Tracker is a library used to track operations per-thread or even between threads; it compliments the stack trace by identifying the reasons for the function calls`, not just the fact that they occur.

Here’s an example of an exception and operation trace (from the Twixt test suite):

ERROR [      nREPL-worker-0] io.aviso.twixt.coffee-script An exception has occurred:
[  1] - Accessing asset `invalid-coffeescript.coffee'
[  2] - Compiling `META-INF/assets/invalid-coffeescript.coffee' to JavaScript
                               io.aviso.twixt-spec/eval4825/fn/fn/fn       twixt_spec.clj: 155
                        io.aviso.twixt/wrap-pipeline-with-tracing/fn            twixt.clj: 194
                 io.aviso.twixt/wrap-pipeline-with-asset-resolver/fn            twixt.clj: 246
                    io.aviso.twixt.compress/with-cache-delegation/fn         compress.clj:  61
           io.aviso.twixt.compress/wrap-pipeline-with-compression/fn         compress.clj:  49
         io.aviso.twixt.memory-cache/wrap-with-invalidating-cache/fn     memory_cache.clj:  75
               io.aviso.twixt.fs-cache/wrap-with-filesystem-cache/fn         fs_cache.clj: 144
               io.aviso.twixt.css-rewrite/wrap-with-css-rewriting/fn      css_rewrite.clj:  64
io.aviso.twixt.js-minification/wrap-with-javascript-minimizations/fn  js_minification.clj:  47
io.aviso.twixt/wrap-pipeline-with-per-content-type-transformation/fn            twixt.clj: 203
                 io.aviso.twixt.coffee-script/coffee-script-compiler    coffee_script.clj:  22
                                             io.aviso.tracker/timer*          tracker.clj: 180
              io.aviso.twixt.coffee-script/coffee-script-compiler/fn    coffee_script.clj:  35
java.lang.RuntimeException: META-INF/assets/invalid-coffeescript.coffee:6:1: error: unexpected indentation
                                  argument: dep2
                            ^^^^^^

Making use of this is as simple as using the track macro; for example, the first line in the logged operation trace above is the result of this code (also from Twixt):

(defn wrap-pipeline-with-tracing
  "The first middleware in the asset pipeline, used to trace the construction of the asset."
  [asset-handler]
  (fn [asset-path context]
    (t/track
      #(format "Accessing asset `%s'" asset-path)
      (asset-handler asset-path context))))

The first value to track is the operation label: either a literal string, or a function that generates the label string. A function will only be invoked if the operation’s label needs to be output, when an exception occurs.

Tracker uses a dynamic binding for the operation stack; this means it can work even when an operation spans multiple threads, such as when using clojure.core.async.

Tracker is available under the terms of the Apache Software License 2.0.

Full Documentation