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Go Client

This project provides a Go client for Atomix Cloud.

Getting Started

Installation

To install the Go client, use go get:

$ GO111MODULE=on go get github.com/atomix/go-client

Usage

To use the client, import the client API:

import "github.com/atomix/go-client/pkg/atomix"

The atomix package provides functions for working with primitives using the default cluster configuration:

counter, err := atomix.GetCounter(context.Background(), "my-counter")

To use a non-default configuration, create a client by calling NewClient:

client := atomix.NewClient(atomix.WithBrokerPort(8000))
counter, err := client.GetCounter(context.Background(), "my-counter")

To create a distributed primitive, call the getter for the desired type, passing the name of the primitive and any additional primitive options:

lock, err := atomix.GetLock(context.Background(), "my-lock")
if err != nil {
panic(err)
}

Primitive names are shared across all clients for a given scope within a given database. Any two primitives with the same name in the same scope and stored in the same database reference the same state machine regardless of client locations. So a Lock call in one container will block will block lock requests from all other containers until unlocked.

version, err := lock.Lock(context.Background())
if err == nil {
// Lock is acquired with version 'version'
}

When a primitive is no longer in used by the client it can be closed with Close to reclaim resources:

lock.Close(context.Background())

Counter

The Counter primitive is a distributed counter that supports atomic increment, decrement, and check-and-set operations. To create a counter, call GetCounter on the database in which to create the counter:

myCounter, err := atomix.GetCounter(context.Background(), "my-counter")
if err != nil {
    ...
}

defer myCounter.Close(context.Background())
count, err := myCounter.Get(context.Background())
if err != nil {
    ...
}
count, err = myCounter.Set(context.Background(), 10)
if err != nil {
    ...
}
count, err = myCounter.Increment(context.Background(), 1)
if err != nil {
    ...
}
count, err = myCounter.Decrement(context.Background(), 10)
if err !=  nil {
    ...
}

Leader Election

The Election primitive supports distributed leader election. Leader elections are implemented using first-in-first-out, but clients can sort election priority through various operations on the Election interface.

To create an Election, call GetElection on the database in which to create the election:

myElection, err := atomix.GetElection(context.Background(), "my-election")
if err != nil {
    ...
}

defer myElection.Close(context.Background())

Each Election object has a globally unique node ID which is used to identify the client and can be read by calling ID():

id := myElection.ID()

The election ID is used to differentiate candidates and can be explicitly assigned by specifying a session ID when getting the election instance:

myElection, err := atomix.GetElection(context.Background(), "my-election", primitive.WithSessionID("node-1"))

The current election Term can be retrieved by calling GetTerm:

term, err := myElection.GetTerm(context.Background())
if err != nil {
    ...
}

The Term contains the complete state of the election: * Leader - the current leader ID * Term - a uint64 per-leader, globally unique, monotonically increasing epoch for the leader * Candidates - a sequence of all candidates participating in the election in priority order, including the current leader

To enter the client into the election, call Enter:

term, err = myElection.Enter(context.Background())
if err != nil {
    ...
}

The Enter call will return the resulting Term struct which can be used to determine whether the client won the election:

if term.Leader == myElection.ID() {
    // This node is the leader
}

Clients can leave the election by calling Leave:

err = myElection.Leave(context.Background())
if err != nil {
    ...
}

When the leader leaves an election, a new leader will be elected. The Watch method can be used to watch the election for changes. When the leader or candidates changes, an event will be published to all watchers.

ch := make(chan election.Event)
err := myElection.Watch(context.Background(), ch)
for event := range ch {
    ...
}

IndexedMap

List

Lock

The Lock primitive is a distributed lock that provides lock version numbers for fencing. To create a lock, call GetLock on the database in which to create the lock.

_Note that it’s recommended distributed locking be used with a strongly consistent database that implements a protocol like raft.

myLock, err := atomix.GetLock(context.Background(), "my-lock")
if err != nil {
    ...
}

defer myLock.Close(context.Background())

To acquire the lock, call Lock:

version, err := myLock.Lock(context.Background())
if err != nil {
    ...
}

If the lock is currently held by another client (or another Lock instance owned by the current client), the Lock() call will block until the lock is Unlocked by the owning client. A timeout can be provided by the Context:

ctx := context.WithTimeout(context.Background(), 10 * time.Second)
version, err := myLock.Lock(ctx)
if err != nil {
    ...
}

Successful calls to Lock() return a uint64 lock version number. The lock version number is guaranteed to be unique and monotonically increasing, so it’s suitable for fencing and optimistic locking.

