Queue

Package queue provides a fast, ring-buffer queue based on the version suggested by Dariusz Górecki. Using this instead of other, simpler, queue implementations (slice+append or linked list) provides substantial memory and time benefits, and fewer GC pauses. The queue implemented here is as fast as it is for an additional reason: it is *not* thread-safe.

Package queue provides a fast, ring-buffer queue based on the version suggested by Dariusz Górecki. Using this instead of other, simpler, queue implementations (slice+append or linked list) provides substantial memory and time benefits, and fewer GC pauses. The queue implemented here is as fast as it is for an additional reason: it is *not* thread-safe.

esQueue

Package redisqueue provides a producer and consumer of a queue that uses Redis streams (https://redis.io/topics/streams-intro). The features of this package include: Here's an example of a producer that inserts 1000 messages into a queue: And here's an example of a consumer that reads the messages off of that queue:

Package msgqueue implements task/job queue with in-memory, SQS, IronMQ backends. go-msgqueue is a thin wrapper for SQS and IronMQ clients that uses Redis to implement rate limiting and call once semantic. go-msgqueue consists of following components: rate limiting is implemented in the processor package using https://github.com/go-redis/redis_rate. Call once is implemented in clients by checking if message name exists in Redis database.

Go bindings for libnetfilter_queue This library provides access to packets in the IPTables netfilter queue (NFQUEUE). The libnetfilter_queue library is part of the http://netfilter.org/projects/libnetfilter_queue/ project.

Package zap provides fast, structured, leveled logging. For applications that log in the hot path, reflection-based serialization and string formatting are prohibitively expensive - they're CPU-intensive and make many small allocations. Put differently, using json.Marshal and fmt.Fprintf to log tons of interface{} makes your application slow. Zap takes a different approach. It includes a reflection-free, zero-allocation JSON encoder, and the base Logger strives to avoid serialization overhead and allocations wherever possible. By building the high-level SugaredLogger on that foundation, zap lets users choose when they need to count every allocation and when they'd prefer a more familiar, loosely typed API. In contexts where performance is nice, but not critical, use the SugaredLogger. It's 4-10x faster than other structured logging packages and supports both structured and printf-style logging. Like log15 and go-kit, the SugaredLogger's structured logging APIs are loosely typed and accept a variadic number of key-value pairs. (For more advanced use cases, they also accept strongly typed fields - see the SugaredLogger.With documentation for details.) By default, loggers are unbuffered. However, since zap's low-level APIs allow buffering, calling Sync before letting your process exit is a good habit. In the rare contexts where every microsecond and every allocation matter, use the Logger. It's even faster than the SugaredLogger and allocates far less, but it only supports strongly-typed, structured logging. Choosing between the Logger and SugaredLogger doesn't need to be an application-wide decision: converting between the two is simple and inexpensive. The simplest way to build a Logger is to use zap's opinionated presets: NewExample, NewProduction, and NewDevelopment. These presets build a logger with a single function call: Presets are fine for small projects, but larger projects and organizations naturally require a bit more customization. For most users, zap's Config struct strikes the right balance between flexibility and convenience. See the package-level BasicConfiguration example for sample code. More unusual configurations (splitting output between files, sending logs to a message queue, etc.) are possible, but require direct use of go.uber.org/zap/zapcore. See the package-level AdvancedConfiguration example for sample code. The zap package itself is a relatively thin wrapper around the interfaces in go.uber.org/zap/zapcore. Extending zap to support a new encoding (e.g., BSON), a new log sink (e.g., Kafka), or something more exotic (perhaps an exception aggregation service, like Sentry or Rollbar) typically requires implementing the zapcore.Encoder, zapcore.WriteSyncer, or zapcore.Core interfaces. See the zapcore documentation for details. Similarly, package authors can use the high-performance Encoder and Core implementations in the zapcore package to build their own loggers. An FAQ covering everything from installation errors to design decisions is available at https://github.com/uber-go/zap/blob/master/FAQ.md.

