queue is full") // ErrQueueNoCredit is returned by the Add method of a queue when the queue has // exceeded its soft quota and there is insufficient burst credit. ErrQueueNoCredit = errors.New("insufficient burst credit") // ErrQueueClosed is returned by the Add method of a closed queue, and by // the Wait method of a closed empty queue. ErrQueueClosed = errors.New("queue is closed") )
queue implements a dynamic FIFO queue with a fixed upper bound and a flexible quota mechanism to handle bursty load.
var ErrConfigurationMalformed = errors.New("configuration error")
ErrConfigurationError is the returned by the queue and deque constructors if their configurations are malformed.
Functions ¶
func DistributorIterator ¶ added in v0.7.0
func DistributorIterator[T any](dist Distributor[T]) fun.Iterator[T]
DistributorIterator allows iterator-like access to a distributor. These iterators are blocking and destructive. The iterator's close method does *not* close the distributor's underlying structure.
Types ¶
type Broker ¶
type Broker[T any] struct { // contains filtered or unexported fields }
Broker is a simple message broker that provides a useable interface for distributing messages to an arbitrary group of channels.
func MakeDistributorBroker ¶ added in v0.7.0
func MakeDistributorBroker[T any](ctx context.Context, dist Distributor[T], opts BrokerOptions) *Broker[T]
MakeDistributorBroker constructs a Broker that uses the provided distributor to handle the buffering between the sending half and the receiving half.
In general, you should configure the distributor to provide whatever buffering requirements you have, and
func NewBroker ¶
func NewBroker[T any](ctx context.Context, opts BrokerOptions) *Broker[T]
NewBroker constructs with a simple distrubtion scheme: the incoming and outgoing messages are not buffered, but the client subscription channels are not buffered.
All brokers respect the BrokerOptions, which control how messages are set to subscribers. The specific configuration of these settings can have profound impacts on the semantics and ordering of messages in the broker.
func NewDequeBroker ¶
NewDequeBroker constructs a broker that uses the queue object to buffer incoming requests if subscribers are slow to process requests. The semantics of the Deque depends a bit on the configuration of it's limits and capacity.
This broker distributes messages in a FIFO order, dropping older messages to make room for new messages.
func NewLIFOBroker ¶
NewLIFOBroker constructs a broker that uses the queue object to buffer incoming requests if subscribers are slow to process requests. The semantics of the Deque depends a bit on the configuration of it's limits and capacity.
This broker distributes messages in a LIFO order, dropping older messages to make room for new messages. The capacity of the queue is fixed, and must be a positive integer greater than 0, NewLIFOBroker will panic if the capcity is less than or equal to 0.
func NewQueueBroker ¶
NewQueueBroker constructs a broker that uses the queue object to buffer incoming requests if subscribers are slow to process requests. Queue have a system for sheding load when the queue's limits have been exceeded. In general the messages are distributed in FIFO order, and Publish calls will drop messages if the queue is full.
All brokers respect the BrokerOptions, which control the size of the worker pool used to send messages to senders and if the Broker should use non-blocking sends. All channels between the broker and the subscribers are un-buffered.
func (*Broker[T]) Stop ¶
func (b *Broker[T]) Stop()
Stop cancels the broker, allowing background work to stop.
func (*Broker[T]) Subscribe ¶
Subscribe generates a new subscription channel, of the specified buffer size. You *must* call Unsubcribe on this channel when you are no longer listening to this channel.
Subscription channels are *not* closed and should never be closed by the caller.
func (*Broker[T]) Unsubscribe ¶
Unsubscribe removes a channel from the broker.
type BrokerOptions ¶
type BrokerOptions struct {
// BufferSize controls the buffer size of the internal broker
// channels that handle subscription creation and deletion
// (unsubscribe.) Buffering
BufferSize int
// ParallelDispatch, when true, sends each message to
// subscribers in parallel, and waits for all messages to be
// delivered before continuing.
ParallelDispatch bool
// WorkerPoolSize controls the number of go routines used for
// sending messages to subscribers, when using Queue-backed
// brokers. If unset this defaults to 1.
//
// When this value is larger than 1, the order of messages
// observed by individual subscribers will not be consistent.
WorkerPoolSize int
}
BrokerOptions configures the semantics of a broker. The zero-values produce a blocking unbuffered queue message broker with every message distributed to every subscriber. While the default settings make it possible for one subscriber to block another subscriber, they guarantee that all messages will be delivered. Buffered brokers may lose messages.
type Deque ¶
type Deque[T any] struct { // contains filtered or unexported fields }
Deque proves a basic double ended queue backed by a doubly linked list, with features to support a maximum capacity, burstable limits and soft quotas, as well as iterators, that safe for access from multiple concurrent go-routines. Furthermore, the implementation safely handles multiple concurrent blocking operations (e.g. Wait, iterators).
