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Changes between 1.0.0 and 2.0.0

Clojure 1.4 and 1.5 Support Dropped

Clojure versions 1.4 and 1.5 are no longer supported.

Reactor Update

Reactor is updated to 1.1.x.

Changes between 1.0.0-beta12 and 1.0.0

Reactor Update

Reactor is updated to 1.1.0.RELEASE.

Changes between 1.0.0-beta11 and 1.0.0-beta12

Reactor Update

Reactor is updated to 1.1.0.RC1.

Changes between 1.0.0-beta10 and 1.0.0-beta11

Set Membereship Selector

clojurewerkz.meltdown.selectors/set-membership is a new selector that matches on element membership in a set:

(require '[clojurewerkz.meltdown.reactor   :as mr])
(require '[clojurewerkz.meltdown.selectors :as ms)

(let [r   (mr/create)]
  (mr/on r (ms/set-membership #{"white" "red" "blue"} (fn [evt])))

Changes between 1.0.0-beta9 and 1.0.0-beta10

Reactor Update

Reactor is updated to 1.1.0.M3.

2-arity of clojurewerkz.meltdown.reactor/on is Removed

Reactor 1.1.0.M3 no longer supports default key (selector), so 2-arity of clojurewerkz.meltdown.reactor/on was removed.

Clojure 1.6

Meltdown now depends on org.clojure/clojure version 1.6.0. It is still compatible with Clojure 1.4 and if your project.clj depends on a different version, it will be used, but 1.6 is the default now.

Changes between 1.0.0-beta8 and 1.0.0-beta9

Consumer and Selector Introspection

clojurewerkz.meltdown.selectors/selectors-on is a new function that returns a list of selectors registered on a reactor:

(require '[clojurewerkz.meltdown.reactor   :as mr])
(require '[clojurewerkz.meltdown.selectors :as ms :refer [$])

(let [r   (mr/create)]
  (mr/on r ($ "a.key) (fn [evt]))
  (ms/selectors-on r))

clojurewerkz.meltdown.consumers/consumer-count is a new function that returns a number of consumers registered on a reactor:

(require '[clojurewerkz.meltdown.reactor   :as mr])
(require '[clojurewerkz.meltdown.selectors :refer [$])
(require '[clojurewerkz.meltdown.consumers :as mc])

(let [r   (mr/create)]
  (mr/on r ($ "a.key) (fn [evt]))
  (mc/consumer-count r))

Changes between 1.0.0-beta7 and 1.0.0-beta8

Key in Event Payload

Meltdown now includes event key when transforming them into Clojure maps.

Example event map:

{:data {:event delivered}, :reply-to nil, :headers {}, :key events.dummy, :id #uuid "5714bb01-ac7e-11e3-64b3-6b2c231ad83a"}

Changes between 1.0.0-beta6 and 1.0.0-beta7

Match-All Selector

clojurewerkz.meltdown.selectors/predicate is a new function that creates a match-all selector (a predicate selector that unconditionally returns true).

Predicate Selectors

clojurewerkz.meltdown.selectors/predicate is a new function that creates a predicate selector:

(require '[clojurewerkz.meltdown.reactor   :as mr])
(require '[clojurewerkz.meltdown.selectors :as ms])

(let [r   (mr/create)
      ;; will filter out events with keys that are
      ;; odd numbers
      sel (ms/predicate even?)]

Changes between 1.0.0-beta5 and 1.0.0-beta6

Reactor Update

Reactor is updated to 1.1.0.M2.

Changes between 1.0.0-beta4 and 1.0.0-beta5

Environment Reuse

Previously Meltdown instantiated a new Environment per clojurewerkz.meltdown.reactor/create invocation without a provided environment. This lead to excessive thread creation which could eventually exhaust system resources.

Meltdown 1.0.0-beta5 will reuse the same environment for all created reactors unless its asked to use a specific Environment instance.

Environment Functions

clojurewerkz.meltdown.env/environment is a function that returns a shared environment. To create a completely new environment from scratch, use clojurewerkz.meltdown.env/create.

clojurewerkz.meltdown.env/shutdown shuts down environments and all associated dispatchers.


clojurewerkz.meltdown.fn/->filter is a new function that reifies Reactor filters from Clojure functions.

Changes between 1.0.0-beta3 and 1.0.0-beta4

Moved Functions

clojurewerkz.meltdown.streams/fn->function and clojurewerkz.meltdown.streams/fn->predicate are removed, use clojurewerkz.meltdown.fn/->function and clojurewerkz.meltdown.fn/->predicate instead.