Package pq implements a priority queue data structure on top of container/heap. As an addition to regular operations, it allows an update of an items priority, allowing the queue to be used in graph search algorithms like Dijkstra's algorithm. Computational complexities of operations are mainly determined by container/heap. In addition, a map of items is maintained, allowing O(1) lookup needed for priority updates, which themselves are O(log n).

Package pubsub provides an easy way to publish and receive Google Cloud Pub/Sub messages, hiding the details of the underlying server RPCs. Pub/Sub is a many-to-many, asynchronous messaging system that decouples senders and receivers. More information about Pub/Sub is available at https://cloud.google.com/pubsub/docs See https://godoc.org/cloud.google.com/go for authentication, timeouts, connection pooling and similar aspects of this package. Pub/Sub messages are published to topics. A Topic may be created using Client.CreateTopic like so: Messages may then be published to a Topic: Topic.Publish queues the message for publishing and returns immediately. When enough messages have accumulated, or enough time has elapsed, the batch of messages is sent to the Pub/Sub service. Topic.Publish returns a PublishResult, which behaves like a future: its Get method blocks until the message has been sent to the service. The first time you call Topic.Publish on a Topic, goroutines are started in the background. To clean up these goroutines, call Topic.Stop: To receive messages published to a Topic, clients create a Subscription for the topic. There may be more than one subscription per topic ; each message that is published to the topic will be delivered to all associated subscriptions. A Subscription may be created like so: Messages are then consumed from a Subscription via callback. The callback is invoked concurrently by multiple goroutines, maximizing throughput. To terminate a call to Subscription.Receive, cancel its context. Once client code has processed the Message, it must call Message.Ack or Message.Nack; otherwise the Message will eventually be redelivered. Ack/Nack MUST be called within the Subscription.Receive handler function, and not from a goroutine. Otherwise, flow control (e.g. ReceiveSettings.MaxOutstandingMessages) will not be respected, and messages can get orphaned when cancelling Receive. If the client cannot or doesn't want to process the message, it can call Message.Nack to speed redelivery. For more information and configuration options, see Ack Deadlines below. Note: It is possible for a Message to be redelivered even if Message.Ack has been called. Client code must be robust to multiple deliveries of messages. Note: This uses pubsub's streaming pull feature. This feature has properties that may be surprising. Please take a look at https://cloud.google.com/pubsub/docs/pull#streamingpull for more details on how streaming pull behaves compared to the synchronous pull method. The number of StreamingPull connections can be configured by setting NumGoroutines in ReceiveSettings. The default value of 10 means the client library will maintain 10 StreamingPull connections. This is more than sufficient for most use cases, as StreamingPull connections can handle up to 10 MB/s https://cloud.google.com/pubsub/quotas#resource_limits. In some cases, using too many streams can lead to client library behaving poorly as the application becomes I/O bound. By default, the number of connections in the gRPC conn pool is min(4,GOMAXPROCS). Each connection supports up to 100 streams. Thus, if you have 4 or more CPU cores, the default setting allows a maximum of 400 streams which is already excessive for most use cases. If you want to change the limits on the number of streams, you can change the number of connections in the gRPC connection pool as shown below: The default pubsub deadlines are suitable for most use cases, but may be overridden. This section describes the tradeoffs that should be considered when overriding the defaults. Behind the scenes, each message returned by the Pub/Sub server has an associated lease, known as an "ack deadline". Unless a message is acknowledged within the ack deadline, or the client requests that the ack deadline be extended, the message will become eligible for redelivery. As a convenience, the pubsub client will automatically extend deadlines until either: Ack deadlines are extended periodically by the client. The period between extensions, as well as the length of the extension, automatically adjusts based on the time it takes the subscriber application to ack messages (based on the 99th percentile of ack latency). By default, this extension period is capped at 10m, but this limit can be configured by the "MaxExtensionPeriod" setting. This has the effect that subscribers that process messages quickly have their message ack deadlines extended for a short amount, whereas subscribers that process message slowly have their message ack deadlines extended for a large amount. The net effect is fewer RPCs sent from the client library. For example, consider a subscriber that takes 3 minutes to process each message. Since the library has already recorded several 3-minute "ack latencies"s in a percentile distribution, future message extensions are sent with a value of 3 minutes, every 3 minutes. Suppose the application crashes 5 seconds after the library sends such an extension: the Pub/Sub server would wait the remaining 2m55s before re-sending the messages out to other subscribers. Please note that by default, the client library does not use the subscription's AckDeadline for the MaxExtension value. For use cases where message processing exceeds 30 minutes, we recommend using the base client in a pull model, since long-lived streams are periodically killed by firewalls. See the example at https://godoc.org/cloud.google.com/go/pubsub/apiv1#example-SubscriberClient-Pull-LengthyClientProcessing To use an emulator with this library, you can set the PUBSUB_EMULATOR_HOST environment variable to the address at which your emulator is running. This will send requests to that address instead of to Pub/Sub. You can then create and use a client as usual: Deprecated: Please use cloud.google.com/go/pubsub/v2.

