[debug] Use Java method for injecting breakpoint instrumentation

Author: alexander-yakushev

project.clj

@@ -52,6 +52,7 @@
   :filespecs [{:type :bytes :path "cider/cider-nrepl/project.clj" :bytes ~(slurp "project.clj")}]
 
   :source-paths ["src"]
+  :java-source-paths ["src"]
   :resource-paths ["resources"]
   :test-paths ["test/clj" "test/cljs" "test/common"]
 

src/cider/nrepl/middleware/DebugSupport.java

@@ -0,0 +1,33 @@
+package cider.nrepl.middleware;
+
+import clojure.lang.*;
+
+/**
+ * Contains instrumentation helpers for cider.nrepl.middleware.debug. The main
+ * purpose of having these helpers in Java is reducing the instrumentation
+ * footprint (measured in bytecode size). Invoking Java methods usually takes
+ * fewer bytecode instructions than a corresponding Clojure function. Java also
+ * allows us to have primitive overrides which further reduces overhead when
+ * instrumenting code that contains primitives, but also preserves type hints
+ * (so instrumented code behaves closer to original code).
+ *
+ * The reason we care about bytecode size is 65KB method limit that JVM imposes.
+ */
+public class DebugSupport {
+
+    private static volatile IFn breakFn = null;
+
+    public static Object doBreak(Object coor, Object val, Object locals, Object STATE__) {
+        if (breakFn == null)
+            breakFn = (IFn)RT.var("cider.nrepl.middleware.debug", "break");
+        return breakFn.invoke(coor, val, locals, STATE__);
+    }
+
+    public static long doBreak(Object coor, long val, Object locals, Object STATE__) {
+        return (long)doBreak(coor, Numbers.num(val), locals, STATE__);
+    }
+
+    public static double doBreak(Object coor, double val, Object locals, Object STATE__) {
+        return (double)doBreak(coor, Numbers.num(val), locals, STATE__);
+    }
+}

src/cider/nrepl/middleware/debug.clj

@@ -15,6 +15,7 @@
    [orchard.print]
    [orchard.stacktrace :as stacktrace])
   (:import
+   (cider.nrepl.middleware DebugSupport)
    (clojure.lang Compiler$LocalBinding)
    (java.util UUID)))
 
@@ -557,7 +558,7 @@ this map (identified by a key), and will `dissoc` it afterwards."}
     ;; Keep original forms in a separate atom to save some code
     ;; size. Unfortunately same trick wouldn't work for locals.
     (swap! *tmp-forms* assoc coor original-form)
-    `(break ~coor ~val-form ~locals ~'STATE__)))
+    `(DebugSupport/doBreak ~coor ~val-form ~locals ~'STATE__)))
 
 (def irrelevant-return-value-forms
   "Set of special-forms whose return value we don't care about.