To determine whether the lock is currently held by any client, call IsLocked:

locked, err := myLock.IsLocked(context.Background())
if err != nil {
    ...
}

A lock version number can also be passed using WithVersion to determine whether the lock is held by an owner with the given version number:

locked, err = myLock.IsLocked(context.Background(), atomixlock.WithVersion(version))
if err != nil {
    ...
}

Once the client has finished with the lock, unlock it by calling Unlock:

unlocked, err := myLock.Unlock(context.Background())
if err != nil {
    ...
}

Clients can also release any process’s lock by passing the owner’s lock version number:

unlocked, err = myLock.Unlock(context.Background(), lock.IfMatch(lock))
if err != nil {
    ...
}

Map

The Map primitive provides a distributed map that supports concurrency control through optimistic locking. Maps store string keys and []byte values, and map entries are represented in return values as a KeyValue object with the following fields: * Key - the string map key * Value - the []byte entry value * Version - a monotonically increasing, unique int64 entry version suitable for use in optimistic locks

To create a distributed map, get a Database and call GetMap on the database:

myMap, err := atomix.GetMap[string, string](
    context.Background(), 
    "my-map", 
    _map.WithKeyType(generic.String()),
    _map.WithValueType(generic.String()))
if err != nil {
    ...
}

defer myMap.Close(context.Background())

To put a value in a map, call Put:

entry, err := myMap.Put(context.Background(), "foo", "bar")
if err != nil {
    ...
}

The returned Entry contains the metadata for the entry that was written to the map. Get also returns the Entry:

entry, err = myMap.Get(context.Background(), "foo")
if err != nil {
    ...
}

This entry metadata can be used for optimistic locking when updating the entry using the IfTimestamp option:

entry, err := myMap.Update(context.Background(), "foo", "baz", _map.IfTimestamp(entry.Timestamp))
if err != nil {
    ...
}

To remove a key from the map, call Remove:

entry, err = myMap.Remove(context.Background(), "foo")
if err != nil {
    ...
}

Again, optimistic locking can be used when removing an entry:

entry, err = myMap.Remove(context.Background(), "foo", _map.IfTimestamp(entry.Timestamp))
if err != nil {
    ...
}

Call Clear to remove all entries from the map:

err = myMap.Clear(context.Background())
if err != nil {
    ...
}

The Watch method can be used to watch the map for changes. When the map is modified an event will be published to all watchers.

ch := make(chan _map.Event[string, string])
err := myMap.Watch(context.Background(), ch)
for event := range ch {
    ...
}

Set

The Set primitive is a partitioned distributed set. Set values are stored as strings. To create a set, call GetSet on the database in which to create the set:

mySet, err := atomix.GetSet[string](context.Background(), "my-set", set.WithElementType(generic.String()))
if err != nil {
    ...
}

defer mySet.Close(context.Background())

To add an element to the set, call Add:

added, err := mySet.Add(context.Background(), "foo")
if err != nil {
    ...
}

To check if the set contains an element, call Contains:

contains, err := mySet.Contains(context.Background(), "foo")
if err != nil {
    ...
}

And to remove an element from the set, call Remove:

removed, err := mySet.Remove(context.Background(), "foo")
if err != nil {
    ...
}

Or to remove all elements from the set, call Clear:

err := mySet.Clear(context.Background())
if err != nil {
    ...
}

The Watch method can be used to watch the set for changes. When an element is added to or removed from the set, an event will be published to all watchers.

ch := make(chan set.Event)
err := mySet.Watch(context.Background(), ch)
for event := range ch {
    ...
}

Value

The Value primitive is a distributed []byte value that supoorts atomic set-and-get and compare-and-set operations.

myValue, err := atomix.GetValue[string](context.Background(), "my-value", value.WithType(generic.String()))
if err != nil {
    ...
}

defer myValue.Close(context.Background())

To set the value call Set:

ts, err := myValue.Set(context.Background(), "Hello world!")
if err != nil {
    ...
}

To get the current value use Get:

value, ts, err := myValue.Get(context.Background())
if err != nil {
    ...
}

The Timestamp returned by Get and Set calls contains versioning information that can be used to perform atomic check-and-set operations using optimistic locking:

if value == "Hello world!" {
    _, err := myValue.Set(context.Background(), "Goodbye world.", value.IfTimestamp(ts))
}

The Watch method can be used to watch the value for changes. Each time the value is updated, an event will be published to all watchers.

ch := make(chan value.Event)
err := myValue.Watch(context.Background(), ch)
for event := range ch {
    ...
}
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