Package nfqueue provides an API to interact with the nfqueue subsystem of the netfilter family from the linux kernel. This package processes information directly from the kernel and therefore it requires special privileges. You can provide this privileges by adjusting the CAP_NET_ADMIN capabilities.

Package tview implements rich widgets for terminal based user interfaces. The widgets provided with this package are useful for data exploration and data entry. The package implements the following widgets: The package also provides Application which is used to poll the event queue and draw widgets on screen. The following is a very basic example showing a box with the title "Hello, world!": First, we create a box primitive with a border and a title. Then we create an application, set the box as its root primitive, and run the event loop. The application exits when the application's Application.Stop function is called or when Ctrl-C is pressed. You will find more demos in the "demos" subdirectory. It also contains a presentation (written using tview) which gives an overview of the different widgets and how they can be used. Throughout this package, styles are specified using the tcell.Style type. Styles specify colors with the tcell.Color type. Functions such as tcell.GetColor, tcell.NewHexColor, and tcell.NewRGBColor can be used to create colors from W3C color names or RGB values. The tcell.Style type also allows you to specify text attributes such as "bold" or "italic" or a URL which some terminals use to display hyperlinks. Almost all strings which are displayed may contain style tags. A style tag's content is always wrapped in square brackets. In its simplest form, a style tag specifies the foreground color of the text. Colors in these tags are W3C color names or six hexadecimal digits following a hash tag. Examples: A style tag changes the style of the characters following that style tag. There is no style stack and no nesting of style tags. Style tags are used in almost everything from box titles, list text, form item labels, to table cells. In a TextView, this functionality has to be switched on explicitly. See the TextView documentation for more information. A style tag's full format looks like this: Each of the four fields can be left blank and trailing fields can be omitted. (Empty square brackets "[]", however, are not considered style tags.) Fields that are not specified will be left unchanged. A field with just a dash ("-") means "reset to default". You can specify the following flags to turn on certain attributes (some flags may not be supported by your terminal): Use uppercase letters to turn off the corresponding attribute, for example, "B" to turn off bold. Uppercase letters have no effect if the attribute was not previously set. Setting a URL allows you to turn a piece of text into a hyperlink in some terminals. Specify a dash ("-") to specify the end of the hyperlink. Hyperlinks must only contain single-byte characters (e.g. ASCII) and they may not contain bracket characters ("[" or "]"). Examples: In the rare event that you want to display a string such as "[red]" or "[#00ff1a]" without applying its effect, you need to put an opening square bracket before the closing square bracket. Note that the text inside the brackets will be matched less strictly than region or colors tags. I.e. any character that may be used in color or region tags will be recognized. Examples: You can use the Escape() function to insert brackets automatically where needed. When primitives are instantiated, they are initialized with colors taken from the global Styles variable. You may change this variable to adapt the look and feel of the primitives to your preferred style. Note that most terminals will not report information about their color theme. This package therefore does not support using the terminal's color theme. The default style is a dark theme and you must change the Styles variable to switch to a light (or other) theme. This package supports all unicode characters supported by your terminal. If your terminal supports mouse events, you can enable mouse support for your application by calling Application.EnableMouse. Note that this may interfere with your terminal's default mouse behavior. Mouse support is disabled by default. Many functions in this package are not thread-safe. For many applications, this is not an issue: If your code makes changes in response to key events, the corresponding callback function will execute in the main goroutine and thus will not cause any race conditions. (Exceptions to this are documented.) If you access your primitives from other goroutines, however, you will need to synchronize execution. The easiest way to do this is to call Application.QueueUpdate or Application.QueueUpdateDraw (see the function documentation for details): One exception to this is the io.Writer interface implemented by TextView. You can safely write to a TextView from any goroutine. See the TextView documentation for details. You can also call Application.Draw from any goroutine without having to wrap it in Application.QueueUpdate. And, as mentioned above, key event callbacks are executed in the main goroutine and thus should not use Application.QueueUpdate as that may lead to deadlocks. It is also not necessary to call Application.Draw from such callbacks as it will be called automatically. All widgets listed above contain the Box type. All of Box's functions are therefore available for all widgets, too. Please note that if you are using the functions of Box on a subclass, they will return a *Box, not the subclass. This is a Golang limitation. So while tview supports method chaining in many places, these chains must be broken when using Box's functions. Example: You will need to call Box.SetBorder separately: All widgets also implement the Primitive interface. The tview package's rendering is based on version 2 of https://github.com/gdamore/tcell. It uses types and constants from that package (e.g. colors, styles, and keyboard values).

