Restore :debug functionality

Author: alexander-yakushev

README.md

@@ -56,6 +56,27 @@ Once loaded, you can measure objects like this:
 (mm/measure (object-array (repeatedly 100 #(String. "hello"))) :bytes true)
 ;=> 2848
 
+-;; :debug true can be passed to print the object hierarchy. You can also pass an
+-;; integer number to limit the number of nested levels printed.
+-
+-(mm/measure (apply list (range 4)) :debug true)
+-
+-; root [clojure.lang.PersistentList] 256 bytes (40 bytes)
+-;   |
+-;   +--_first [java.lang.Long] 24 bytes (24 bytes)
+-;   |
+-;   +--_rest [clojure.lang.PersistentList] 192 bytes (40 bytes)
+-;     |
+-;     +--_first [java.lang.Long] 24 bytes (24 bytes)
+-;     |
+-;     +--_rest [clojure.lang.PersistentList] 128 bytes (40 bytes)
+-;       |
+-;       +--_first [java.lang.Long] 24 bytes (24 bytes)
+-;       |
+-;       +--_rest [clojure.lang.PersistentList] 64 bytes (40 bytes)
+-;         |
+-;         +--_first [java.lang.Long] 24 bytes (24 bytes)
+
 ;; Custom MemoryMeter object can be passed. See what you can configure here:
 ;; https://github.com/jbellis/jamm/blob/master/src/org/github/jamm/MemoryMeter.java
 ```

src/clj_memory_meter/core.clj

@@ -128,9 +128,6 @@
         builder (.getDeclaredMethod mm-class "builder" (into-array Class []))]
     (.invoke builder nil (object-array 0))))
 
-(def ^:private memory-meter
-  (delay (.build (meter-builder))))
-
 (defn- convert-to-human-readable
   "Taken from http://programming.guide/java/formatting-byte-size-to-human-readable-format.html."
   [bytes]
@@ -147,12 +144,21 @@
 (defn measure
   "Measure the memory usage of the `object`. Return a human-readable string.
 
+  :debug   - if true, print the object layout tree to stdout. Can also be set to
+             a number to limit the nesting level being printed.
   :shallow - if true, count only the object header and its fields, don't follow
              object references
   :bytes   - if true, return a number of bytes instead of a string
   :meter   - custom org.github.jamm.MemoryMeter object"
   [object & {:keys [debug shallow bytes meter]}]
-  (let [m (or meter @memory-meter)
+  (let [m (or meter
+              (let [builder (meter-builder)]
+                (cond (and debug (boolean? debug))
+                      (.printVisitedTree builder)
+
+                      (integer? debug)
+                      (.printVisitedTreeUpTo builder debug))
+                (.build builder)))
         byte-count (if shallow
                      (.measure m object)
                      (.measureDeep m object))]

test/clj_memory_meter/core_test.clj

@@ -1,5 +1,6 @@
 (ns clj-memory-meter.core-test
   (:require [clj-memory-meter.core :as sut]
+            [clojure.string :as str]
             [clojure.test :refer :all])
   (:import org.spdx.library.model.license.LicenseInfoFactory))
 
@@ -10,10 +11,39 @@
   (is (= 80 (sut/measure (java.io.File. "/") :bytes true)))
   (is (= 24 (sut/measure (java.time.Instant/now) :bytes true))))
 
+(defmacro capture-system-out [& body]
+  `(let [baos# (java.io.ByteArrayOutputStream.)
+         sw# (java.io.PrintStream. baos#)
+         bk-out# (System/out)]
+     (System/setOut sw#)
+     ~@body
+     (.flush (System/out))
+     (System/setOut bk-out#)
+     (String. (.toByteArray baos#))))
+
 (deftest output-test
   (is (= "240 B" (sut/measure [])))
   (is (= "3.1 KiB" (sut/measure (vec (range 100)))))
-  (is (= "2.8 MiB" (sut/measure (vec (range 100000))))))
+  (is (= "2.8 MiB" (sut/measure (vec (range 100000)))))
+
+  (testing ":debug true"
+    (is (str/ends-with? (str/trim (capture-system-out (sut/measure (apply list (range 4)) :debug true)))
+                          (str/trim "
+root [clojure.lang.PersistentList] 256 bytes (40 bytes)
+  |
+  +--_first [java.lang.Long] 24 bytes (24 bytes)
+  |
+  +--_rest [clojure.lang.PersistentList] 192 bytes (40 bytes)
+    |
+    +--_first [java.lang.Long] 24 bytes (24 bytes)
+    |
+    +--_rest [clojure.lang.PersistentList] 128 bytes (40 bytes)
+      |
+      +--_first [java.lang.Long] 24 bytes (24 bytes)
+      |
+      +--_rest [clojure.lang.PersistentList] 64 bytes (40 bytes)
+        |
+        +--_first [java.lang.Long] 24 bytes (24 bytes)")))))
 
 (deftest error-test
   ;; Only test this against JDK14+.