A simple Clojure profiler that works as a drop in defn replacement. Its output is to be loaded in chrome://tracing.

• Supports multi-process and multi-thread profiling.
• Minimal performance impact in debug mode, negligible otherwise (see example bellow).
• Cleaning and export of the data done in a separate tread.

(ns example
  (:require [needle.trace :refer [defn-trace dump-log]]))

(def my-agent
  (when (= (System/getenv "DEBUG") "true")
    (agent [])))

(defn-trace my-function my-agent
  "Document string"
  [max-val somefn setarg]
  (reduce somefn 0 (range max-val)))

(def max-vals
  (map
   #(+ 500000 (rand-int 1000000) %)
   (range 10)))

(doseq [i max-vals]
  (my-function i + {#{:a :b} :c}))

(when (= (System/getenv "DEBUG") "true")
  (send my-agent dump-log "target.json" "Test log" "PERF"))

If you run the above code without the DEBUG env variable set to true, then my-agent will be nil and defn-trace will behave exactly like defn. If DEBUG=true, then profiling data will be sent to my-agent, cleaned and exported to target.json.

You can then load target.json into chrome://tracing to see the associated graph.

fn-trace is to defn-trace what fn is to defn, with the difference that fn-trace functions cannot be anonymous and require a name, for tracing purpose.

Reference document for the Chrome Tracing Format.

More detailed examples can be found in the examples folder.

defn-trace and fn-trace can alternatively take a map as parameter. The map can have the following keys, the default value is in brackets.

• :agent → the agent itself, must be set.
• :save-args true | [false] → whether arguments' value should be saved.
• :args-mask [(true|false|fn)+] [nil] → detailed lists of arguments to save false will result in the value of the variable appearing as __unsaved__.
• :save-output true | [false] → whether to save the output or not
• :mode :EB [:X] → which event mode is to be used
• :flow-mode :s :t :f [nil] → if nil, disabled, otherwise saves an additional flow event, :s and :t at the end of the :EB event, :f at the beginning. See reference doc for explanation.

Example:

(defn-trace my-function
  {:agent my-agent
   :save-args true
   :args-mask [true false (fn [arg] (count arg))]
   :save-output true
   :mode :EB}
  "Document string"
  [max-val somefn setarg]
  (reduce somefn 0 (range max-val)))

Notice that :args-mask can have a processing function for the arg to only save the argument partially.

• Support for async events
• Support for multimethods
• [DONE] Support for flow events
• [DONE] None of the macros work on multi arity functions.

Copyright © 2020

This program and the accompanying materials are made available under the terms of the Eclipse Public License 2.0 which is available at http://www.eclipse.org/legal/epl-2.0.

This Source Code may also be made available under the following Secondary Licenses when the conditions for such availability set forth in the Eclipse Public License, v. 2.0 are satisfied: GNU General Public License as published by the Free Software Foundation, either version 2 of the License, or (at your option) any later version, with the GNU Classpath Exception which is available at https://www.gnu.org/software/classpath/license.html.