Package amqp is an AMQP 0.9.1 client with RabbitMQ extensions Understand the AMQP 0.9.1 messaging model by reviewing these links first. Much of the terminology in this library directly relates to AMQP concepts. Most other broker clients publish to queues, but in AMQP, clients publish Exchanges instead. AMQP is programmable, meaning that both the producers and consumers agree on the configuration of the broker, instead of requiring an operator or system configuration that declares the logical topology in the broker. The routing between producers and consumer queues is via Bindings. These bindings form the logical topology of the broker. In this library, a message sent from publisher is called a "Publishing" and a message received to a consumer is called a "Delivery". The fields of Publishings and Deliveries are close but not exact mappings to the underlying wire format to maintain stronger types. Many other libraries will combine message properties with message headers. In this library, the message well known properties are strongly typed fields on the Publishings and Deliveries, whereas the user defined headers are in the Headers field. The method naming closely matches the protocol's method name with positional parameters mapping to named protocol message fields. The motivation here is to present a comprehensive view over all possible interactions with the server. Generally, methods that map to protocol methods of the "basic" class will be elided in this interface, and "select" methods of various channel mode selectors will be elided for example Channel.Confirm and Channel.Tx. The library is intentionally designed to be synchronous, where responses for each protocol message are required to be received in an RPC manner. Some methods have a noWait parameter like Channel.QueueDeclare, and some methods are asynchronous like Channel.Publish. The error values should still be checked for these methods as they will indicate IO failures like when the underlying connection closes. Clients of this library may be interested in receiving some of the protocol messages other than Deliveries like basic.ack methods while a channel is in confirm mode. The Notify* methods with Connection and Channel receivers model the pattern of asynchronous events like closes due to exceptions, or messages that are sent out of band from an RPC call like basic.ack or basic.flow. Any asynchronous events, including Deliveries and Publishings must always have a receiver until the corresponding chans are closed. Without asynchronous receivers, the sychronous methods will block. It's important as a client to an AMQP topology to ensure the state of the broker matches your expectations. For both publish and consume use cases, make sure you declare the queues, exchanges and bindings you expect to exist prior to calling Channel.Publish or Channel.Consume. SSL/TLS - Secure connections When Dial encounters an amqps:// scheme, it will use the zero value of a tls.Config. This will only perform server certificate and host verification. Use DialTLS when you wish to provide a client certificate (recommended), include a private certificate authority's certificate in the cert chain for server validity, or run insecure by not verifying the server certificate dial your own connection. DialTLS will use the provided tls.Config when it encounters an amqps:// scheme and will dial a plain connection when it encounters an amqp:// scheme. SSL/TLS in RabbitMQ is documented here: http://www.rabbitmq.com/ssl.html This exports a Session object that wraps this library. It automatically reconnects when the connection fails, and blocks all pushes until the connection succeeds. It also confirms every outgoing message, so none are lost. It doesn't automatically ack each message, but leaves that to the parent process, since it is usage-dependent. Try running this in one terminal, and `rabbitmq-server` in another. Stop & restart RabbitMQ to see how the queue reacts.