Use the NewDeque constructor to instantiate a Deque object.
func NewDeque ¶
func NewDeque[T any](opts DequeOptions) (*Deque[T], error)
NewDeque constructs a Deque according to the options, and errors if there are any problems with the configuration.
func (*Deque[T]) Close ¶
Close marks the deque as closed, after which point all iterators will stop and no more operations will succeed. The error value is not used in the current operation.
func (*Deque[T]) ForcePushBack ¶
ForcePushBack is the same as PushBack, except, if the deque is at capacity, it removes one item from the front of the deque and then, having made room prepends the item. Returns an error if the deque is closed.
func (*Deque[T]) ForcePushFront ¶
ForcePushFront is the same as PushFront, except, if the deque is at capacity, it removes one item from the back of the deque and then, having made room appends the item. Returns an error if the deque is closed.
func (*Deque[T]) Iterator ¶
IteratorReverse starts at the back of the queue and iterates towards the front. When the iterator reaches the beginning of the queue it ends.
func (*Deque[T]) IteratorBlocking ¶
IteratorBlocking starts at the front of the deque, iterates to the end and then waits for a new item to be pushed to the back of the queue, the queue to be closed or the context to be canceled.
func (*Deque[T]) IteratorBlockingReverse ¶
IteratorBlockingReverse starts at the back of the deque and iterates toward the front, and then waits for a new item to be pushed to the front of the queue, the queue to be closed or the context to be canceled.
func (*Deque[T]) IteratorReverse ¶
IteratorReverse starts at the back of the queue and iterates towards the front. When the iterator reaches the end of the queue it ends.
func (*Deque[T]) Len ¶
Len returns the length of the queue. This is an O(1) operation in this implementation.
func (*Deque[T]) PopBack ¶
PopBack removes the last (tail) item of the queue, with the second value being false if the queue is empty or closed.
func (*Deque[T]) PopFront ¶
PopFront removes the first (head) item of the queue, with the second value being false if the queue is empty or closed.
func (*Deque[T]) PushBack ¶
PushFront adds an item to the back or end of the deque, and erroring if the queue is closed, at capacity, or has reached its limit.
func (*Deque[T]) PushFront ¶
PushFront adds an item to the front or head of the deque, and erroring if the queue is closed, at capacity, or has reached its limit.
func (*Deque[T]) WaitBack ¶
WaitBack pops the last (tail) item in the deque, and if the queue is empty, will block until an item is added, returning an error if the context canceled or the queue is closed.
func (*Deque[T]) WaitFront ¶
WaitFront pops the first (head) item in the deque, and if the queue is empty, will block until an item is added, returning an error if the context canceled or the queue is closed.
func (*Deque[T]) WaitPushBack ¶ added in v0.6.0
WaitPushBack performs a blocking add to the deque: if the deque is at capacity, this operation blocks until the deque is closed or there is capacity to add an item. The new item is added to the back of the deque.
func (*Deque[T]) WaitPushFront ¶ added in v0.6.0
WaitPushFront performs a blocking add to the deque: if the deque is at capacity, this operation blocks until the deque is closed or there is capacity to add an item. The new item is added to the front of the deque.
type DequeOptions ¶
type DequeOptions struct {
Unlimited bool
Capacity int
QueueOptions *QueueOptions
}
DequeOptions configure the semantics of the deque. The Validate() method ensures that you do not produce a configuration that is impossible.
Capcaity puts a firm upper cap on the number of items in the deque, while the Unlimited options
func (*DequeOptions) Validate ¶
func (opts *DequeOptions) Validate() error
Validate ensures that the options are consistent. Exported as a convenience function. All errors have ErrConfigurationMalformed as their root.
type Distributor ¶ added in v0.7.0
type Distributor[T any] interface { Send(context.Context, T) error Receive(context.Context) (T, error) }
Distributor provides a layer of indirection above queue-like implementations (e.g. Queue, Deque and channels) for buffering and queuing objects for use by higher level pubsub mechanisms like the Broker.
