Workaround locking issue in 1.10

Author: taylorwood

.gitignore

@@ -1,3 +1,3 @@
 .cpcache
 classes
-clojurl
+/clojurl

README.md

@@ -154,3 +154,16 @@ should satisfy
 -------------------------
 Detected 1 error
 ```
+
+## Compiling with Clojure 1.10
+
+GraalVM native-image won't work with Clojure's `locking` macro, and Clojure 1.10 depends on a version of clojure.spec
+(see [this commit](https://github.com/clojure/spec.alpha/commit/31165fec69ff86129a1ada8b3f50864922dfc88a)) that uses `locking`.
+You can workaround this by compiling a Java class with a special locking mechanism, and patching any usages of `locking` e.g. in clojure.spec.
+
+You must first compile the Java class:
+```
+➜ javac java/src/clojurl/LockFix.java -cp ~/.m2/repository/org/clojure/clojure/1.10.0/clojure-1.10.0.jar
+```
+
+Then patch any usages of `locking` and you should be able to compile a native image. See `clojurl.clj` for example.

deps.edn

@@ -1,8 +1,9 @@
 {:deps {expound {:mvn/version "0.7.1"}
-        org.clojure/clojure {:mvn/version "1.9.0"}
+        org.clojure/clojure {:mvn/version "1.10.0"}
         org.clojure/tools.cli {:mvn/version "0.4.1"}
         org.martinklepsch/clj-http-lite {:mvn/version "0.4.1"}
         hickory {:mvn/version "0.7.1"}}
+ :paths ["src" "java/src"]
  :aliases {:native-image
            {:main-opts ["-m clj.native-image clojurl"
                         "--report-unsupported-elements-at-runtime"

java/src/clojurl/LockFix.java

@@ -0,0 +1,11 @@
+package clojurl;
+
+import clojure.lang.IFn;
+
+public class LockFix {
+    static public Object lock(final Object lockee, final IFn f) {
+        synchronized (lockee) {
+            return f.invoke();
+        }
+    }
+}

src/clojurl.clj

@@ -6,10 +6,32 @@
             [clojure.pprint :refer [pprint]]
             [expound.alpha :as expound]
             [hickory.core :as hick])
-  (:gen-class))
+  (:gen-class)
+  (:import (clojurl LockFix)))
 
 (set! *warn-on-reflection* true)
 
+(defmacro locking* ;; patched version of clojure.core/locking to workaround GraalVM unbalanced monitor issue
+  "Executes exprs in an implicit do, while holding the monitor of x.
+  Will release the monitor of x in all circumstances."
+  {:added "1.0"}
+  [x & body]
+  `(let [lockee# ~x]
+     (LockFix/lock lockee# (^{:once true} fn* [] ~@body))))
+
+(defn dynaload ;; patched version of clojure.spec.gen.alpha/dynaload to use patched locking macro
+  [s]
+  (let [ns (namespace s)]
+    (assert ns)
+    (locking* #'clojure.spec.gen.alpha/dynalock
+      (require (symbol ns)))
+    (let [v (resolve s)]
+      (if v
+        @v
+        (throw (RuntimeException. (str "Var " s " is not on the classpath")))))))
+
+(alter-var-root #'clojure.spec.gen.alpha/dynaload (constantly dynaload))
+
 (def cli-options
   [["-u" "--uri URI" "URI of request"
     :id :url