Streams Flushing

Stream operations are now lazier in Reactor. To enforce stream sources to be drained, use clojurewerkz.meltdown.streams/flush which accepts a stream or deferred.

Reactor Update

Reactor is updated to 1.1.0.M1 which has multiple breaking API changes.

Changes between 1.0.0-beta2 and 1.0.0-beta3

Reactor Update

Reactor is updated to 1.0.0.RELEASE.

Changes between 1.0.0-beta1 and 1.0.0-beta2

Reactor Update

Reactor is updated to 1.0.0.RC1.

Error handling improvements

You can add listeners for Exceptions that are occuring inside of your processing pipeline by subscribing to events based on the class of exception. For example, in order to subscribe to all Exceptions, you can:

(mr/on-error r Exception (fn [event]
                           (println event)))

In order to subscribe to only RuntimeExceptions:

(mr/on-error r RuntimeException (fn [event]
                                  (println event)))

Changes between 1.0.0-alpha3 and 1.0.0-beta1

Reactor Update

Reactor is updated to 1.0.0.M3.

Added dispatcher option to reactor and stream composition

When creating reactor, it's now possible to plug in a custom dispatcher or configure an underlying dispatcher in a way that's most suitable for your application, for example:

(ns my-app.core
  (:import [reactor.event.dispatch RingBufferDispatcher]
           [com.lmax.disruptor.dsl ProducerType]
           [com.lmax.disruptor YieldingWaitStrategy]))

;; Creates a RingBuffer Dispatcher, with a custom queue size of 4096
(def reactor (mr/create :dispatcher (RingBufferDispatcher. "dispatcher-name"

Changes between 1.0.0-alpha2 and 1.0.0-alpha3

Environment option is added to stream creation

It is only possible to specify type of dispatcher when there's an Environment attached to reactor. Option was previously missing.

Changes between 1.0.0-alpha1 and 1.0.0-alpha2

Building declarative graphs

New namespace,, was added for building graphs in a declarative manner

(ns my-stream-graphs-ns

(def res (atom nil))

(def channel (graph (create)
                    (map* inc
                          (reduce* #(+ %1 %2) 0
                                   (consume #(reset! res %))))))

(accept channel 1)
(accept channel 2)
(accept channel 3)

;; => 9

In order to attach and detach graph parts, you can use attach and detach functions from same namespace:

(let [even-sum (atom nil)
      odd-sum (atom nil)
      even-summarizer (detach
                       (filter* even?
                                (reduce* #(+ %1 %2) 0
                                         (consume #(reset! even-sum %)))))

      odd-summarizer (detach
                      (filter* odd?
                               (reduce* #(+ %1 %2) 0
                                        (consume #(reset! odd-sum %)))))
      summarizer #(+ %1 %2)
      channel (graph (create)
                     (map* inc
                           (attach even-summarizer)
                           (attach odd-summarizer)))]

  (accept channel 1)
  (accept channel 2)
  (accept channel 3)
  (accept channel 4)

  ;; => 6

  ;; => 8

Custom streams

Added an ability to create custom streams, whenever map*, reduce*, filter* and batch* are not enough. For that, you can use clojurewerkz.meltdown.streams/custom-stream. For example, you'd like to create a stream that will only dispatch every 5th value further. For state, you can use let-over-lamda:

(defn every-fifth-stream
  "Defines a stream that will receive all events from upstream and dispatch
   every fifth event further down"
  (let [counter (atom 0)]
     (fn [event downstream]
       (swap! counter inc)
       (when (= 5 @counter)
         (reset! counter 0)
         (accept downstream event)))

You can use custom streams same way as you usually use internal ones:

(def channel (create))

(def result (atom nil))

(def incrementer (map* inc channel)
(def inst-every-fifth-stream (every-fifth-stream incrememter))
(consume inst-every-fifth-stream #(reset! res %))

(accept channel 1) ;; @res is still `nil`
(accept channel 2) ;; @res is still `nil`
(accept channel 3) ;; @res is still `nil`
(accept channel 4) ;; @res is still `nil`
(accept channel 5)
@res ;; => 6

Initial Release: 1.0.0-alpha1

Initial release

Supported features:

  • Reactor operations, such as notify, on, send, receive
  • Reactor configuration options, such as dispatcher and routing-strategy
  • Selectors, $ and regexp ones
  • Support for raw operations on reactor to avoid overhead of wrapping and deserialization on Meltdown side
  • Stream & deferred operations such as map*, reduce*, filter* and batch*