Package queue provides a lock-free queue and two-Lock concurrent queue which use the algorithm proposed by Michael and Scott. https://doi.org/10.1145/248052.248106. see pseudocode at https://www.cs.rochester.edu/research/synchronization/pseudocode/queues.html It will be refactored after go generic is released.

Package bigqueue provides embedded, fast and persistent queue written in pure Go using memory mapped file. bigqueue is currently not thread safe. To use bigqueue in parallel context, a Write lock needs to be acquired (even for Read APIs). Create or open a bigqueue: bigqueue persists the data of the queue in multiple Arenas. Each Arena is a file on disk that is mapped into memory (RAM) using mmap syscall. Default size of each Arena is set to 128MB. It is possible to create a bigqueue with custom Arena size: bigqueue also allows setting up the maximum possible memory that it can use. By default, the maximum memory is set to [3 x Arena Size]. In this case, bigqueue will never allocate more memory than `4KB*10=40KB`. This memory is above and beyond the memory used in buffers for copying data. Bigqueue allows to set periodic flush based on either elapsed time or number of mutate (enqueue/dequeue) operations. Flush syncs the in memory changes of all memory mapped files with disk. *This is a best effort flush*. Elapsed time and number of mutate operations are only checked upon an enqueue/dequeue. This is how we can set these options: In this case, a flush is done after every two mutate operations. In this case, a flush is done after one minute elapses and an Enqueue/Dequeue is called. Write to bigqueue: bigqueue allows writing string data directly, avoiding conversion to `[]byte`: Read from bigqueue: we can also read string data from bigqueue: Check whether bigqueue has non zero elements: bigqueue allows reading data from bigqueue using consumers similar to Kafka. This allows multiple consumers from reading data at different offsets (not in thread safe manner yet). The offsets of each consumer are persisted on disk and can be retrieved by creating a consumer with the same name. Data will be read from the same offset where it was left off. We can create a new consumer as follows. The offsets of a new consumer are set at the start of the queue wherever the first non-deleted element is. We can also copy an existing consumer. This will create a consumer that will have the same offsets into the queue as that of the existing consumer. Now, read operations can be performed on the consumer:

Package rabbitpubsub provides an pubsub implementation for RabbitMQ. Use OpenTopic to construct a *pubsub.Topic, and/or OpenSubscription to construct a *pubsub.Subscription. RabbitMQ follows the AMQP specification, which uses different terminology than the Go CDK Pub/Sub. A Pub/Sub topic is an AMQP exchange. The exchange kind should be "fanout" to match the Pub/Sub model, although publishing will work with any kind of exchange. A Pub/Sub subscription is an AMQP queue. The queue should be bound to the exchange that is the topic of the subscription. See the package example for details. For pubsub.OpenTopic and pubsub.OpenSubscription, rabbitpubsub registers for the scheme "rabbit". The default URL opener will connect to a default server based on the environment variable "RABBIT_SERVER_URL". To customize the URL opener, or for more details on the URL format, see URLOpener. See https://gocloud.dev/concepts/urls/ for background information. RabbitMQ supports at-least-once semantics; applications must call Message.Ack after processing a message, or it will be redelivered. See https://godoc.org/gocloud.dev/pubsub#hdr-At_most_once_and_At_least_once_Delivery for more background. rabbitpubsub exposes the following types for As:

Package redisqueue provides a producer and consumer of a queue that uses Redis streams (https://redis.io/topics/streams-intro). The features of this package include: Here's an example of a producer that inserts 1000 messages into a queue: And here's an example of a consumer that reads the messages off of that queue:

Package sqs provides the API client, operations, and parameter types for Amazon Simple Queue Service. Welcome to the Amazon SQS API Reference. Amazon SQS is a reliable, highly-scalable hosted queue for storing messages as they travel between applications or microservices. Amazon SQS moves data between distributed application components and helps you decouple these components. For information on the permissions you need to use this API, see Identity and access management in the Amazon SQS Developer Guide. You can use Amazon Web Services SDKs to access Amazon SQS using your favorite programming language. The SDKs perform tasks such as the following automatically: Cryptographically sign your service requests Retry requests Handle error responses Amazon SQS Product Page Making API Requests Amazon SQS Message Attributes Amazon SQS Dead-Letter Queues Amazon SQS in the Command Line Interface Regions and Endpoints

Package zap provides fast, structured, leveled logging. For applications that log in the hot path, reflection-based serialization and string formatting are prohibitively expensive - they're CPU-intensive and make many small allocations. Put differently, using json.Marshal and fmt.Fprintf to log tons of interface{} makes your application slow. Zap takes a different approach. It includes a reflection-free, zero-allocation JSON encoder, and the base Logger strives to avoid serialization overhead and allocations wherever possible. By building the high-level SugaredLogger on that foundation, zap lets users choose when they need to count every allocation and when they'd prefer a more familiar, loosely typed API. In contexts where performance is nice, but not critical, use the SugaredLogger. It's 4-10x faster than other structured logging packages and supports both structured and printf-style logging. Like log15 and go-kit, the SugaredLogger's structured logging APIs are loosely typed and accept a variadic number of key-value pairs. (For more advanced use cases, they also accept strongly typed fields - see the SugaredLogger.With documentation for details.) By default, loggers are unbuffered. However, since zap's low-level APIs allow buffering, calling Sync before letting your process exit is a good habit. In the rare contexts where every microsecond and every allocation matter, use the Logger. It's even faster than the SugaredLogger and allocates far less, but it only supports strongly-typed, structured logging. Choosing between the Logger and SugaredLogger doesn't need to be an application-wide decision: converting between the two is simple and inexpensive. The simplest way to build a Logger is to use zap's opinionated presets: NewExample, NewProduction, and NewDevelopment. These presets build a logger with a single function call: Presets are fine for small projects, but larger projects and organizations naturally require a bit more customization. For most users, zap's Config struct strikes the right balance between flexibility and convenience. See the package-level BasicConfiguration example for sample code. More unusual configurations (splitting output between files, sending logs to a message queue, etc.) are possible, but require direct use of go.uber.org/zap/zapcore. See the package-level AdvancedConfiguration example for sample code. The zap package itself is a relatively thin wrapper around the interfaces in go.uber.org/zap/zapcore. Extending zap to support a new encoding (e.g., BSON), a new log sink (e.g., Kafka), or something more exotic (perhaps an exception aggregation service, like Sentry or Rollbar) typically requires implementing the zapcore.Encoder, zapcore.WriteSyncer, or zapcore.Core interfaces. See the zapcore documentation for details. Similarly, package authors can use the high-performance Encoder and Core implementations in the zapcore package to build their own loggers. An FAQ covering everything from installation errors to design decisions is available at https://github.com/uber-go/zap/blob/master/FAQ.md.

