piotr-yuxuan.closeable-map — piotr-yuxuan/closeable-map 0.19.0

In your project, require:

(require '[piotr-yuxuan.closeable-map :as closeable-map :refer [with-tag]])

Then you can define an application that can be started, and closed.

(defn start
  "Return a running context with values that can be closed."
  [config]
  (closeable-map/closeable-map
    {;; Kafka producers/consumers are `java.io.Closeable`.
     :producer (kafka-producer config)
     :consumer (kafka-consumer config)

     ;; Closeable maps can be nested.
     :backend/api {:response-executor (flow/utilization-executor (:executor config))
                   :connection-pool (http/connection-pool {:pool-opts config})

                   ;; File streams are `java.io.Closeable` too:
                   :logfile (io/output-stream (io/file "/tmp/log.txt"))

                   ;; This will be called as final closing step for
                   ;; this nested map backend/api. See also
                   ;; `::closeable-map/before-close` which is called
                   ;; before closing a map.
                   ::closeable-map/after-close
                   (fn [m]
                     ;; Some classes have similar semantic, but do not
                     ;; implement `java.io.Closeable`. We can handle
                     ;; them anyway.
                     (.shutdown ^ExecutorService (:response-executor m))
                     (.shutdown ^IPool (:connection-pool m)))}

     ;; Any exception when closing this nested map will be swallowed
     ;; and not bubbled up.
     :db ^::closeable-map/swallow {;; Connection are `java.io.Closeable`, too:
                                   :db-conn (jdbc/get-connection (:db config))}

     ;; Some libs return a zero-argument function which when called
     ;; stops the server, like:
     :server (with-tag ::closeable-map/fn (http/start-server (api config) (:server config)))
     ;; Gotcha: Clojure meta data can only be attached on 'concrete'
     ;; objects; they are lost on literal forms (see above).
     :forensic ^::closeable-map/fn #(metrics/report-death!)

     ::closeable-map/ex-handler
     (fn [ex]
       ;; Will be called for all exceptions thrown when closing this
       ;; map and nested items.
       (println (ex-message ex)))}))

Then you can start/stop the app in the repl with:

(comment
  (def config (load-config))
  (def system (start config))

  ;; Stop/close all processes/resources with:
  (.close system)
)

You can use it in conjunction with with-open like in test file:

(with-open [system (start config)]
  (testing "unit test with isolated, repeatable context"
    (is (= :yay/🚀 (some-business/function context)))))

When (.close system) is executed, it will:

• Recursively close all instances of java.io.Closeable and java.lang.AutoCloseable;

• Recursively call all stop zero-argument functions tagged with ^::closeable-map/fn;

• Skip all nested Closeable under a ^::closeable-map/ignore;

• Silently swallow any exception with ^::closeable-map/swallow;

• Exceptions to optional ::closeable-map/ex-handler in key or metadata;

• If keys (or metadata) ::closeable-map/before-close or ::closeable-map/after-close are present, they will be assumed as a function which takes one argument (the map itself) and used run additional closing logic:

  (closeable-map
    {;; This function will be executed before the auto close.
     ::closeable-map/before-close (fn [this-map] (flush!))
  
     ;; Kafka producers/consumers are java.io.Closeable
     :producer (kafka-producer config)
     :consumer (kafka-consumer config)
  
     ;; This function will be executed after the auto close.
     ::closeable-map/after-close (fn [this-map] (garbage/collect!))
    }
  )
  

• You can easily extend this library by giving new dispatch values to multimethod {{piotr-yuxuan.closeable-map/close!}. It is dispatched on the concrete class of its argument.

  (import '(java.util.concurrent ExecutorService))
  (defmethod closeable-map/close! ExecutorService (memfn ^ExecutorService destroy))
  

*?ex-handler* clj

Dynamic var. If non-nil, will be invoked with the exception as argument A one-argument function is excepted.

Because clojure.walk/walk is used for map traversal, it is not possible to pas s down any argument. Also, as we iteratively walk through nested data structures, some of them do not support metadata. As a result, a binding on this dynamic var in the execution thread enables a simple way to remember the parent value as we visit the children.

*ignore?* clj

Dynamic var. If bound to a logically true value in closing thread, will ignore any closeable items. You may change its value is some nested maps with meta {::ignore false}.

Because clojure.walk/walk is used for map traversal, it is not possible to pass down any argument. Also, as we iteratively walk through nested data structures, some of them do not support metadata. As a result, a binding on this dynamic var in the execution thread enables a simple way to remember the parent value as we visit the children.

*swallow?* clj

Dynamic var. If bound to a logically true value in closing thread, will swallow any java.lang.Throwable, the apex class for all exceptions in Java and Clojure. You may change its value is some nested maps with meta {::swallow false}.

Because clojure.walk/walk is used for map traversal, it is not possible to pass down any argument. Also, as we iteratively walk through nested data structures, some of them do not support metadata. As a result, a binding on this dynamic var in the execution thread enables a simple way to remember the parent value as we visit the children.

close! clj multimethod

Perform a side effect of the form x passed as argument and attempts to close it. If it doesn't know how to close it, does nothing. Functions tagged with ^::fn are considered closeable as java.io.Closeable and java.lang.AutoCloseable.

This multimethod is dispatched on the concrete class of its argument. You can extend this method like any other multimethod.

(import '(java.util.concurrent ExecutorService))

(defmethod closeable-map/close! ExecutorService (memfn ^ExecutorService destroy))

closeable-map clj

(closeable-map m)

Take any object that implements a map interface and return a new map that can later be closed. You may use this map like any other map for example with update or assoc. When you call (.close m), inner closeable items will be closed.

Map keys ::before-close and ::after-close will be evaluated before and after other keys of the map. Will ignore items marked with ^::ignore, and exceptions thrown under ^::swallow will be silently swallowed. Functions tagged with ^::fn will be considered closeable. No checks on closing functions, the minimal requirement is they be invokable.

empty-map clj

An empty, immutable closeable map that you may use like any other map. When you call (.close m) on it, inner closeable items will be closed.

ignored clj

An empty, immutable closeable map that ignores all closeable. A nested closeable may be no longer ignored if its metadata contain {::ignore false}. You may use it like any other map.

swallowed clj

An empty, immutable closeable map that swallows all exceptions. A nested closeable item may throw an exception by setting its metadata to {::swallow false}. You may use it like any other map.

visitor clj

Take a form x as one argument and traverse it while trying to {{close!}} inner items.

Map keys ::before-close and ::after-close will be invoked before and after other keys of the map. Will ignore items marked with ^::ignore. Exceptions when closing some item will be passed to an optional ::ex-handler. With ^::swallow they will not be raised higher and will stay silently swallowed. Functions tagged with ^::fn will be considered closeable and will thus be called on .close.

For advance usage, no checks on closing functions, the minimal requirement is they be invokable. Map keys can also be tagged. Maps values ::before-close and ::after-close are not expected to be tagged with ^::fn for they would be executed twice.

with-tag clj

(with-tag tag x)

By design, the Clojure shortcut notation ^::closeable-map/fn {} works only on direct objects, not on bindings, or literal forms. use this function to circumvent this limitation.

(meta
  (let [a {}]
    ^::closeable-map/fn a))
;; => nil

(meta
  (let [a {}]
    (with-tag ::closeable-map/fn a)))
;; => #:piotr-yuxuan.closeable-map{:fn true}

with-tag- clj macro

(with-tag- x tag)

The code is the docstring:

(defmacro -with-tag
  "The code is the docstring:"
  [x tag]
  `(vary-meta ~x assoc ~tag true))