Add explanation for synchronization here. #4739.

jruby · Aug 18, 2017 · a0892f6 · a0892f6
1 parent 9fbb25e
commit a0892f6
Showing 2 changed files with 6 additions and 0 deletions.
diff --git a/core/src/main/java/org/jruby/compiler/BlockJITTask.java b/core/src/main/java/org/jruby/compiler/BlockJITTask.java
@@ -47,6 +47,9 @@ public BlockJITTask(JITCompiler jitCompiler, MixedModeIRBlockBody body, String c
     }
 
     public void run() {
+        // We synchronize against the JITCompiler object so at most one code body will jit at once in a given runtime.
+        // This works around unsolved concurrency issues within the process of preparing and jitting the IR.
+        // See #4739 for a reproduction script that produced various errors without this.
         synchronized (jitCompiler) {
             try {
                 String key = SexpMaker.sha1(body.getIRScope());

diff --git a/core/src/main/java/org/jruby/compiler/MethodJITTask.java b/core/src/main/java/org/jruby/compiler/MethodJITTask.java
@@ -53,6 +53,9 @@ public MethodJITTask(JITCompiler jitCompiler, MixedModeIRMethod method, String c
     }
 
     public void run() {
+        // We synchronize against the JITCompiler object so at most one code body will jit at once in a given runtime.
+        // This works around unsolved concurrency issues within the process of preparing and jitting the IR.
+        // See #4739 for a reproduction script that produced various errors without this.
         synchronized (jitCompiler) {
             try {
                 // Check if the method has been explicitly excluded