/
closeable_map.clj
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/
closeable_map.clj
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(ns piotr-yuxuan.closeable-map
"In your project, require:
``` clojure
(require '[piotr-yuxuan.closeable-map :as closeable-map :refer [with-tag]])
```
Then you can define an application that can be started, and closed.
``` clojure
(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:
``` clojure
(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:
``` clojure
(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:
``` clojure
(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.
``` clojure
(import '(java.util.concurrent ExecutorService))
(defmethod closeable-map/close! ExecutorService
[x]
(.shutdown ^ExecutorService x))
(import '(io.aleph.dirigiste IPool))
(defmethod closeable-map/close! IPool
[x]
(.shutdown ^IPool x))
```
"
(:require [clojure.data]
[clojure.walk :as walk]
[potemkin :refer [def-map-type]])
(:import (java.io Closeable)
(java.lang AutoCloseable)
(java.util Map)))
(def ^:dynamic *swallow?*
"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."
false)
(def ^:dynamic *?ex-handler*
"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."
nil)
(def ^:dynamic *ignore?*
"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."
false)
(defmulti close!
"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.
``` clojure
(import '(java.util.concurrent ExecutorService))
(defmethod closeable-map/close! ExecutorService
[x]
(.shutdown ^ExecutorService x))
(import '(io.aleph.dirigiste IPool))
(defmethod closeable-map/close! IPool
[x]
(.shutdown ^IPool x))
```"
class)
(defmethod close! :default
[x]
;; AutoCloseable is a superinterface of Closeable.
(cond (instance? AutoCloseable x) (.close ^AutoCloseable x)
(::fn (meta x)) (x)))
(def visitor
"Take a form `x` as one argument and traverse it while trying to
[[piotr-yuxuan.closeable-map/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."
(letfn [(before-close [x f] (when-let [close! (or (and (instance? Map x)
(::before-close x))
(::before-close (meta x)))]
(f x close!)))
(after-close [x f] (when-let [close! (or (and (instance? Map x)
(::after-close x))
(::after-close (meta x)))]
(f x close!)))
(?ex-handler [x] (cond (contains? (meta x) ::ex-handler) (::ex-handler (meta x))
(and (instance? Map x) (contains? x ::ex-handler)) (::ex-handler x)
:else *?ex-handler*))
(swallow? [x] (cond (contains? (meta x) ::swallow) (::swallow (meta x))
(and (instance? Map x) (contains? x ::swallow?)) (::swallow? x)
:else *swallow?*))
(swallow [x f] (if (or (swallow? x)
(swallow? f))
(try (f x)
(catch Throwable th
(when (?ex-handler x)
(*?ex-handler* th)))
(finally x))
(doto x f)))
(ignore? [x] (cond (contains? (meta x) ::ignore) (::ignore (meta x))
(and (instance? Map x) (contains? x ::ignore?)) (::ignore? x)
:else *ignore?*))]
(fn visitor
[x]
(binding [*swallow?* (swallow? x)
*ignore?* (ignore? x)
*?ex-handler* (?ex-handler x)]
(walk/walk visitor
#(do (when-not (ignore? %)
(swallow % close!)
(after-close % swallow))
%)
(do (when-not (ignore? x)
(before-close x swallow))
x))))))
(def-map-type CloseableMap [m mta]
(get [_ k default-value] (get m k default-value))
(assoc [_ k v] (CloseableMap. (assoc m k v) mta))
(dissoc [_ k] (CloseableMap. (dissoc m k) mta))
(keys [_] (keys m))
(meta [_] mta)
(with-meta [_ mta] (CloseableMap. m mta))
Closeable ;; Closeable is a subinterface of AutoCloseable.
(^void close [this] (visitor m)))
(defn ^CloseableMap closeable-map
"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."
[m]
{:pre [(instance? Map m)]}
(CloseableMap. m (meta m)))
(def ^:constant ^CloseableMap empty-map
"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."
(closeable-map {}))
(def ^:constant ^CloseableMap swallowed
"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."
(closeable-map ^::swallow {}))
(def ^:constant ^CloseableMap ignored
"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."
(closeable-map ^::ignore {}))
(defmacro with-tag-
"The code is the docstring:
``` clojure
(defmacro -with-tag
\"The code is the docstring:\"
[x tag]
`(vary-meta ~x assoc ~tag true))
```"
[x tag]
`(vary-meta ~x assoc ~tag true))
(defn with-tag
"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.
``` clojure
(meta
(let [a {}]
^::closeable-map/fn a))
;; => nil
(meta
(let [a {}]
(with-tag ::closeable-map/fn a)))
;; => #:piotr-yuxuan.closeable-map{:fn true}
```"
[tag x]
(with-tag- x tag))