Package pubsublite provides an easy way to publish and receive messages using the Pub/Sub Lite service. Google Pub/Sub services are designed to provide reliable, many-to-many, asynchronous messaging between applications. Publisher applications can send messages to a topic and other applications can subscribe to that topic to receive the messages. By decoupling senders and receivers, Google Pub/Sub allows developers to communicate between independently written applications. Compared to Cloud Pub/Sub, Pub/Sub Lite provides partitioned data storage with predefined throughput and storage capacity. Guidance on how to choose between Cloud Pub/Sub and Pub/Sub Lite is available at https://cloud.google.com/pubsub/docs/choosing-pubsub-or-lite. More information about Pub/Sub Lite is available at https://cloud.google.com/pubsub/lite. See https://pkg.go.dev/cloud.google.com/go for authentication, timeouts, connection pooling and similar aspects of this package. Examples can be found at https://pkg.go.dev/cloud.google.com/go/pubsublite#pkg-examples and https://pkg.go.dev/cloud.google.com/go/pubsublite/pscompat#pkg-examples. Complete sample programs can be found at https://github.com/GoogleCloudPlatform/golang-samples/tree/master/pubsublite. The cloud.google.com/go/pubsublite/pscompat subpackage contains clients for publishing and receiving messages, which have similar interfaces to their pubsub.Topic and pubsub.Subscription counterparts in cloud.google.com/go/pubsub. The following examples demonstrate how to declare common interfaces: https://pkg.go.dev/cloud.google.com/go/pubsublite/pscompat#example-NewPublisherClient-Interface and https://pkg.go.dev/cloud.google.com/go/pubsublite/pscompat#example-NewSubscriberClient-Interface. The following imports are required for code snippets below: Messages are published to topics. Pub/Sub Lite topics may be created like so: Close must be called to release resources when an AdminClient is no longer required. See https://cloud.google.com/pubsub/lite/docs/topics for more information about how Pub/Sub Lite topics are configured. See https://cloud.google.com/pubsub/lite/docs/locations for the list of locations where Pub/Sub Lite is available. Pub/Sub Lite uses gRPC streams extensively for high throughput. For more differences, see https://pkg.go.dev/cloud.google.com/go/pubsublite/pscompat. To publish messages to a topic, first create a PublisherClient: Then call Publish: Publish queues the message for publishing and returns immediately. When enough messages have accumulated, or enough time has elapsed, the batch of messages is sent to the Pub/Sub Lite service. Thresholds for batching can be configured in PublishSettings. Publish returns a PublishResult, which behaves like a future; its Get method blocks until the message has been sent (or has failed to be sent) to the service: Once you've finishing publishing all messages, call Stop to flush all messages to the service and close gRPC streams. The PublisherClient can no longer be used after it has been stopped or has terminated due to a permanent error. PublisherClients are expected to be long-lived and used for the duration of the application, rather than for publishing small batches of messages. Stop must be called to release resources when a PublisherClient is no longer required. See https://cloud.google.com/pubsub/lite/docs/publishing for more information about publishing. To receive messages published to a topic, create a subscription to the topic. There may be more than one subscription per topic; each message that is published to the topic will be delivered to all of its subscriptions. Pub/Sub Lite subscriptions may be created like so: See https://cloud.google.com/pubsub/lite/docs/subscriptions for more information about how subscriptions are configured. To receive messages for a subscription, first create a SubscriberClient: Messages are then consumed from a subscription via callback. The callback may be invoked concurrently by multiple goroutines (one per partition that the subscriber client is connected to). Receive blocks until either the context is canceled or a permanent error occurs. To terminate a call to Receive, cancel its context: Clients must call pubsub.Message.Ack() or pubsub.Message.Nack() for every message received. Pub/Sub Lite does not have ACK deadlines. Pub/Sub Lite also does not actually have the concept of NACK. The default behavior terminates the SubscriberClient. In Pub/Sub Lite, only a single subscriber for a given subscription is connected to any partition at a time, and there is no other client that may be able to handle messages. See https://cloud.google.com/pubsub/lite/docs/subscribing for more information about receiving messages. Pub/Sub Lite utilizes gRPC streams extensively. gRPC allows a maximum of 100 streams per connection. Internally, the library uses a default connection pool size of 8, which supports up to 800 topic partitions. To alter the connection pool size, pass a ClientOption to pscompat.NewPublisherClient and pscompat.NewSubscriberClient:

Package asynq provides a framework for Redis based distrubted task queue. Asynq uses Redis as a message broker. To connect to redis, specify the connection using one of RedisConnOpt types. The Client is used to enqueue a task. The Server is used to run the task processing workers with a given handler. Handler is an interface type with a method which takes a task and returns an error. Handler should return nil if the processing is successful, otherwise return a non-nil error. If handler panics or returns a non-nil error, the task will be retried in the future. Example of a type that implements the Handler interface.

Package workerpool queues work to a limited number of goroutines. The purpose of the worker pool is to limit the concurrency of tasks executed by the workers. This is useful when performing tasks that require sufficient resources (CPU, memory, etc.), and running too many tasks at the same time would exhaust resources. A task is a function submitted to the worker pool for execution. Submitting tasks to this worker pool will not block, regardless of the number of tasks. Incoming tasks are immediately dispatched to an available worker. If no worker is immediately available, or there are already tasks waiting for an available worker, then the task is put on a waiting queue to wait for an available worker. The intent of the worker pool is to limit the concurrency of task execution, not limit the number of tasks queued to be executed. Therefore, this unbounded input of tasks is acceptable as the tasks cannot be discarded. If the number of inbound tasks is too many to even queue for pending processing, then the solution is outside the scope of workerpool. It should be solved by distributing load over multiple systems, and/or storing input for pending processing in intermediate storage such as a database, file system, distributed message queue, etc. This worker pool uses a single dispatcher goroutine to read tasks from the input task queue and dispatch them to worker goroutines. This allows for a small input channel, and lets the dispatcher queue as many tasks as are submitted when there are no available workers. Additionally, the dispatcher can adjust the number of workers as appropriate for the work load, without having to utilize locked counters and checks incurred on task submission. When no tasks have been submitted for a period of time, a worker is removed by the dispatcher. This is done until there are no more workers to remove. The minimum number of workers is always zero, because the time to start new workers is insignificant. It is advisable to use different worker pools for tasks that are bound by different resources, or that have different resource use patterns. For example, tasks that use X Mb of memory may need different concurrency limits than tasks that use Y Mb of memory. When there are no available workers to handle incoming tasks, the tasks are put on a waiting queue, in this implementation. In implementations mentioned in the credits below, these tasks were passed to goroutines. Using a queue is faster and has less memory overhead than creating a separate goroutine for each waiting task, allowing a much higher number of waiting tasks. Also, using a waiting queue ensures that tasks are given to workers in the order the tasks were received. This implementation builds on ideas from the following: http://marcio.io/2015/07/handling-1-million-requests-per-minute-with-golang http://nesv.github.io/golang/2014/02/25/worker-queues-in-go.html

Package queue provides multiple thread-safe generic queue implementations. Currently, there are 2 available implementations: A blocking queue, which provides methods that wait for the queue to have available elements when attempting to retrieve an element, and waits for a free slot when attempting to insert an element. A priority queue based on a container.Heap. The elements in the queue must implement the Lesser interface, and are ordered based on the Less method. The head of the queue is always the highest priority element. A circular queue, which is a queue that uses a fixed-size slice as if it were connected end-to-end. When the queue is full, adding a new element to the queue overwrites the oldest element. A linked queue, implemented as a singly linked list, offering O(1) time complexity for enqueue and dequeue operations. The queue maintains pointers to both the head (front) and tail (end) of the list for efficient operations without the need for traversal.