Implementations should provide Send/Recieve operations that are blocking and wait for the underlying structure to be "closed", the context to be canceled, or have capacity (Send), or new objects (Recieve). These operations *should* mutate the underlying data structure or service.
func DistributorBuffer ¶ added in v0.7.0
func DistributorBuffer[T any](d *Deque[T]) Distributor[T]
DistributorBuffer produces a Distributor with FIFO semantics and blocking Push/Pop operations when the Queue is at capacity. This should have similar semantics as a channel, but callers may (carefully) interact with the Deque structure while it's in use.
func DistributorChannel ¶ added in v0.7.0
func DistributorChannel[T any](ch chan T) Distributor[T]
DistributorChannel provides a bridge between channels and distributors, and has expected FIFO semantics with blocking reads and writes.
func DistributorDeque ¶ added in v0.7.0
func DistributorDeque[T any](d *Deque[T]) Distributor[T]
DistributorDeque produces a Distributor that always accepts new Push operations by removing the oldest element in the queue, with Pop operations returning the oldest elements first (FIFO).
func DistributorLIFO ¶ added in v0.7.0
func DistributorLIFO[T any](d *Deque[T]) Distributor[T]
DistributorLIFO produces a Deque-based Distributor that, when the user attempts to Push onto a full Deque, it will remove the first element in the list, while all Pop operations are also to the front of the Deque.
func DistributorQueue ¶ added in v0.7.0
func DistributorQueue[T any](q *Queue[T]) Distributor[T]
DistributorQueue uses a Queue implementation for FIFO distribution of items. If the queue is at capacity, push operations will return ErrQueueFull errors, effectively allowing the user of the distributor to drop new messages before they enter the queue..
type Queue ¶
type Queue[T any] struct { // contains filtered or unexported fields }
A Queue is a limited-capacity FIFO queue of arbitrary data items.
A queue has a soft quota and a hard limit on the number of items that may be contained in the queue. Adding items in excess of the hard limit will fail unconditionally.
For items in excess of the soft quota, a credit system applies: Each queue maintains a burst credit score. Adding an item in excess of the soft quota costs 1 unit of burst credit. If there is not enough burst credit, the add will fail.
The initial burst credit is assigned when the queue is constructed. Removing items from the queue adds additional credit if the resulting queue length is less than the current soft quota. Burst credit is capped by the hard limit.
A Queue is safe for concurrent use by multiple goroutines.
func NewQueue ¶
func NewQueue[T any](opts QueueOptions) (*Queue[T], error)
NewQueue constructs a new empty queue with the specified options. It reports an error if any of the option values are invalid.
func NewUnlimitedQueue ¶
NewUnlimitedQueue produces an unbounded queue.
func (*Queue[T]) Add ¶
Add adds item to the back of the queue. It reports an error and does not enqueue the item if the queue is full or closed, or if it exceeds its soft quota and there is not enough burst credit.
func (*Queue[T]) BlockingAdd ¶ added in v0.6.0
BlockingAdd attempts to add an item to the queue, as with Add, but if the queue is full, blocks until the queue has capacity, is closed, or the context is canceled. Returns an error if the context is canceled or the queue is closed.
func (*Queue[T]) Close ¶
Close closes the queue. After closing, any further Add calls will report an error, but items that were added to the queue prior to closing will still be available for Remove and Wait. Wait will report an error without blocking if it is called on a closed, empty queue.
func (*Queue[T]) Iterator ¶
Iterator produces an iterator implementation that wraps the underlying queue linked list. The iterator respects the Queue's mutex and is safe for concurrent access and current queue operations, without additional locking. The iterator does not modify the contents of the queue, and will only terminate when the queue has been closed via the Close() method.
func (*Queue[T]) Remove ¶
Remove removes and returns the frontmost (oldest) item in the queue and reports whether an item was available. If the queue is empty, Remove returns nil, false.
type QueueOptions ¶
type QueueOptions struct {
// The maximum number of items the queue will ever be
// permitted to hold. This value must be positive, and greater
// than or equal to SoftQuota. The hard limit is fixed and
// does not change as the queue is used.
//
// The hard limit should be chosen to exceed the largest burst
// size expected under normal operating conditions.
HardLimit int
// The initial expected maximum number of items the queue
// should contain on an average workload. If this value is
// zero, it is initialized to the hard limit. The soft quota
// is adjusted from the initial value dynamically as the queue
// is used.
SoftQuota int
// The initial burst credit score. This value must be greater
// than or equal to zero. If it is zero, the soft quota is
// used.
BurstCredit float64
}
QueueOptions are the initial settings for a Queue or Deque.
func (*QueueOptions) Validate ¶
func (opts *QueueOptions) Validate() error
Validate ensures that the options are consistent. Exported as a convenience function. All errors have ErrConfigurationMalformed as their root.
Source Files